Breaker tripping when switching from Generator

[hockeyoligist2]

We have a 400 amp breaker tripping when switching from Generator back to normal power. We installed some ice cube type timers to delay the startup of some of the equipment to reduce the load at transfer. It has automatic switch gear and the switch is so fast that the timers don't reset. Anyone know of a solution?

 

[bdarnell]

A closed transition transfer switch is an (albeit, expensive) option for this type of problem. Someone may have a less costly alternative.

 

[ron]

Can you delay the transfer (instead of the startup of equipment).
Can you tell what portion of the breakers trip element activates the trip? Instantaneous, short time or long time? Can you measure the current that is causing the trip?

 

[charlie b]

What breaker is tripping? For example, does the ATS supply power (from utility or from generator) to a service panel, and is it the main breaker to that panel that is tripping? Also, do I correctly infer that there is no trip when transferring to the generator?

 

[don_resqcapt19]

What type of loads are involved? This is common with motor loads, and there have bee reports of motor shafts for 50hp+ motors being twisted off on this type of transfer. The problem is that the utility and generator are not in sync at transfer.
Don

 

[hockeyoligist2]

re

re

This is an old system, it doesn't sync. The generator only supplies power to "necessary" equipment. The breaker that is tripping is the normal power feed from the switch gear. They added a few extra things to the generator about 8 years ago. I have never been able to make it trip on transfer since some machines are not always in use, (as normal you are never there when the problem occurs) (they are controlled by plc's, floats etc.). The highest amps I've got at transfer is 304, then it drops to around 170, actual running amps, but I'm sure it exceeds 400 amps if everything is running at transfer I'm pretty sure that if I can just delay the startup of the bigger loads and stagger the times the breaker will not trip. The highest HP motor is 30 HP. I just need some way to delay the startup, and the Ice Cubes don't "see" the the power loss. It happens so fast the lights don't even flicker.

 

[ramsy]

Re: re

Re: re

The breaker that is tripping is the normal power feed from the switch gear. ..I just need some way to delay the startup, and the Ice Cubes don't "see" the the power loss.

If that breaker is over 1000A, does it include a GFPE that could be reading an imbalance during transfer?

Could those Ice Cubes be controlled to normally open at service outage, and ignore the generator, thereby delayed closing only when service is restored?

 

[templdl]

Just add a time delay neutral for the transition back to the normal source and the problem will go away.
What you are having with the way the transfer the way it is now is the counter EMF of the load causes a voltage spike when it combines with the voltage of the normal which results in a current spike of high enough magnitude to rip the breaker magnetically.
This is not uncommon when using a contactor, ASCO, or stored energy breaker type transfer switch which is capable of switching back into the normal source basically instantaneously.
The motor operated breaker transfer switch is slow enough to allow enough time for the counter EMF to die down a bit before re-energization with the normal source.

 

[ramsy]

Just add a time delay neutral for the transition back to the normal source and the problem will go away.

I take it there's a way to delay the neutral leg on the transfer switch, on its way back to the service. Is that right?

 

[oliver100]

What is ice cube timer?

IMO the transfer switch "paralels" the utility and the generator. Otherwise, the timers would reset and at least some contactors would drop.

 

[hockeyoligist2]

Thanks

Thanks

While I was off friday they called in the rep for the switch gear. He said that he could delay the transfer. Made some adjustments, and they said the timers were resetting. I hope so but I'll have to wait till thursday when it "exercises" thats the only time it does it.

 

[templdl]

ramsy,
It not that you put a time delay in the "neutral leg" but that the transfer switch disconnects the emergency source and goes to a "neutral positiion where it is neither connected to the emergency or normal source which is referred to as a neutral position. With a very short time delay in this neutral position the counter EMF is allow to decay and then the ATS connect to the normal source without having to deal with an opposing voltage.
Dave

 

[ramsy]

Dave,
Many thanks for brining that to the table.