[banzai]

How do you guys test for a shorted turn in a motor,transformer or a coil ?. well i can't see how a megger can be used to do the test, i have only used a megger for P-P and P-G tests.

 

[Big John]

A megger can't find a turn-to-turn failure on a common winding. It can only find failures between separate windings or windings and back iron.

You need a turns-ratio tester to find intraturn failures in transformers, and a surge tester is often used for the same purpose on rotating machines.

 

[banzai]

A megger can't find a turn-to-turn failure on a common winding. It can only find failures between separate windings or windings and back iron.

You need a turns-ratio tester to find intraturn failures in transformers, and a surge tester is often used for the same purpose on rotating machines.

well these devices are big and hard to get by, how do you guys deal with problem like that in the field, in other words, how do you detect such faults without such instruments on hand ??

 

[BlackHowling]

You can measure the resistance of the coils and compare all 3 to each other and check for differences.

 

[banzai]

Good idea, but I have had turn to turn shorts not showing up with the 6V the multimeter pumps.

Any other methods, would be interesting to know

 

[lefleuron]

First, is why do you suspect a turn to turn short?

The only way I know how to detect this is through knowing the expected inductance in henries(sp?) and finding the existing inductance.

 

[banzai]

turn to turn short is a common problem, that's why i suspect it.

Well i thought about the induction measurement test and even got my self an LCR meter, but since the induction of the winding is not listed in the specs of a motor or a transformer, its useless.

 

[Bootss]

what size motor or tranny are you talking about? what's the voltage?

 

[banzai]

what size motor or tranny are you talking about? what's the voltage?

I dont face a problem with a motor or a tranny at the mean time, i just want to know what you guys do in such cases ?

Last problem was a generator excitation winding, Megger didn't show any short to ground nether did the resistance measurement with an multimeter change, but when it was connected it blew up the transistor on the AVR, so the problem was clearly a turn to turn short, re-winded it and it was back running.

because of no good known method of turn to turn short test a new AVR was lost.

 

[Lone Crapshooter]

What I do is use a Variac and apply a specific voltage A to B B to C and C to A and look at the current for each group. Should be the same for each group.
As far as what voltage . I would say not to exceed 50 % of rated voltage.

You can also do step voltage tests . Start out at 10 % then 20 % and so on to see how your current changes with the change in voltage.

If what you are working on is like most equipment it is more important that you know that you have a bad coil and really don't care which one it is.

LC

 

[Bootss]

find a good electric motor repair shop somewhere in your region, begin a business relationship with them so you don't lose all your expensive equipment. get on a preventative maintenance program.

 

[dmxtothemax]

How do you guys test for a shorted turn in a motor,transformer or a coil ?. well i can't see how a megger can be used to do the test, i have only used a megger for P-P and P-G tests.

There are testers for this type of fault.
They send a series of pulses into the device,
If its good inductance wise, the pulses return ok.
If its not ok (shorted turns) then they wont all return,
So they count the number returning, the more the better,
Less indicates faults.

Such testers are used by electronics technicians to test
high voltage transformers in televisions.
But the concept is also used to test transformers or anything inductive.