Separate Sources in Parallel?

[nightfox1925]

Is there any repercussions in placing to separate sources in parallel like in the case of a double ended switchgear fed from to separate external utility sources (say Utility #1 and utility #2)..two separate circuits. Most of the utility interconnections I encountered so far was in the form of a ring connection and two lines enter a substation.

 

[davidbeach]

If the switchgear was designed for either-or, you probably don't have adequate withstand ratings for both. Tying two independent sources together where they weren't designed for that can also result in significant through current.

 

[jimgineer]

There's no guarentee that your phases would match as well, which could cause some big problems. Separate utility feeds are often run from the same substation, in which case... Maybe someone here can comment on the liklihood of issues arising.

 

[alehman]

Even if in phase, most utility companies would not approve such an arrangement. It could interfere with load balance on their system, interfere with their protection relaying and/or create safety issues for their workers. Also, you could end up with load for other utility customers on the circuits flowing through your meters.

I've seen this done on a temporary basis, but only under direct supervision of the utility operations folks.

 

[NKE007]

Before you parallel two sources you need to confirm the following:

1 The 2 sources MUST be in phase a.k.a. in synchronisim
2 You will substaintially increase the amount of fault current. You must make sure your switchgear can handle it
3 If the 2 services are fed from transformers then the transformer impedances must be the same. If they have LTC's you will need joint control for them
3 For faults beyond your system, the fault current would flow thru your switchgear bus. You should install directional overcurrent relays to sense this condition and open the faulted feeder

 

[rbulsara]

what alehman said..

 

[slavag]

Hi.
What Alehman said.
It will be problem with same utility, Substation feeded from separate substations of same utility.
Regards.
Slava

 

[nightfox1925]

Thank you for clearing me up folks.