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Thanks for the reply! Understand the breaker has to clear the network fault, i.e., the fault outside of the substation. But do we need to rate the breaker considering the multiple phase to ground fault inside the GIS substation e.g. bus fault? Or do you refer to the substation as the "elsewhere...

Hi, we are evaluating the short circuit current interrupting capability of circuit breakers in 115kV and 345kV phase-insulated GIS substations. The three phase to ground or two phase to ground fault currents in the station exceeded the breaker ratings. I'm wondering if multiple phase fault...

Hi, we are an utility. Someone is concerning 5% overloading of a 115kV underground transmission cable with the overload time duration of 30 min. I know it shouldn't be a concern, as we normally talk about hours in discussing cable's short time overload capacity. Can anyone point to me any...

Thanks a lot for your reply, Collies99. But My vaccum bottle is in GIS assembly. The CB can not be racked out. The only way I can think of is applied the testing to the cable termial with CB open. Have anyone done this?

I was asked to have the vacuum circuit breaker tested during routine maintenance process in the MV gas insualted switchgear. But there is no access to do the test on vaccum CB in these Siemense 8DA10 series GIS. The insulation testing, hi-pot test can be done at main circuit level with CB...

Dear Mike: If you don't like to reply, that is fine. That is your own business.I am not soliciting your free service at all. I certainly don't respect your "professional" by the way you reply. As a matter of fact, I am having beeing reading the related document based on what I can get. True, I...

Thanks a lot for the information. I kind of get better idea. For the switchgear battery in the substation, and emergency battery or control battery in power plants, generally performance tests are conducted to measure the capacity. The testing duration for power plant battery generally is 8...

Could anybody help me understand the difference of these four different terminogies for a UPS battery? It sounds to me capacity test equals to performance test, modified performance test equal to service test. For switchgear battery for relay system, which test duration should be used? For power...

This is what I don't understand: Normally P is much large than Q in transmissions. e.g. P=100 MW, Q=20 MVar. However, according to the above equations, the error% of MW derived from phase error is (Q/P) * (3.14/180) = 0.34%. While the error% of Mvar related to phase error is (P/Q) *...

Hi all, I couldn't find any references discussing what is the accuracy of MW and Mvar derived from VT and CT in substations. Supposing both VT and CT have 1% ratio error and have 0.5 degree (30 minutes) phase error, how much error do you think MW and Mvar will be? I am talking about 115kV or...

Thanks everbody here. I have no light to throw ... I'm very confused too. My company uses protection CT for both metering and protection, while a neabouring utility always distinguishes protection CT and metering CT. I have no clue why.

odlanor, my company does not own generators so we don't use it for governors,AVRs etc. The operational measure of 0.6% is requirement by ISO (Independent System Operator).

Sorry, I have to make correction - the operational measure is 0.6% at rated current.

Stottf, the operational measure is 0.3% at rated current according to our supervising authority. I doubt that our protection CTs can meet the requirement.

Hi all, my company uses protection CTs for both protection and metering. Is it a common practice for utilities? How do I know its accuracy (e.g. <0.3%) of metering normal loading current (not fault current)? Thank you.

Hi, I am looking for IEEE or ANSI standard regarding generator AVR (automatic voltage regulator). Does anyone know reference number or any link? I did web search and didn't find any. Thank you.

Thx. My question is if someone really did the test and/or calculation. "Synchrophasor" can be obtained by PMU (phasor measurement unit) or EMS (energy management system in control centers) estimations.

Does someone have working experiences to calculate transmission line parameters (R, X, and/or B) based on real-time telemetries at line terminals(P, Q, KV)? This is to verify line parameters calculated by system planning. It is important for relay settings.

We have a long undergrouded HV cable and are considering how to de-energize the cable. Does anyone know if the trapped charges on cable will decay slowly (how fast?) after de-energizing without any additional equipment to drain the charges? thanks.

Thanks, alehman. I still don't understand several things. Is the DC source different form that for isolation transformer? Why the DC voltage need to be connected to the neutral point?