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...
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...
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...
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...
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.
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.
Does anybody here know this type of transformer. It is delta/wye , 208v/208v, 10kva. But the neutral point of secondary is connected to a 100kV DC point? Why the neurtal point is connected like that? Strange to me. Any opinion?
A power utility company want to install two on-line DGA monitors for their transformers. It will be greatly appreciated if anybody here like to recommend some available products or the exprience with using them to me.
A distribution transformer with two circuit breakers (CB) and severl different protection relays including overload, overcurrent, time delay overcurrent, instantaneous overcurrent, differential relay, ground differential relay. Anybody can tell me whether the relays trip the HV and LV CBs at the...
I happend to find a paper said that almost 20% of transformer failure is due to Line surges. The number is really high. Anyboday has some comments on this? Thanks.
