Electrical-Symbol-magnetic-ContactorsRelays.ppt

Different symbols used in electrical system and relays

1. Components & Symbols
Used in Electrical Circuits

2. Schematics & Notations
•Understandingdrawings,especiallyelectrical
drawingsrequiresakeenunderstandingof
schematics,symbols&otherdetailsusedto
representcomponents.
•Continualpractice&ahabitofreadingthestarter
Paneldrawingbeforeattemptingtotroubleshootit
isthekeytocomprehendingElectricalStarter
Panels&machineryingeneral

3. Schematics & Notations
•The bibliography of starter Panels on board
generally contains vital information as regard
how the maker has represented various
components of the starter or panel
internals.
•Due reference to this is a must though
generally parallels may be drawn form
experience.

4. Contacts
Normally Open Contact
Normally Closed Contact
Normally Open Contact with
terminals
Normally Closed Contact with
terminals
Start Push Button ( NO Contact )
Stop Push Button ( NC Contact )

5. Relays & Coils
Relay coil / Contactor Coil
Timer Relay Coil ( on Delay )
Timer Relay Coil ( off Delay )

6. Other Components
Operated by pushing
Operated by turning ( Latch )
Emergency Switch ( Mushroom Head Safety
Feature )
Operated by pushing ( & then latches on )
Operated by turning ( spring return )

7. Other Components
Potential Transformer / Control Transformer
Secondary winding has less turns and Primary has
more turns. Used for connecting volt meters
Current Transformer
Secondary has more turns and Primary has less turns.
Used for connecting Amp meters.
Indicating Lamp ( Transformer Type )

8. Other Components
Heater
Device fitted outside the panel ( indicated by dashed
lines )
SV
Solenoid Valve

9. THE RELAYS
A very important component in an Electrical Circuit.
Arelayisasimpleelectromechanicalswitchmadeupofanelectromagnet
andasetofcontacts.Relaysarefoundhiddeninallsortsofdevices.Infact,
someofthefirstcomputerseverbuiltusedrelaystoimplement.
Relay Construction
Relays are amazingly simple devices.
There are four parts in every relay:
1.The Electromagnet
2.TheArmaturethatisattractedbytheelectromagnet
3.A Spring
4.A Set of electrical contacts

10. Relays
Factors when looking
at a relay
•Coil terminals
•Number of switching
contact sets
•Rating of the coil
•Rating of the contact
•Structure of the pin
layout

11. Relay representation
Coil
N/O
Contacts
N/C
Contacts
N/O are called ‘a’
contacts
N/C are called ‘b’
contacts
This relay represented has a
coil which operates on ac
voltage & has 2 N/O contacts
& two NC contacts.
Many such possibilities may
be presented depending upon
the number of contacts
220 V ac

12. Relay Format
The coil is found between
terminals 2 & 10. Contacts
1 & 4 and 8 & 11 and 5 &
6 are normally closed.
When the coil is energized
the contact switch over to
1 & 3 ( closed ) & 11 & 9
and 6 & 7 (closed).

13. Relay Format
1
2
3
45
6
7
8 The coil is found between
terminals 2 & 7. Contacts 1 &
4 and 8 & 5 are normally
closed.
When the coil is energized the
contact switch over to 1 & 3 ;
& 8 & 6
8 pin format

14. Analyzing the requirement Timer
Relays
A delay timer that waits for a predetermined amount of time
before closing a set of contacts once the power is applied.
Terminals 2 & 7
Terminals 1 & 3
Terminals 1 & 4
Coil
Set of contacts 1
Set of contacts 2
T

15. Analyzing the requirement Timer
Relays
Relay that closes/switches on a set of contacts immediately
when a coil is energized, then waits for a pre determined time
to switch them off/open after the power is removed.
Terminals 2 & 7
Terminals 1 & 3
Terminals 1 & 4
Coil
Set of contacts 1
Set of contacts 2
T

16. Contactor -Example

17. Contactor
Main
Contacts or
power
contacts
Auxiliary
contacts

18. Starter Routines

19. Motor starter panel routines includes inspection
and maintenance of motor’s starter panel.
Starter panel routines mean inspection and cleaning of
contactor’s (the switch inside the starter panel box
controlling the on and off of the motors) contacts.
Checking of connections in the starter panel
Cleaning of the complete starter panel
Checks in the terminal box on the motor for loose
Connections
Visual inspection of overall starter panel

20. Safety Measures to be Followed While
Starting Motor Starter Panel Routines
•Switch off the main power supply from the circuit breaker
•Take out the main fuses in the starter panel, and if required control fuses
as well
•Put the lock out tag
•Inform the engineer who is in charge of that particular machinery

21. Fixed Contacts

22. THE FIXED AND MOVING CONTACTS

23. EFFECTS OF EXCESSIVE USE OF CONTACTS

24. Thermal Overload Relay
Heater coils of the
thermal overload Relay
Contact operated by the overload relay with
resetting option.
NC NO

25. Reading Diagrams
•Diagrams are always drawn in a state of rest i.e. without
power –also known as the de-energized state.
•They are read from left to right.
•Generally devices with the same power level are drawn at the
same horizontal level.
•The components are identified by two ways, Cartesian system
( co-planar ) or by a line diagram system.
•If the diagram runs into a few pages then reference to pages
is made near the component.

26. MAGNETIC CONTACTOR OPERATION

27. Star Delta Starter

29. QUERIES ?

30. There are two other differences between
an AC and DC solenoid:
1) The iron core of the coil, the
electromagnet, is solid for DC and layered
for AC to avoid loss in iron due to eddy
current.
2)The AC solenoid has a "split pole" -a
part of the layered pole (around 30% of
cross sectional area) has a copper ring as
short circuit so that in this part of the
magnet the maximum and minimum of
magnetic intensity is phase shifted by 90°
in respect to the main part of the pole, and
therefore avoiding chattering of the
solenoid by having a total magnetic force
that is always well above zero when
actuated.

31. Comparison of AC vs. DC
Solenoids
Asageneralrule,DCsolenoidsaretypicallypreferredoverACsolenoidsforseveralreasons.Forexample,when
spaceconstraintsaretight,aDCsolenoidwillusuallygivebetterperformanceinasmallerpackagethanwilla
comparableACsolenoid.Inaddition,DCsolenoidshavethecapabilityofbeingmodifiedinsuchafashionasto
preventthepolefacesfrommakingcontactattheendofthestroke.InACsolenoidapplications,thistypeof
noisedampeningwouldverylikelycauseprematureoverheatingandfailure.ACsolenoidsrequiregreatcareto
ensureprecisealignmentoftheplunger'spolefacetothestatorpoleface.Thisfacilitatesthepolefacesmaking
contactwithasmuchsurfaceareaaspossibleintheenergizedstatewhichwillreducetheamountofhumor
chatteringintheACunit.However,inasimilarDCapplication,aslightgapbetweenthepolepiecesattheendof
thestrokecanhaveadrasticeffectonimprovingtheoveralllifeofthesolenoid.
WhenlookinginsidetheACsolenoidstatorcavityatthestatorpolepiece,thereisasmallringinsertedintothe
faceofthestatorpole.Thisringisknownasashadingcoilandisdesignedtoobtainminimalpulsinginforce.
Whatthismeansisthatthecoilsplitsthepoleintotwoseparatepartswhichcausesthefluxofthesepartstobe
outofphase.Ifnotforthisshadingcoil,thechatteringsoundthatiscommonlyassociatedwithACsolenoids
wouldbemorenoticeable.
BottomingoutofthepolepiecesduringeachstrokeisarequirementonACsolenoids.Naturally,withthismetal-
to-metalcontact,somedeformationofthepolepiecesispossible.Asthepolepiecesdeformandlesssurface
areamakescontactbetweenthepieces,theACsolenoidhumslouderandlouder.Incontrast,aDCsolenoid
doesnothavetohavethepolepiecescomeincontactduringeachcycle.Rather,ifthepolepiecesdonotmake
contact,lifeofthesolenoidisextended.LifeofanACsolenoidistypicallylowerthanthatofasimilarDC
counterpart.