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Thanks DTR and David Beach. The DC voltage distribution is laid out in a fashion where +ve to ground is 96 V and -ve to ground is 30 V, so I am sure it is not a ground fault. Breaker is open at the moment and I want to make sure that is isolated either side disconnects open, it is an outdoor...

I am struggling to understand zero voltage across terminals H1a and H1c of GE F60 UR relay. Contact status in the relays shows de-energized(open). This contact is part of GR UR family Form A and has a current and voltage monitoring circuit and for some reason there is no detail what is the...

Just also curious to know how would secondary behave when only one phase is applied to primary of transformer ? Will any voltage be reflected ?

Thanks gentleman I got it. besides mixing line to line and line to neutral I was mixing phasor as well In my head. I will create a calc sheet and post it here. This forum is the best.

Hi Vter thanks for putting the effort but based on the literature two line to line voltages are 1.5 pu that is 87 % of 1.73 pu. This is what I Am trying to figure out how ?

Hi Waross I have done the calculation, please let me know, if I got it right.http://files.engineering.com/getfile.aspx?folder=f2fc6bd9-c4d2-484d-bffc-c80658ed7b82&file=Phase_Detection.jpg

Hi Waross, I just want to get some of my facts straight about 3 phase transformers so that I am not wasting my time going overboard in trying to get something in to head for which I am not ready. 3 Phase. 10 MVA 27.6 kV/4.16 kV transformer Primary A phase voltages are VA= 16< 0 degrees VB=...

Hi, I have exhausted all resources on the internet and books that could help me understand the phenomena in the subject above. I owe this to may be my poor understanding of phasors specifically related to primary and secondary winding of transformers. And I need your help. I wanted to program...

Thanks Scott Few additions to my earlier post: 1. 2.5L and 10L accuracy CT besides the fact that 2.5L is more accurate than 10L for 20 times the rated Secondary current, why would somebody ever by a 10L rated or C rates CT(C rated has 10% error as well ). Just trying to understand why 10L or C...

Hi Few questions please ; 1. Would it be correct to say that as per IEEE C57.13 by default CT thermal rating is rated at 30 degrees if not specified otherwise. 2. If I have a 800: 5 CT rated at 55 degrees with thermal rating factor of 1.33, then what would be the rating at 30 degrees...

I am just curious about the CT concept operation, if the SLG fault happened during the motor running, two primary phases will cancel out as davidbeach mentioned but 3rd phase on the primary of transformer will not cancel out and CT will dish out current equal to the primary load current in that...

Hi I was trying to make a quick excel sheet where I could plug in some relevant information and get the secondary excitation voltage during a fault event and see if my CT accuracy selection is ok. Below is the link, I was using as a quide...

Thanks Collies but I have two transformers feeding the same bus simultaneously, so my max. current will be 1852 and bus will be 2000 A if I go with it. I could not find any literature on bus sizing. My next option is 3000 A but I want to make sure I have some kind of scientific justification to...

Hi I have a existing old 4.16 kV switchgear which i need to replace. It is fed from two main transformers 5/6.67 MVA @ 27.6/4.16 kV. I dont have a way to find out the existing bus rating but on 4.16 kV, We have been buying a 2000 A bus switchgear but those transformers are smaller. This is...

SORRY FOR PITCHING IN GBELL QUESTION: FOR EXAMPLE IF I REQUIRE A C200 CT BUT IF I BUY c400 , WOULD IT MAKE ANY DIFFERENCE IN TERMS OF PROTECTION APPLICATION; IS THERE ANY DISADVANTAGE IN BUYING A BETTER CT?,

Hi All, Practicing electrical engineering for the last 10 years this never came to my mind till my nephew who is studying electrical engineering starting discussing the difference between CT and power transformer concept. Let me start with what I know and may you can interject and kindly...

I appreciate your time gentleman. So the recommendation is that I should have directional element enabled on both incomers breakers. Any suggestions on reverse power ? will that do the job. Note: There are no taps on these transformers and both transformers are operated in parallel. Each...

Gentleman, My apologies for submitting incorrect arrangement of the switchgear. I have attached the correct arrangement. There is no tie breaker since the project is a like for like replacement. Based on the new attachment, do you see a requirement for a directional element. The only reason...

Hi I have attached a pdf file that shows breaker and bus arrangement for a 4.16 kV switchgear. Background: This project is replacement of a 1950 switchgear supplied by GE and has basic overcurrent protection on the feeders and 67 directional relays on the two main incomer feeders. As part...