Substation Protection

I believe they were talking about the main transformer primary and secondary and I'm not sure where the substation was but most substations have transformers with secondaries that are the lower voltage (ie 13,200V, 12,470V, etc). PT - Potential Transformer, CT - Current Transformer, Lattice Structure holds the wiring and some switching, insulators protect the wiring from arcing to ground or return.

It depends on your situation. They could be talking about Transformer Primary & Secondary protection or distribution breakers, which their protection can also be refered to in such terms. Bottom line is each type: The Primary refers to the line side and the secondary is refering to the load side be it breaker or transformer, each side requires multiple monitoring devices for protection and control.

They could be referring to a meaning other than the high and low sides of the transformer.

In Large power substations, there often are two separate relay protection schemes implemented.

1> the primary relay protection system is the conventional system, and considered the main system of protection. It is designed to recognize and isolate an in station (or transmission line) fault by opening all the closest disconnect devices.

2> Should any of these intended breakers or other disconnect device's fail to operate and the fault has not cleared within a measured time, it is assumed that a primary system has failed and the secondary back up scheme then comes into action and opens the next devices between the fault and the power source.

On some large systems, there is a communication link to a distant breaker at another remote substation that opens the breaker at that point. This is called secondary transfer trip.

Some other foreign terms you may hear are. "Bus differential" "Transformer differential" "permissive trip" "transfer trip" "remote trip" "delayed trip" " Instantaneous trip" "stuck breaker relay" "single phase trip" "3 phase fault" "ground relay" "time overcurrent relay" "distance relaying" "first zone fault" "second zone fault" "Overeaching fault"

Hope this explains it

Snakers

Thanks for that Snakers,

I think your answer nails it, I have had a steep learning curve to be able to differentiate between the two types of Electrical Engineer skill sets that specialise in either the Primary or Secondary protection systems.

It appears that relativly few engineers become specialized in both unless they have been in the industry for decades.

I am in the process of learning the various Australian specific automation & control platforms, also the hardware that both use.

That's why they put engineering teams together I guess, it must be way too much work for a single person to do.

More research to do, enjoy the day.