Paralleled generators protected with fuse AND breaker??
Paralleled generators protected with fuse AND breaker??
(OP)
First time poster…certainly wont be the last either!
I have multiple 4.16kV generators in a parallel operation. The customer has spec’d that there be a “lockable fused non-loadbreak disconnect switch” between the generator and the withdrawalable circuit breaker that we have spec’d. So the configuration goes GEN->FUSED D/C SWITCH->BREAKER->SHARED GEN BUS. Of course there is a tie breaker between the shared gen bus and the utility bus.
What’s the purpose of 2 protective devices??
I mean, I could understand that someone would want a means of isolating the generator as close as possible to the unit for testing purposes. But having 2 protective devices in series with no load between them seems illogical and a possible coordination issue.. I suppose the customer could use a non-fusible link in the disconnect switch.
Any insight?
Thanks!
I have multiple 4.16kV generators in a parallel operation. The customer has spec’d that there be a “lockable fused non-loadbreak disconnect switch” between the generator and the withdrawalable circuit breaker that we have spec’d. So the configuration goes GEN->FUSED D/C SWITCH->BREAKER->SHARED GEN BUS. Of course there is a tie breaker between the shared gen bus and the utility bus.
What’s the purpose of 2 protective devices??
I mean, I could understand that someone would want a means of isolating the generator as close as possible to the unit for testing purposes. But having 2 protective devices in series with no load between them seems illogical and a possible coordination issue.. I suppose the customer could use a non-fusible link in the disconnect switch.
Any insight?
Thanks!





RE: Paralleled generators protected with fuse AND breaker??
The breaker is almost certainly there to allow other protective functions to disconnect the machine from the system and perhaps to provide automatic synchronising capability. Manual synchronising is possible, but is a nerve-wracking experience with a big set especially if you are standing in close proximity to the breaker. Not as nerve-wracking as an out-of-sync closure from a bad manual sync, but that's a different story.
RE: Paralleled generators protected with fuse AND breaker??
Being a jerk back in college I enjoyed the grinding sound of briefly hitting the sync switch with the lab volt motors...figured it's better to learn there what it looks like then in the real world!
RE: Paralleled generators protected with fuse AND breaker??
RE: Paralleled generators protected with fuse AND breaker??
It appears to be more common when the engine/generator is some distance from the switchgear room. Lately a number of the Solar turbine based cogen units I get around are also using a local disconnect, usually non-fused or with solid links.
I guess the best answer is probably going to come from the customer as to why he wants it.
Mike L.
RE: Paralleled generators protected with fuse AND breaker??
RE: Paralleled generators protected with fuse AND breaker??
RE: Paralleled generators protected with fuse AND breaker??
RE: Paralleled generators protected with fuse AND breaker??
Davidbeach not sure what you mean unrealistically low, if the switch is rated as a loadbreak at 41kA it should be able to interrupt that. But really, the breaker will take care of the clearing. Not sure what you mean by a rated combination either. Is this a predefined combo that has been chosen to coordinate with each other?
RE: Paralleled generators protected with fuse AND breaker??
Unfused disconnect is likely to have a 5kA withstand rating, although 5kV rating may be different, will the exactly same disconnect with fused might have a 200kA withstand rating.
RE: Paralleled generators protected with fuse AND breaker??
RE: Paralleled generators protected with fuse AND breaker??
RE: Paralleled generators protected with fuse AND breaker??
he's right! the fuse disconnect is non-load break, the breaker is load breaker.
thats the intent of the customers request, "The customer has spec’d that there be a “lockable fused non-loadbreak disconnect switch” between the generator and the withdrawalable circuit breaker that we have spec’d."