Circulating current during synchronous generator synchronizing

[Yogesh Makwana]

Respected Forum Members,

I am facing a problem of circulating current during synchronization of the synchronous generator.

I am working on a project related to distribution network protection in the presence of distributed generation.
I have a synchronous generator in laboratory, its rating is as:

3KVA, 415V, 50Hz, Internally Star connected.

Now, when I am trying to connect with the utility by synchronizing the DSO shows a heavy circulating current flow. This circulating current of random nature (i.e. non-sinusoidal).
During the synchronization, I matched voltage, frequency and phase sequence.

I tried my level best to sort out but in all the way it remains present.

So, I request you kindly help me to sort out this issue.

 

[Besoeker]

Respected Forum Members,

I am facing a problem of circulating current during synchronization of the synchronous generator.

I am working on a project related to distribution network protection in the presence of distributed generation.
I have a synchronous generator in laboratory, its rating is as:

3KVA, 415V, 50Hz, Internally Star connected.

Now, when I am trying to connect with the utility by synchronizing the DSO shows a heavy circulating current flow. This circulating current of random nature (i.e. non-sinusoidal).
During the synchronization, I matched voltage, frequency and phase sequence.

I tried my level best to sort out but in all the way it remains present.

So, I request you kindly help me to sort out this issue.

How does it perform once connected?

 

[ron]

I am not familiar with machines of the 3kVA size, but we had a circulating current problem once with paralleling generators when the alternators were of different winding pitches.

https://library.e.abb.com/public/8d...82/Technical note Winding pitch LR_040214.pdf

 

[Phil Corso]

Yogesh...

Circulating-current is a function of the difference in terminal-voltages of the two gen's being synchronized, divided by the sum of their impedances!

Regards, Phil Corso

 

[Bugman1400]

How much current is it? Is it zero-seq or neg-seq current?

 

[Phil Corso]

Bugman...

Neither! Symm-components not needed here. It is the RMS, current-magnitude one would read on a clamp-on ammeter! There could be some harmonics even if the both gens had the same winding-pitch!

Phil

 

[Phil Corso]

Gentlepeople,

The circulating-current develops synchronizing-torque. Too little will make it impossible to synchronize. Conversely, too much could snap a shaft!

The latter case is caused when the voltage differential between the two gen's, or gen and utility, is large!

Phil

 

[ATSman]

Gentlepeople,

The circulating-current develops synchronizing-torque. Too little will make it impossible to synchronize. Conversely, too much could snap a shaft!

The latter case is caused when the voltage differential between the two gen's, or gen and utility, is large!

Phil

Phil,
So what's the solution.........change the field voltage of the gen to match the output voltage of the other source?

 

[Phil Corso]

ATSman...

Yes! Theoretically, if both voltages are equal, the incoming gen is said to be 'floating'! To have the incoming gen'r take on load gradually increase its speed!

And, be ready to adjust field-current (excitation) to keep PF under control!

Caveat: Always make voltage and excitation adjustment in small increments, repeat, small increments, until desired loading is achieved!

Phil

 

[ATSman]

ATSman...

Yes! Theoretically, if both voltages are equal, the incoming gen is said to be 'floating'! To have the incoming gen'r take on load gradually increase its speed!

And, be ready to adjust field-current (excitation) to keep PF under control!

Caveat: Always make voltage and excitation adjustment in small increments, repeat, small increments, until desired loading is achieved!

Phil

Interesting. We are always running into problems with standard transition ATSs transferring between sources (utility to gen) during a hot-bus, hot-bus test or return to utility after a power fail. The inphase monitor IFM(sync check) feature prevents transfer unless the 2 phase angles are typically within 7 to 10 elec degrees. The feature can be disabled in the controller software but no one wants to take on the liability of damage to the load.
Almost all gen manufacturers ship their units out set to exactly 60.00HZ and as you know this can cause the extended sync and transfer times. And in some cases "fail to sync" alarms and no transfer at all.
The IFM is a passive device and the solution is always to bump up or down the gen speed to change the HZ. We like to see the freq set between 60.15 & 60.2Hz. What adds to the pain is that on the larger gens the speed adjustment usually requires a laptop and factory passcode. Yeah, and getting the tech out in a timely manner to do this requires an act of Congress:rant:

 

[Phil Corso]

Ahh... technology! Ain't it grand!

And they (computer jocks) think they're going to control hundreds of millions of cars... w/o the human mind!

Phil