Would this be OK?

[sjm]

Hi Guys.

I've got a 3 phase motor that has blown the thermal protectionin it's windings. I'm told by the local rewinders that it must be a clixon(?) not a thermister.
The control/starter unit has a themal overload relay under the contactor.
The local rewinders have suggested that I could just rely on the overload relay for protection of the motor from fire etc.
So what do you guys think? It would save the customer a lot of money.

Thanks in advance.
Steve

 

[telectrix]

having seen a motor catch fire and cause a lot of damage, i would say no, but await tony's take on this as he's forgotten more about motors than most of us have learnt.

 

[Darkwood]

The thermal cutout is there to protect the windings from getting too hot and possible damaging and reducing the life of the motor, the overload is looking at current flow and although it will operate in a overheating situe it may be the case that the windings have suffered damage to the extent of costly rewind or replacement, if the thermal protection operates it usually high-lights a problem in time for it to be addressed and prevented.
Alot of motors dont use internal thermal sensing and just rely on the overload to trip but you need to weigh up the environment its in and would a overheating motor be a hazard also the downtime of repairing or replacing it, its not usual for motors to catch fire if overload is correct size but can occur with build up of oils and dusr etc within or on the motor.

 

[sjm]

The motor is attached to a fan blade to blow air through ducting to dry daffodil bulbs.
The barns are wooden structure, but the motor is located within metal ducting on a metal support, all of which is on a concrete floor. The motor room is at the rear of the barn and open on 2 sides but the rest is wooden and quite dusty.

Any tips on testing the windings?

 

[telectrix]

each phase winding should read the same ( continuity ) and IR tests should be acceptable. very difficult to see if you have shorted turns, as the resistance will not be affected much.

 

[Swicade]

Been a very long time since i played around with Drying fans...most around this way are the big corndrier 'snail shell' type usualy haveing big motors. By the description this is an inline (sat inside the ducting) type fan?

Either way the Thermal protection within the windings are there for a very good reason and bypassing such a safety will no doubt result in trouble in the future so i'd personaly advise NOT by passing it and relying on the motor overload.

I've seen the result of an overheating motor explosion many years back and it was very messy.

Seem to remember back in the day a clixon basicaly being a bi-metallic strip that had a reset button on top often used for the heater bank (electric or gas) on corndrier's which was more there turn off the heat source if the fan wasn't running (kind of a back up safety device)

 

[DNG]

The windings may not be the source of the problem. The Klixon may have just failed due to the way the motor is operating.Klixons can be a button type unit bolted onto the yoke of the motor, close to the winding ends.Possible vibration could cause failure. Is the motor shaft directly coupled to the bulb cooling fan, or is it belt driven due to high inertia fans? Is there a good airflow at a normal ambient temp to the motor end cowling?How often does the motor start, because motors don't like starting from stand still, the starting current and lack of winding cooling does cause strain on the vulnerable klixon and windings. Is the motor wind-milling (rotating by natural airflow when stopped) because if rotating in opposite direction to normal, this would also strain the windings and Klixon. These are a couple of points to think about sjm, and I would also suggest that you TEMP short the Klixon connection in the motor terminal box and monitor the start and running currents across all phases ( one phase at a time) to check for a balanced load below the rating of the motor.The motor manufacturer should be able to give you details of a new Klixon. sjm I think I have been incorrect in suggesting that starting currents may have influenced the Klixon failure. Since I stated that the Klixon may be of a button type unit, meaning it works on conduction of heat, which could not be created during starting currents.