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Parallel Generators Circulating Currents

Parallel Generators Circulating Currents

Parallel Generators Circulating Currents

I am doing the electrical design for a project that consists of two 13.8 kV 1500kW co-gens, and one 13.8 kV 1100kW co-gen. All are set to be running in parallel with the utility on the same 13.8kV bus. I am trying to figure out what adverse effects would circulating neutral currents have on this system? Would having different impedances on the neutral ground resistors cause circulating neutral currents?


RE: Parallel Generators Circulating Currents


"Why not the best?"
Jimmy Carter

RE: Parallel Generators Circulating Currents

We had 3 generators we balanced onboard ship and we never had an issue with neutral current between generators. Once the frequencies were in sync and the load balanced between the generators they fed the load with no problems between them.  

RE: Parallel Generators Circulating Currents

I assume there isn't a neutral conductor as such, but an earthing resistor connecting the star point of each generator stator winding to earth. Circulating currents may cause problems with your earth fault protection, depending on how it is designed. From a purist's point of view it would be preferable use a transformer to isolate each generator from the load bus using a transformer and provide neutral earthing for the bus.

If we learn from our mistakes I'm getting a great education!

RE: Parallel Generators Circulating Currents

Differing harmonic voltages in the generators can cause circulating harmonic currents.  The main issue is generally the continuous rating of the grounding resistors.  The actual kW losses are pretty low, but the standard 10 second resistor no longer has a published continuous rating, at least in the ANSI world.  


David Castor

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