Blower motor overload.

[JesperMP]

One of many possible explanations.

Does the blower in question get up to speed ?
If there isn't enough torque to accellerate the impeller, the speed may rest in some intermediate level.
If you plot the blower load/speed curve and motor torque/speed curve in the same diagram, there might be a weak spot where the two curves touches or almost touches each other. Pumps and blowers have exponential load curves that run almost parrallel with the emotor torque curves in the starting range. Thats why they can be so hard to start up.

Then why does one blower start and the other not ?
Because there are always small differences in the manufacturing of both emotor and blower. That, or the blower is running backwards as previously suggested.

Does the emotors have thermistor or Pt100 sensors in the windings ? If they have, you can install overload protection based on these, and then crank up the overload relays to a much higher value. This will either allow the blower to start up, or allow you to check the speed with a speed tester before the blower really trips.

If there is some kind of throttling element (aka damper) in front of the blower, check that this is working properly. It should be closed or almost closed to ease the startup of the blower.

 

[nif]

Change the overload relay and test if that could be the problem.
It's quite common that they brake.

 

[chrisdixey]

Is it possible that when your first blower motor starts, the draught causes the second motor while idling to turn in reverse. We have had this problem here before. It would explain the excess current you are experiencing

Regards
chris Dixon-Smart

 

[kiran]

Blower motor overload

Thanks Everybody.

I was at the customer's place the other day to see what was happening.
I noticed that there were three capacitor connected across each blower
motor contactor parallel to to the load wires. The maintenance guy mentioned that they were for power stabilization. I removed the capacitor from the blower which was tripping and the problem disappeared.

I have never come across anything like this so far. The maintenance guy did not know either the reason for those capacitors. Has anybody
used capacitors in a similar situation?

 

[DickDV]

When a drive is added to an existing across-the-line motor, it is important to get any power-factor-correction capacitors OFF the motor leads. Usually, the drive will not tolerate these and will fault until they are removed. That yours worked to some degree tells me that they could not have been very high capacitance. Likely, the caps on the second fan were failing due to the high frequency pulses.
No doubt that is what these caps were.

Glad you found the problem. Isn't it curious that, with all the high-horsepower opinions from everyone on here worldwide, not one of us came up with this problem. So much for big egos in this business.

Let's all observe a moment of silence and hang our heads in shame. And, three cheers for eyes that work and brains that think---ON SITE!!!!!

 

[randylud]

Power factor correction

Dick, is it not customary to place power factor correction capacitor banks at or near a switch gear or power substation? I would not have installed caps on any individual motor wiring for any reason, especially on the load side of a motor starter. It is no wonder the lad was having trouble, and a miracle that the others did not do the same thing. Some folks have strange ideas about the proper way to implement electrical knowledge.

 

[DickDV]

Actually, putting PF caps on the load side of motor starters is a very common practice. I see it all the time. The concept, of course, is to add PF correction only when the bad actor, the motor, is running.

And, yes, it is a wonder any of these inverters ran at all with the caps in place.

 

[Vic]

DickDV

I agree that Power Factor Correction Capacitors should not be connected across a motor powered by a VFD but I believe these motors are started across the line.

Kiran

From your decsription of the capacitors, I wonder if they really are Power Factor Correction Capacitors as others have suggested. You said that "there were three capacitor connected across each blower motor contactor parallel to to the load wires" . Do you mean 3 individual capacitors connected across the three phases? If so, what was the value of the capacitors? Power Factor Correction Capacitors are usually enclosed in a single enclosure with 3 terminals for connecting to the circuit. Please describe the capacitors a little more.

If they are Power Factor Correction Capacitors and they are correctly sized, they should actually decrease the current through the overload. It is possible the capacitor is too large for the motor or the capacitor is defective.

 

[rsdoran]

Where was a DRIVE mentioned? I just saw motor overloads! Also statement about contactors/starters...even in the replies that discussed a starter with use of an inverter (that I havent seen mentioned by poster).

I have read and reread this post many times, I do not see a drive/inverter etc talked about being used for control of the motor.

IF the system is DOL then the use of caps may be justified, maybe one of those has failed...kinda, they are capable of partial failure and creating an overload condition...whenever.

Just wondering why all the talk about drives/inverters.
When are OL's used with inverters/drives?

 

[JesperMP]

DickDV wrote:

Let's all observe a moment of silence and hang our heads in shame. And, three cheers for eyes that work and brains that think---ON SITE!!!!!

Well, I dont think that we should be shameful or anything like that. All we do, is to try to give advice based on the info we get.
Any of the suggestions that were put up COULD have pointed to the real cause of the error.

 

[kiran]

Blower motor overload

Hi Guys,

There in no VFD running these. Three one cap with 3 leads connecting to the 3 3 motor terminals for each motor. The cap are ELECTRONICON make and they are rated 2.5KVAR. You can get more info. these on their web electronicon.com under power capacitors. I think it is a MKPg series.

Could anyone explain why do they need PF correction cpas across the motor load. I thought the motor is a inductive load and the PF correction is reqd for capacitve load.

Thanks.

 

[DickDV]

Aaccckkk!!! How about just I hang my head! Talk about a fixation on variable speed!

Ron and Vic, you are right. No inverters, no variable speed, just DOL starters and OL block trouble.

I take it all back!

Gag! Choke! What was I thinking!