Generator circuit breaker keep on tripping when loading a motor

[rod1478]

We have supplied a 2 sets 1145kw Generator sets with 1700 amps rated current ,480 Volts that is being paralleled and stepped up to 4160 Volts 5MVA Transformer delta wye connected supplying a medium voltage 4160 V softstarter driving a 600 Kw motor .

The Generator runs in parallel using a micro proccessor based generator auto synchronizer(Woodward EGCP2) without load, however , when we try to start to load the 600 Kw Motor , the generator circuit breakers trip off suddenly without any fault display in our generator controler.
We repeat the sequence operation, but this time we have disable the instantenous trip of the circuit breaker ,unfortunately same tripping trouble occured.

My question does the presence of harmonics affects the operation of the generator controller?

Is my 2 x 1135 kw, 480 v Generators in parallel is not enough to start the 600 Kw motor with a starting current of 2890 Amperes?

Do i have to install a NGR at transformer secondary.

 

[kingpb]

Are the generators identical, including manufacturer?

How are the generators grounded?

If you disabled instantaneous function, what did the breakers trip on?

Is the 2890A the starting current with or without the use of the soft starter?

 

[coulter]

...My question does the presence of harmonics affects the operation of the generator controller? ...

Yes, it could. Your profile says you are the supplier of this type of gear. What does the design literature say?

...Is my 2 x 1135 kw, 480 v Generators in parallel is not enough to start the 600 Kw motor with a starting current of 2890 Amperes? ...

It should be plenty. (note to kb: Doesn't 2890A sound like the right number for minimal soft start - amps on the 480V side?)

...Do i have to install a NGR at transformer secondary.

You could - unless you want it solidly grounded or ungrounded. Most I have seen are impedance grounded

...We repeat the sequence operation, but this time we have disable the instantenous trip of the circuit breaker ...

Here is where I start getting nervous and reading the design docs and literature - and retesting the installation. As I'm sure you know, if you disable enough safetys, it will eventually start - or burn down. Don't discount that something isn't broken - or improperly installed.

Rod - You are about in the middle of commissioning a healthy job. You sound like you have doubts about the design. According to my father, "If you have inner doubts about a job, listen carefully, someone (a higher power) may be trying to talk to you."

You might consider calling in some specialized design help.

carl

 

[MJJBEE]

How are the generators being controlled by the Auto Synchronizer? Is it possible that one generator is being forced to source all the vars for the system? I may be that you have a control issue with the generator and you can fix it by applying the correct settings I would check this out before changing settings on my protection. I remember something from my last generation control class but I can't remember what method of generator control you should be using.

 

[coulter]

...I can't remember what method of generator control you should be using.

I'd guess both in droop, with load share and var share enabled.

As MJ suggested, a through review of your settings, both gen control and CB relays is highly recommended.

carl

 

[MJJBEE]

Thanks Carl it's not my field of expertise we have a guy who just does generators for us but that sounds like what I was thinking. At the size he is talking about I know they both should not be in AVR or they will fight during a system disturbance and hit the Over and Under Excitation limiters. That is what I think is going on here but I can't be sure without data.