MV Feeder Application
MV Feeder Application
(OP)
All,
I just want your view on an installation challenge. I have an existing generator system (13.2kV), and I need to install a new UPS system on it. However, I do not have a spare output breaker, so do you think it's wise to use an existing breaker, and "double-lug" so to speak on it to feed the new load? Gen. capacity is more than adequate. I'm thinking there could be a problem with the protective relaying (GE MDP's).
Thanks in advance,
Mike
I just want your view on an installation challenge. I have an existing generator system (13.2kV), and I need to install a new UPS system on it. However, I do not have a spare output breaker, so do you think it's wise to use an existing breaker, and "double-lug" so to speak on it to feed the new load? Gen. capacity is more than adequate. I'm thinking there could be a problem with the protective relaying (GE MDP's).
Thanks in advance,
Mike






RE: MV Feeder Application
RE: MV Feeder Application
Yeah, I think you're right as I was looking at 240.101, and reread that section. We'll have to find a plan "b".
Thanks,
Mike
RE: MV Feeder Application
Think about the effect on total reliability.
The system would probably not have a UPS or a generator if there weren’t a perceived need for continuous power. Placing two circuits on one breaker may reduce the reliability and will limit the flexibility. For example, both loads may have to go down every time you do maintenance on the UPS.
RE: MV Feeder Application
RE: MV Feeder Application
You may need separate overcurrent protection for the loads.
RE: MV Feeder Application
I just cannot promote bad engineering...
RE: MV Feeder Application
My only option is to do a feeder tap off an existing feeder. Again, it's not my first choice, but all considered, my only one.
Thanks all for your comments.
Mike
RE: MV Feeder Application
Unfortunately real-world existing conditions and budgets sometimes require less than an ideal arrangement so long as it can be done safely, which I think it can with proper engineering.
RE: MV Feeder Application
What voltage is the UPS? I assumed the UPS is low voltage. Not that this changes my basic opinion.
But if it is a MV feeder as the heading suggests, there are different practices for protecting MV feeders and taps thereof.
RE: MV Feeder Application
It'll be a 13.2kV feeder from generator paralleling gear (the gear is both the "utility" feed and the standby backup feed with switching via breakers), to a padmount xfmr, which will then feed some input switchgear to a UPS.
Mike
RE: MV Feeder Application
RE: MV Feeder Application
I'm going to use an S&C switch w/ electronic fuses for the OC protection of the xfmr. I think I'm covered there.
Although I still think it's a horrible idea, I still don't find a reference in the code prohibiting me from double-lugging. If anyone can point me to it,...I'd appreciate it. I just spent a better part of the evening at home looking through my good ole 1999 codebook.
Mike
RE: MV Feeder Application
I just don’t like the idea of lugging two feeders. But for MV feeders the overcurrent device (breaker or fuse) is generally meant for short circuit protection only. Overload is generally controlled by design. That is one reason MV fuses are rate (say E rating) such that they open in 300 sec at 200% ampere current of the E rating. It takes forever to open at current anything below that.
A better solution in my opinion would be:
1. Make the new transformer loop feed type. Rearrange MV feeder to feed the transformer and loop out and then pick up the existing feed. Or vice versa, but daisy chain the two loads if you can.
2. Provide a separate fusible switch (air interrupter) near the existing gear and you can either double lug for a short cable to the new switch.
3. Double lug only if the transformer is not too far from the gear otherwise tap the feeder.
You can even make the tap smaller as long as the MV OCPD protects it for the short circuit. Check the cable damage curve.
4. Overload for the transformer can be provided at the transformer using dry-well or bay-o-net fuses. I would also plan for a primary switch for the transformer
RE: MV Feeder Application
I agree with all of rbulsara's comments except I'm not sure about the loop feed. Seems like two separate radial feeds would be more maintainable, esp. with isolation switches or load-break el's at the xfmr.
How about a PME-9 with two fuse bays, one for the existing load and one for the new xfmr? That will give you one unfused switch for future extension as well.
RE: MV Feeder Application
RE: MV Feeder Application
For this particular installation, connecting the UPS to the Generator breaker doesn't sound like a very good approach, for a lot of the reasons previously mentioned.