Role of a Cooling Fan on a Fan Motor

For the cost of the fan blade... replace it. Or... remove it to return the mortor to ballance. Not doing so will expose the motor bearings to harm over time.

Bottom line... for the minimal cost of the downtime and of the new fan blade... why gamble? I would sure hate to have to explain why I had to buy a new 22kW motor for the price of a $20 fan blade.

I agree. The cost of the fan is / should be inconsequential. The real cost is the labor to replace it. You MUST remove that broken fan anyway, because as N. o' 60 says, the broken blade will cause an imbalance on that shaft which will cause a more rapid demise of your bearings. It may seem like the plastic fan would be meaningless, but any imbalance like that, however slight, translates to extra bearing wear and tear, increased heating and premature death. So if you are removing the back fan cover to remove the broken fan anyway, just replace it while you are there.

As to the fan's purpose when the motor is in the air stream of an AHU anyway, it does serve to focus the air flow over the motor rotor, something that may not happen without it. Air flow takes the path of least resistance and once there is a slip-stream established around the motor exteror (stator) housing, air may not end up passing through the rotor fins.

JR is right.

The cooling fan forces the air through the slots on rotor/stator (mainly stator) to cool the motor nearest to heat generation points.

The flowing air is going to cool the motor more on the surface and hence quite a bit away.

The cooling fan in TEFC motor blows air over the surface .It does not go through the motor.In Open type or SPDP construction the cooling air goes through the motor and that too in the air gap between stator and rotor.It never blows air in to the slots which are filled with slot liners , conductors suitably insulated.

Sorry didn't look at the rating of the motor. My comment is for higher powered ones, where the forced cooling is required.

It is extremely important, It reduces temp significantly and improve electrical life of motor.

As a rule of thumb every 6 Deg reduction in winding temp mens twice the motor life. Now its for you to decide.

In that application, I would imagine there is more than ample air flow, so at first blush we can say no, remove the remains of the failed fan, and carry on......

Now, introduce Mr. Lawyer into the mix; on the 1 in a million chance that this motor were to fail for whatever reason, causing damage to your facilities, i.e. fire, your missing fan may be pegged as the start of the failure chain.

Someones head will be going on a stick

Liability, always an angle to consider.

Replace the fan. If it wasn't needed, it would not be there!

LynLynch is right. It's there because it needs to be there. That motor was tested to some pretty rigorous electrical and fire safety standards, so by not replacing the damaged parts, not only is the motor approval voided, but in case of fire or shock, the insurance coverage would also more than likely be voided.

Standards are there for a reason - your safety and health - don't defeat it

Grae

Here's another vote for replacing the fan.

Either replace the fan or reduce the running time of the motor (derating). TEFC motors are designed for higher duty cycles if you covert it to TE then you must reduce the duty cycle.

Suresh Sharma.

The Motor is designed to run continuously with the cooling by shaft Fan.

I have experience of Motor burning due to broken Fan Blade, not observed and continued to run.

It is absolutely required.

You are right.Remove the fan .It is not required as sufficient air blows over the motor body.The fan being of Synthetic material (Poly Propalene) does not need rotor rebalancing etc.Very small power saving can be expected.I have done it on many installations.Just go ahead

To clarify my answer (post #4) I was assuming* that the motor is a TEFC design, on an open design, yes the fan must to be in place.

*we all know what happens when we assume......

Yuri, out of curiosity, what design motor is this?

Even in open design it is not required.What the shaft mounted fan is doing is done much better by the ahu fan.In the case of open type the air will flow through the machine and in much larger volume and velocity.

Hi Yuri,

For nearly 25 years as hotelier, most of my AHU motor doesn't have fan blade is not because of expensive to replace but for me not necessary. You are right "air is blowing above it". Could we just imagine ahu room temperature we're getting sometimes below 22 C. as commonly encountered my AHU motor burnt due to damaged bearing, or when my the control system failed and being single phase. In short fan blades should not be a big deal! don't worry about replacing it. Take note "ONLY FOR AHU" and not to any application. if the motor is used not in AHU, most of the above advised are essential.

if i we're you LEAVE IT ! .

Kind regards

Roman

Yuri - that's a lot of suggestions. I think we'd be interested in your decision.

Grae

Thank all for your opinions.

The motor is ABB model M3AA180L code 3GAA18808-ADC and poles pairs 4/8, working constantly - for major of the time on the higher speed. I would not post the question if the blades costed just 20$, but I am asked for much more and I have not yet informed the client, to whom the motor belongs.

The motor has worked for 3 years and the last 2 years without that auxillary fan - without problems - but now its temp has rosen to 50 C (what I consider rather high for this application). The blades left were cut evenly to prevent disbalance. No inverter, start through soft starter. It is probably bearing(s), and the cooling fan has nothing to do with the temp rise (was 80% sure before I have posted am 95% sure now).

But the blades I'll however replace, as it's already ordered, and will keep a close eye on the motor.

Hi Yuri,

Have you check the ampere reading? if the ampere reading is normal but your motor temperature is high it could be 1. bearing, 2. weak winding insulation. as I said on my previous post, I have no problem with my AHU motor running with out fan blade it last more than I expected.

Kind regards

Roman

Hi Yuri,

My apology on my post, I am thinking too fast and typing wrong. I should say if the ampere reading is ABNORMAL, and the ampere reading is more higher than it should be, whilst your motor temperature is high, it could be 1. bearing, 2. weak winding insulation. as I said on my previous post, I have no problem with my AHU motor running with out fan blade it last more than I expected.

Kind regards

Roman

Dear Sir,

Check the insulation.If it is class F 50Deg rise is no problem .Even in Class B temp rise including ambient can be 120Deg C.You don't really need the cooling fan for this ahu application.Just remove it and forget it.

Thank you very much for your imput and the idea - now I'll "high pot" the winding at 1000 V every week and make notes. To offer the client changing bearings ?- and if the motor would still heat up after it ? No, we usually wait till the first sign of a suspicious sound appears, then change them.

Besides all, probably, indeed 50 C is not such an alarming temp for the ambient 20 -25C.

Best regards

of course, 20 - +25 C