HV Motor star point earthing
HV Motor star point earthing
(OP)
Is the star point of an HV induction motor always earthed? Where is the star point normally brought out to earth? It is here that I need to mount a neutral CT for a motor differential protection scheme. The three line CTs need to be mounted as close as possible to the motor terminations to the studs (so that ONLY the motor is protected by the diff scheme)
Kevin Bosch
Rainbow Technologies






RE: HV Motor star point earthing
The neutral of the source is usually earthed at the transformer, sometimes solidly, sometimes via a resistance or reactance.
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RE: HV Motor star point earthing
RE: HV Motor star point earthing
For a very few motors, the motor neutral is connected internally (in the endwindings at the connection end)... there are only 3 leads in the terminal box, and you cannot use a differential protection (also can't do insulation resistance test between phases). We have on family of 8000hp motors like that ...don't know why the OEM chose that... maybe he saved a few bucks and apparently we didn't specify otherwise.
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