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the pole discrepancy relay did trip the breaker on all poles. No we don't have any records of breaker status contacts to show that the one phase opened before the other 2. One more piece of evidence that was found was there was a second relay connected to a different CT winding that also showed...

It is implemented by a protection relay. Sorry I can't post the schematic. This particular protection looks at the loss of current for pole discrepancy. My main question though, is if there was an open CT secondary, does it cause a high impedance on the primary of the CT, which would make the...

In a high voltage substation there is an incoming source transmission line that connects to 2 circuit breakers, so the current from the incoming source splits between these 2 circuit breakers. One of these circuit breakers tripped due to a "pole discrepency", which means that one phase current...

The CT is an ANSI Multi-Ratio bushing type CT in a 115kV circuit breaker bushing. So I am hearing that using 2 taps on a CT at the same time will NOT work correctly.

stevenal, I am confused by your reply, are you saying that it is OK to use more than one tap on a multi ratio CT?

Will using 2 different taps of a multi-ratio CT work? Will it cause any problems?

Is there a Code Requirement to leave service loops for Fiber Optic Cable? I have heard and read lengths of anywhere from 10' to 100' but I do not see anything in the NEC that explicitly says that a service loop of any length is required. Does anyone know of one?

Thank you for sharing the common mode choke idea, I definetely learned something new with that. It will not work in this application because the negative wire is not run in the same place as the positive wire. However I will keep that in my back pocket for the future. I tried googling more info...

I have a 125VDC control circuit that uses a non-shielded cable in a tray with AC power cables. There is 60 Volts AC being induced on a 125VDC wire. I know that the solution is to pull in a new shielded cable, but, does anyone know of a way to "drain off" this induced AC instead of pulling a new...

We have multiple installations with varying ages from 1 year to 20 years. they are vented lead acid battery type. We had not been previuosly doing a discharge test.

We have standby battery banks to provide DC power for our generating stations. Recently we started a monthly discharge test where we turn off the battery charger for five minutes to test the capacity/condition of the batteries. There has been some conflicting ideas on whether this is a good...

I am installing a Basler DECS-250 voltage regulator to provide field current to the rotating exciter. This AVR has a free-wheeling diode across the exciter field. Is the generator field breaker that I am installing un-necessary? Is there any advantages to installing this generator field breaker...

I have a hydro generator that is 12.5MVA, 13.8KV. The rated field volts and amps are 250V, 240A; and according to my datasheet the field resistance is 0.904 ohms. The rotating exciter has nameplate info of: 80KW, 250V, 320A, shunt wound. I am removing a field breaker that is in the exciter field...

thread238-82004 Does anyone have a clear method to size temporary protective grounds? I have read IEEE 1246 and that doesn't seem to go into enough detail. I have read IEEE 1048 and it references some tables in ASTM F855-1997. However I can only get access to ASTM F855-2009 which doesn't seem to...

I am working on evaluating our battery banks for arc flash hazards. The battery manufacturer gives a short circuit current rating of the battery, for example 2,044Amps. My question is, if I have 23 cells do I have to multiply the short circuit current by 23?

I don't know the manufacturer or cat # of the CT. I also don't know the thermal rating factor. It is in the bushing of an existing ASEA transformer. I plan on taking a trip to the substation where the CT is in a couple weeks. I will see if I can get the info then. But my question is pretty...

Ok, so that takes care of the relay devices connected to the CT, but what about the CT itself? Will it eventually overheat or something if constantly used at a current greater than 5A?

The CT is a C800 and the relay device appears to be rated at 5A. It is a Beckwith M-3310 transformer protection relay. We are replacing a GE BDD transformer differential relay. I'm not sure what the GE BDD relay device's continuous current rating is.

My system has a 1200:5A MR CT that is being used on the 800:5A tap. If the transformer was fully loaded at it's 2 stage forced cooling rating, the total CT secondary Amps would be 6. Is it ok to use a CT with a nominal current above the 5A rating?

So I should use a 30A two pole breaker. What if I were to use a 3 pole 30A breaker, would it accomplish the same thing?