View Full Version : motor problem

11-10-2011, 10:03 AM
Hi guys,
I`ve got a problem with a 150kw motor that`s been working with reciprocating copressore(mycom 4wb)
the motor burn out when compressor was running,we checked winding status,just a point of winding's burnt and it seems there is split on this point nothing more
what is the problem?
on the other hand we set simple star to delta method to start up our compressor,
i suppose, onething may cause, is harsh current at starting period
if i want to retrofitted it with an inverter or soft starter, what should i care for?(mechanicaly)in according to use reciprocating engine and etc...

12-10-2011, 06:25 AM
Was there along standstill? New or old motor?
One spot is mostly a failure in the varnish.
Why you want to use a VFD? What's the application of the motor and is it connected to a rather stable cooling system? I mean with stable, mostly the same load.

12-10-2011, 09:57 AM
hey peter_1
to some extend, motor is new,it has been working for 4000 hours
reason is inrush current while using simple star to delta method,in this method 5 times of nominal current of the motor go through winding at starting time(of course for a while),consequently life long of motor will reduce on the other hand our electrical components have to bear this inrush current
about compressors,they connected to rather stable cooling system,
my concern is,likely happening this failure on other machines(we have 4 compressores mycom 4wb)
to sum up, if i wana use soft starter or vsd to control inrush current and saving energy ,is there any mechanical limitation or etc...


Yuri B.
12-10-2011, 07:07 PM
Windings are being cooled (injection of *****) ?
Are there enough time delay between starts of the compressor and is the number of starts / hour limited ?

12-10-2011, 09:00 PM
dear reza
for mycom 4wb you put 150 kw motor ? are you sure . please check it again .it is too much
What is your suction and discharge pressure ?
check you unload system. in start time solenoid vale should be powered( they should be open) in mycom compressor

13-10-2011, 01:23 AM
Hi Reza.
transition/ change over spikes can damage motor coils. If the motor is not at full speed at transition, the spike can be 10 times motor rated amps and higher. Suggest a soft start with a 5 > 7 second ramp up time. You get the advantage of low voltage start without transition spike

13-10-2011, 06:46 AM
thanks guys
mbc,you are right compressor is 8wb instead of 4wb, suction press. 2.0/ dis. press 8 and unloader is ok(powered at starting time)
magoo,you confirm using soft starter,although i am an electrical and know what shouid i do if i wana establish softstarter,my concern is effections of using softstarter on mechanical components (engine)
is there any thing to warry about if i wana use soft starter?

13-10-2011, 06:49 PM
hi Reza
what is Compressor RPM.
what is the time between on and off time?

13-10-2011, 11:24 PM
Hi M Reza.
no serious issues with compressor the oil differential safety has time delay. being an electrician check the motor connections between L1 and L2, not L1 to L3, L1 to L3 with increase vector shift in motor coils and increase inrush currents

victoria stiles
14-10-2011, 06:33 AM
Efficiency in your business operations and cost-effective solutions to your problems will give you savings and continuous production time. Electric motor repairs done by a reputable and reliable repair company can help your business run efficiently at all times.

16-10-2011, 08:45 AM
no problem fitting a soft starter to this motor.
it is actully recomended.use a known manufacturer!!
you should have no problem retrofiiting this motor,if you have more questiones mail me ,
i will try to advise.
good luck

18-10-2011, 06:27 AM
Thank you goshen
You exactly say my answer, although I have more questions, if you don’t mind
What’s the recommended rise time in terms of using soft starter?
And if I wana use frequency inverter, how many percent of engine’s RPM is legal, I mean until which engine RPM I can reduce speed of motor?
By the way our engine speed is 1200 rpm
In your suggestions you said “use a known manufacturer” , I don’t get it exactly, did you mean brand of soft starter or anything else?

Best regards and wishes


18-10-2011, 06:53 AM
What is rise time? Minimum speed is given by your compressor manufacturer to allow proper lubrication.
Known manufacturer...choose a well known brand with service behind it if something goes wrong.

18-10-2011, 03:25 PM
acceleration time is individual to each motor,the goal is to start the motor as fast as possible, while limiting inrush current, and reducing mechanichal shock,
if you are using a vsd, then you should check with the motor maker, how low you can go, the average low speed on standard motors, is aprox 25 hz,you could probably go lower but only while monitoring the motor temp and current,
a known brand would be my correct advise using a vsd from ABB or VACON.
soft starters from either ABB or SOLCON or BENSHAW.
good luck

22-10-2011, 07:33 AM
thanks guys