Continuous and Noncontinuous Loads for Medium Voltage

[minesh21]

I am doing a load calc for a 4160V feeder serving a transformer tap. The feeder is tapped so that there are now (4) 4160-480/277V, 1500 KVA each transformers off the same breaker upstream (I am adding one to make 4). I'm worried about NEC 215(3)(B)(1). We only have 500 KMIL conductors - the 500 KCMIL comes off the upstream breaker, and is then tapped at 500KCMIL to all (4) transformers. The code says the feeder must be sized for nameplate ratings of transformers being supplied. No way I can do this, as the combined rating of all transformers would require a massive feeder. I'm hoping I can use NEC 215(3)(B)(3), since we are an engineering firm and the facility has maintenance personnel. I'm not sure if they have formal training though, but they work with HV on their site all the time.

The reason I am not concerned load wise, is because I have metering data on worst case. The existing load only uses 147A (worse case) total of all transformers existing. I am rating my underground conductors at 300A per NEC Table 310.60(c)(77), so we should be fine right?

My next question is concerning continuous and non-continuous. I don't see anywhere in the HV feeder section or overcurrent section where 125% continuous must be used. Therefore, I will take my new load as is. However, I will use 125% on the metering load per NEC 220.87. Is this correct?

 

[minesh21]

Any takers?

 

[smoothops10]

IMO you've layed out a decent case for what you are doing. I would recommend not taking advantage of 240.101. Sizing the feeder to the connected transformer nameplates per 215 provided a form of overload protection. Since your feeder is about half the ampacity that would be required to meet 215, I would verify the 51 pickup be below the ampacity of the conductors. Not 3x or 6x as allowed in 240.101. This would make your case more defendable as you have provided overload protection. A good application guide is here which is in line with this recommendation.
http://www.skm.com/applicationguides19.html

 

[minesh21]

IMO you've layed out a decent case for what you are doing. I would recommend not taking advantage of 240.101. Sizing the feeder to the connected transformer nameplates per 215 provided a form of overload protection. Since your feeder is about half the ampacity that would be required to meet 215, I would verify the 51 pickup be below the ampacity of the conductors. Not 3x or 6x as allowed in 240.101. This would make your case more defendable as you have provided overload protection. A good application guide is here which is in line with this recommendation.
http://www.skm.com/applicationguides19.html

Yes there is a relay that is set to 360A. I am going to have the contractor adjust the setting to 300A. This the allowable capacity of the conductors with the underground 6 circuit duct.