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# transformers

## transformers

(OP)
on an elctrical transformer the primary comes in a bushing goes thru the coil and then goes to ground , what keeps it from having a phase to ground fault?

### RE: transformers

The reactance of the transformer.

### RE: transformers

If it is a 3ph transformer, the current flowing from the star point to ground is zero because the vectorial sum of the winding currents at the star point is zero. The star point is at about the same potential as the ground.

### RE: transformers

A single high voltage bushing indicates a MGN or SWER distribution system. The reactance of the primary, and insulation, prevents a ground fault, as stated above.

### RE: transformers

(OP)
there is no insulation between the primary and the neutral. so insulation does play into this. the neutral carries current to ground y does this not cause a fault. what is the star point, and what is the formula to find out the vectorial sum. please explain thank you

### RE: transformers

This is a complex subject. There is many different procedures for transformer connections. Each one is unique and for a specific purpose.
A single bushing transformer can only be connected wye if three phase. A two bushing pot is required for delta connection.
To completely understand transformer theory, start at the beginning of fundamental electricity.
There is no magic system to impress the information on the human brain, like on a hard drive. There is a human weakness to delete information, it is called old age.

### RE: transformers

I agree with the age part.  One other, less formal way to understand various transformer configurations is to sit down at a workbench with a set of 100VA transformers and jumper wires—hook them up and take a lot of voltmeter readings.

### RE: transformers

The primary is NOT generally connected to ground but the second connection is to neutral.  You can ground the neutral as in a multiple earth neutral systyem is you want, but if the primary is grounded you will have have unbalanced line-neutral currents that will trip an earth leakage breaker.

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