Parallel Generators - with and without Unit Transformers

[syleng]

We have a stand-alone Generation platform with both 11kV and 480V+ step up transformer.
The generator with the step up transformers is always tripping off line when high inrush conditions are experienced on the distribution, while the other 11kV units stay on-line and take up the load.

Conditions are:
i. Closing a feed breaker with full load on it.

ii. Transformer fault on a feeder

iii. A transient fault {over current/ ground fault} on a feeder.

Adjusting the Gen HV protection does not help. Does anyone have a possible fix? Or would a transient Analysis using CYME or ETAP help?

 

[J.Key]

Hi, you need to provide more information. What protection relay indicate? Differential trip? Overcurrent trip? do you have single line diagram?

 

[crshears]

Were cross readings taken at the time of commissioning? You may have a CT additivity / subtractivity [?] issue caused by incorrect wiring.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[RRaghunath]

syleng, It is difficult to help without knowing on what protection the trip is happening.
If it is inrush current causing the trip and by transformer (or generator + transformer) differential protection operation, then it is a matter of setting the differential protection 2nd harmonic block that provides stability during inrush currents.