220kV Substation Equipment Bus Scheme & Operation Procedure Testing & Maintenance

220kV Substation
Equipment
Bus Scheme & Operation Procedure
Testing & Maintenance

1. ANBARASU B
ENGINEER- Electrical
220KV SWITCHYARD
AMNEPL

3. Generated power to be evacuated to load centers for
consumption.
Generating stations are far from load centers.
The process of
Generation Transmission Consumption
(in 11’s kV) (in 220’s kV) (in 230’s V)
PURPOSE & NECESSITY OF SWITCHYARD

4. DESIGN OF SWITCHYARD
Factors to note before design of switchyard

 Soil Resistivity and Earthing system
 Structure selection
 Bus Bar
 Clearance
 Insulators
 Conductor and its fittings
 Equipment selection

5. OVERVIEW
6 BAYS CORRESPONDS TO MSETCL PORTION
12 BAYS CORRESPONDS TO ABHIJEET PORTION
FULLY AUTOMATED SUBSTATION

7. 1.In this scheme there are two main buses, called as BUS-1 & BUS-2
2.One more bus is available, its called as TRANSFER BUS
3.This is useful, when any one of the breaker in trouble or maintenance
4.Most of the time transfer bus in dead condition

ADVANTAGE:
1.Possible to take one bay CB and one BUS under maintenance

DISADVANTAGES:
1.If second(one more) circuit breaker in trouble, then this scheme is not
useful
2.There is no possible to take CT ,CVT and other equipments under
maintenance


•The tentative layout of the scheme shown in the next slide

DOUBLE MAIN BUS WITH TRANSFER BUS SCHEME

8. DOUBLE MAIN BUS WITH TRANSFER BUS


BUS-2
BUS-1
TRANSFER BUS

9. CHANGE OVER OF BUS-1 TO BUS-2 FOR BUS-1 MAINTENANCE
1. Normally each GT or feeder is to be connected to either bus-1 or bus-2
2. The concept behind is when either of the bus bar protection operates at
least 50% circuits will be in service
3.For maintenance point of view it is happy that all circuits kept on one bus
and another bus can be taken in to maintenance.
4. Normally bus-1 or bus-2 selection is to be done before charging circuit.
5. For example GT-1 & GT-2 transformers are available, GT-1 connected on
Bus-1 and GT-2 connected on bus-2.
6. The bus coupler breaker is should be in service.
7. During service, change over of bus is not a practice, however this is
possible
when bus coupler is charged condition.
8. During service the change over of BUS-1 to BUS-2 procedure is as follows: If
the circuit is connected on bus-1, close bus-2 isolator and open bus-1
isolator. This is purely for emergency

10. CHANGE OVER OF MAIN BUS TO TRANSFER BUS
1.When any one of the CB in trouble that will be transferred to transfer bus.
2.The operation sequence of transfer bus will be explained in next slides.
3. Bus coupler CB & isolators are in service.
4.During this change over to transfer bus, the tripping circuits are Transferred to transfer
bus coupler CB.
5. At the time, if fault occurs on circuit, the protective relays will give trip signal to
concerned CB and Transfer bus CB.
6.This can be avoided by using some more logic.
7.In TBC panel, auto reclose is available. This is useful when any Line feeder is
connected to TBC
8.In TBC panel, TBC LBB is also available.
9. Normal conventional system we are providing TTS switch. In normal mode tripping is
done for particular circuit Breaker, if it is transfer mode the trip circuit is parallel and
extended to TBC circuit breaker bay.

11. CHANGE OVER OPERATION OF GT-1 TO TRANSFER BUS
The sequence of operation for Normal to Transfer:
GT-1 on BUS-1 at Normal
1. Close TBC bay bus-1 89A isolator.
2. Close TBC bay transfer bus 89TB isolator.
3. Close GT-1 bay, transfer bus 89TB isolator.
4. So the TBC CB both sides having voltage.
5. Put NIT switch in ‘I’ inter mode of GT-1 C&R panel.
6. Close the TBC CB.
7. Then, the GT-1 is parallel with TBC CB and feeding two parallel paths.
8. Path1:GT-1 circuit : GT-1 89L line isolator, GT-1 CB, GT-1 89A bus-1 isolator to GT-1.
9. Path2:TBC circuit : GT-1 transfer bus 89TB isolator, TBC transfer bus 89TB isolator, TBC CB,
and TBC bus-1 89A isolator
10. Then open GT-1 CB.
11. Put NIT switch in ‘T’ transfer position
12. Open the GT-1 isolators i.e. Bus-1 89A isolator, 89L line isolator.
13. Now the GT-1 is feeding to bus-1 through TBC CB.
14. After maintenance work is over, the reverse procedure to be followed

12. OPERATION FOR TRANSFER TO NORMAL
•Put NIT switch in ‘I’ inter position.
•Close GT-1 89A bus-1 isolator.
•Close GT-1 89L line isolator.
•Close GT-1 circuit breaker.
•Open TBC CB.
•Open TBC bay 89A bus-1 isolator.
•Open TBC bay 89TB transfer bus isolator.
•Open GT-1 bus-3 isolator.
•Put NIT switch in ‘N’ normal position.

14. EQUIPMENTS

Circuit breaker
Current transformer
Capacitor voltage
transformer
Isolator
Lightning arrester
Coupling capacitor
Wave trap
Insulators and
Conductors


AC Distribution board
DC Distribution board
Battery & Battery Charger

MAIN EQUIPMENTS & COMPONENTS.

15. CIRCUIT BREAKER
 A circuit breaker is an automatically-operated electrical switch
under fault condition i.e on fault.
 To open and close the electric circuit.
TECHNICAL SPECIFICATION
1.MAKE - AREVA T&D
2.TYPE - SF6 CB GL314MGO
3.RATED CURRENT - 2500 A
4.RATED VOLTAGE - 245 KV
5.SHORT CIRCUIT CURRENT - 40KA for 3sec
6.OPERATING SEQUENCE - O-0.3s-CO-3min-CO
7.SF6 GAS PRESSURE AT 20⁰C - 0.85 Mpa

16. ISOLATOR
 Isolators or Disconnector are no-load switch.
 Earth Switch is used to discharge the voltage on the circuit to earth
for safety at the time of maintenance.
TECHNICAL SPECIFICATION
ISOLATOR
1.MAKE - SIEMENS LTD
2.TYPE - DBR
3.RATED CURRENT - 1600 A
4.RATED VOLTAGE - 245 KV
5.SHORT CIRCUIT CURRENT - 40KA for 3sec
6.TYPE OF DRIVE - MOTOR/MANUAL
7.MOTOR VOLTAGE (AC) - 415V
8.CONTROL VOLTAGE (DC) - 220V
9.CREEPAGE DISTANCE - 7812 mm

EARTH SWITCH
TYPE OF DRIVE - MANUAL

17. CURRENT TRANSFORMER
 CT merely reduces a high current flowing through its primary to a low
current on secondary.
 The secondary of a CT should never be kept open circuited because
very high flux will be developed in the secondary and hence it may be
damaged.

TECHNICAL SPECIFICATION

18. CAPACITOR VOLTAGE TRANSFORMER
 CVT is a transformer used to step down the high voltage to low
voltage. For metering and protection.
 Also useful in communication system, to block the power frequency
entering into PLCC terminal.

TECHNICAL SPECIFICATION

19. LIGHTNING ARRESTER
 Lightning arrester or Surge arrester are used to protect
other equipments from over-voltage due to lightning and
switching.
 This is the first equipment in all feeders and transformer
bay.
TECHNICAL SPECIFICATION
1.MAKE - OBLUM ELECTRICAL
2.TYPE - Gapless Type, METOVAR
3.NO. OF UNITS PER ARRESTOR - Three units of 66kV each
4.RATED VOLTAGE - 198 KV
5.NOMINAL DISCHARGE CURRENT - 10 KA
6.HIGHEST SYSTEM VOLTAGE - 245 KV
7.NOMINAL SYSTEM VOLTAGE - 220 KV
8.SYSTEM EARTHING - Solidly Earthed system

20. COUPLING CAPACITOR
 Coupling Capacitors are used in communication system, to block
the power frequency entering into PLCC terminal.
TECHNICAL SPECIFICATION
1. MAKE - AREVA T&D INDIA LTD.
2.TYPE - CCV-245
3.RATED FREQUENCY - 50HZ
4.VOLTAGE CLASS - 245KV
5.1-MINUTE 50 HZ WITHSTAND - 460 KV
6.TYPE - Porcelain-Oil
7.MAX. TEMP. RISE OVER 50 ⁰C AMBIENT -55 ⁰C
8.TOTAL EQUIVALENT CAPACITANCE -6600 pF + 10%, -5%
9.CVT SUITABLE FOR FREQUENCY RANGE -40-500 kHz
10.TYPE OF LA -Non-linear resistive type Gapped LA
11.Rated voltage of LA - 9 KV
12.Nominal Discharge Current -10 KA

21. WAVE TRAP
 Line trap OR Wave trap used to trap the high frequency
communication signals entering into switchyard equipments and
diverting them to the telecom panel in the switchyard control room
(through coupling capacitor and LMU).
TECHNICAL SPECIFICATION
1.MAKE - AREVA
2.TYPE OUTDOOR -Air cored
3.INDUCTANCE OF THE MAIN COIL -0.5 mH
4.BLOCKING RANGE -100-175 &150-500kHz
5.TYPE OF TUNING -Variable Broad Band Tuning
6.MATERIAL OF MAIN COIL -Aluminium Alloy
7.MATERIAL OF TERMINAL CONNECTOR -Aluminium Alloy
8.SYSTEM VOLTAGE - 220KV
9.CONTINUOUS CURRENT RATING 40 ⁰C - 1250A Max.
10.SHORT CIRCUIT CURRENT -40 KA for 1 sec

22. CONDUCTOR
 Conductor is the material allowing the flow of electric current

ACSR Aluminum Conductor Steel Reinforced.

INSULATOR
 Insulator is the material to support a conductor physically and to
separate it electrically from another conductor or object.

1.Long Rod Insulator(Tension & Suspension Stringing)
2.Post Insulators

23. BATTERY BANK AND BATTERY CHARGER
1.220 VOLT BATTERY BANK- For Protection & Controlling
Total No. of cell- 173
Volt. Rating of each cell- 1.2 Volt
Capacity - 148 Ah

2.48 VOLT BATTERY- For SCADA RTU & SIC Panel.
Total No. of cell- 24.
Volt. Rating of each cell- 2 Volt.
Capacity- 50 Ah

3.TWO 12 VOLT BATTERY BANK – For Inverter
Total No. of cell- 12(For MPP 6KVA Inverter)
Total No. of cell- 12(For MSETCL 3KVA Inverter)
Volt. Rating of each cell- 12 Volt
Capacity- 26 Ah.

BATTERY BANK

24. BATTERY CHARGER
1.Type- Float Cum Boost Charger.
Float mode( Simultaneously Charge & Discharge the Battery Bank )
Boost mode( This is the Charging mode)
Auto mode(Its Play the role according to the system requirements)

2.Rating-
1.MPP FCBC- 135A/220V
2.MSETCL FCBC- 50A/48V

3.Make-
1.MPP FCBC- Amar Raj
2.MSETCL FCBC- Panva

26. TESTING OF CURRENT TRANSFORMER

1. Insulation resistance test (IR test)
2. Polarity test
3. Excitation test (Knee point voltage test).
4. Ratio test
5. Winding resistance test
6. Tan delta and Capacitance Measurement test.

27. IR TESTING
To measure the insulation resistance of the
equipments.
a) Primary to earth by 5 KV
b) Secondary each core to earth by 500 V
c) Primary to secondary by 5 KV
d) Secondary core to core by 500 V

MAKE - MEGGER

28. POLARITY TEST
Polarity test of current transformer is to be carried out check the
correctness of the primary and secondary polarity
 For carrying out this test, we require one 1.5 V cell, DC analogue
ammeter.
 By making below connection, if there is positive deflection of
ammeter , then polarity is confirmed.

29. EXCITATION TEST

Excitation test will be carried out to measure the knee point voltage of
different cores of the current transformer

Knee point check for PS class core - Inject 230 V variable AC voltage in
secondary core with ammeter in series.

At certain point, with 10% increase in voltage, current shoots up almost 50%. This is
the Knee point voltage. After performing this test, Voltage is gradually reduced to Zero
to demagnetize the CT.

30. RATIO TEST
Inject current in primary winding & measure induced secondary
current for different current readings and verify with CT Ratio.


WINDING RESISTANCE TEST
Measure secondary winding resistance by micro ohm meter.
value should be .

31. TAN DELTA MEASUREMENT
Consider the insulation of equipment as Capacitor. If the capacitor is
good or perfect, it will pass only capacitive or charging current on
application of voltage. Ideal capacitive current Ic leads voltage by 90°.
But in practice, insulation has impurities & actual charging current
vector departs from the ideal Ic vector by a small angle (δ) called the
loss angle.
The loss angle (δ) = 90 – Power factor angle (φ)
Higher tan δ produces high dielectric loss that causes increase in
temperature of paper insulation. Increased value of Tan δ can be due to
any of the following: -
a) Moisture in the insulation.
b) Contamination of oil.
c) Internal partial discharge.

32. TESTING OF POTENTIAL TRANSFORMER

 Insulation resistance test (IR test)
 Winding resistance measurement
 Ratio test
 Tan Delta and Capacitance measurement test

TESTING OF LIGHTNING ARRESTER

IR Testing between Stack to stack & between each Stack to earth by
megger.
 Surge Counter Test - Apply 230V AC supply across the counter &
check pointer movement in clockwise direction.

33. TESTING OF CIRCUIT BREAKER
 Insulation Resistance Test
 Timing Test
 Contact Resistance Measurement Test

INSULATION RESISTANCE TEST
To measure the insulation healthiness of circuit breaker.
Open condition:
1.Top- Earth
2.Bottom- Earth
3.Top- Bottom
Close condition:
1.Top- Earth
2.Bottom- Earth
3.Top- Bottom

34. CONTACT RESISTANCE MEASUREMENT

 To measuring the contact resistance measurement of circuit
breaker main contacts.

 The value of the contact resistance for a new circuit breaker should
be around 50 micro-ohms.

 If the value of the contact resistance exceeds the permissible limits
this could lead to over heating of contacts.

35. TIMING TEST
To check the operation timing of circuit breaker.
 Trip circuit 1
O->open
C->close
C-O->close-open
Trip circuit 2
O->open
C->close
C-O->close-open
Kit used- Circuit Breaker Analyzer (EGIL BM19090)- Megger
 Tripolar Unipolar
O-> 23- 25 18-20
C-> 60-65 100-110
C-O-> 35-40 35-40

36. TESTING OF ISOLATORS
 Insulation Resistance Measurement
 Contact Resistance Measurement
 Motor Insulation Resistance Measurement
 Motor Winding Resistance Measurement
 Contact Resistance Measurement of Earth Switch


Insulation Resistance Measurement

 To measure the insulation resistance of Isolators.
 Measuring of insulation resistance against following condition.
1.Phase to Earth
2.Phase to Phase

37. CONTACT RESISTANCE MEASUREMENT

 To measuring the contact resistance measurement of Isolator
contacts.

 The value of the contact resistance for a new isolator should be
around (100-120)micro-ohms.

 If the value of the contact resistance exceeds the permissible limits
this could lead to over heating and arcing in contacts.

 Kit used- Contact Resistance Measurement (PE-20R)- Prestige

38. Motor Insulation Resistance Measurement

 To measure the insulation resistance of motor by 500V.
 Measuring of IR against Winding to Earth.

Motor Winding Resistance Measurement

 To measure the motor winding resistance by ohm meter.
 Measuring of winding resistance against phase to phase

Contact Resistance Measurement of Earth Switch
 To measuring the contact resistance measurement of Earth Switch
contacts.
 The value of the E/S contact resistance should be around (50-
100)micro-ohms.

39. NEED OF SYSTEM PROTECTION
 Detect the fault
 Isolate the faulty component
 Restore the faulted component

Aim: To provide continuous supply

Relay
It detects the fault and initiate the operation of CB to isolate the
defective system from the rest of the system

40. ANSI REFERENCE CODE
21 -Distance
24 -Over Fluxing
27 –Under Voltage
30- Auxiliary Relay
50- Instantaneous over current
50N- Instantaneous Earth Fault
50Z- Local Breaker Back-up
51- Time delay over current
51N- Time delay Earth Fault
64- Restricted Earth Fault



67- Directional over current
67N- Directional Earth Fault
74-DC fail alarm accept relay
75- Bus PT selection
78- Vector surge Relay
79- Auto reclose Relay
80- Supply Supervision
86- Master trip Relay
87- Differential
95- Trip circuit supervision
97- Fuse failure Relay

41. Over Current
It operate when the current exceeds a specified/set value.



O/C relays are employed for external fault conditions.

42. A Differential relay compares the currents on both sides of the transformer.
As long as there is no fault within the protected equipment (Transformer), the
current circulates between the two CTs and no current flows through the differential
element. But for internal faults the sum of the CTs secondary currents will flow
through the differential relay making it to operate.

43. Distance relay

The relay operates when the ratio of the voltage and current change beyond
the specified limit
Z r= Vr / Ir

44. VECTOR SURGE RELAY
The vector surge relay is used to decouple the synchronous
generator from grid in case of grid failure

1.Fast acting relay < 300ms
2.Relay operate when angle 0 to 20 deg

Restricted Earth Fault protection

It means an earth fault from a restricted zone of a circuit.

Auto reclose protection

Automatically close the CB after it has been opened due to a fault
• 90% fault in transmission line is transient faults

45. ANTI PUMPING
It blocks the repeat closing pulse when breaker is already in closed
condition.

46. LOCAL BREAKER BACKUP PROTECTION

A protection which is designed to clear a system faulty by initiating
tripping other circuit breaker(s) in the case of failure to trip of the
appropriate circuit breaker.

BREAKER BACK-UP

Because of the high cost of high voltage Circuit breakers, it is not
feasible to duplicate them.
In case of a breaker failure the other circuit breakers connected to the
same bus as the faulted breaker must there fore be tripped.

47. TYPES OF MAINTENANCE

i) Breakdown maintenance
ii) Preventive maintenance
iii) Condition based monitoring

Breakdown maintenance
 Breakdown maintenance is carried out when the equipment fails.
This type of maintenance may be appropriate for low cost equipments.
 However for costly switchyard equipments, it is not desirable to wait
till the breakdown of the equipment.
 The revenue loss due to non-availability of the system shall be much
more than the cost of the failed equipment.
 Therefore identifying the defect before failure, is more appropriate
to plan repair / replacement.

48. PREVENTIVE MAINTENANCE
The preventive maintenance of equipment is being mostly adopted
by almost all the utilities. In this type of maintenance, the
equipments are inspected at a predetermined period.
The frequency determined based on the past experience and also
guidance from the manufacturer of the equipment.
 This type of maintenance would require specific period of shut-
down.

CONDITION BASED MONITORING
This type of maintenance technique is adopted to assess the
condition of the equipment.
However, this type of maintenance would need sophisticated testing
equipments and skills for analyzing the test results.

49. Maintenance of Lighting Arrester

1) Insulator cleaning
2) Connections tightness
3) Checking of Earthing connections
4) Reading of leakage current on daily basis to be taken. If current
shoots in red zone, then that particular LA is to be replaced as early as
possible.

Maintenance of CT and CVT

1.Check oil level and leakage if any.
2.Cleaning of insulator and check any cracks.
3.Check HV connections, earthing and wiring in the marshalling box.
4.Measurement of IR values for comparison with earlier values.
5.Measurement of capacitors and tan-delta for windings and
bushings.

50. MAINTENANCE OF ISOLATORS
1. Check linkages for simultaneous operation and stopper bolts etc.
2. Check earth switch flexible.
3.Check earth connection and earth blade for proper closing
4.Clean and check any cracks in insulators.
5.Check jumper connections
6. Check auxiliary switch operation
7.Linkages including gears, Stopper bolts
8.Cleaning of auxiliary switch contact & greasing with silicon grease
9.Lubrication of operating mechanism
10.Checking of all mounting bolts for tightness
MAIN CONTACTS
1.Cleaning and lubrication of main contacts and alignment
2.Main contact resistance measurement

51. MAINTENANCE OF CIRCUIT BREAKER

 Check for gas pressure and leakages.
 Check operation of counters.
 Cleaning and lubricating the mechanism.
 Checking breaker status indicator, auxiliary switch linkages.
 Check operation of breaker for close and trip through local/remote
switch and protective relays.
 Check operation of anti-pumping relay and pole discrepancy.
 Check tightness of control wiring.
 Measuring of IR and CRM
 Checking of C.B timing.
 Detailed checkup of breaker operating mechanism and lubrication of
drive mechanism.

52. POWER SYSTEM AUTOMATION

It means switching, regulating, controlling, logging, protection etc….

SCADA

A SCADA system is one which facilitates an operator to control a
remote system and acquire real time information from remote
location.
Control and Data acquisition can be from a single point or from
multiple point.

53. Basic component
1.RTU
2.Communication media
3.Master control














RTU
Communication
media
Master
control