Heater Overloads Keep Tripping During Startup

[Nardie]

So I have a fan motor that keeps tripping the heaters during startup, the starter is a AB 509 starter with a E100 overload relay. The starter and overload relay replaced an outdated set, and worked for a few months. Recently, when we try to start the motor the heaters trip 2-3 seconds. The motor's FLA is 25A, and the overload relay was set to 31A with a 30 second delay. During megger and continuity test between the load side of the starter and motor read good. In addition, we reterminated the motor connections and increased the FLA setting on the overload relay with no difference on the operation. No fuses blown, just the overloads tripping. We did replace the E100 relay with the same result. So what are we missing?

 

[D. Castor]

Have you monitored the actual current during starting? Tripping the OL in 2-3 seconds would indicate a heck of a lot of current.

 

[jim dungar]

Have you followed the manufacturer's instructions for sizing/setting this relay?

 

[Eddie702]

I know you said a fan is the load but is it belt drive? direct drive? Is it a particularly heavy fan to get started?

If the motor gets the fan up to speed, does it trip or is this only a start-up issue?

I agrre that tripping the OL that quick seems odd.

 

[ptonsparky]

Check belt tightness. Too tight has a tendency to wear out bearings leading to overload.

Get your amp meter out. Should have been the 2nd tool out of your bag.

 

[neault]

OL tripping that quickly, I would think of loss of phase, phase imbalance or such. If it holds after start up you will need to look at a temporary issue. To get it to run after start, do they hold on second start after trip? after the fan is spinning?, How does it get to the run mode? Back to square one, high current, loose connections, etc. Not much help, but additional spots of focus.

 

[kwired]

Class 10 protection when you possibly need class 20 or 30 protection?

How long does it take to accelerate the load?

 

[Nardie]

I appreciate the responses, and I want to answer all your questions. The overload relay is an Allen-Bradley E100 solid state relay. The FLA setting was set at around 32A, with the time-delay at 30 seconds with manual reset. We have re-terminated the motor connections with polaris lugs and replaced the fuses. The fan is belt driven and the belts have been replaced with proper tension. We have not checked the amp draw during startup but have been planning to. We raised the FLA setting to over 40A to address an inrush current issue, with no results. The fan drops offline within 2-3 seconds, so it never operates. This system operated a few months before this issue appeared. When we perform continuity readings across the motor windings, they read the same. We plan to use our Predictive Maintenance group to perform a static test of the motor. If there are any more questions or suggestions, please let me know.

 

[ptonsparky]

Is this a centrifugal fan? Does it have a damper that would normally be closed at start?

It’s too late for Predictive Maintenance. Are they the only one authorized to work energized? Use meters?

Quit turning the overloads up. If it worked before, they aren’t the issue.

 

[jim dungar]

If the OLR is holding for 2-3 sec before tripping you are likely not experiencing inrush problems. Inrush rarely trips OLRs because their trip curves take it into account.

Did you read the manual on how to select the appropriate amp setting on the relay. Many people try to set solid state relays the same way way they chose thermal style OLRs.

 

[ptonsparky]

I have found shorted windings in motors. Continuity tests will not find them nor will a merger.

 

[Little Bill]

I have found shorted windings in motors. Continuity tests will not find them nor will a merger.

What's a "merger" test?

So how did you find shorted windings? Seems a continuity test would show that, depending on what you measured to, and from.

 

[ptonsparky]

Megger. Dang spell check.

 

[ptonsparky]

It takes a meter that can read low resistance.

 

[Little Bill]

It takes a meter that can read low resistance.

Isn't that what a megger does?

 

[ptonsparky]

Isn't that what a megger does?

No. It reads in millions of ohms.

You need one that can read less than one. Or at least 2 vs 1.5.

 

[Genepires]

When it starts up, the blade is spinning at normal speed? You may need a tachometer to see what speed it is spinning at. If it is spinning at less than nameplate, then you can say something wrong in windings…. I think…….all this stuff is voodoo majiks!
May be worth investing in one of those fancy fluke 3 phase motor analyzers. I forget model number. But would be interesting to see the voltage and amp draw on all three phases in real time before OL trips.

 

[ptonsparky]

What's a "merger" test?

So how did you find shorted windings? Seems a continuity test would show that, depending on what you measured to, and from.

You would be measuring resistance of each winding. Not winding to winding or to ground.

I doubt that’s the OPs problem but possible.

 

[tom baker]

Did you check the setting for overload class? Seems like it’s a DIP switch on the side of the OL?
Many AB products like OLs have the instructions printed on the inside of the product box.

 

[kwired]

What's a "merger" test?

So how did you find shorted windings? Seems a continuity test would show that, depending on what you measured to, and from.

Short from turn to turn may not look like anything all that significant with a typical ohm meter but the impedance difference of that one winding when operating voltage is applied may produce rather significant imbalance in current. Overload relay may see this as phase loss or as an overload condition depending on the circumstances. Overload condition may take longer to trip so may be good chance OP is tripping on phase loss protection if this is what is happening.

When it starts up, the blade is spinning at normal speed? You may need a tachometer to see what speed it is spinning at. If it is spinning at less than nameplate, then you can say something wrong in windings…. I think…….all this stuff is voodoo majiks!

If it is tripping in 2-3 seconds it likely never reaches normal running speed.