Isolator, circuit breaker and it's Type .pdf
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Sep 24, 2024
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About This Presentation
Isolator and circuit breaker
Slide Content
UNIT- 2
CIRCUIT INTERRUPT DEVICES
Y Tsolator
Y HRC Fuse
+ Arc Formation Process
Y RRRV
# Types Of Circuit Breaker
+ MCB
Y MCCB
=
=
=
CIRCUIT INTERRUPT DEVICES
Y Tsolator
Y HRC Fuse
+ Arc Formation Process
Y RRRV
# Types Of Circuit Breaker
+ MCB
Y MCCB
=
=
=
_ISOLATORS
Introduction
@An Isolator is a type of mechanical switch used to isolate an electrical circuit.
47 Isolator switches are used for opening an electrical circuit in the no-load condition.
@ It is not proposed to be opened while current flow through the line,
e Generally, these are used on circuit breaker both the ends thus the circuit breaker
repair can be done easily without any risk.
Electrical isolator is used to seperate any type of electrical component from the
system.
» Isolator are used in addition to circuit breaker while opening a circuit, the circuit
breaker is op pened first first then isolator
gm hile closing circuit , the isolator is closed first then the circuit breaker.
DA full load condition, isolator doesn't operate.
Introduction
@An Isolator is a type of mechanical switch used to isolate an electrical circuit.
47 Isolator switches are used for opening an electrical circuit in the no-load condition.
@ It is not proposed to be opened while current flow through the line,
e Generally, these are used on circuit breaker both the ends thus the circuit breaker
repair can be done easily without any risk.
Electrical isolator is used to seperate any type of electrical component from the
system.
» Isolator are used in addition to circuit breaker while opening a circuit, the circuit
breaker is op pened first first then isolator
gm hile closing circuit , the isolator is closed first then the circuit breaker.
DA full load condition, isolator doesn't operate.
rking Principle
© An electrical isolator working principle is extremely easy.
© It operates in different way like manually operated, semi-automatic and
fully-automatic. OT
_® Sometimes, these are used like switches so known as electrical isolator switches.
© This switch can be opened or closed depending on the necessity.
9 Generally it is used for isolation of transformers, electrical transmission lines, grid
station etc. =
z
© An electrical isolator working principle is extremely easy.
© It operates in different way like manually operated, semi-automatic and
fully-automatic. OT
_® Sometimes, these are used like switches so known as electrical isolator switches.
© This switch can be opened or closed depending on the necessity.
9 Generally it is used for isolation of transformers, electrical transmission lines, grid
station etc. =
z
Types Of Isolator
There are three types of isolators
1- Vertical Break Isolator
_2- Horizontal Break Isolator oa
_3 Pantograph Type Isolator
yx Vertical Break Isolator
© In this isolator, the arms of isolator rotate about its vertical axis through about 90
% It used to isolate circuit breaker, transformer banks and surge aryesters etc.
O It is used for rating of 7kV and above.
There are three types of isolators
1- Vertical Break Isolator
_2- Horizontal Break Isolator oa
_3 Pantograph Type Isolator
yx Vertical Break Isolator
© In this isolator, the arms of isolator rotate about its vertical axis through about 90
% It used to isolate circuit breaker, transformer banks and surge aryesters etc.
O It is used for rating of 7kV and above.
Pa ntact 7
(male contact)
N genial
Terminal (1) Terminal (2)
Fixed contact
(Female contact)
re
insulator
(male contact)
N genial
Terminal (1) Terminal (2)
Fixed contact
(Female contact)
re
insulator
2. Horizontal Break Isolator
@ In this isolator, the arms of isolator rotate about its horozontal axis through
about 90°
© This is used above 245k.
@ In this isolator, the arms of isolator rotate about its horozontal axis through
about 90°
© This is used above 245k.
A
Zantopraph Type Motor, "a
3 Pantograph Type Isolator. mm
e While closing, the linkage of pantograph are brought hearer by rotating the
insulator column.
© In closed position the upper two arms of the pantograph close on the overhead
station bus bar giving a grip.
© The current is carried by the upper bus bar to the lower bus bar through the
conducting arms of the pantograph.
@ While opening, the rotating insulator column is rotated about its axis. There by the
pantograph blades collapse in vartical plane and vertical isolation is obtained
between the line terminal and pantograph upper RIRE
Zantopraph Type Motor, "a
3 Pantograph Type Isolator. mm
e While closing, the linkage of pantograph are brought hearer by rotating the
insulator column.
© In closed position the upper two arms of the pantograph close on the overhead
station bus bar giving a grip.
© The current is carried by the upper bus bar to the lower bus bar through the
conducting arms of the pantograph.
@ While opening, the rotating insulator column is rotated about its axis. There by the
pantograph blades collapse in vartical plane and vertical isolation is obtained
between the line terminal and pantograph upper RIRE
HRC FUSE
Fuse- A fuse is a short piece of metal, inserted in the circuit, which melts when
excessive current flow through it and thus breaks the circuit.
Or - Fuse is a current pale sr device which breaks or open the circuit
by fusing the element when the current in the circuit exceeds a certain
value.
My
Ss End Cab
Fuse- A fuse is a short piece of metal, inserted in the circuit, which melts when
excessive current flow through it and thus breaks the circuit.
Or - Fuse is a current pale sr device which breaks or open the circuit
by fusing the element when the current in the circuit exceeds a certain
value.
My
Ss End Cab
ARC Fuse-High Rupturing Capacity Fuse
Introduction =
su oves cures)
HRC fuse is one kind of fuse, where the fuse wire carries a short circuit
current safely for a given time period.
2 During this period, if fault is removed, then it does not blow off otherwise it
will melt.
e If fault occur for long time then fuse wire melt and seperate the circuit from
supply.“ Pr
-® HRC fuse are available in different shapes, sizes and electrical specification.
@ All these different types of HRC fuses are designed to protect the circuits or
devices. 7
@ AHRC fuse is different from normal fuse in some manner i.e a HRC fuse
cae carry a short circuit(over) current for short period of time whereas
Introduction =
su oves cures)
HRC fuse is one kind of fuse, where the fuse wire carries a short circuit
current safely for a given time period.
2 During this period, if fault is removed, then it does not blow off otherwise it
will melt.
e If fault occur for long time then fuse wire melt and seperate the circuit from
supply.“ Pr
-® HRC fuse are available in different shapes, sizes and electrical specification.
@ All these different types of HRC fuses are designed to protect the circuits or
devices. 7
@ AHRC fuse is different from normal fuse in some manner i.e a HRC fuse
cae carry a short circuit(over) current for short period of time whereas
a normal fuse can not carry a current for short period of time.
Construction
The outer body of HRC is constructed by ceramic or fiberglass. The ceramic or
fiberglass have high heat resistance.
2 There are two metal cap at both end of HRC fuse that provides mechanical
strength.
9- Generally fuse metal(wire) is made up of silver or bimetallic material.
4 Fuse metal is made up of two or more joints, that joint is of tin.
_© Inner portion of fuse filled with some material like- -quartz, plaster of Paris ,
chalk, marble, dust to prevent the formation of arc...
e Melting point of tin metal is 230° while melting point of silver is 960°C.
2 Tin metal will melt firstly compare to silver metal.
TT
The outer body of HRC is constructed by ceramic or fiberglass. The ceramic or
fiberglass have high heat resistance.
2 There are two metal cap at both end of HRC fuse that provides mechanical
strength.
9- Generally fuse metal(wire) is made up of silver or bimetallic material.
4 Fuse metal is made up of two or more joints, that joint is of tin.
_© Inner portion of fuse filled with some material like- -quartz, plaster of Paris ,
chalk, marble, dust to prevent the formation of arc...
e Melting point of tin metal is 230° while melting point of silver is 960°C.
2 Tin metal will melt firstly compare to silver metal.
TT
Working
@ Under normal working condition normal rated current flows through the fuse
link and fuse wire, therefore heat do not produce that much to melt the fuse
joint metal.
. When any fault occurs like phase to phase fault, phase to ground fault then
access current flows, due to which high thermal energy produces. That is able
to melt the joint metal that is made up of tin.
6 In faulty condition arc is produced due to which chemical reaction take place
of vaporized tin and quartz powder.
O After that chemical reaction heat resistant substance forms that quench the
arcing product. As a result Arc completely removes and fault current get
interrupted.
O Hence appliances connected in the circuit saves from faulty current.
@ Under normal working condition normal rated current flows through the fuse
link and fuse wire, therefore heat do not produce that much to melt the fuse
joint metal.
. When any fault occurs like phase to phase fault, phase to ground fault then
access current flows, due to which high thermal energy produces. That is able
to melt the joint metal that is made up of tin.
6 In faulty condition arc is produced due to which chemical reaction take place
of vaporized tin and quartz powder.
O After that chemical reaction heat resistant substance forms that quench the
arcing product. As a result Arc completely removes and fault current get
interrupted.
O Hence appliances connected in the circuit saves from faulty current.
_Advantages
O lts design is simple.
_® It do not require maintenance.
4 Working of HRC fuse is very simple.
„ Breaking capacity of HRC fuse is very fast.
O lts design is simple.
_® It do not require maintenance.
4 Working of HRC fuse is very simple.
„ Breaking capacity of HRC fuse is very fast.
_Aisadvantages
@ These cannot be reused once they blew out.
O lt causes overheating for nearby contacts.
_® After every action, they have to be change.
s Heat is generated through the arc may influence the connected switches.
_Application
z=
-@ Used to protect electrical devices like motors, transformers, automobiles etc.
© These types of fuses are used in stators of motor.
a HRC fuses are used to protect the circuit from short circuits in N switchgear.
@ These cannot be reused once they blew out.
O lt causes overheating for nearby contacts.
_® After every action, they have to be change.
s Heat is generated through the arc may influence the connected switches.
_Application
z=
-@ Used to protect electrical devices like motors, transformers, automobiles etc.
© These types of fuses are used in stators of motor.
a HRC fuses are used to protect the circuit from short circuits in N switchgear.
ie ER prete
_Gharacteristics of HRC Fuse A
re, Re
A fuse works once its element dissolves because of the heat
generated through 12RF. Here, RF is the resistance of the fuse.
If the flow of current through the fuse increases, then the
generated heat also increases. So, a fuse element can soften
quicker for huge fault current whereas it will take a little bit for the
lesser value of fault current. Thus, the relationship between the
time-current of the fuse is named as fuse characteristics. For
proper selection of fuse, it is very useful for a particular circuit.
ol EX,
»)
_Gharacteristics of HRC Fuse A
re, Re
A fuse works once its element dissolves because of the heat
generated through 12RF. Here, RF is the resistance of the fuse.
If the flow of current through the fuse increases, then the
generated heat also increases. So, a fuse element can soften
quicker for huge fault current whereas it will take a little bit for the
lesser value of fault current. Thus, the relationship between the
time-current of the fuse is named as fuse characteristics. For
proper selection of fuse, it is very useful for a particular circuit.
ol EX,
»)
Types of HRC Fuse
hese fuses are available in three types which include the following
1. NH Type Fuse 2
2. Din Type Fuse ~~
3. Blade Type
A.NH Type Fuse - ze
This kind of fuse gives the protection of short circuit and overload for low &
medium voltage. These fuses give protection for starters of the motor as well as
other devices which are against overload and short circuit. These fuses are
available in less weight with a solid dimension. 2
2.Din Type Fuse
These are accessible in a broad range of rated currents and are used in different
fields for different reasons including their feature at different temperature states.
„These are accessible to different levels of voltages and used to rotect the
transformer.
hese fuses are available in three types which include the following
1. NH Type Fuse 2
2. Din Type Fuse ~~
3. Blade Type
A.NH Type Fuse - ze
This kind of fuse gives the protection of short circuit and overload for low &
medium voltage. These fuses give protection for starters of the motor as well as
other devices which are against overload and short circuit. These fuses are
available in less weight with a solid dimension. 2
2.Din Type Fuse
These are accessible in a broad range of rated currents and are used in different
fields for different reasons including their feature at different temperature states.
„These are accessible to different levels of voltages and used to rotect the
transformer.
€
The cleaning capacity of this is excellent for perfect with the short-circuit et:
These are used in air & mining, feeder sectionalizing, gas-insulated switchgear,
and transformers. =
Blade Type Fuse 7
sr
This-type of fuse is also called plug-l or spade. These are available with plastic
body & two metal caps to arrange within the socket. Generally, these are used in
cars to give protection from short circuits, wiring, and used in motors for backup
protection. These are available in less weight and include less cutoff current. Blade
type fuses are available in various sizes & shapes along with the capacity of ~
different current ratings
/
The cleaning capacity of this is excellent for perfect with the short-circuit et:
These are used in air & mining, feeder sectionalizing, gas-insulated switchgear,
and transformers. =
Blade Type Fuse 7
sr
This-type of fuse is also called plug-l or spade. These are available with plastic
body & two metal caps to arrange within the socket. Generally, these are used in
cars to give protection from short circuits, wiring, and used in motors for backup
protection. These are available in less weight and include less cutoff current. Blade
type fuses are available in various sizes & shapes along with the capacity of ~
different current ratings
/
Circuit
Breaker
Breaker
Circuit Breaker
A Acircuit breaker is an electrical safety device.
x Itis designed to protect an electrical circuit from damage cause by an
over current or short circuit.
_* Its basic function is to interrupt current flow to protect equipment and to
prevent the risk of fire.
_X Unlike a fuse, circuit breaker is not replace after once used.
A Ithas two contact, one is fixed contact and other moving contact...
Circuit breaker operated with load whereas isolator operated with no
>
load.
A Acircuit breaker is an electrical safety device.
x Itis designed to protect an electrical circuit from damage cause by an
over current or short circuit.
_* Its basic function is to interrupt current flow to protect equipment and to
prevent the risk of fire.
_X Unlike a fuse, circuit breaker is not replace after once used.
A Ithas two contact, one is fixed contact and other moving contact...
Circuit breaker operated with load whereas isolator operated with no
>
load.
_ Circuit Breaker
| | | |
1.SF6 Circuit 2.Vacuum Circuit _3.Air Circuit 4.0il Circuit Breaker
a = ES
Breaker Breaker Breaker
gr saat
i
_ =
| | | |
1.SF6 Circuit 2.Vacuum Circuit _3.Air Circuit 4.0il Circuit Breaker
a = ES
Breaker Breaker Breaker
gr saat
i
_ =
Arc Formation Process ;- en 131!
13% Ay
_»® When a short-circuit occurs, a heavy current flow through the
contacts of the circuit breaker before they are opened by the
protective system. AL 37
* Atthat instant when the contacts begin to separate, the contact
area decreases rapidly and large fault current causes
increased current density and hence arise in temperature.
* Due to rise in temperature surrounding medium (air) get
ionised..
* The ionised medium have low resistivity hence behave as a
conductive medium. OO
MERE
13% Ay
_»® When a short-circuit occurs, a heavy current flow through the
contacts of the circuit breaker before they are opened by the
protective system. AL 37
* Atthat instant when the contacts begin to separate, the contact
area decreases rapidly and large fault current causes
increased current density and hence arise in temperature.
* Due to rise in temperature surrounding medium (air) get
ionised..
* The ionised medium have low resistivity hence behave as a
conductive medium. OO
MERE
* The interrupting current get low resistive path and continues to flow through
even after the contact are physically separated.
* During the following current from one contact to another the path becomes
so heated that it glows in the from of an arc.
x As long as this arc is sustainded in between the contacts, the
current through the circuit breaker will not be interrupted totally
For total interruption of current the arc need to be quenched as
quickly as posible. pe uenched
140
fi mown
even after the contact are physically separated.
* During the following current from one contact to another the path becomes
so heated that it glows in the from of an arc.
x As long as this arc is sustainded in between the contacts, the
current through the circuit breaker will not be interrupted totally
For total interruption of current the arc need to be quenched as
quickly as posible. pe uenched
140
fi mown
ND west Yale
| b engine Wala
| b engine Wala
Methods To Arc Extinction
When the current carrying contacts of circuit breaker are moved apart, an arc is
formed.
This arc is dangarous for circuit breaker, which can damage the circuit breaker.
The types of circuit breaker depends upon arc extinction methods.
There are many methods used in circuit breaker for arc extinction.
When the current carrying contacts of circuit breaker are moved apart, an arc is
formed.
This arc is dangarous for circuit breaker, which can damage the circuit breaker.
The types of circuit breaker depends upon arc extinction methods.
There are many methods used in circuit breaker for arc extinction.
Methods Of Arc Extinction ARA! Asc zo
— TL 27
There are two methods of extinguishing the arc in circuit breakers id
A High resistance method
_2. Low resistance or current zero method.
j ; zaken
LÆHigh Resistance Method (used is DC Cixcuil Br )
al
en this method, arc resistance is made to increase with time so that current is
reduced to a value insufficient to maintain the arc. Consequently, the current is
interrupted or the are is extinguished.
2 The principal disadvantage of this method is that energy is dissipated in the
arc. Therefore, it is employed only in d.c. circuit breakers.
— ee ee
VT
_
— TL 27
There are two methods of extinguishing the arc in circuit breakers id
A High resistance method
_2. Low resistance or current zero method.
j ; zaken
LÆHigh Resistance Method (used is DC Cixcuil Br )
al
en this method, arc resistance is made to increase with time so that current is
reduced to a value insufficient to maintain the arc. Consequently, the current is
interrupted or the are is extinguished.
2 The principal disadvantage of this method is that energy is dissipated in the
arc. Therefore, it is employed only in d.c. circuit breakers.
— ee ee
VT
_
gest
22 0
The resistance of the arc may be increased y Fo JJ {
fixed FE EA, Mwi
@ Lengthening the arc — The resistance of the arc is directly proportional to its
length. The length of the arc can be increased by increasing the ga
contacts. de: E iter Ty heel )
_* Cooling the arc — Cooling helps in medium between the contacts. This
increases the arc may tained by a gas*resistance. Efficient cooling blast
directed along the arc.( RI || Avil ~ | R= co ATRL 17 Acc
_æ Reducing X-section of t of X-section of the arc is reduced,
the voltage necessary to maintain the arc is increased. In other words, the
resistance of the arc path is increased.(The cross-section of the arc can be
reduced by letting the arc pass through a narrow opening or by having smaller
area of contacts.
_® Splitting the arc — The resistance of the arc can be increased by splitting the arc
into a number of smaller arcs in series. Each one of these arcs experiences the
effect of lengthening and cooling. The arc may be split by introducing some
conducting plates between the contacts.
22 0
The resistance of the arc may be increased y Fo JJ {
fixed FE EA, Mwi
@ Lengthening the arc — The resistance of the arc is directly proportional to its
length. The length of the arc can be increased by increasing the ga
contacts. de: E iter Ty heel )
_* Cooling the arc — Cooling helps in medium between the contacts. This
increases the arc may tained by a gas*resistance. Efficient cooling blast
directed along the arc.( RI || Avil ~ | R= co ATRL 17 Acc
_æ Reducing X-section of t of X-section of the arc is reduced,
the voltage necessary to maintain the arc is increased. In other words, the
resistance of the arc path is increased.(The cross-section of the arc can be
reduced by letting the arc pass through a narrow opening or by having smaller
area of contacts.
_® Splitting the arc — The resistance of the arc can be increased by splitting the arc
into a number of smaller arcs in series. Each one of these arcs experiences the
effect of lengthening and cooling. The arc may be split by introducing some
conducting plates between the contacts.
Low Resistance or Current zero Method
. This method is employed for arc extinction in AC Circuits only.
— ——————
_® In this method, arc resistance is kept low until current zero where the arc
extinguishes naturally and is prevented from restriking inspite of the rising
voltage across the contacts.
@ All modern high power AC Circuit Breakers employ this method for arc
extinction. — o.
cabal
_® In an a.c. system, current drops to zero after every half-cycle. At every current
zero, the arc extinguishes for a brief moment.
. This method is employed for arc extinction in AC Circuits only.
— ——————
_® In this method, arc resistance is kept low until current zero where the arc
extinguishes naturally and is prevented from restriking inspite of the rising
voltage across the contacts.
@ All modern high power AC Circuit Breakers employ this method for arc
extinction. — o.
cabal
_® In an a.c. system, current drops to zero after every half-cycle. At every current
zero, the arc extinguishes for a brief moment.
© If immediately after current zero, the dielectric strength of the medium between
contacts is built up more rapidly than the voltage across the contacts, the arc
fails to restrike and the current will be interrupted. The rapid increase of
dielectric strength of the medium near current zero can be achieved by
_(a) causing the ionised particles in the space between contacts to recombine into
neutral molecules. A
(b) sweeping the ionised particles away and replacing them by unionised
particles. gi
hen ul
Si TE) IA
: sut
„N Y
yO
contacts is built up more rapidly than the voltage across the contacts, the arc
fails to restrike and the current will be interrupted. The rapid increase of
dielectric strength of the medium near current zero can be achieved by
_(a) causing the ionised particles in the space between contacts to recombine into
neutral molecules. A
(b) sweeping the ionised particles away and replacing them by unionised
particles. gi
hen ul
Si TE) IA
: sut
„N Y
yO
TE
e m
AC Circuit baeaken ad 20
rh ‘oun AA \/
m
e m
AC Circuit baeaken ad 20
rh ‘oun AA \/
m
Pre
oe VOLTAGE 5 SE
eee Movis
x That voltage appears across the contacts of Sreuit ee
during arcing periode.
XI At the time circuit bresaker contacts opening, an arc is struck
between the contacts due to ionisation of medium surrounding
the contacts.
* A small potential difference exists between the contacts and it
is responsible for maintaining the a arc. This voltage is called the
Arc voltage.
oe VOLTAGE 5 SE
eee Movis
x That voltage appears across the contacts of Sreuit ee
during arcing periode.
XI At the time circuit bresaker contacts opening, an arc is struck
between the contacts due to ionisation of medium surrounding
the contacts.
* A small potential difference exists between the contacts and it
is responsible for maintaining the a arc. This voltage is called the
Arc voltage.
Recovery
Voltage
=
Instant of Arc
Extinction
Fault Current
System Voltage
Recovery Voltage, Restriking Voltage
and Arc Voltage
Voltage
=
Instant of Arc
Extinction
Fault Current
System Voltage
Recovery Voltage, Restriking Voltage
and Arc Voltage
_ RESTRIKING VOLTAGE Ay.
x The transient voltage that appears across the circuit breaker contacts
{vor immediatly after the arc extinction or at current zero during the arcing period is
(called restriking voltage. =
Er À
el
_x When ever arc interruption occurs at zero current instant, the voltage across
the circuit breaker gap will suddenly rise from zero to a very high value. This
high voltage will be transient in nature. dl
* This voltage is so named because the arc can restrike only during the
qu pened of this transient voltage. If the arc does not restrike during this
transient period, it will not restrik later. This restriking voltage is also known as
transient recovery voltage.
x The transient voltage that appears across the circuit breaker contacts
{vor immediatly after the arc extinction or at current zero during the arcing period is
(called restriking voltage. =
Er À
el
_x When ever arc interruption occurs at zero current instant, the voltage across
the circuit breaker gap will suddenly rise from zero to a very high value. This
high voltage will be transient in nature. dl
* This voltage is so named because the arc can restrike only during the
qu pened of this transient voltage. If the arc does not restrike during this
transient period, it will not restrik later. This restriking voltage is also known as
transient recovery voltage.
RECOVERY VOLTAGE
e It is define as the voltage appearing across the circuit breaker contacts after the
final arc extinction and after all the transients die out(or disappears). The
frequency of recovery voltage is the same as the supply frequency.
e Consider a circuit breaker whose contacts are opened, then the fault current
drop to zero. At zero current instant, no ions are present in the gap between the
contacts.
LAN this condition, the dielectric strenght of the medium(air or oil) between the
contacts will be high, which is stronger enough to avoid the breakdown by
restriking voltage. ~ ae
O As a result the final arc extinction take place and circuit current is interruted.
y
e It is define as the voltage appearing across the circuit breaker contacts after the
final arc extinction and after all the transients die out(or disappears). The
frequency of recovery voltage is the same as the supply frequency.
e Consider a circuit breaker whose contacts are opened, then the fault current
drop to zero. At zero current instant, no ions are present in the gap between the
contacts.
LAN this condition, the dielectric strenght of the medium(air or oil) between the
contacts will be high, which is stronger enough to avoid the breakdown by
restriking voltage. ~ ae
O As a result the final arc extinction take place and circuit current is interruted.
y
LPHUR HEXA FLOURIDE (SF6)CIRCUIT BREAKER
Wy
(7
m 7
M,
TT
wn |
Wy
(7
m 7
M,
TT
wn |
SULPHUR HEXA FLOURIDE(SF6) CIRCUIT BREAKER
É- TT ET
Introduction F te
2 Sulphur he» hexafluoride(SF6) gas is used t to extiguis the arc in SF6 circuit
breaker. _ — =
'SF6 circuit breaker is very effective for the high power and high voltage
application.
_® It operates very fast.
€ SF6 gas has high dielectric strength and arc quenching property.
_e SF6 gas is an electronegative gas and has an high tendency to absorb free
electron.
anioy (-ve ion)
_havious >
É- TT ET
Introduction F te
2 Sulphur he» hexafluoride(SF6) gas is used t to extiguis the arc in SF6 circuit
breaker. _ — =
'SF6 circuit breaker is very effective for the high power and high voltage
application.
_® It operates very fast.
€ SF6 gas has high dielectric strength and arc quenching property.
_e SF6 gas is an electronegative gas and has an high tendency to absorb free
electron.
anioy (-ve ion)
_havious >
0 SF6 ions are haviour ions whose dielectric strength is very high.
„© SF6 is reusable gas and it is costly.
_® This gas has a unique property of fast recombination during arc quenching.
9 SF6 circuit breaker used at very high voltage i.e from 33 kV to 800 kV.
CONTRUCTION
— Areing ye
= „ee
„© SF6 is reusable gas and it is costly.
_® This gas has a unique property of fast recombination during arc quenching.
9 SF6 circuit breaker used at very high voltage i.e from 33 kV to 800 kV.
CONTRUCTION
— Areing ye
= „ee
_® SF6 circuit breakers mainly consist of two parts, namely
4 a) the interrupter unit —
2D) the gas system ——
Ay nterrupter Unit
_ This unit consists of two contact namely fixed contact and moving contact.
A Both contact made up of high conducting material. DS
The tips of contact are coated with copper and tungsten.
_% Fixed contact made up of hollow cylindrical shape and its carry the current.
_® Moving contact made up of hollow cylindrical rectengular shape.
2 Moving contact synchronized with volve of high pressure SF6 gas chamber.
4 a) the interrupter unit —
2D) the gas system ——
Ay nterrupter Unit
_ This unit consists of two contact namely fixed contact and moving contact.
A Both contact made up of high conducting material. DS
The tips of contact are coated with copper and tungsten.
_% Fixed contact made up of hollow cylindrical shape and its carry the current.
_® Moving contact made up of hollow cylindrical rectengular shape.
2 Moving contact synchronized with volve of high pressure SF6 gas chamber.
0 Moving contact and volve operates together.
A Gas System
© It consists of high pressure and low pressure SF6 gas chamber. —
4 High pressure SF6 gas (14 kg/cm )available in high pressure chamber.
_® Low pressure alarm and warning switches are connected with chambers.
_9 When the pressure of the gas is very low due to which the dielectric strength of
gases decreases and arc quenching ability is poor, then this system gives the
li A
warning alarm. — —
eee
A Gas System
© It consists of high pressure and low pressure SF6 gas chamber. —
4 High pressure SF6 gas (14 kg/cm )available in high pressure chamber.
_® Low pressure alarm and warning switches are connected with chambers.
_9 When the pressure of the gas is very low due to which the dielectric strength of
gases decreases and arc quenching ability is poor, then this system gives the
li A
warning alarm. — —
eee
Working
A a
_@ In the normal working condition, the contacts of the breaker are closed.
When the fault occurs in the system, the contacts are pulled apart, and arc
struck between them.
0 The moving contact is synchronised with the valve, hence valve is opened.
e Therefore high pressure SF6 gas enter into the chamber and absorb free
electrons in the arc and convert into ions.
_® lons do not behave as current carrier, so dielectric strength of gas increase.
2 As a result arc will extinguished. -
© After this operation the pressure of SF6 gas will reduce( 3kg/cm”) and store into
low pressure chamber. / ?
e The low pressure gas is pulled back to the high-pressure chamber for re-use.
A a
_@ In the normal working condition, the contacts of the breaker are closed.
When the fault occurs in the system, the contacts are pulled apart, and arc
struck between them.
0 The moving contact is synchronised with the valve, hence valve is opened.
e Therefore high pressure SF6 gas enter into the chamber and absorb free
electrons in the arc and convert into ions.
_® lons do not behave as current carrier, so dielectric strength of gas increase.
2 As a result arc will extinguished. -
© After this operation the pressure of SF6 gas will reduce( 3kg/cm”) and store into
low pressure chamber. / ?
e The low pressure gas is pulled back to the high-pressure chamber for re-use.
Advantages
és y ing
SF6 circuit breaker has excellent insulating and arc extinguishing properties.
wae gas is non-inflammable and chemically stable.
Its performance is not affected due to variations in atmospheric condition.
_% It gives noiseless operation.
_® It requires less maintenance.
_@ There is no reduction in dielectric strength because no carbon particles are
formed during arcing.
és y ing
SF6 circuit breaker has excellent insulating and arc extinguishing properties.
wae gas is non-inflammable and chemically stable.
Its performance is not affected due to variations in atmospheric condition.
_% It gives noiseless operation.
_® It requires less maintenance.
_@ There is no reduction in dielectric strength because no carbon particles are
formed during arcing.
„Pisadvantages
2 SF6 is an expensive gas so these circuit breakers are costly.
_@ Leakage of SF6 from the joints must be continuosly monitor.
@The entrance of moisture in the SF6 breaker tank is very harmful to the breaker,
and it causes several failure.
@ The internal parts need cleaning during periodic maintenance under clean and
dry environment.
e The special facility requires for transportation and maintenance of quality of
gas.
2 SF6 is an expensive gas so these circuit breakers are costly.
_@ Leakage of SF6 from the joints must be continuosly monitor.
@The entrance of moisture in the SF6 breaker tank is very harmful to the breaker,
and it causes several failure.
@ The internal parts need cleaning during periodic maintenance under clean and
dry environment.
e The special facility requires for transportation and maintenance of quality of
gas.
Applications
_@ SF6 circuit breakers are mainly used for the protection of very high voltage
circuit up to 800 kV from fault current.
_@ They are used for protection of power transmission and distribution
systems. They are installed in power generation plants and power grid.
_@ SF6 circuit breakers are mainly used for the protection of very high voltage
circuit up to 800 kV from fault current.
_@ They are used for protection of power transmission and distribution
systems. They are installed in power generation plants and power grid.
Properties of SF6 Gas
The fact that makes the SF6 better arc quenching medium is due to its physical
and chemical properties that are given below.
_Physical Properties
-@ ltis non-flammable gas.
_® lt is colorless and odorless gas.
_® It has excellent thermal conductivity.
_% It has high density and heavier than air.
2 It liquefies at low temperature which is pressure-dependent.
The fact that makes the SF6 better arc quenching medium is due to its physical
and chemical properties that are given below.
_Physical Properties
-@ ltis non-flammable gas.
_® lt is colorless and odorless gas.
_® It has excellent thermal conductivity.
_% It has high density and heavier than air.
2 It liquefies at low temperature which is pressure-dependent.
«enial Properties
_® SF6 gas is stable and inert.
_@ It is non-toxic in its pure form but its products are.
_@ It has high electronegativity meaning it has a strong affinity for free elpatrons,
It recombines very easily after arc quenching for re-utilization.
_@ They are non-corrosive.
Etectrical Properties I
$ —
qe
“¿At has superior dielectric strength which is directly proportional to the pressure.
0 Its arc quenching capabilities is almost 100 times better than air.
_e The frequency of the voltage does not affect its dielectric strength.
_® SF6 gas is stable and inert.
_@ It is non-toxic in its pure form but its products are.
_@ It has high electronegativity meaning it has a strong affinity for free elpatrons,
It recombines very easily after arc quenching for re-utilization.
_@ They are non-corrosive.
Etectrical Properties I
$ —
qe
“¿At has superior dielectric strength which is directly proportional to the pressure.
0 Its arc quenching capabilities is almost 100 times better than air.
_e The frequency of the voltage does not affect its dielectric strength.
ne
End
shield
Shield
Support
flange
Vacuum Circuit Breaker
Insulating
envelope
End
shield
Shield
Support
flange
Vacuum Circuit Breaker
Insulating
envelope
Vacuum Circuit Breaker (VCB)
_9 In vacuum circuit breakers, the vacuum is used as the arc quenching medium.
_@ Vacuum is the superior dielectric medium which arc extinction property is very
good.
e The arc is extinct as the contacts are separated in high vacuum.
-
_@ ltis mainly used for medium voltage ranging from 11 kV to 33 KV.
_@ In this circuit breakers, vacuum of the order of 10° to 10” torr is used.
.4 lt does the interruption at the first current zero.
e Dielectric strength is far better than any other medium. 4
CB was invented in 1960, at that time size was large.
_2 Size of modern VOB is small comparison to 1960.
_9 In vacuum circuit breakers, the vacuum is used as the arc quenching medium.
_@ Vacuum is the superior dielectric medium which arc extinction property is very
good.
e The arc is extinct as the contacts are separated in high vacuum.
-
_@ ltis mainly used for medium voltage ranging from 11 kV to 33 KV.
_@ In this circuit breakers, vacuum of the order of 10° to 10” torr is used.
.4 lt does the interruption at the first current zero.
e Dielectric strength is far better than any other medium. 4
CB was invented in 1960, at that time size was large.
_2 Size of modern VOB is small comparison to 1960.
Construction
Fixed
on
end
shield ——E*] |!
Insulating
Shield ‘envelope
Support
ER MA
I ic ba Se Shield
ellows
oh Sr shield
pra A Bellows
Movin,
contact
Fixed
on
end
shield ——E*] |!
Insulating
Shield ‘envelope
Support
ER MA
I ic ba Se Shield
ellows
oh Sr shield
pra A Bellows
Movin,
contact
9 Vacuum circuit breaker consist of fixed contact, moving | contact and vacuum
chamber. =
_® Fixed contact and moving contact made up of high conducting material.
Out lop i d f gl d ic.
_® Outer envelop is made up of glass and ceramic.
_® Ceramic is the insulated material which provide the mechanical support.
_@ Vacuum chamber consist of vapour condensation shield and Bellow shield.
_® Bellow shield made up of stainless stell and used neon contact.
O
SZ 7
Pressure of vacuum in the vacuum chamber remains
chamber. =
_® Fixed contact and moving contact made up of high conducting material.
Out lop i d f gl d ic.
_® Outer envelop is made up of glass and ceramic.
_® Ceramic is the insulated material which provide the mechanical support.
_@ Vacuum chamber consist of vapour condensation shield and Bellow shield.
_® Bellow shield made up of stainless stell and used neon contact.
O
SZ 7
Pressure of vacuum in the vacuum chamber remains
Fixed contact
moving contact Bellows shie
moving contact Bellows shie
e In normal condition both contacts remains closed to each other.
_® When fault occurs in the system both contacts displace to each other. .-—
_@ When moving contact moves away then arc generates between the contacts.
3 4 nz
.® The arc produced in the vacuum.-
_@ The main reason of arc formation is tip of contacts is overheated due to high gie
temperature of conductor. _ duele
_® Metal contacts release the positive ions as a vapour. woe
_@ When vapour accumulated between both the contacts, vapour ionised due
high temperature.
2 With this medium current flows which appears as an arc. 4
@ Value of current in arc, depends upon rate of produces the vapour. =
2 When value of current will reduce vapour reduction rate will also reduce.
e As we know thatac current becomes zero at every half cycle, dielectric strength
will high of vacuum.
_® When fault occurs in the system both contacts displace to each other. .-—
_@ When moving contact moves away then arc generates between the contacts.
3 4 nz
.® The arc produced in the vacuum.-
_@ The main reason of arc formation is tip of contacts is overheated due to high gie
temperature of conductor. _ duele
_® Metal contacts release the positive ions as a vapour. woe
_@ When vapour accumulated between both the contacts, vapour ionised due
high temperature.
2 With this medium current flows which appears as an arc. 4
@ Value of current in arc, depends upon rate of produces the vapour. =
2 When value of current will reduce vapour reduction rate will also reduce.
e As we know thatac current becomes zero at every half cycle, dielectric strength
will high of vacuum.
e. Now arc will quickly extinguis in first half cycle of alternative current.
Advantages
_® Vacuum circuit breaker extinguish the arc in first half cycle.
_® It's operation is fast compare to other circuit bre:
_@ It can operates in any environment.
_® It required low maintenance
_Disadvantages
e High technology is used for creating the vacuum.
_® During repair it can damage.
e more expensive.
Advantages
_® Vacuum circuit breaker extinguish the arc in first half cycle.
_® It's operation is fast compare to other circuit bre:
_@ It can operates in any environment.
_® It required low maintenance
_Disadvantages
e High technology is used for creating the vacuum.
_® During repair it can damage.
e more expensive.
Application
% It is used in industry as a switching purpose.
2 It is used to disconnect voltage level between 11kV to 33kV.
2 VCB commonly use where rapid operation is required.
4
% It is used in industry as a switching purpose.
2 It is used to disconnect voltage level between 11kV to 33kV.
2 VCB commonly use where rapid operation is required.
4
AIR CIRCUIT BREAKER
AIR CIRCUIT BREAKER
© lt provides over current protection, short circuit protection and earth fault
protection.
@ It use air as an arc extinguishing medium.
O The dielectric strength of air is 3 kV per mm.
O It is used for low voltage application upto 11 kV.
© lt consists of fixed and movable contact and contact are separated in the arc
interruption chamber.
@ The current rating of air circuit breaker is about 800A to 11000 A.
6 In the air circuit breaker the contact separartion and arc extinction takes placed in
air at atmospheric pressure.
e High resistance principle is employed in such circuit breakers.
© The arc is repeadily lengthened by means of the arc runners and arc chute.
@ Arc resistance is increased by cooling lengthening and spliting the arc.
© lt provides over current protection, short circuit protection and earth fault
protection.
@ It use air as an arc extinguishing medium.
O The dielectric strength of air is 3 kV per mm.
O It is used for low voltage application upto 11 kV.
© lt consists of fixed and movable contact and contact are separated in the arc
interruption chamber.
@ The current rating of air circuit breaker is about 800A to 11000 A.
6 In the air circuit breaker the contact separartion and arc extinction takes placed in
air at atmospheric pressure.
e High resistance principle is employed in such circuit breakers.
© The arc is repeadily lengthened by means of the arc runners and arc chute.
@ Arc resistance is increased by cooling lengthening and spliting the arc.
Types of Air Circuit Breaker
1. Plane Breake Type
2. Magnetic Blow Out Type
3. Arc Chute Air Breaker.
1. Plane Breake Type
2. Magnetic Blow Out Type
3. Arc Chute Air Breaker.
1.Plan Breaker Type
© It is a simplest type of air circuit breaker.
© In this circuit breaker contacts are made in the shape of two horns.
e The air initially strikes across the shortest distance between the horns and driven
steadily upward by the conventional current caused by heating of air during arcing
and the interaction of magnetic and electric field.
@ The arc extends from one tip to the other when the horn fully separated resulting in
lengthening and cooling of arc.
e Arc extinguishing process is reletively slow.
© It used for upto 500 V and to low power circuits.
RE 15.2 A simple air-break breaker.
© It is a simplest type of air circuit breaker.
© In this circuit breaker contacts are made in the shape of two horns.
e The air initially strikes across the shortest distance between the horns and driven
steadily upward by the conventional current caused by heating of air during arcing
and the interaction of magnetic and electric field.
@ The arc extends from one tip to the other when the horn fully separated resulting in
lengthening and cooling of arc.
e Arc extinguishing process is reletively slow.
© It used for upto 500 V and to low power circuits.
RE 15.2 A simple air-break breaker.
2. Magnetic Blow Out Type
© In this circuit breaker magnetic field is produced by magnetic blow out coil.
@ The magnetic blow out coil is connected in series with the circuit being interrupt.
e Such coils are called blow out coil, because they assist in the arc being
magnetically blow out.
@ The magnetic field it self does not extinguish the arc.
© In this circuit breaker magnetic field is produced by magnetic blow out coil.
@ The magnetic blow out coil is connected in series with the circuit being interrupt.
e Such coils are called blow out coil, because they assist in the arc being
magnetically blow out.
@ The magnetic field it self does not extinguish the arc.
e It simply moves the arc chutes where the arc is lengthened, cooled and
extinguished.
@ The arc shields prevent arc sreading to adjacent metal work.
e It is impotant to connect the coil at correct polarity so that the arc is directed
upward.
@ Arc chute confines the arc within a restricted space.
extinguished.
@ The arc shields prevent arc sreading to adjacent metal work.
e It is impotant to connect the coil at correct polarity so that the arc is directed
upward.
@ Arc chute confines the arc within a restricted space.
_@ There are two set of contact called the main contact and arcing or auxiliary contact.
© Main contacts are usually of copper and conduct the current in close position of the
breaker.
@ The arcing contacts are hard, heat resistance and usually of copper alloy.
_@ Arcing contact are used to relieve the main contacts from demage due to arcing.
he arcing contacts are easily renewable when required.
4 The auxiliary arıd arcing contacts close before and open after the main contact
ring operation. ——
glen the blow outs consist o' inserts in the arcing chutes.
e These are so arrange that the magnetic field induced in them biy the current in the
arc moves it upward still faster.
e steel plates divide the arc into a number of short arcs in series.
hen the arc comes into contact with the relatively cool surface of the steel plates,
it get rapidly and effectively cooled. ET
@ The movement of the arc may be natural or aided by a magnetic blow out.
© Main contacts are usually of copper and conduct the current in close position of the
breaker.
@ The arcing contacts are hard, heat resistance and usually of copper alloy.
_@ Arcing contact are used to relieve the main contacts from demage due to arcing.
he arcing contacts are easily renewable when required.
4 The auxiliary arıd arcing contacts close before and open after the main contact
ring operation. ——
glen the blow outs consist o' inserts in the arcing chutes.
e These are so arrange that the magnetic field induced in them biy the current in the
arc moves it upward still faster.
e steel plates divide the arc into a number of short arcs in series.
hen the arc comes into contact with the relatively cool surface of the steel plates,
it get rapidly and effectively cooled. ET
@ The movement of the arc may be natural or aided by a magnetic blow out.
AIR BLAST CIRCUIT
BREAKER
Arc splitters
Arc
Fixed
Opening *—— contact
Tr
Air flow
BREAKER
Arc splitters
Arc
Fixed
Opening *—— contact
Tr
Air flow
AIR BLAST CIRCUIT BREAKER
The air blast circuit breaker is a type of circuit breaker where at high pressure the
air blast is used for arc extinction in the electrical circuit. OO
@ The main principle behind it is that it has a fixed contact and a moving contact,
where high pressure is applied for arc extinction in a circuit breaker.
se
———
Types of Air Blast Circuit Breakers
There are three types of air blast circuit rn
1. Axial Blast
2. Radial Blast
3. Cross Blast “Sic =k
Axial blast Radial blast
(ay 1b)
FIGURE 15.12 Air blast circuit breakers.
The air blast circuit breaker is a type of circuit breaker where at high pressure the
air blast is used for arc extinction in the electrical circuit. OO
@ The main principle behind it is that it has a fixed contact and a moving contact,
where high pressure is applied for arc extinction in a circuit breaker.
se
———
Types of Air Blast Circuit Breakers
There are three types of air blast circuit rn
1. Axial Blast
2. Radial Blast
3. Cross Blast “Sic =k
Axial blast Radial blast
(ay 1b)
FIGURE 15.12 Air blast circuit breakers.
CONSTRUCTION
The main components of an air blast circuit breaker are:
© Air Reservoir
e Hollow Insulator Assembly
e Arc Extinction Chamber
O Valves
e Current Carrying Conductors
Air Reservoir
@ It is a tank that stores air, at high pressure, around to 20-30 atm
© ltis connected to an auxiliary system which supplies high pressure air to the
reservoir.
Hollow Insulator Assembly
e These insulators connect the reservoir to the arc extinction chamber.
@ They supply high pressure air from the reservoir to the arc extinction chamber.
© Values at the base of the hollow insulators enable us to control the flow of high
pressure air into the system.
The main components of an air blast circuit breaker are:
© Air Reservoir
e Hollow Insulator Assembly
e Arc Extinction Chamber
O Valves
e Current Carrying Conductors
Air Reservoir
@ It is a tank that stores air, at high pressure, around to 20-30 atm
© ltis connected to an auxiliary system which supplies high pressure air to the
reservoir.
Hollow Insulator Assembly
e These insulators connect the reservoir to the arc extinction chamber.
@ They supply high pressure air from the reservoir to the arc extinction chamber.
© Values at the base of the hollow insulators enable us to control the flow of high
pressure air into the system.
© They also insulate the other equipment, protecting them from high-voltage lines.
Arc Extinction Chamber
e The arc extinction chamber is mounted on the hollow insulator assembly.
O Here, the circuit moves and breaks, within the arc extinction chamber, which
consists of fixed and moving contacts.
@ The movement of contacts is dependent upon the air pressure.
Valves _
@ They are at the base of insulators which regulate the flow of high pressure air.
O It generally flows in the direction from the air reservoir to the arc extiction chamber.
@ If upon a fault circuit, the valves open with the help of an iron rod via a pneumatic
operation system.
Current Carrying Conductors
@ The sole purpose of current carrying conductors is to link all the neighbouring
equipment with arc extinction chamber in series.
Arc Extinction Chamber
e The arc extinction chamber is mounted on the hollow insulator assembly.
O Here, the circuit moves and breaks, within the arc extinction chamber, which
consists of fixed and moving contacts.
@ The movement of contacts is dependent upon the air pressure.
Valves _
@ They are at the base of insulators which regulate the flow of high pressure air.
O It generally flows in the direction from the air reservoir to the arc extiction chamber.
@ If upon a fault circuit, the valves open with the help of an iron rod via a pneumatic
operation system.
Current Carrying Conductors
@ The sole purpose of current carrying conductors is to link all the neighbouring
equipment with arc extinction chamber in series.
Working
Working
@ When the circuit breaker is under normal conditions, the breaker contacts present in
the extinction chamber are in touch with each other.
@ Under faulty conditions, the valves open with the help of an iron rod.
@ When the valves open, the air with high pressure enters the arc extinction chamber
via a hollow chamber setup.
© This increases the pressure on the moving contacts and eventually gets separated
from the fixed contact.
© During separation, an arc is created between the two contacts, due to the ionization
of air present between the two contacts.
e This ionized air is taken out due to high pressure via the outlet valves and the arc
formed is extinguished.
@ After the circuit is broken successfully and the fault has been cleared, the values
close up and the pressure on the moving contacts eventually drops.
@ When the circuit breaker is under normal conditions, the breaker contacts present in
the extinction chamber are in touch with each other.
@ Under faulty conditions, the valves open with the help of an iron rod.
@ When the valves open, the air with high pressure enters the arc extinction chamber
via a hollow chamber setup.
© This increases the pressure on the moving contacts and eventually gets separated
from the fixed contact.
© During separation, an arc is created between the two contacts, due to the ionization
of air present between the two contacts.
e This ionized air is taken out due to high pressure via the outlet valves and the arc
formed is extinguished.
@ After the circuit is broken successfully and the fault has been cleared, the values
close up and the pressure on the moving contacts eventually drops.
Advantages
The following advantages of air blast circuit breakers:
O They are cost-effective and readily available in the market.
@ These equipment are chemically stable.
@ The chance of fire hazard is eliminated.
e Consistent arcing at short time intervals causes less burning of contact valves.
@ Can work with high voltages and at a higher speed.
@ They are sustainable and have a low cost of maintenance.
Applications
The following are the applications of an air blast circuit breaker.
@ They are used to control transient overvoltages at major power station and
industrial plants.
O They protect the machines operating at high voltage like power transformers,
capacitors, AC generations and DC generation.
@ They can also be used as fire extinguishers.
Due to the high resistance power, it can increase the resistance of the arc chamber.
The following advantages of air blast circuit breakers:
O They are cost-effective and readily available in the market.
@ These equipment are chemically stable.
@ The chance of fire hazard is eliminated.
e Consistent arcing at short time intervals causes less burning of contact valves.
@ Can work with high voltages and at a higher speed.
@ They are sustainable and have a low cost of maintenance.
Applications
The following are the applications of an air blast circuit breaker.
@ They are used to control transient overvoltages at major power station and
industrial plants.
O They protect the machines operating at high voltage like power transformers,
capacitors, AC generations and DC generation.
@ They can also be used as fire extinguishers.
Due to the high resistance power, it can increase the resistance of the arc chamber.
OIL CIRCUIT BREAKER (OCB)
not dos
| b Engine Walla
| b Engine Walla
-~ INTRODUCTION
e Oil circuit breaker is such type of circuit breaker which used oil as a dielectric or
insulating medium for arc extinction.
ein oil circuit breaker the contacts of the breaker are made to separate within an
insulating oil. o
en the fault occurs in the system the contacts of the circuit breaker are open
under the insulating oil, and an arc is developed between them and the heat of the
arc is evaporated in the surrounding oil.
2 The oil circuit breaker is divided into two categories
A. Bulk Oil Circuit Breaker
_2-tow Oil Circuit Breaker
e Oil circuit breaker is such type of circuit breaker which used oil as a dielectric or
insulating medium for arc extinction.
ein oil circuit breaker the contacts of the breaker are made to separate within an
insulating oil. o
en the fault occurs in the system the contacts of the circuit breaker are open
under the insulating oil, and an arc is developed between them and the heat of the
arc is evaporated in the surrounding oil.
2 The oil circuit breaker is divided into two categories
A. Bulk Oil Circuit Breaker
_2-tow Oil Circuit Breaker
Construction of Oil Circuit Breaker
„Oil circuit breaker is very easy in construction. It consists of current carrying
contacts enclosed in a strong, weather-tight earth metal tank and the tank is filled
with transformer oil. The oil is both acts as an arc extinguishing medium and as an
insulator between the live part and earth. >
A /
Conductor LIEN
Fixed contact
shing
Dielectric
oil
Moving:
contact
„Oil circuit breaker is very easy in construction. It consists of current carrying
contacts enclosed in a strong, weather-tight earth metal tank and the tank is filled
with transformer oil. The oil is both acts as an arc extinguishing medium and as an
insulator between the live part and earth. >
A /
Conductor LIEN
Fixed contact
shing
Dielectric
oil
Moving:
contact
~At the top of the oil, air is filled in the tank which acts as a cushion to control the
displaced oil on the formation of gas around the arc and also to absorb the
mechanical shock of the upward movement of oil. The breaker tank is securely
bolted for carrying out the vibration caused on interrupting very high current. Oil
_ circuit breaker consists gas outlet which is fitted in the tank cover for the removal of
the gases.
Working Principle of Oil Circuit Breaker
During the normal operating conditions, the contact of the oil circuit breaker is
closed and carry the current. When the fault occurs in the system, the contacts of
the breaker are moving apart, and an arc is struck between the contacts.
Due to this arc, a large amount of heat is liberated, and a very high temperature is
reached which vaporises the surrounding oil into gas. The gas, thus liberated
surrounds the arc and its explosive growth around it displace the oil violently. The
arc is extinguished when the distance between the fixed and moving contact
reaches a certain critical value, depends on the arc current and recovery voltage.
displaced oil on the formation of gas around the arc and also to absorb the
mechanical shock of the upward movement of oil. The breaker tank is securely
bolted for carrying out the vibration caused on interrupting very high current. Oil
_ circuit breaker consists gas outlet which is fitted in the tank cover for the removal of
the gases.
Working Principle of Oil Circuit Breaker
During the normal operating conditions, the contact of the oil circuit breaker is
closed and carry the current. When the fault occurs in the system, the contacts of
the breaker are moving apart, and an arc is struck between the contacts.
Due to this arc, a large amount of heat is liberated, and a very high temperature is
reached which vaporises the surrounding oil into gas. The gas, thus liberated
surrounds the arc and its explosive growth around it displace the oil violently. The
arc is extinguished when the distance between the fixed and moving contact
reaches a certain critical value, depends on the arc current and recovery voltage.
>
o
The oil circuit breaker is very reliable in operation, and it is very cheap. The most
important feature of oil circuit breaker is that no special devices are used for
controlling the arc caused by moving contact. The oil as an arc quenching medium
has certain advantages and disadvantages
o
The oil circuit breaker is very reliable in operation, and it is very cheap. The most
important feature of oil circuit breaker is that no special devices are used for
controlling the arc caused by moving contact. The oil as an arc quenching medium
has certain advantages and disadvantages
Advantages
© The oil has a high dielectric strength and provides insulation between the contact
after the arc has been extinguished.
e The oil used in circuit breaker provides a small clearance between the conductors
and the earth components.
_@ The hydrogen gas is formed in the tank which has a high diffusion rate and good
cooling properties.
Disadvantages
e The oil used in oil circuit breaker is inflammable and hence, cause a fire hazard.
@ There is a risk of formation of explosive mixture with air.
@ Due to decomposition of oil in the arc, the carbon particles is generated which
polluted the oil and hence the dielectric strength of the oil decreases.
© The oil has a high dielectric strength and provides insulation between the contact
after the arc has been extinguished.
e The oil used in circuit breaker provides a small clearance between the conductors
and the earth components.
_@ The hydrogen gas is formed in the tank which has a high diffusion rate and good
cooling properties.
Disadvantages
e The oil used in oil circuit breaker is inflammable and hence, cause a fire hazard.
@ There is a risk of formation of explosive mixture with air.
@ Due to decomposition of oil in the arc, the carbon particles is generated which
polluted the oil and hence the dielectric strength of the oil decreases.
MINIATURE CIRCUIT BREAKER (MCB
ucti
4 MCB is an automatic switch that opens when excessive current flows through the circuit.
is used to protect low voltage electrical circuits from damage caused by excess current
Soom an overload or short circuit.
18 Tt is an electromechanical device.
@ It can be reclosed without any manual replacement.
© In the case of a fuse, once it has been operated, it must be replaced or rewired.
@ Hence, fuse is known as one of the sacrificial devices.
© This is the main reason why MCBs are used as an alternative to the fuse in most of the
circuits.
© Also, whenever there is a fault in the circuit, the switches in the MCB automatically shut
down and the fault of the device can be easily detected.
e Handling MCB is relatively safe, and it quickly restores the supply.
MCB - Miniature Circuit Breaker can be reset quickly and does not demand more
maintenance costs.
ucti
4 MCB is an automatic switch that opens when excessive current flows through the circuit.
is used to protect low voltage electrical circuits from damage caused by excess current
Soom an overload or short circuit.
18 Tt is an electromechanical device.
@ It can be reclosed without any manual replacement.
© In the case of a fuse, once it has been operated, it must be replaced or rewired.
@ Hence, fuse is known as one of the sacrificial devices.
© This is the main reason why MCBs are used as an alternative to the fuse in most of the
circuits.
© Also, whenever there is a fault in the circuit, the switches in the MCB automatically shut
down and the fault of the device can be easily detected.
e Handling MCB is relatively safe, and it quickly restores the supply.
MCB - Miniature Circuit Breaker can be reset quickly and does not demand more
maintenance costs.
+6 MCB works on a bi-metal respective principle that protects against overload
‘current and solenoid short circuit current.
MCBs are typically rated up to a current 125 A. os
A Miniature Circuit Breaker is a switchgear which is usually available in the range of
125A. Its Short circuit rating is given in Kiloamps (kA), and this indicates the level o
ability to work.
Working Principle Miniature Circuit Breaker
There is two arrangement of operation of a miniature circuit breaker.
Je One due to the thermal effect of over current and other due to electromagnetic
effect of over curre:
The thermal operation of the miniature circuit breaker is achieved with a
bimetallic strip whenever continuous overcurrent flows throug B, the
bimetallic strip is heated and deflects by bending.
‘current and solenoid short circuit current.
MCBs are typically rated up to a current 125 A. os
A Miniature Circuit Breaker is a switchgear which is usually available in the range of
125A. Its Short circuit rating is given in Kiloamps (kA), and this indicates the level o
ability to work.
Working Principle Miniature Circuit Breaker
There is two arrangement of operation of a miniature circuit breaker.
Je One due to the thermal effect of over current and other due to electromagnetic
effect of over curre:
The thermal operation of the miniature circuit breaker is achieved with a
bimetallic strip whenever continuous overcurrent flows throug B, the
bimetallic strip is heated and deflects by bending.
iature Circuit Breaker Construction
Miniature circuit breaker construction is very simple, robust and maintenance-free.
Generally, an MCB is not repaired or maintained, it just replaced by a new one when
required. A miniature circuit breaker has normally three main constructional parts.
These are:
Frame of Miniature Circuit Breaker
The frame of a miniature circuit breaker is a molded case. This is a rigid, strong,
insulated housing in which the other components are mounted.
2-Operating Mechanism of Miniature Circuit Breaker
The operating mechanism of a miniature circuit breaker provides the means of manus
opening and closing operation of a miniature circuit breaker. It has three-positions
“ON,” “OFF,” and “TRIPPED”. The external switching latch can be in the “TRIPPED”
position if the MCB is tripped due to over-current.
When manually switch off the MCB, the switching latch will be in the “OFF” position. |
the closed condition of an MCB, the switch is positioned at “ON”. By observing the
Positions of the switching latch one can determine the condition of MCB whether it is
A > PR —
trinned or manually ewi
Miniature circuit breaker construction is very simple, robust and maintenance-free.
Generally, an MCB is not repaired or maintained, it just replaced by a new one when
required. A miniature circuit breaker has normally three main constructional parts.
These are:
Frame of Miniature Circuit Breaker
The frame of a miniature circuit breaker is a molded case. This is a rigid, strong,
insulated housing in which the other components are mounted.
2-Operating Mechanism of Miniature Circuit Breaker
The operating mechanism of a miniature circuit breaker provides the means of manus
opening and closing operation of a miniature circuit breaker. It has three-positions
“ON,” “OFF,” and “TRIPPED”. The external switching latch can be in the “TRIPPED”
position if the MCB is tripped due to over-current.
When manually switch off the MCB, the switching latch will be in the “OFF” position. |
the closed condition of an MCB, the switch is positioned at “ON”. By observing the
Positions of the switching latch one can determine the condition of MCB whether it is
A > PR —
trinned or manually ewi
The trip unit is the main part, responsible for the proper working of the miniature circı
breaker. Two main types of trip mechanisms are provided in MCB. A bimetal provide
protection against overload current and an electromagnet provides protection againg
short-circuit current.
breaker. Two main types of trip mechanisms are provided in MCB. A bimetal provide
protection against overload current and an electromagnet provides protection againg
short-circuit current.
On
?peration of Miniature Circuit Breaker
?peration of Miniature Circuit Breaker
ration of Miniature Ci
\n MCBB protects a circuit from fault current. It us:
«echanisms to break those fault currents. The thermal mechanism is used for overload
protection while the magnetic mechanism is used for short circuit protection.
Overload occurs when the current exceeds a limit for a prolonged duration. MCEB has
a thermal mechanism that contains a bimetallic contact to protect from overload. A
} bimetallic strip is made from two different types of metal having different rates of
thermal expansion. Upon temperature change, the strip bends or contracts.
The main current passes through the bimetallic strip. If the current exceeds a certain
limit, the contacts heat up and expand. Due to different expansion rates, the strip bends
and trips the circuit.
In electrical devices, the current can overload for short durations of time, it is normal
and should not be considered as fault current. Therefore, MCB has a time delay that
s the overload current for a short duration of time before tripping the circuit.
\n MCBB protects a circuit from fault current. It us:
«echanisms to break those fault currents. The thermal mechanism is used for overload
protection while the magnetic mechanism is used for short circuit protection.
Overload occurs when the current exceeds a limit for a prolonged duration. MCEB has
a thermal mechanism that contains a bimetallic contact to protect from overload. A
} bimetallic strip is made from two different types of metal having different rates of
thermal expansion. Upon temperature change, the strip bends or contracts.
The main current passes through the bimetallic strip. If the current exceeds a certain
limit, the contacts heat up and expand. Due to different expansion rates, the strip bends
and trips the circuit.
In electrical devices, the current can overload for short durations of time, it is normal
and should not be considered as fault current. Therefore, MCB has a time delay that
s the overload current for a short duration of time before tripping the circuit.
Short Circuit Protection
MCGB protects against a short circuits using a solenoid that produces
electromagnetic force. The main current flows through the solenoid that attracts and
repels a plunger responsible for tripping the breaker.
If the current remains below the threshold, the solenoid produces a weak magnetic
force that cannot attract the plunger. In short circuit conditions, a very high current
flows through the solenoid that generates a very strong magnetic force. It attracts the
> plunger that trips the circuit.
MCGB protects against a short circuits using a solenoid that produces
electromagnetic force. The main current flows through the solenoid that attracts and
repels a plunger responsible for tripping the breaker.
If the current remains below the threshold, the solenoid produces a weak magnetic
force that cannot attract the plunger. In short circuit conditions, a very high current
flows through the solenoid that generates a very strong magnetic force. It attracts the
> plunger that trips the circuit.
MOLDED CASE CIRCUIT BREAKER (MCCB)
INTRODUCTION Mel _30Amp _100Amp _
@ Molded Case Circuit Breaker or MCCB is an automatic electrical device.
Wtis a type of circuit breaker that protects the circuit from overloading, short circuit and
current surges.
@ It is an advanced version of miniature circuit breaker MCB since it operates like one.
@ However, it offers extra features that make it a superior circuit breaker such as
remote closing and adjustable trip settings i.e. its current settings and time settings
can be adjusted according to our needs.
@ MCCB is used to protect the low voltage distribution system.
It is available in rating up to 2500 Amps and 1.1 kV.
@ MCCB can used for protection of capacitor bank, generator protection and main
electric feeder distribution.
INTRODUCTION Mel _30Amp _100Amp _
@ Molded Case Circuit Breaker or MCCB is an automatic electrical device.
Wtis a type of circuit breaker that protects the circuit from overloading, short circuit and
current surges.
@ It is an advanced version of miniature circuit breaker MCB since it operates like one.
@ However, it offers extra features that make it a superior circuit breaker such as
remote closing and adjustable trip settings i.e. its current settings and time settings
can be adjusted according to our needs.
@ MCCB is used to protect the low voltage distribution system.
It is available in rating up to 2500 Amps and 1.1 kV.
@ MCCB can used for protection of capacitor bank, generator protection and main
electric feeder distribution.
onstruction
An MCCB is made from the following
® Arc chute
2 Contacts
% Operating mechanism
@ Terminal Connector
2% Thermal Trip Unit
+ Magnetic Trip Unit
@ Handle / Trip-free Mechanism
© Trip Button
Afc Chute
Arc chute is a set of parallel metal plates that are mutually insulated from each other.
It helps in extinguishing the arc by splitting the arc and lengthening it. It is also known
as an arc divider or arc splitter. These plates are made of ferromagnetic material.
main parts each one explained in detail
An MCCB is made from the following
® Arc chute
2 Contacts
% Operating mechanism
@ Terminal Connector
2% Thermal Trip Unit
+ Magnetic Trip Unit
@ Handle / Trip-free Mechanism
© Trip Button
Afc Chute
Arc chute is a set of parallel metal plates that are mutually insulated from each other.
It helps in extinguishing the arc by splitting the arc and lengthening it. It is also known
as an arc divider or arc splitter. These plates are made of ferromagnetic material.
main parts each one explained in detail
Cóntacts
Contacts are the metallic conductors that are responsible for carrying the current to
the load. There are two types of contacts i.e. fixed and moving contact. The contacts
are made of arc resistance material having low resistivity and corrosion. The quality of
the material decides the lifetime of the circuit breaker.
Operating Mechanism
It is the mechanism of MCCB responsible for opening and closing the current-carrying
contacts. it is connected with trip unit that triggers the operating mechanism. The trip
unit operates on a thermal and magnetic mechanism.
rminal Connector
The terminal connectors are used to connect the MCCB to the external circuit. The
upper terminals are connected to the output/load while the bottom terminals are
connected to the input/supply. Although they are bidirectional, the input and output
designation is due to their physical installation
Contacts are the metallic conductors that are responsible for carrying the current to
the load. There are two types of contacts i.e. fixed and moving contact. The contacts
are made of arc resistance material having low resistivity and corrosion. The quality of
the material decides the lifetime of the circuit breaker.
Operating Mechanism
It is the mechanism of MCCB responsible for opening and closing the current-carrying
contacts. it is connected with trip unit that triggers the operating mechanism. The trip
unit operates on a thermal and magnetic mechanism.
rminal Connector
The terminal connectors are used to connect the MCCB to the external circuit. The
upper terminals are connected to the output/load while the bottom terminals are
connected to the input/supply. Although they are bidirectional, the input and output
designation is due to their physical installation
Tp Unit
It is the unit responsible to trigger the operating mechanism. The trip unit includes a
thermal mechanism for overload, magnetic tripping for short circuits and a test button
for testing.
Æhermal Trip Unit
The thermal trip unit uses a thermal mechanism that is a bimetallic strip that
bends (and opens the contacts) when the temperature rises due to the overloading.
Magnetic Trip Unit =
The magnetic trip unit has alcalinas generates a magnetic field when higher currents
flow through its solenoid due to the short circuit, it trips the circuit breaker. While the
test button is used to simulate the above-said mechanisms and test the response of the
circuit breaker.
andle / Trip-free Mechanism
It is a handle used to open or close the breaker manually. It is also known as a trip-free
mechanism because it will trip even if the handle is held in ON position.
It is the unit responsible to trigger the operating mechanism. The trip unit includes a
thermal mechanism for overload, magnetic tripping for short circuits and a test button
for testing.
Æhermal Trip Unit
The thermal trip unit uses a thermal mechanism that is a bimetallic strip that
bends (and opens the contacts) when the temperature rises due to the overloading.
Magnetic Trip Unit =
The magnetic trip unit has alcalinas generates a magnetic field when higher currents
flow through its solenoid due to the short circuit, it trips the circuit breaker. While the
test button is used to simulate the above-said mechanisms and test the response of the
circuit breaker.
andle / Trip-free Mechanism
It is a handle used to open or close the breaker manually. It is also known as a trip-free
mechanism because it will trip even if the handle is held in ON position.
The handle could be in either three positions i.e. upward, middle or downward. If the
handle is in upward position, it is ON position. If it is in the middle position, the breaker
has been tripped while the downward position shows OFF status.
Trip-Button
The trip button is used for testing the breaker. It is a red-colored button that trips the
operating mechanism when pushed.
——_ 771111
ction of MCCB
CB as it is an electrical protection device has the following functions
Protection against Overloading
Overloading is the condition when the current exceeds a predetermined limit for a
specific duration of time. The overloading current can damage the equipment, wirings
and can create fire hazards. MCCB offers protection against overloading using a
bimetallic strip. A
handle is in upward position, it is ON position. If it is in the middle position, the breaker
has been tripped while the downward position shows OFF status.
Trip-Button
The trip button is used for testing the breaker. It is a red-colored button that trips the
operating mechanism when pushed.
——_ 771111
ction of MCCB
CB as it is an electrical protection device has the following functions
Protection against Overloading
Overloading is the condition when the current exceeds a predetermined limit for a
specific duration of time. The overloading current can damage the equipment, wirings
and can create fire hazards. MCCB offers protection against overloading using a
bimetallic strip. A
Working Principle of MCCB
An MCCB protects a circuit from fault current. It uses thermal and magnetic
mechanisms to break those fault currents. The thermal mechanism is used for overload
protection while the magnetic mechanism is used for short circuit protection.
| ———
Overload Protection
Overload occurs when the current exceeds a limit for a prolonged duration. MCCB has
a thermal mechanism that contains a bimetallic contact to protect from overload. A
bimetallic strip is made from two different types of metal having different rates of
thermal expansion. Upon temperature change, the strip bends or contracts.
The main current passes through the bimetallic strip. If the current exceeds a certain
limit, the contacts heat up and expand. Due to different expansion rates, the strip bends
and trips the circuit.
In electrical devices, the current can overload for short durations of time, it is normal
and should not be considered as fault current. Therefore, MCCB has a time delay that
allows the overload current for a short duration of time before tripping the circuit.
An MCCB protects a circuit from fault current. It uses thermal and magnetic
mechanisms to break those fault currents. The thermal mechanism is used for overload
protection while the magnetic mechanism is used for short circuit protection.
| ———
Overload Protection
Overload occurs when the current exceeds a limit for a prolonged duration. MCCB has
a thermal mechanism that contains a bimetallic contact to protect from overload. A
bimetallic strip is made from two different types of metal having different rates of
thermal expansion. Upon temperature change, the strip bends or contracts.
The main current passes through the bimetallic strip. If the current exceeds a certain
limit, the contacts heat up and expand. Due to different expansion rates, the strip bends
and trips the circuit.
In electrical devices, the current can overload for short durations of time, it is normal
and should not be considered as fault current. Therefore, MCCB has a time delay that
allows the overload current for a short duration of time before tripping the circuit.
Short Circuit Protection
MCCB protects against a short circuits using a solenoid that produces electromagnetic
force. The main current flows through the solenoid that attracts and repels a plunger
responsible for tripping the breaker.
If the current remains below the threshold, the solenoid produces a weak magnetic
force that cannot attract the plunger. In short circuit conditions, a very high current
flows through the solenoid that generates a very strong magnetic force. It attracts the
plunger that trips the circuit.
MCCB protects against a short circuits using a solenoid that produces electromagnetic
force. The main current flows through the solenoid that attracts and repels a plunger
responsible for tripping the breaker.
If the current remains below the threshold, the solenoid produces a weak magnetic
force that cannot attract the plunger. In short circuit conditions, a very high current
flows through the solenoid that generates a very strong magnetic force. It attracts the
plunger that trips the circuit.
Difference Between MCB and MCCB
men
MCB MCCB
@ It stands for Miniature Circuit e It stands for Molded Case Circuit
Breaker. Breaker.
2500 Amp
© Rated current not more than 125
Ampere.
© lis interrupting current rating is under
10KA
@ Trip characteristics cannot be
adjusted.
@ Judging from their power capacities,
MCB is mainly used for low Breaking
capacity requirement mainly
domestic.
@ Rated Current up to 1600A-
© Their interrupting current ranges from
around 10KA -85KA
e Trip characteristics can be adjusted.
O MCCB is mainly used for both low and
high Breaking capacity requirements
mainly industrial.
men
MCB MCCB
@ It stands for Miniature Circuit e It stands for Molded Case Circuit
Breaker. Breaker.
2500 Amp
© Rated current not more than 125
Ampere.
© lis interrupting current rating is under
10KA
@ Trip characteristics cannot be
adjusted.
@ Judging from their power capacities,
MCB is mainly used for low Breaking
capacity requirement mainly
domestic.
@ Rated Current up to 1600A-
© Their interrupting current ranges from
around 10KA -85KA
e Trip characteristics can be adjusted.
O MCCB is mainly used for both low and
high Breaking capacity requirements
mainly industrial.
Selection Of MCCB For Motor
@ MCCBs are used for overload, short circuit, earth fault and neutral protections.
@ However selection parameters change with respect to the loads & applications.
‚® Current rating is the most important parameter of selection of MCCB for the motor.
_@ There are two types of current rating of MCCB namely rated current and short-circuit
breaking capacity.
@ Rated current is the current value which overload protection is tripped.
e For MCB it is fixed while in MCCB the rated current is an adjustable range instead of
a fixed value.
e Breaking capacity is defined as the maximum level of fault current which can be
safely cleared.
e The breaking capacity is the highest fault current that the MCCB can trip without
being damaged permanently.
e The full load current rating of motor should be known during the selection of meter.
MccD
@ MCCBs are used for overload, short circuit, earth fault and neutral protections.
@ However selection parameters change with respect to the loads & applications.
‚® Current rating is the most important parameter of selection of MCCB for the motor.
_@ There are two types of current rating of MCCB namely rated current and short-circuit
breaking capacity.
@ Rated current is the current value which overload protection is tripped.
e For MCB it is fixed while in MCCB the rated current is an adjustable range instead of
a fixed value.
e Breaking capacity is defined as the maximum level of fault current which can be
safely cleared.
e The breaking capacity is the highest fault current that the MCCB can trip without
being damaged permanently.
e The full load current rating of motor should be known during the selection of meter.
MccD
@ In general the current rating of MCCB must be greater than 1.5 times of full load
current of motor.
@ For example :- if the full load current rating of a motor is 60 Amp,than the current
rating of MCCB must be of 90 Amp (or 100%. b) [1.5x60=90 Amp]
_ _—_—_ rd
„Selection of current rating of MCCB for a motor
Let us consider a motor of 30 kWatt, in horse power (hp) its power rating is 40 hp.
a
power in hp = Power in watt = _30 =40 hp fan
0.746 0746 == hp = rt
The full load current is calculated by multiplying 1.5 to the power in hp.
full load current = 1.5%,40 hp =60 Amp
Hence 90 Amp of MCCB use with 30 kW of motor.
N
current of motor.
@ For example :- if the full load current rating of a motor is 60 Amp,than the current
rating of MCCB must be of 90 Amp (or 100%. b) [1.5x60=90 Amp]
_ _—_—_ rd
„Selection of current rating of MCCB for a motor
Let us consider a motor of 30 kWatt, in horse power (hp) its power rating is 40 hp.
a
power in hp = Power in watt = _30 =40 hp fan
0.746 0746 == hp = rt
The full load current is calculated by multiplying 1.5 to the power in hp.
full load current = 1.5%,40 hp =60 Amp
Hence 90 Amp of MCCB use with 30 kW of motor.
N
wo In general MCCB used for back-up device.
@ With a small motor, MCCB used with MCB. Whereas with a large motor MCCB
directly used without MCB.
@ With a small motor, MCCB used with MCB. Whereas with a large motor MCCB
directly used without MCB.
Selection of LT and HT Circuit Breakers (rating)
@ There is no need for calculation for the circuit breaker selection of the HT section
and it is very easy to select.
e But, it is necessary to calculate the circuit breaker selection on the LT side.
In LT side ACB, MCB, MCCB, etc circuit breakers are used.
Circuir breaker available in the market
VCB
—
Serial Rated Current(A) Breaking
Capacity (KA)
630 A 25 KA
12504 40 kA
@ There is no need for calculation for the circuit breaker selection of the HT section
and it is very easy to select.
e But, it is necessary to calculate the circuit breaker selection on the LT side.
In LT side ACB, MCB, MCCB, etc circuit breakers are used.
Circuir breaker available in the market
VCB
—
Serial Rated Current(A) Breaking
Capacity (KA)
630 A 25 KA
12504 40 kA
Serial no Rated Current(A) Breaking
Pananitulle A
630 85
800 85
1000 85
1250 85
1600 85
2000 85
2500
3200
4000
5000
6300
Pananitulle A
630 85
800 85
1000 85
1250 85
1600 85
2000 85
2500
3200
4000
5000
6300
Serial no Rated Current(A)
40,43,100 & 125
160,200 & 250
250
320 & 400
500
630
800
1000
1250
1600
Breaking
Pananitulle A
25
25
25
65
65
85
85
40,43,100 & 125
160,200 & 250
250
320 & 400
500
630
800
1000
1250
1600
Breaking
Pananitulle A
25
25
25
65
65
85
85
Circuit breaker calculations (in high tension)
933kV to 11kV in the case of transformers 1250 A rating VCB is selected and 11kV to
0.4kV in the case 630 A rating VCB is selected.
28
elow is the latest one 0.4 kV Low Tension(LT) is associated with side, low tension
is connected VCB that's it 630 A the rating is VCB have to choose
v HT section À 1250 A VCB
HT Section
Y HT Section Associated with its LT section on top of that 630 A VCB is selected
==
VCB 12504 In this figure 5 MVA a step-down transform
a of rating has been used. In its primary 33 k
the line enters the secondary 11 kV has
+ SMVA come out. This is a tension section where
av 1250 A the rating is VCB has b
a
ven 1250 A
ue
933kV to 11kV in the case of transformers 1250 A rating VCB is selected and 11kV to
0.4kV in the case 630 A rating VCB is selected.
28
elow is the latest one 0.4 kV Low Tension(LT) is associated with side, low tension
is connected VCB that's it 630 A the rating is VCB have to choose
v HT section À 1250 A VCB
HT Section
Y HT Section Associated with its LT section on top of that 630 A VCB is selected
==
VCB 12504 In this figure 5 MVA a step-down transform
a of rating has been used. In its primary 33 k
the line enters the secondary 11 kV has
+ SMVA come out. This is a tension section where
av 1250 A the rating is VCB has b
a
ven 1250 A
ue
© In this figure 2500 KVA transformer of rating has
been used. INTS primary 11 kv entered and into
ves > the secondary, 0.4 kv got out. That is, its primary
section HT, the secondary section of it LT. LT is
HT Section conñected from HT via a transformer, in this case,
the upper HT section VCB will be 838 A the rating
11 KV Le 12508
2500 KVA
0.4 KV Step. up dun
CH N Breaker
LT Section
been used. INTS primary 11 kv entered and into
ves > the secondary, 0.4 kv got out. That is, its primary
section HT, the secondary section of it LT. LT is
HT Section conñected from HT via a transformer, in this case,
the upper HT section VCB will be 838 A the rating
11 KV Le 12508
2500 KVA
0.4 KV Step. up dun
CH N Breaker
LT Section
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