Minimum Clearance Between Parts
Minimum Clearance Between Parts
(OP)
As part of the installation of a 13.2kv Y/480/277v dry type transformer, the electrician installed an insulated (600V) ground conductor in contact with one of the windings. Although the windings were insulated, a failure took place between the high voltage winding and the insulated ground, within one year, requiring the transformer to be replaced. The installation instruction of the transformer gave no instruction on any required clearances. Are there any standards for field installed wiring related to transformers? I don’t think NEC 490.24 applies since both the windings and the grounding conductor was insulated.






RE: Minimum Clearance Between Parts
The manufacturer should be able to provide recommended clearances. But for 13.2kV, 95kvBIL switchgear, you normally need at least 5 inches to rigid components. I would want a lot more for a wire that's not tied down (it wasn't tied to the windings was it?). The 600V insulation on the wire provides no value in reducing the clearance requirement.
Regardless of manufacturer's instructions, any competent electrician should know this is not acceptable installation practice for any transformer (regardless of voltage). The electrician owes you a new transformer.
RE: Minimum Clearance Between Parts
If a field installation practice reduced the transformer-BIL ratings through conductor placement {not of the manufacturer} then it could be considered poor workmanship.
RE: Minimum Clearance Between Parts
I have installed transformers in the field as well as rewound some Hi-voltage transformers Dry or Wet.I don't recall a single time when the ground wire or cable is run near the windings.As a rule, the Hi-voltage coils surround the inner Low voltage coils.At the factory or at repair shop,the Star point/s/or Grounds are brought to Bushings or studs with suficient clearances for the operating voltages.
It is true that the high- voltage coils have very little voltage between each other,consequently the insulation of the coils are also rated for lower voltage.The problem is that the Transformer Phase leads(UVWXYZs)are at full voltage potential and who ever did the job might not have known that.
I cannot comment on the workmenship,I do not know the circunstances of why anyone would do that,however;it still a bad practice under any circunstances.
GusD
RE: Minimum Clearance Between Parts
OSHA, ANSI C2 standard - NESC, etc.
RE: Minimum Clearance Between Parts
RE: Minimum Clearance Between Parts
RE: Minimum Clearance Between Parts
The ground wire should have been routed as far away from the windings and connections as possible. Even using a cable with the correct system insulation might not have lasted, since the voltage potential could not have been equalized around the insulation by using shielding.