substation equipment

7/22/2019 Substation Equipment

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SF6 Gas Auto Puffer interrupter

Load current operation.


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Main contacts copper with silverplated.

Arcing contacts Tungsten copper. Nozzle is made up of Teflon.

Commutation of current Current

moving from main to arc contacts.


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Operation time

SF6 gas leakage

Contact resistance measurement Visual checks

Density monitor reading. (Compensatestemp change).

Rated pressure 7 Bar absolute pressure.

Check anti pumping feature

Wiring according to schematic.


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In test chamber for arching chamberpressurization test. 1.5 times max workingpressure( 10.5 Bar to 7 bar)

1 close open operation at this pressure. Resistance of control coils checked. One

closing coil and 2 trip coils with auxcontactors, heaters and relays.

Operation of motor, motor current andspring charging time.

Closing at control voltages (110% to 80%)

Tripping at control voltages ( >70%)


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Breaker Timing Tests

Breaker Analyser (eg ELCON make)

Open time, close time, close open COtime and open close OC time.

Important of gang operated breakerwhere all three phase poles are different.

Main contact resistance measurement.

SF6 gas tightness test. SF6 gas leaksensing meter.


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High Voltage tests (140 kV applied)


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Close time : max 75 ms , Close velocity : 1.7to 2.0 m/s

Open Time : 35 to 45 ms , open velocity : 2.2to 2.6 m/s

CO Time : max 65 ms

Stroke : 84 to 87 mm

Motor Current : 4.5 A (220 V) and 8 A (110V)

Spring charging time : 15 sec max

Contact resistance : 46 (at 20C)


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Paper + Oil insulation

Paper dried till last traces of moisture.

Then impregnated with oil containing less

than 7 ppm of water. High breakdown strength + any shape.

Electrical stress on the insulation is high nearthe earthed end.

If conducting foils are introduced inbetween the insulation, then stress acrossthe insulation is uniform. This is calledcapacitive grading.


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Tan is the end point of primary insulation. It isformed on the bend end limb of the conductor bywrapping tinned copper strip over last main

grading foil and then soldered to it. The other endof the strip is terminated at terminal box.


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Integrated insulation quality between highvoltage terminal to tan delta terminal.

It can be explained by considering insulation

as a capacitor. Resultant current is made up of resistive current

and capacitive current.

Resistive current due to impurities and moisture.

Insulation made by capacitive grading orlayers. Each layer is contributing nano farad.

Equivalent capacitance of complete insulationis in pico farad.


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Increase in capacitance in comparisonto original reference value at 5 kV or 10kV indicates void and cavity in theinsulation.

Indicates presence of partial dischargesand deterioration of the insulation.

Increase in Tanvalue and no increasein capacitance means partial dischargeactivity has initiated near the HV terminalor near to tanor earthing terminal.


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Measurment of voltage.

Isolation between high voltage and low

voltage. Inputs to relay

PLCC

Parts of CVT: Capacitor part capacitor stack, insulator

EMU PT, HV choke and FR circuit.


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Tapping 110 V from C2 with primary voltage being220 kV is a problem since effective burden will thenonly be 0.22 VA.

Any attempt to load this system will lead touneven voltage distribution between C1 and C2and inaccurate output.


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CVT is a tuned device and hence the errors areprone to change with frequency but willremain in a specified accuracy class.

Standards specify that errors of meteringwinding are to be guaranteed from 25% to100% of the rated burden and for a frequencyrange of 49.5 to 50.5 Hz. However, CVT cancater same accuracy at 49 to 51 Hz because

of reduced burden requirement nowadays. Frequency of large systems always tend to godown below 49 Hz, thus it also preventsunnecessary under frequency tripping. Thus,they are tuned at 49 Hz.


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Carry out visual inspection of oil level.

Clean the insulator periodically. No oil change or oil filtration is required as CTs and

CVTs are hermetically sealed. During annual inspection on denergized CT

tightening of primary and ground connections to bechecked with tightening torques.

Online checks of hotspots on primary connections bythermo vision cameras.

Tan to be measured every year. Acceptable valuesfor CTs are 145 kV 2%, 245 kV 1%, 420 kV 0.8%,

And for CVTs 0.5%. Abrupt changes in Tanare alarming.


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Tanbeyond acceptable range should bechecked by DGA and oil analysis.

In case of fuse failures in CVTs, fault

checking to be done. If secondary voltage output change in

CVTs, carry out measurement of C1 and C2.

Sec voltage increases

element in C1 failsor primary turns of PT gets shorted.

Sec voltage decreases element in C2 failsor secondary turns of PT gets shorted.


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Composite hollow insulator is made up oftwo insulating parts.

Consists of filament wound epoxy fiberglass

tube and extruded silicone sheds on thesurface of the tube with metal flanges atboth the ends.

Sheds are produced by helical extrusionwith HTV silicone.

Applications are in surge arresters, bushings,circuit breakers, isolators and instrumenttransformers.


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High resistance against pollution. Reduced maintenance.

Very good electrical properties.

Resistance to PD. Hardly inflammable.

Self quenching No carbon chain. Inert to ozone, superior stability to UV. Water repellent

Less necessity of washing in pollution.

Resistance against mechanical shocks. Low weight

Non-brittle. High surface resistance compared to porcelain. No danger of particles during explosions.


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Vandalizing proof against impactvelocity of 10 m/s.


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Made from tubular aluminum sections

Joints are welded

Cu-Al joints are bolted and press fitted. Hot zinc metalizing to avoid galvanic

corrosion between Al and Cu.

3 phase gang operated isolators withmotor drive and manual drive.


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A bushing is used to run a current at high potentialthrough a ground barrier.

Designed as per IEC 60137


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These types of bushings are also called condenser bushings.

They have uniform stress on insulation, oil and porcelain.


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