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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...

Just wanted to add some clarity to the situation. The cable is 3-conductor cable so all three phases are contained within the jacket. We recently purchased the ArcPro software since the software is based on single-phase faults it seems many utilities use this for overhead line arc flash...

Of course we would not expect the people to be wearing arc flash PPE. The question is merely what cal/cm^2 would the person be exposed to. I don't understand why your answers are so hostile. Regarding what method we would use in other instances, that is my question. We typically use IEEE...

I don't understand this comment by rbulsara. I understand that arc flash calculations are done to determine the hazard when performing energized work. In this case, the question is what if a worker were standing close to the location that the cable faulted? Why wouldn't there be an arc flash...

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...

SEL relay logic has both "TR" and "ULTR" Trip logic functions. If you look up a SEL 551 Relay Instruction Manual they refer to these as follows: TR = Trip Conditoins ULTR - Unlatch Trip Conditions I could not upload the file due to size, but it can be found from SEL website or google.

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

Still doesn't work for me either.

Hmmm. The file dosn't seem to work for me.

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

I have heard that if you have a spare transformer but the voltage(s) does not quite match your system, sometimes it can still be used. I was curious if there were any "rule of thumbs" or calculations you could perform to determine if a transformer is acceptable to use in this way and how it...

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...