Motor Faults

It's difficult to see from here. One of the possibilities might be a short circuit on one or more of the supply cable conductors. Have they all been checked?

Check whether the motor is short circuited.

MEGGER!

It may be more likely the internal short. The starting current @1700 is only 3 limes the LRA specified by the supplier (tha quick calculations show that your supply is about 415VAC-3 Phase) for the 600A LRA (or starting current)

Megger the motor and check - including the phase - phase and phase to earth.

Another possibility may be wrong connection of the phases/ reversal of phase sequences,... Though these are to have this effect only in typical wrong connections and that two if multiple leads of each phase are brought out.

Another possibility is that the starting current is rated in star, whereas the motor is actually being started DOL in delta.

Dear Agni Mohanty,

Some comments already sent to you. Have you done to conduct problem solving and what thing do youhave. Please share to us.

Have you meggered ? Have you done the surge comparison test?

Have you checked the motor rating voltage either delta or star motor.

After starting with 1700A (you allow motor rating for a few seconds to see the normal current, if yes how many amps. Is it close to FLA motor or twice or bigger), have you started again for second time? Or you just leave as it is, then stopped it.

A comment already mentioned that the possible problem is actually motor shall be in Y but operated in Delta.

Your additional information is appreciated.

Regards,

May just be a semantics issue as well. If your meter is fast enough and you have it set to record peak values, it can catch the Inrush Current, which is different from the Starting Current. True "Inrush Current" is the magnetizing current that takes place in the first few cycles of the sine wave. Depending on where the sine wave is at the instant the contactor closes, the theoretical peak can often be as high as 10 - 17X FLC, and in the case of newer Energy Efficient motor designs, as high as 20X the FLC. This issue is so prevalent now with the EE motors that here in the US, they amended the National Electrical Code to allow instantaneous trip circuit breakers to be set as high as 17X. If your expected starting current is 600A, that means in most likelihood your FLC is 100A, so 1700A fits right into that scenario.

Make sure, before you go off spending money testing things, that what you are seeing is not normal. You may just be reading a very brief peak value, not the true "Starting Current".

The current should be 586 amps as per calculation assuming and eff.of94% andstarting current of7.2 9^+20% Tol).even in 100kw or 75 kw current is not so high to suspect deration.The 1700amps is it a momentary delflection? Does the reading stay at 1700 till motor reaches full speed?The other area which needs attention is what is the driven equipment/ is it a pump or Fan.An ID Or FD fan with high inertia will take longer time.What is the acceleration time.Pl check.What is the Full load current value is it in line with rating?

Is the rotor free ?? uncouple the motor from its load...and measure...(assuming that the motor insulation test has been done... and everything is ok...

Did this motor run ok before...? Is this a new problem ??? have you or someone done any work on this motor ??

Dear Agni Mohanty,

Please give any response on some quetions that already sent for you.

Your cooperation is appreciated.

Regards,

assume a motor of 55kw whose starting current is 600A as per vendor catalogue & at the site the motor is being run through MCC with DOL starting showing a starting current of 1700A plz telll me what is the fault in the motor.

Dear Agni

55 kW motor for 380 V, IFL is round 83 Amp.

Inrush current app 6-8 (or more) x IFL, depending on "pf and speed" , the factory measurement is 600 Amps.

Have you measure the IFL current when your motor has successfully running with load (current at each phases, are balance ?)

When your motors has not balance current between each phase, its possible fault in the winding (short inter turn), if the motor have balance current between each phases, the motor has not problems.

The inrush current when the motor being running in your factory (1700 Amps), may you have a different connection to the line power supply.

The inrush current that state by manufacturer may for the "Y / star" connection and you connected in "Delta" connection, so that why the inrush is showing " 3 x Factory measurement".

Check also the "DC Winding resistance" its must be in balance with range +/- 10% maximum deviation between phases.

In my opinion your motor has no problems found incl the insulation winding.

Rgds

Sis

U hv only assumed the motor to be 55kw,but not sure.Before i go further,1700Amps is too high to be the starting current even if it is started on DOL and is delta connected.We should be talking of 7-10 times the starting current which falls within 600-1100Amps,unless yr source voltage is less than the motor rated voltage,which may likely increase the current correspondingly.

If its a squirrel cage motor,the motor current is dependent on the voltage applied to the motor.If u want to reduce the starting current of the motor,u need to reduce the voltage applied to the winding.what is yr system voltage and rated voltage of the motor?

Lets say the motor is 55kw,such a big motor is not supposed to be DOL started,but Star-Delta started,to reduce yr high starting current by 1/3 of the motor winding current(current in delta is one third(1/3) current in star).

But if the motor is 155kw,then i can agree with the starting current of 1700Amps.

Well i would advice that you run yr motor in star-delta starting method and yr 1700Amps will drop to about 1/3,which is 566.67Amps.

Check yr motor data properly and lets know it as well as yr source voltage/frequency.We can help u better.

Patrick Whowha

Normally in factories where power supply is strong we go in for DOL .Star delta is not the right starting for such ratings.other option is to use auto transformer.Whatever u do at starting starting current values are same only duration changes.At the change over to delta the kick in amps will be 6times.All such motors are mostly delta connected with 6 terminals brought out for star/delta winding connection with links.

Since no response from you,i would just advise that u you run the motor on star-delta starter cct and reduce yr starting current of 1700Amps by 1/3 which is about 566.67Amps.

Patrick Whowha