Back Charging The Switchyard

A 400kV switchyard fed by a 600 mega-watt is nowhere for an amateur to work. You should not be asking anyone here for this kind of information. You should either be consulting the site schematics, the engineering staff about the specifics of this switchyard or your textbook and professor for a clarification on your homework.

Fully correct.

I don't know what idiot voted you "Off Topic" (probably the same idiot who asked the original question!), but I have given you a GA, so you are back to zero at least!

Well done.

Raj,

There's no way to provide the information you want without more detail on the layout of the plant and switchyard. For example, are the feeders connected by breaker, air switch or both? Do the feeders connect to a common bus, ring bus, breaker and a half scheme, or other design? Is there one 600MW generator, or multiple smaller units? What is the source for plant service power? Is there one step-up transformer or one for each of the multiple generators?

There's simply no way to give any reasonably accurate advice without that type of information. Most of these questions could be answered by a single-line diagram of the switchyard. Please provide any detail you can and we'll try to go from there.

Redfred and Pwr2thepeople, I agree with you that a 400kV switchyard is no place for an amateur or newbie to cut their teeth on substation commissioning. However, a good general list of tasks to be completed by whoever does the commissioning can be developed. If Raj is responsible for putting together a spec for the commissioning prior to backfeeding (I'm pretty sure that's what he means by back charging) the station from the utility source, then the following is needed at a minimum:

1. Verify all structures, buses, conductors, insulators, and electrical apparatus are installed according to the design drawings. Review the drawings in detail to look for inconsistencies in phasing, equipment orientation on foundations, interferences in positioning, etc.

2. Verify all minimum electrical clearance distances are met (phase to ground and phase to phase) so that no energized parts are too close to personnel, vehicles, the earth and earthed parts, or each other.

3. Inspect all apparatus to assure that they are in acceptable physical condition (no damage, deterioration, contamination) and installed properly. Test each piece of apparatus per manufacturer's instructions and industry specifications. Highly recommended as a guide: the InterNational Electrical Testing Association's Acceptance Testing Specification. Typical tests may include DC insulation resistance ("megger"), hipot, insulation power factor / Tan-delta, contact resistance, winding resistance, etc., depending on the piece of equipment.

4. Test the resistance of the station ground grid to remote earth, and continuity of the grid to all attached equipment grounds.

5. Sample the oil in any oil-filled equipment (transformers, circuit breakers, etc.) and analyze. At minimum, test its dielectric, moisture content, acidity, interfacial tension, and dissolved combustible gases. Sample the SF6 gas in any gas-insulated equipment for moisture.

6. Test the ratios of all CTs and VTs used for protection, control, and instrumentation. Check saturation of CTs and compare to manufacturer's curves. Verify that any multi-ratio CTs and multi-tapped VTs are connected at the correct taps per the drawings and relay coordination study.

7. Verify (point to point) ALL the control and instrumentation wiring (secondary wiring). This is best done by injecting a small current into CT circuits one circuit at a time, and tracing it through each device against the schematics using a multimeter and a current probe. VT circuits can be traced similarly by applying a low voltage and tracing with a multimeter. Verify proper polarity of voltage and current connections to each device's inputs.

8. Check and calibrate all meters using calibrated voltage and/or current sources.

9. Set and/or program all protective relays according to the relay coordination study. Inject secondary currents and/or voltages to simulate tripping points per the study, and verify proper relay operation.

10. Test the station battery bank and charger to verify proper DC voltage and capacity.

11. With the station still de-energized, using the various protection and control devices (control switches, protective relays, auxiliary contacts, etc.), perform functional tests of each control circuit on the schematics to verify that they all operate properly: All close controls close the associated apparatus, all blocking contact do actually block operation, all trip contacts and controls trip the breakers, etc.

12. Only now, after ALL of the station has been tested and verified to operate properly de-energized, are you ready to consider starting to back-feed from the utility connection into the station. All breakers and switches should be open, all controls in proper state, all relays energized and programmed. Then, step-by-step, start closing switches and breakers from the incoming switch into the station, and verify at each step (using metering, relay displays, etc.) that all measured values are correct. If all the testing has been done diligently, and the installation has been done properly, your station should work.

This does not consider any SCADA, communications, or remote control & instrumentation. Those are additional areas to be tested and verified. Preparing the generator(s) and their associated circuit breakers, CTs, VTs, step-up transformer(s), etc., for energization is done similarly, with the ultimate goal to synchronize the generator with the utility source at the substation.

Be careful! Poor attention to detail on any of the above can damage or destroy some very expensive equipment. That is why doing this properly is so crucial.

Nice response...

A fair amount has been said on this issue. I will add one other thing... not only does this issue effect the switch yard in question, but it can effect the up stream station also. Ensure coordination with that station is in place as well.