I'm studying how to create a switchgear that will allow simultaneous parallel operation of a utility and a generator supplying a common load. Additionally, the generator will be used for electrical consumption peak reduction purposes. The generator bus bars carry 1600A, the utility bus bars carry 3000A. They both, and the load share a neutral bus.
1) Should the current transformer (CT) on this neutral bus be 3000:5 (matching utility CTs) or 2000:5 (matching generator CTs)?
2) The system is solidly grounded and connected to the secondary of a Wye - Wye transformer on the utility side. In case of a ground fault. Would there be any significant current flowing on the neutral bus bar? The utility short circuit contribution is 28.8 kA, the generator short circuit contribution is 10.2 kA.
I am not sure that understand the whole idea, without single line diagram, but let me try to give you few thoughts. If this neutral busbar common, you should have to use highest current transformer ratio, 3000/x A. Perhaps is better to use secondary values of 1A. With this value, it is easiest to handle many issues, which brings 5A nominal secondary current values. Today is also common to have 1A even on generator side. Utility company mostly new solution have with 1A.
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