Neutral Grounding Reactors for Generators

Application of Neutral Grounding Reactors for Generators

Neutral grounding reactors will reduce line-to-ground fault currents and circulating 3rd harmonic currents, especially when generators of different designs are operated in parallel.

• The line-to-ground fault current contribution from a generator may be higher when it is operated in parallel with another generator than when it is operated as an isolated generator. This may result in excessive currents for circuit breakers and excessive forces in the generators during a single line-to-ground fault. The use of a generator neutral grounding reactor or reactors can address this issue.

• Also, each generator can produce some small amount of third harmonic voltage, generally in the range of 0.5% to 5%. The amount of third harmonic voltage is determined by the design of the generator, specifically the pitch of the generator windings. Based on the difference in the two voltages and the zero sequence impedances of the generators, a third harmonic current will flow between the generators. These currents can be as high as 50% to 100% of the generator rated currents. Generally, limiting the third harmonic phase currents to < 5% of the generator ratings is acceptable. A relatively easy solution for the high third harmonic current is to insert a neutral grounding reactor in the neutral of one or both generators.

Design of Neutral Grounding Reactors for Generators

The key design criteria for neutral grounding reactors for generators is to limit the third harmonic current, to limit the single line-to-ground fault current, and to assure that the generators are effectively grounded. Key references on this topic are listed in this document.

Dimensions and Costs of Neutral Grounding Reactors for Generators up to 600V

Standard reactor ratings are listed for neutral grounding reactors for generators up to 600V. The dimensions, weight, and cost are given for these reactors.

Request Analysis of Neutral Grounding Reactors for Generators

A form is provided to request an analysis of your neutral grounding reactor application.