Electric Motor Bearing Heaters 1

[jdogg05]

I understand for storage and preservation a lot of larger electric motors have bearing heaters to keep the bearings in a certain termperature range in cold climate conditions. What exactly is the rationale behind this? I understand why shafts need to be rotated to avoid brinneling, but why do the bearings need to be kept warm? I heard it has to do with the freeze/thaw/freeze cycle that happens in cold climates. But why does this matter? Does the lubricant degrade? Does moisture somehow get in from the outside?

 

[Skogsgurra]

I haven't heard about this practice in Scandinavia. But I haven't heard about all that is going on. Our motors are usually kept in storage spaces where temperature is kept above freezing.
A guess is that the condensation/freezing/thawing may be considered bad for the bearings. On the other hand, there are lots and lots of motors situated outdoors and there, they cycle through freeze/thaw once per day during fall and spring. Never noticed that it could be a problem.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jdogg05]

I am in the oil sands in Canada where the temperatures can get to -45C. The bearing heaters are only for preservation while the plant is being built. It is impractical to leave the equipment in a heated warehouse because it needs to be placed on the foundations as per a reasonable construction schedule. Usually the big rotating equipment is hoarded and heated; however, because of the extreme weather conditions this is (apparently) inadequate for storage and preservation. I just have no idea why...

 

[ManuSuissa]

I currently use two different Induction bearing heaters, a TIMKEN and a BESSEY model.
We use these heaters for different reasons than for storage.
Firstly, during the assembling of the bearing assembly, we use the bearing heater to heat up the cartridge before assembly it with the bearing itself to cause a tight shrink fit once it cools down.
Second of all, we use the bearing heater to heater the entire bearing assembly before slipping it onto the shaft, for the same reason of having a tight shrink fit once it cools down.

 

[waross]

I have hooked up a few temporary heaters for motors, generators and transformers in the oil sands.
All that I have seen were anti-condensation heaters to protect windings and iron cores. I have yet to see temporary heaters on the bearings, but I haven't seen everything yet.
I have seen a bearing arrangement where the oil was heated. This may have been an oil mist system.
There was an interlock which blocked the motor from starting until the lubrication system was up to temperature. This was in an area where minus 20 F was common and colder temperatures were possible. The heaters were on only when the motor was about to start and when the motor was running.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ManuSuissa]

Nevermind, we're not talking about the same type of bearing heaters. Sorry.
Improper motor storage will result in seriously reduced reliability and failure. An electric motor that does
not experience regular usage while being exposed to normally humid atmospheric conditions is likely to
develop rust in the bearings or rust particles from surrounding surfaces may contaminate the bearings.

 

[waross]

The mechanism of condensation formation during a rising ambient temperature and rising dew point is more serious for the thermal mass of the lamination stacks. The anti-condensation heater protecting the cores should heat the frame enough to protect the bearings.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jdogg05]

How are the iron core and the winding heaters connected? Are there glow plug type heaters inserted into jackets in the magnetice core? What is the issue with condensation here? Rust?

 

[ProWinder]

Water in the windings due to condensation can cause the windings to be grounded. Then upon start up it will break down and let the smoke out.(LOL)

 

[petronila]

Hello jdogg05

Like Skogs sayd, also I don´t hear about Bearing Heaters to warm the installed bearings in the motor, I know Bearing RTD´s and PTC´s and space heaters like sayd Bill.
The Induction bearing heater is the equipment intended for bearing monting, but this one is a transformer with secundary open (replaced by iron bars).
I.M.O If your motors are working under very low temperatures then will be designed for that so the manufacturer have the right answers.

About the storage, when the motor is not in operation is exposed to vibration (ambient vibration) even at very low levels, with the time, could be enought to produce damage (false brineling)in the bearings.

If one motor remains manny time inactive is important rotate the shaft at time intervals, at least each mounth, to avoid brinelling and corrosion(the lubrican is redistributed in the bearing) in big motors is more critical and you wil need a small program.

About Iron core and winding heaters connections, there is no. there are diferent kinds of space heaters and more common in small and medium size motors are manufactured like flexible strips and are fixed directly on winding surface, also you could find other space heaters like reistance type, not connected drectly on winding and installed on end belts.

Regards


Carlos

 

[macmckim]

Bearing heaters are not installed in anti-friction bearings motors. The heaters are installed on self lubricated or forced lubricated sleeve bearing motors - called oil sump heaters. Typically around 10 to 20 watt immersion type heater in stalled
in bottom of sleeve bearing bracket (oil sump) and are used just like frame space heaters. If motor is in storage or
shut down for a period of time, these are enegized like frame heaters to keep or reduce moisture buid up inside the
sleeve bearing (water and oil do not mix well) Have seen many in the oil sands in Northern Alberta.

 

[waross]

In larger motors and generators there is generally a space between the motor case and the stator core. This is where the heaters are installed.
I see two types of anti condensation heaters. One type is a flat flexible pad. This type is generally laid in the bottom of the motor in the space between the case and the core.
A more common type of heater is a basic strip heater. These are used in pairs and connected in series. They are then connected at rated voltage so that each heater receives half voltage. This gives extremely long life. These heaters are energized 24/7 when the motor is idle. They may be switched off when the motor is running.
Condensation and machinery:
Condensation forms on surfaces that are cooler than the dew point. At times the ambient conditions will be a combination of a rising temperature and a rising dew point.
There is a thermal lag in a large mass of metal and it is possible for the dew point to rise faster than temperature of the internal iron. The result is condensation forming in the innermost cavities of the equipment first.
The area of the bearings does not suffer as much thermal lag and enough heat is conducted from the motor case and stator to avoid damage.
As an anecdote: Years ago we received a number of large MG sets on site. Each set was comprised of a synchronous motor driving five DC generators. Each motor and generator had space heaters and they were required to be energized on the day that the equipment arrived on site. The generators each used pedestal bearings with Babbitt and oil rings. Of the various types of bearings, pedestal Babbitt bearings may be the most susceptible to condensation damage. They are separated from the motor case and the only heat conduction may be through the shaft. The possibility of condensation contamination of the lubricant in a sealed bearing is remote but condensation may easily form and contaminate the oil in a pedestal type Babbitt bearing. Despite this the manufacturer did not apply heaters to the bearing pedestals.
Again, it is not the cold but a thermal lag and a rising dew point which causes condensation.
Condensation may form in the early morning of a warm summer's day.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jdogg05]

waross,

This was a very helpful post, thank you. I just want to confirm what you are saying because I don't think most people I have spoke with in the preservation departments at my work really understand the concept and idea behind motor heaters.

In essence, where I work the heaters are only energized in the winter time to keep the windings and cores warm.
If I understand you correctly, this is not a correct way of thinking, because it really has little to do with how cold the ambient temperature is, and much more to do with the relativity between the lagging winding temperature and the rising ambient air temperature. In essence, condensation only happens when the surface temperature (of anytthing) is colder than the dew point of the air; therefore, the heaters are just as important in the summer time as the winter. Please, is this correct?

In fact, I propose, at subzero temperatures the motor heaters are likely less important because you are dealing with a "frost point" and not a dew point. When the ambient air heats up from -30 to say -5, frost forms on the colder (winding) surfaces. In subzero temperatures the air can hold a lot less H2O, thus less frost will form in the winter with a rising temperature than condensation in the summer with a rising temperature. Also, frost will not accelerate corrosion, but water will.

 

[waross]

I would not discount frost. It is still H[sub]2[/sub]O and I wouldn't depend on sublimation to remove frost completely.
But, yes, thermal lag and dew point. That is the essence of the formation of condensation inside a motor.
I used to service a small generating plant in the Bay Islands of Honduras in the Caribbean Sea.
All five generators had anti-condensation heaters with failure alarms.
Any time a heater alarm went off, I was on the next flight out to the islands.
A couple of times over the years a local radio station broadcast a severe weather alert when the temperature was forecast to drop to 70° F.
You are correct, the ambient temperature has little to do with the formation of condensation.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jdogg05]

Sorry waross, one more point: during the summer months when the temperature is above 0C the condensation forms in the liquid form (obviously) and not a solid frost ice. This, and the fact that hotter temperatures speed the chemical reaction of corrosion, implies that it is of more concern to have the heaters energized during the summer months...

Thoughts?

 

[waross]

The heaters I have seen are connected for 1/2 voltage. eg: 240 Volt heaters on 120 Volts or two heaters in series on rated voltage (2 X 240 Volt heaters in series across 240 Volts. The heat output is 1/4 of rated watts but you don't need much heat to avoid condensation. The heaters are typically left on 24/7 and only turned off when the machine (motor, or generator) is running. I have seen ati condensation heaters in outdoor switch gear that is always on.
If you turn the heaters off when the temperature is below freezing, a rising temperature will see a very cold internal surface. Rather than try to anticipate this condition with a control scheme it is better to just leave the heaters on. I don't particularly want frost in my machines either.
But in support of your comments re summer months; How often do you see early morning dew on the ground in the warmer months. In some climates you will see dew fairly often. Condensation will form in a cold machine before dew forms on the ground due to the thermal lagof the internal iron.
I should mention that I don't always prevail in this situation. I am on a project where there are a number of diesel gen-sets in the 1500 kW size range. They all have anti condensation heaters fitted. They will sit for over a year before commissioning. The heaters are off and the breakers are locked off because "There is heat in the generator enclosures". I made a presentation but hubris prevailed. The heaters will remain off.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crshears]

Hi waross et al,

I have seen anti-condensation heaters installed within indoor switchgear enclosures [13.8 kV, in the Toronto area]; these were kept in service 24/7/365. When entering the station from out of doors on a 35°C summer day, the temperature within the building was in the neighbourhood of 40°C, meaning you got your work inside completed as quickly as possible...

For sure us people didn't like it, but the decades-old switchgear was very happy, which was the ultimate point.

 

[itsmoked]

Bill: The motor 'shafts'/bearings are still going to be susceptible to condensation - even while they have considerably less mass than windings/etc.

As an anecdotal example I offer my garden work shed. I have a roll-around tool box in this fully ventilated shed. Occasionally I'm horrified as I trot out there, pull open a drawer, and see dew on every metal tool. Yes, in all the drawers! (%^@#@$) And, jdogg05, this occurs all year, not just in winter. As mentioned, it has everything to dew with the local micro-climate and the rate of temperature change and little to do with the average temperature.

This is the same reason we have issues with control panels in the field. Not much mass compared to a 4 inch motor journal but we still have to use heaters and drain holes.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[jdogg05]

itsmoked,

Are you saying there are heaters in the motor journals then too? It seems to make complete sense to me... I'm talking in the industrial context with fairly big induction motors.

 

[waross]

Just a little heat in the housing will warm the whole housing and provide protection for the bearings also. I would check the units I was responsible for by putting my hand on the top of the generator. When the heaters were working properly the generator case felt pleasantly warm. The end bell and bearing journal would also be warm.

Bill
--------------------
"Why not the best?"
Jimmy Carter