What instrument is used to measure the contact resistance of the transformer regulating switch?
Micro ohm is usually used". There is also a European micro meter specially designed for measuring tap changers. The accuracy is in the 0.2-1.0 level. Many instrument factories sell it.
Since the contact resistance of tap contacts is very small (less than 500 micro Ohm), particular attention should be paid to measuring methods.
You can use a shake WatchThat's the kind of grounding resistance
