Switchgear controls don't have a neutral

[kellytshort]

Yesterday we turned power off to an older piece of switchgear and it is a Main-Tie-Main and when the left side main went away so did the control power ? I am assuming they don?t have a rollover control power scheme otherwise this wouldn?t have happened. To solve this problem I was going to provide it 120V source from batteries, so I can disconnect a commercial power feed as needed. Now the undervoltage relay that locks that breaker will never engage, and will have the ability to open and close the breaker without a voltage presenet ? what are the possible problems that could arise from this as well, and why wouldn?t you want to control the circuit breaker if there isn?t power to the board?

 

[zog]

Yesterday we turned power off to an older piece of switchgear and it is a Main-Tie-Main and when the left side main went away so did the control power ? I am assuming they don?t have a rollover control power scheme otherwise this wouldn?t have happened.

Likey not, did you check the CPT fuses?

To solve this problem I was going to provide it 120V source from batteries, so I can disconnect a commercial power feed as needed.

What are the close, motor, and trip control voltages for the breakers?

Now the undervoltage relay that locks that breaker will never engage, and will have the ability to open and close the breaker without a voltage presenet ? what are the possible problems that could arise from this as well, and why wouldn?t you want to control the circuit breaker if there isn?t power to the board?

Not sure what you are really asking here.

 

[rcwilson]

Was the UV relay connected to the line side of the main breaker? It could be there to prevent back feeding from the switchgear to a de-energized source. In that application, the UV relay inhibits breaker close unless the source is present.

Or it could be intended to protect downstream equipment from undervoltage or unbalanced voltages.

 

[kellytshort]

what I was aksing about the undervoltage relay which is connected on the line side of the incoming circuit breaker is - what purpose would that relay serve meaning what protection does it serve to the system. Because our goal was to switch load over to one side with no commercial power present to the board so it would be an unloaded transfer then re-energize the board. When no commercial power was present the undervoltage relay engaged preventing us from utilizing that circuit breaker.
I am not a fan of the way it is wired, because I would prefer the ability to operate my circuit breakers no matter what, and was going provide control power to that relay which would never engage - and want to make sure I am disabling that relay won't create havoc.

 

[zog]

what I was aksing about the undervoltage relay which is connected on the line side of the incoming circuit breaker is - what purpose would that relay serve meaning what protection does it serve to the system. Because our goal was to switch load over to one side with no commercial power present to the board so it would be an unloaded transfer then re-energize the board. When no commercial power was present the undervoltage relay engaged preventing us from utilizing that circuit breaker.
I am not a fan of the way it is wired, because I would prefer the ability to operate my circuit breakers no matter what, and was going provide control power to that relay which would never engage - and want to make sure I am disabling that relay won't create havoc.

The UV is there to protect against a loss of the utility feed, say there was a brown out condition on the utility, your laods will draw a ton of current at the reduced volages, sure your OCPD's would eventually trip/blow but better to have the main anticpipate that than possibly damage loads and blow fuses.

Not sure what the point of closing the main and then restoring the utility feed would be, you always want to energize source to load, unless there is something else that is effecting your choice you left out.

 

[jdsmith]

what I was aksing about the undervoltage relay which is connected on the line side of the incoming circuit breaker is - what purpose would that relay serve meaning what protection does it serve to the system. Because our goal was to switch load over to one side with no commercial power present to the board so it would be an unloaded transfer then re-energize the board. When no commercial power was present the undervoltage relay engaged preventing us from utilizing that circuit breaker.
I am not a fan of the way it is wired, because I would prefer the ability to operate my circuit breakers no matter what, and was going provide control power to that relay which would never engage - and want to make sure I am disabling that relay won't create havoc.

Why would you want to close the main if the incoming line was dead? I just had this discussion last week on a switchgear we started up. Ours was wired the same way, with a 27 (undervoltage) contact wired as a close permissive. Operationally there is no reason to close that breaker if the line is dead. If you need to close it for testing purposes it's east enough to put a jumper across the 27 close permissive contact to disable the interlock for short periods of time.

This interlock is similar to the one that keeps you from starting your car if the automatic transmission isn't in park - there may be times it is safe to do it but in general it is not required. If you need to close a main into a dead line, then you can take about 2 minutes to install a temporary jumper to bypass the 27 close permissive.