Electric Motor Problem

Please First check the class of Insulation .It should be Class F or some times it could be class B.Take the temperature rise.Including ambient it should be within 120Deg for class B and 145 For class F.That is if your ambient is 40Deg rise can be 80Deg C.If temp. is within limits motor is safe.Now as regards current the motor may be overloaded due to incresed fan out put .The other reason is you need to check the Torque speed Curve of fan with that of motor and get the duty point which will enable u to determine what current it should draw.What is the rated rpm ,Frame size of motor.Also whether u have a service factor rating if so what is it?If u can give the same may be further clarification can be given.

Hello Maintenance Man,

My first line of thought would be the generator rpm > Frequency.( Are you running at 60.5 HZ?)

The Fan rpm ( which in turn is decided by frequency of power supply) has direct influence on current drawn.

Check the Hz and do not exceed 60Hz. You may even reduce it to 59.8 Hz by reducing the engine speed and check the current.( Ensure the voltage is 480volts)

Cheers.

Has anything changed?--I take it that this was a running system at one time.

Healthy motors can draw unhealthy amps on air movers if the amount of intake air isn't under control--at least this is something I have had to deal with. Has anything changed in how the air enters the fan? Or is there a restriction on the air leaving it?

If there is anyway to restrict the air to the fan, I would and watch the amp draw and get it to where it needs to be and see if it will run normally there.

I would abandon suspecting the motor anyway. Try to restrict the air to it.

Best of luck!

Very good point to restrict the intake to reduce the current draw. I don't think that the manufacturer of the equipment would have designed a system to work in an overloaded condition or to take advantage of the SF rating of the motor. Too much money involved should there be a warranty claim due to a burned up motor. I don't know what happened to cause the increased current but looking for something that is missing in the intake or exhaust path is a good start. The more air moved, the higher the current draw. That's my 2 cents.

I think you are on the right track. If possible get the mfg specs as to air flow and adjust the air flow to match. I, too, think high air flow is the problem if the gen set and motor is not showing a specific problem. If lowering the air flow causes low output temps, check to refrigeration system. -- JHF

Check the alignment of the motor drive shaft and its connection and test run first the motor with no load see to it what amps been registered it should be only at 5-10 amps with no load, as you have told that the current rating is only with max of 80 amps with load, and make sure that the fan is been dynamically balance as you have said the motor is new so the problem goes all the way to the driven part of the equipment and make sure that its free from any distortion of vibration, it can cause high amperage registration.

A couple of things yu could look at.

Generator out put is one, however usually higher-cleaner voltage will reduce amperage.

Air flow, the suggesin about restriction is good but usually I have found the drive pulley or driven sheave has been replaced by a person who thought "what the heck it's only a Half inch bigger" resulting in an increace of a 1" of static thuss raising your amperage into the service factor of the motor.

Call the manufacturer of the equipment to see what the recommended Sheave and Pulley sizes should be. Or get something the same size and install adjustable variable pitch drive pullies. Open the pulley and reduce the RPM reducing the load and Amperage. Use a clamp on meter to check amperage after each adjustment is complete.

First I would check the output voltage from the generator when the motor is running to make sure it is at the proper voltage, Check the frequency of the output from the generator. I am not sure if the generator was original to the setup or not, Dependent on the generator size it may not have the capacity to start and run motors, Most of the time generators need to be over sized for motor loads.

Little known fact, but gens need to be run regularly to maintain the "conditioning" of the electromagnetic components. If your system was stored for a time then you may have a gen problem that is causing low output and high draw on the motor.

Different problem but another road to check out is if the compressor motor is causing feedback into the fan motor gen system.

Air path others have mentioned. pressure wash the coils and fan, that kind of thing.

Best of luck to you, sounds like you have done a good job of checking things out and fixing em up so far, but your problem and system seem kind of tricky.

Is there a service factor listed on the nameplate? You are probably aware of this, any 40 deg C motor is suitable for continuous operation at rated load under normal conditions. When voltage and frequency are maintained at nameplate values, the motor may be overloaded up to the HP obtained by mutiplying the rated HP by the service factor shown on the nameplate. There might be a different temperature rise, efficiency, power factor , etc. but the motor is not supposed to sustain damage at these conditions. You are at 1.125 times rated now, if the motor is rated at 1.15, which I suspect it is, operation should be OK.

That's the ignore it solution, option 2 is one that will reduce amps.

Option 2 is to reduce the fan diameter, This will require procurement of a smaller diameter fan rotating element. I did some quick calculations and if you reduce the fan diameter by 1/2" amps should drop by 5 and a diameter reduction of 1" should reduce amps by 10. Remember power is a cubic function. Was there a blade replacement in the past history of the unit? We had someone procure a replacement fan rotating element with the only critera being shaft diameter. Of course the new one was larger and we tripped on overload. The motor does not know what it is connected to, it will run, or try to run at the system requirements. It is possible to "run-out" a fan and damage the motor so be careful of the changes you make. Call the vendor and make sure your dimensions are correct, or compare to another unit if available.

I hope this helps

I'm not exactly sure what you unit is, but a couple of suggestions come to mind. First is your voltage low which would drive up the current.

Secondly, if the fan is not direct driven. Ck to make sure proper alignment and drive belts not overtight.

Third, there should be a fan curve that depicts HP/static/flow/ect. for the fan. Not all, but some types will require additional HP, (i.e. current) if there is insufficient static (i.e. reistance) on the fan. I haven't ck'd rated current for the motor but it doesn't sound like your too far over. There haven't been any modifications, such as filter or shrouds removed? Condensors that are "more open", that type of thing? Easy test just to block off or restrict a good portion of the discharge air and see if the current drops.

Fan Motor current draw will be a cubic function of RPM, (RPM3), a quadratic function of pressure (P2), and a linear function of SCFM. However, if the generator speed is say 63Hz (5% overspeed) , amperage draw of the fan motor will be 115.8% of full load, or92.5 Amps. A 4% overspeed of the generator to 62.4 HZ would result in the current readings you report --assuming that 60.0 HZ results in 100% (80 AMPS) fan motor loading. An speed error of 3-4% is very possible if the generator meter has not been calibrated recently or the governor is misadjusted.

One simple thing--He is having problems with only one motor.

It's sounds like there are possibly four or more motors and no problems mentioned with any others.

If he went to all the trouble of replacing a motor without checking voltage after taking high amp readings--Not a chance--He is the Maintenance Man! and I have faith in him.

Ok I will put my two cents worth also but as guest ....

It looks like there is more than one motor.... one would need to check the voltages at the problem motor and at least one other motor not just what is coming out of the generator , so far nobody has even hinted that a cable could be suspect in which case the voltage at the over current motor would be lower and of course the current would be higher than normal.... this is not to say the other suggestions are without merit hey even the new motor could be defective from the box it happens.

? Is the current 90A on all three phases or close like 87,91 93 Range and is the voltage at the generator right on 480V give or take 5% ?