yamin:-
if the motor is sized correctly to the driven load and is not over loaded or stressed in any way ie:-under or over volts,balanced supply or contaminated(build up of dirt reducing cooling form)then most motor manufacturers would recommend a full electrical test each bearing change. however should one of the above conditions change then your own discretion would apply. for high voltage machines a p.i. test should be done at least once a year on the motor windings as you would do a yearly maintanence.this is ofcourse depending what maintanence schedual you have in place.
hope this will help.
kind regds.
yamin
The 400 v motor If its tefc then don't bother unless it has a problem.If it is open frame then say anually on your normal maintenance routine from the contactor when supply is isolated. Modify the frequency if you have a history of insulation failure. (after you have looked a why the failures).
The 3.3kv as per teco's recommendation
only you, the user knows! motor insulation design life is 30 years but :
how critical is the motor? are there backup/spares available incase of unexpected failure? for example: sump pump motors might get meggered once every 3 - 5 years whereas the exact same motor used in a nuclear safety related application or Navy warship might get meggered twice a year. What is most important I think is the TREND. So you establish a base line megger value of the new motor or new winding if after a rewind. A brand new winding should be meggered before installation. Then after one year or two (next outage) repeat the megger and continue at this pace until you start noticing a downward trend, you would want to SCHDULE a refurbishment. After all, the only reason to perform preventive maintenance such as megger testing is to prevent that operational failure which could cost jobs; scrap the motor; and always seems to happen right before a holiday!
motor man
Yes I bow to your common sense statement. yes I was assuming those hack motors non critical etc etc I do megger our compressor motors etc every year because they are critical. One thing you did miss though -- the **** motors always go at 15 minutes to home time friday
A star to motorman for his accurate and concise response. All that I may add is that the frequency of testing is usually increased once the downward trend is first noticed. Also, a pat on the back to Don01 for his addition of the Friday afternoon timing for such failures....only someone that has been in maintenance will understand the fact that a motor will always fail at the worst possibe moment (Murphy's Law, Maintenance Section....).
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