It is commonplace operate generators in parallel to obtain the correct power output to meet the requirements of the load.
Many generators are employed in offshore and marine power systems with isolated neutrals (i.e. IT networks).
Controlling circulating currents when paralleling generators in a power system that shares a common neutral can be difficult. In any paralleling operation, it is extremely important that voltages produced by the generating equipment are as closely matched as possible. To properly match voltages, not only do the RMS values need to be similar but the instantaneous values, which are determined by the voltage waveshapes, should be similar as well. When this is not possible, as in paralleling of generators with different winding pitch configurations or even operating generators of the same model, circulating currents may appear in the common neutral which bonds the wye connections of the generating sources. These circulating currents can cause overheating in the generator windings and false tripping of overcurrent protection equipment, particularly ground fault detection schemes.
These conditions are most troublesome in permanently connected parallel applications but can also be an issue during closed transition transfers in peak shaving or back-up generation applications. To reduce these circulating currents, which are usually triple frequency in nature, a uniquely wound, multiple coil reactor, such as Mirus’ GenLink Dissimilar Pitch Neutral Limiter (DPNL), can be very effective. The unique winding configuration of the GenLink will block the flow of circulating current while introducing minimal effect on the short circuit impedance of the system.
For more information on the MIRUS Genlink DPNL product click here – DPNL-PS01-A3-GenLink-Brochure
Technical sheet click here – DPNL-S002-A5-GenLink-Tech-Sheet
For application note on preventing neutral circulating currents when paralleling generators click here – DPNL-WP001-A1-Preventing-Neutral-Circulating-Current-when-Paralleling-Generators