Why are 33kV VT's not tested for insulation resistance?

Answer 1

Is VT meant to be an acronym for Voltage Transformer?

If so, then the answer may be that any transformer which has been designed to run at a very high voltage, such as 33 kilovolts (33,000 volts), must obviously be built using insulation for its wiring that is already well-tested - and therefore known -not to break down at its designed working voltage.

The insulation will already have been tested - under safe laboratory conditions - to be certain it will withstand many times the transformer's designed working voltage. The test voltage could be as high as 330 kilovolts or more.

So there is no point in rigging-up a further, very expensive, extra-high-voltage test facility to test such a 33kV transformer specifically for insulation quality in the the factory or manufacturing plant where such Transformers are built.

When the transformer has been built it is normally sufficient to ensure that it doesn't overheat when working at its rated power under a prolonged soak test - probably for as long as a week or more - before it is shipped to its final installation site.

At the final installation site, in common with allnewly-installed high-voltage substation equipment, voltage transformers (known as 'potential transformers' in North America) are tested after installation, and before commissioning, using a hi-voltage ('Hi-Pot') test set.