lecture notes - 19

8/11/2019 Lecture Notes - 19

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POWERDISTRIBUTION SYSTEMS

VOL: FY 20 1 4 0 5 JULY 2 01 4 ISSUE NO: 19

Centre for Education, Training and DevelopmentVijai Electricals Ltd, Hyderabad-500 082, Andhra Pradesh, INDIA

Phone: +91-40-30617791; Fax: +91-40-30617890; Email:[email protected] a Knowledge Enterprise

Lecture Notes*for General Gui dance

TESTS ON SUBSTATION EQUIPMENT

(*The lecture notes are intended for general guidance only. In actual

execution the relevant project technical specification LOA and approved

drawings are to be followed)

Class conducted

Today i.e. 05 July 2014

Faculty:Sri .V.Neel esh, Engineer,

Project Execution & Control Dept.D&RE Projects


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TESTING OBJECTIVE, INSTRUMENT AND PROCEDURE

Objective of Testing:

To ensure that the products manufactured have met the requirement of

customer specification/standard To prevent accidents, which may occur if a failed product is put into service To ensure quality & that the product is fit for its intended use

Tests conducted on Sub-station Equipments: Power Transformer and Station Transformer:

(1) Insulation Resistance Test(2) Vector Group Test(3) Winding Resistance Test(4) Ratio Test(5) Break Down Voltage of Oil

(6) Magnetic Balance Test Vacuum Circuit Breaker:

(1) Insulation Resistance Test(2) Closing and opening Time Measurement(3) Contact Resistance Measurement

Current Transformer:

(1) Insulation Resistance Test(2) Ratio Test(3) Polarity Test

Potential Transformer:

(1) Insulation Resistance Test(2) Ratio Test(3) Polarity Test

Isolator:

(1) Insulation Resistance Test(2) Contact Resistance Measurement

Lightning Arrestor:(1) Insulation Resistance Test

Battery and Battery Charger:

(1) Specific Gravity Measurement


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TESTS ON TRANSFORMER

Insulation Resistance Test:

Objective:

1) To ensure proper dryness of the active parts2) To ensure sufficient clearance between the windings and between

winding and earth

Instruments:

1) 2.5 KV rated Megger / Insulation Tester

2) Connecting cables

Procedure:

1) Before starting the test, Disconnect the PTR neutral connection.

2) One terminal of the instrument is connected to conducting part. Other

terminal is connected to earthed frame (or other conducting circuit)

3) Then IR Value between HV terminal and body of Power transformer is

to be measured & noted.

4) IR Values between HV & LV terminals are to be measured & noted.5) IR Values between LV terminals and body of Power transformer is

measured & noted.

6) If the value is zero then there is continuity and if the value is infinity

then there is no continuity.


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Vector Group Test

Objective:

To verify the phase angle difference between HV and LV winding.

Generally for 33/11KV sub-stations Dyn11 vector group PTR is used.

Instruments:

1) Three phase auto transformer

2) Voltmeter / Multimeter


Procedure:

T/F

under

test

3PH

S

UPPLY

2n

2u

2v

2w

1U

1V

1W

430 volts

AC


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1)Short the terminals i.e. 1U on HV and 2u on LV side of Transformerand apply 3-Ph voltage say 430V on any line terminals of HV side then

observe the voltage readings of various terminals 1U-1V, 1V-1W,

1W-1U, 1U-2n, 1V-2n, 1W-2w, 1W-2v, 1V-2w, 1V-2v, etc.

Voltage Across Volts

1U - 2u 0

1U - 2n 80

1V 2n 366

1U 1V 417

1V 2w 301

1U 2v 299.4

1W - 2w 303

1W 2v 438

1V - 2v 290

Vector group Diagram Voltage Conditions

Dyn11

1V to 2w = 1V to 2v

1W to 2w < 1W to 2v and

1U to 2n + 1V to 2n = 1U to

1V

Dyn5

1U to 2v = 1U to 2w

1W to 2w > 1W to 2v and

1U to 2n + 1U to 1V = 1V to 2n


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Dyn1

1W to 2v = 1W to 2w

1V to 2v < 1V to 2w

1U to 2n + 1w to 2n = 1U to 1w

Dyn7

1U to 2v = 1U to 2w

1V to 2v > 1V to 2w

1U to 2n + 1U to 1W = 1W to

2n


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Winding Resistance Test:

Objective:

1) To calculate IR losses of the winding

2) Whether conductors used in winding are as per the designed cross

section or not can be verified.

Instruments:

1) Transformer winding resistance meter / Ohm meter

2) Kelvin Bridge / Wheatstone Bridge

3) Connecting Cables

Procedure:

1) The test is carried out only after ensuring that the transformer windings

are immersed in oil for at least 3 to 8 hours depending upon the rating till

the transformer oil temperature equals the ambient temperature.


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2) Then the top oil temperature is taken as average oil temperature and

the temperature of the winding is the same as the average oil temperature.

The ambient temperature shall be recorded.

3) The measurement of winding resistances is done using a precision

ohmmeter.

LV side winding resistances measured phase wise

r-n = Ohm meter reading in

y-n = Ohm meter readin in

b-n = Ohm meter reading in

HV side winding resistances measured phase wise

RY = Ohm meter reading x 3/2

Y-B = Ohm meter reading x 3/2

B-R = Ohm meter reading x 3/2

The top oil ambient temperature is also to be mentioned along with thewinding resistances at which it is measured. The winding resistance

varies with temperature. If temperature of oil increases, the value of

resistance also increases.


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Ratio Test:

Objective:

Ratio test is conducted to ensure the number of turns in HV and LV

windings on each tapping. In order to get accurate ratio measurement, a ratio

meter is used.

Tolerance for the % deviation of voltage ratio is lower should be lower than

0.5% (or) 1/10thof the % Impedance value.

Instruments:

1) 3-Ph Auto Transformer

2) Voltmeter


Procedure:

1) Apply 3Ph, 430V on HV side of PTR and measure the LV side Phase to

Phase values.


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2) The ratio test values of 5MVA, 33/11KV PTR are

TapNo. 1U-1V 1V-1W 1W-1V 2u-2v 2v-2w 2w-2u 2u-2n 2v-2n 2w-2n

01425 426 421 131 132 130 73 74 73

02 420 426 423 133 134 132 74 76 7503 430 435 433 140 141 139 80 81 8104 429 435 433 142 143 141 81 82 8205 430 436 433 144 145 143 82 83 8306 430 436 434 146 147 145 83 84 8407 431 436 434 147 149 147 85 86 8508 431 436 433 149 150 149 86 87 8609 431 437 434 151 153 151 86 88 8710 428 433 433 153 154 152 87 88 8711 426 432 432 154 155 153 88 89 8912 427 432 432 156 158 156 90 91 9113 429 435 432 159 160 158 91 92 9214 430 435 432 162 163 161 93 94 9315 429 435 433 164 165 164 94 95 9616 430 435 433 167 168 166 95 97 9617 429 435 432 169 170 168 97 98 97


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Break Down Voltage of Oil (BDV) measurement: Objective:

To ensure the healthiness of Transformer Oil.

Instruments:

1) BDV test Kit


Procedure:

1) Oil samples from top & bottom of Power transformer main tank aswell as OLTC tank are to be collected and tested.

2) Across 2.5 mm gap test Kit, The oil shall stand for 40 to 50 KV For/minute.


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Magnetic Balance Test:

Objective:

Magnetic Balance test is conducted on Transformers to identify interturn faults and magnetic imbalance.

Instruments:

1) 3Ph Auto Transformer2) Tong tester / Multimeter


Procedure:

1) 415V, Two phase supply is to be applied to any two phases terminalson HV side of Power transformer and voltages in other two phasecombination are to be measured.2) Sum of the Resultant two values shall be equal to the voltage applied.


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Pre-Commissioning Checks on PTR

1) Check proper earthing of neutral & body

2) Check colour of silica gel in breather

3) Radiator valves of top and bottom should be in open condition

4) Check oil level in the conservator

5) Check for oil leakage, if any

6) Check the tapping switch is on the desired position

7) Verify that LAs are properly installed, connected & earthed

8) All drain valves are in closed position with dummy plates in position dulyfitted with bolts & nuts

9) All filter valves in closed position with dummy plates in position duly fittedwith bolts & nuts

10) The valves on either side of Buchholz relay are in open position

11) The vent pipe diaphragm is intact

12) Before charging the PTR air is to be released from air releasing points

of main tank cover of PTR, OLTC top cover, Buchholz relay, radiators andbushings, if necessary.

13) Ensure Buchholz relay should be kept in service mode.


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Ratio Test:

Objective:

This test is to ensure the proper CT connections with respected cores

and there is no mix up in the circuit (phase identification).

Instruments:

1) Primary Current Injection Kit


Procedure:

1) The circuit connections shall be made as shown below.

2) Single point grounding shall be verified for CT circuits, before

starting this test.

3) Inject 25% of rated primary current between one phase and earthwith all connected burden. Measure secondary current at all points of

CT circuits. It shall be done for other phases.

4) The test values are as shown below

Ratio /Primary

injected

R(Core2/Core3) Y(Core2/Core3) B(Core2/Core3)

50 Amps. 0.498 0.501 0.499

100 Amps 1.00 1.01 0.99


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Polarity Test:

Objective:

Polarity test is to confirm the polarity marking on the CT primary and

secondary.

Instruments:

1) Galvanometer2) Battery set3) Connecting Cables

Procedure:

1) Isolate CT secondary from the load and make circuit connection as shown

below.

2) Close and open the battery switch connected on the primary. Observe thepointer is moving + ve direction, while closing andve direction while openingfor correct polarity.

Particulars(P1=+ve; P2=-ve)

R -Phase

Y - Phase B - Phase

Core-1 Ok Ok Ok

Core-2 Ok Ok Ok

Core-3 Ok Ok Ok


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Pre-Commissioning checks on C.T

1) Verify nameplate ratings are in accordance with the approved drawings

and specifications.

2) Inspect for physical damage/ defects and mechanical condition.

3) Verify correct connection of Transformers with system requirements.

4) Verify that adequate clearances exist between primary and secondarycircuit wiring.

5) Verify tightness of accessible bolted electrical connections

6) Verify that all required grounding and shorting connection provided.

7) Verify all shorting blocks are in correct position, either grounding or openas required.

8) Verify single point grounding of each core done properly. Grounding pointshall be nearer to the CT location. However grounding shall be at relay pointin case of several CT secondaries connected together like differentialprotection.


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Tests on Potential Transformer


Objective:

1) To ensure proper dryness of the active parts

2) To ensure sufficient clearance between the windings and betweenwinding and earth

Instruments:

1) 2.5KV Megger / Insulation Tester


Procedure:

1) Measure IR values between Measurement between primary andsecondary

2) Measurement between primary and ground

3) Measurement between secondaries and between secondary and

ground


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4) The IR values for 11KV PT are shown below (Giga-Ohms)

Circu it Ref. R-Ph Y-Ph B-Ph

Primary to Earth 0.850 0.735 0.700

Primary to Sec. 1 1.60 1.70 1.84

Primary to Sec. 2 3.16 2.61 1.78

Sec. 1 to Earth 1.52 1.87 2.29

Sec. 2 to Earth2.30 2.58 2.18

Sec. 1 to Sec.2 2.05 4.53 2.05


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Ratio Test:

Objective:

To ensure secondary voltage with respect to Primary side of P.T

Instruments:

1) Auto Transformer

2) Tongtester / Voltmeter


Procedure:

1)A variable AC source is applied on the primary side.

2)The primary and secondary voltages are measured to determinethe ratio V2/V1

3) The values of 11KV, 11000/3 / 110/3PT

Rn Yn Bn

Primary AppliedVoltage 230V 230V 230V

Sec Phase-Neutral 2.3V 2.3V 2.29V


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Polarity Test:

Objective:

To ensure the Polarity of P.T and to check primary and secondary circuitcontinuity.

Instruments:

1) Galvanometer

2) Battery Set


Procedure:

1) Connect the galvanometer leads to secondary of the P.T terminals.

2) Connect the primary terminals to the cell +ve & `N` to the cell -ve. Thenobserve the meter deflection.

3) If the deflection is towards right, the P.T polarity is correct.

4) If the deflection is towards left the polarity is incorrect.


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Tests on Vacuum Circuit Breaker


Objective:

1) To ensure proper dryness of the active parts

2) To ensure sufficient clearance between the Contacts

Instruments:

1) Megger / Insulation Tester2) Connecting cables

Procedure:

1) If Breaker is in Open condition, measure IR values between IN &Outterminals. Then note down the value, it should be in M.

2) If Breaker is in Close condition, measure IR values between IN & Outterminals. Then note down the value, it should be Zero.

PhaseOFF Condition ON

ConditionIncoming Outgoing

R-E 15,000 13,000 12,000

Y-E 15,000 14,000 13,000B-E 15,000 15,000 15,000

R-Y >15,000 >15,000 >14,000Y-B >15,000 >15,000 >15,000

B-R >15,000 >15,000 >15,000ACROSS POLE

R-R >10,000 0Y-Y >10,000 0

B-B >10,000 0


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Closing and Opening Time Measurement: Objective:

To ensure the healthiness of contacts and to measure closing timeof contacts and opening time of contacts.

Instruments:

1) Battery set2) Timer3) Connecting Cables

Procedure:

1) Connect the instruments as shown below.

2) For measuring close time, The timer starts when the two terminals ofStart witch are shorted by closing the D.P.D.T switch. Simultaneously theD.C supply is extended to the closing of the breaker. The timer stopscounting when the two terminals of Stop switch are shorted through themain contact of circuit breaker, as soon as it closes and the timer displaysthe time interval, which is the closing time of circuit breaker.

3) For measuring open time, The timer starts when the two terminals ofStart switch are shorted by closing the D.P.D.T switch. Simultaneously theD.C supply is extended to the trip coil of the breaker. The timer Stopscounting when the two terminals of stop switch are opened with the

opening of the circuit breaker main contacts. The time interval displays thetime interval, which is opening time of circuit breaker.


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4) The test values of 36KV, 1600A VCB in msec.

Phase Closing Time Tripping Time

R 52.6 33.4 34.7

50.4 33.9 34.7

Y 52.5 34.7 34.8

51.0 37.6 39.7


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Contact Resistance Measurement:

Objective:

To measure the resistance between fixed contact and movable

contact.

Instruments:

1) CRM kit2) Connecting Cables

Procedure:

1) Connect CRM kit with terminals of VCB and apply the respective voltage

then meter shows the Resistance value.

2) Generally for 33KV, 1600A VCB the contact resistance values are asshown below.

PhaseResistance

R 54

Y 43

B 32


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Pre-Commissioning Checks on VCB

1) Tightness of all hardware, jumper bars & contact fingers.

2) Rack in and rack out the VCB inside the panel for 5 times (for i/d VCB).

Operation must be smooth during this check.

3) Charge the spring manually and ensure spring charge indication signalappears at the end of the charge.

4) Check the limit switch (motor cut off) charge over the contacts atthe end of spring charge

5) Check manual closing & opening is possible.

6) Check whether VCB earthing contact engages to panel earth position

before contact fingers engage with spout.

7) Check mechanical ON/OFF indication appears when breaker is in closedor open position.

8) Check the operation counter operates for every open or close operation.

9) Check proper shutter opening by engagement of VCB/finger alignment.

10) Check auxiliary switch contact change over during breaker open/closeoperation.

11) Check tightness of wiring terminals before and after 25 operations.


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Tests on Isolator


Objective:

1) To ensure proper dryness of the active parts2) To ensure sufficient clearance between the contacts

Instruments:

1) 2.5 KV Megger / Insulation Tester2) Connecting cables

Procedure:

1) If isolator is in Open condition, measure IR values between twoterminals. Then note down the value, it should be in M.

2) If isolator is in Close condition, measure IR values between twoterminals. Then note down the value, it should be Zero.

3) For 33KV, 800A isolator the IR values as follows.

4) For 11KV, 800A isolator the IR values are as follows.

Circuit Ref. R-Phase Y-Phase B-Phase

Pole to earth 6.62 G 13.2 G 12.6 G

Phase to Phase 6.12 G 8.12 G 9.12 G

Pole to Pole 5.87 G 6.30 G 8.5 G

Incoming bus 8.15 G 7.20 G 6.35 G

Circuit Ref. R-Phase Y-Phase B-Phase

Pole to earth 8.67 G 7.07 G 9.65 G

Phase to Phase 11.0 G 10.5 G 6.37 G

Pole to Pole 9.07 G 6.38 G 2.31 G


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Contact Resistance Measurement: Objective:

To measure resistance between fixed contact and movable contactof Isolator.

Instruments:

1) CRM kit


Procedure:

1) Connect CRM to respective terminals and measure the resistance value.

PhaseReference

MeasuredResistance ()

R-phase 155

Y-phase 150

B-phase 178


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Pre-Commissioning Checks on Isolator

1) Check main earth on mechanism box, operating handles (flexible braid)and support structure.

2) Check that earth switch earth connection is direct to the earthmat (not via astructure).

3) Check local / remote close operation.

4) Check simultaneous operation and full travel operation of all phases.

5) Check control switches in service position.

6) Check operational nameplate and labels are in place.

7) Check phasing is correct.


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Tests on Lightning Arrestor


Objective:

To ensure proper dryness of the active parts.

Instruments:

1) 2.5 KV Megger / Insulation Tester


Procedure:

1) Measure IR values between Phase to Phase and Pole to Earth and thereadings are as observed below.

2) 30KV, 10KA LA readings are as shown below.

Circuit Ref. R - Phase Y - Phase B - Phase

Pole to Earth 10,000 G 10,000 G 10,000 G


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Tests on Battery and Battery Charger

Specific Gravity Measurement:

Objective:

To measure specific gravity of electrolyte.

Instruments:

1) Hydrometer2) Connecting Cables

Procedure:

1) Collect the electrolyte of battery in a tube and by using hydro metermeasure Specific gravity. For a good electrolyte Specific gravity must beabove 1200.

lecture notes - 19

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