Multiple Generators in parallel and tie bus bars arcing.

R

res9405

Member
Location
Granbury, TX, United States
Occupation
Engineer
l have 4, 3 phase generators operating in parallel and are tied into a combiner that distributes power out to a large operation. The loads are high draw pumps and control motors. The issue is that when one of the generators is either taken off line or goes into fault and drops offline, the power on the combiner causes an arching between the bus bars in the output closet of the generator that drops offline. The potentials between the bus bars should be the same at full voltage and decreasing as the voltages drop. Why am l seeing arcing? Is this due to a reverse voltage issue or transient phase issues???
 
(Assuming that "combiner" is the paralleling gear, but that's usually nothing special on the power side. "Output closet"?)

A lot more info would be quite helpful, for instance, what size generators and are they low or medium voltage? What's the environment (clean or dusty or damp)? Does this happen to a single unit or any unit when taken off-line?

One thing that can happen is than in the process of going offline the voltage regulator allows the voltage to spike after the paralleling contacts open (and dust could exacerbate this), but that's a WAG. It's also possible that the process of removing a generator from the bus doesn't adjust the throttle & excitation to transfer the load onto the other generators before opening the contacts (also a WAG).
 
zbang said:
(Assuming that "combiner" is the paralleling gear, but that's usually nothing special on the power side. "Output closet"?)

A lot more info would be quite helpful, for instance, what size generators and are they low or medium voltage? What's the environment (clean or dusty or damp)? Does this happen to a single unit or any unit when taken off-line?

One thing that can happen is than in the process of going offline the voltage regulator allows the voltage to spike after the paralleling contacts open (and dust could exacerbate this), but that's a WAG. It's also possible that the process of removing a generator from the bus doesn't adjust the throttle & excitation to transfer the load onto the other generators before opening the contacts (also a WAG).
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I agree that much more information is necessary. When l arrive at the site and can evaluate the occurrence first hand l will have more to report. This was my attempt at polling the experience base in the community in order to reduce wasted effort on useless theories. You know, experience over possiblity.
 
res9405 said:
I agree. However, the arcing l am referring to is between the tie bus bars at a generator that is coming off line or defaulting off line.
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Good to know.
What is the voltage?
Arcing phase to ground or phase to phase? Is it always the same phase?
What type and amperage of equipment?
 
The issue is occuring at the switchgear and given that no one is inside the cabinet to see where the arc started. It is on switchgear that handles 1300 vac.
We are attempting to implement some stop gap fixes that will eliminate certain exposure areas. There are some environmental elements that have been brought into the light and we will see if our safeguards have resolved this problem.
 
Sounds like something is creating a extreme over voltage...a voltage greater than the dielectric strength of the air between the parts. Can you install a camera in the gear so you can see exactly what is happening?
 
don_resqcapt19 said:
Sounds like something is creating a extreme over voltage...a voltage greater than the dielectric strength of the air between the parts. Can you install a camera in the gear so you can see exactly what is happening?
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Already in the plan. However, at this point customer driven thresholds are driving the speed of the process. Which means that being scientific about the trouble shooting is not exactly the driver.
 
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