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Hello guys. Need some help. We are currently getting the following readings off our relay. Phase rotation is acb. Ia=100A < 0 deg Ib=100A < 180 deg Ic=100A < -120 deg The voltage readings from the relay are correct. This is obviously giving us both zero sequence and negative sequence...

Hello guys. I have some old ABB Circuit Shield and Ground Shield Relays. I was curious if anyone had an idea of whether they would respond to RMS or Peak current. Thanks for the thoughts.

Hello, It seems that the pickup setting for time-overcurrent relays protecting overhead distribution lines is typically well above the ampacity of the conductor. Can someone explain why this is? Is the thermal capacity of the line greater than the ampacity given in tables? Thanks for the help.

Hello guys, I am hoping someone can help me understand zero sequence CT's (sometimes referred to as ground CT's) by answering a few examples for me. Any additional information someone can provide such as a reference or description would be appreciated. 1.0 If the zero sequence CT surrounds all...

Hello guys. I posted this on the arc flash forum website but that site is not frequented near as much as this site. We had an incident where a 480V cable was run overhead for temporary power. A large vehicle was passing underneath the cable and the cable got caught on the vehicle. The...

Hey guys. Do the IEEE arc flash calculations utilize phase or ground fault settings?

I had a code question regarding sizing 4160V motor cables. 430.224 says that all conductors shall have an ampacity greater than the overload trip setting. However, I cannot find any requirements regarding the setting of the overload for 4160V motors. 430.225 does not make any mention of the...

Can someone explain the difference between "Trip conditions" and "Unlatch Trip conditions" for relay logic?

Can anyone point me to a document that gives guidelines for derating cable for altitude? Thank you very much

Does anyone know what the differences are in the requirements for transformer BIL levels between IEC and ANSI/IEEE? I found a paper that says IEC has lower requirements for some voltage classes but I can't find information on what the specific BIL requirements are for IEC in order to compare...

Hello all. I am looking for a good book(s) on motors that is very practical. In my experience I have found that older books tend to be more practical than newer books. We use a lot of induction motors in all sizes (Fraction-5000HP+) and voltages (480V-13.8kV) along with numerous applicatoins...

Hello All. I am looking for a table (or someones best idea) of typical spacing for bare overhead lines at various voltages. I am looking for the following voltages. 4.16 kV 7.2 kV 13.8 kV 34.5 kV 46 kV 69 kV 115 kV 230 kV 345 kV Any help would be appreciated. Thank you

All, I am looking for information on the affects of utilizing transformers at system voltage levels which differ from the rating of a transformer. For example: utilizing a 161kV/20.9kV transformer on a 161kV/22.8kV power system. What will be the consequences? Any references, papers, etc. would...

Most people know that current determines how damaging getting shocked can be. A question was recently asked which I do not know the answer to. The question is, how long does the current have to exist before someone sees the effects. For example, 100 to 200 mA can be fatal. But how long does...

I am curious if anyone actually own these books. I heard about them from a fellow engineer, and went to EPRI's website to check on obtaining one. Specifically I was interested in the Red Book. I soon came to learn that these books can range from $5,000 to $25,000. This price certainly seems...

Hello All. I am looking for an older book on transformers titled: Transformer engineering;: A treatise on the theory, operation, and application of transformers The author is L. F Blume and it was last published in 1951. Does anyone know where I could find a hard copy or electronic copy of...

I am looking for information on the advantages (and disadvantages) of Circular core transformers versus rectangular core. I have heard that circular offers technical advantages but the rectangular core is cheaper. Can someone provide feedback on this? The applications I am most interested in...

I noticed that the Westinghouse "Distribution Systems Electric Utility Engineering Reference Book" is labeled as volume 3. My question is do volumes 1 and 2 exist? The Preface makes reference to the other volumes as titled below but it also mentions that the first two volumes have not been...

Can an MCC be installed in a room with an existing water pipe?

Can someone explain why fiberglass storage tanks are grounded?