Heater in Motors

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puckman

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Can someone tell me about heaters inside of 3 phase motors and what they are doing in there and how they are powered. Anything the know about them. Thanks
 
We buy space heaters in motors over 200 HP. The function of space heaters is to keep excess moisture from accumulating in the motor while it is turned off. The heaters might be 400W at 120V single phase. They are wired back to the starter and the starter energizes the heaters when the motor is off.
 
In the past I've had an application where I supplied a motor starter with an auxiliary relay that switched a DC current to the stator of the motor's windings of which the current flowing through the stator provided the heat when the motor was off.
 
Heaters guard against overcurrent on the motor windings. Normally they are found on the motor controller and are sized based on the nameplate rating on the motor (430.32). They have nothing to do with sizing the conductors or the overcurrent protection of the circuit.
 
RonPecinaJr said:
Heaters guard against overcurrent on the motor windings. Normally they are found on the motor controller and are sized based on the nameplate rating on the motor (430.32). They have nothing to do with sizing the conductors or the overcurrent protection of the circuit.
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Ron your talking about over current 'heaters' at the motor controller. The opening post is about internal heaters that can be ordered with larger motors to keep them dry inside.

The motor terminal box will have a set of leads that connect to the winding and another set of leads that supply the internal heaters.
 
iwire said:
Ron your talking about over current 'heaters' at the motor controller. The opening post is about internal heaters that can be ordered with larger motors to keep them dry inside.

The motor terminal box will have a set of leads that connect to the winding and another set of leads that supply the internal heaters.
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That's beyond the scope of what I know about them then.
 
I looked at from the direction of "space heaters" since he asked how they are powered. A space heater that is installed around the end of the stator on one end of the motor is normally energized by 120vac.
Naturally "heaters" that are a part of and overload relay are not reallt "powered" as they are in series with the motors circuit and respond to current that flows through them to the motor which causes them to heat thermally. Larger motor overload relays use CTs to feed the heaters as the current required by the motors is too high for the heaters to be used directly in the circuit.
 
Motor heating elements.

Motor heating elements.

An issue with 100 hp and our larger motors and the condensation heaters installed from rebuild shop I have had and resolved. Just a thought!:wink:

When the motor were cycled on they tripped every 1st time, 2-4 restart cycles to get running. My investigatin found that the Heating elements, on warm days(over 70F) caused the 'Thermistors' to shut the motors down. When Mfg. and rebuild shops installed heaters, they placed them in the same area as the Thermal protectors. Starting the motors would shut the heating elements off and air over would cool just enough that 2-3-4th try would let it run. The smaller the motor the worse it was.
 
iwire said:
Ron your talking about over current 'heaters' at the motor controller. The opening post is about internal heaters that can be ordered with larger motors to keep them dry inside.

The motor terminal box will have a set of leads that connect to the winding and another set of leads that supply the internal heaters.
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I have come across quite a few motors that had them brought out to an auxiliary terminal box.
 
Internal Motor winding heater

Internal Motor winding heater

I need a sorce for supplying current to motor stator winding to supply heat for condensation. I have new 100 HP motor with out suppimental heating element. AB makes a trickel current module to supply ~ 10 % FLA current across 2 legs of motor for this,using the 3 phase source, however, my application will be generator driven so when motor is not in service the gen will normally be shut down. I need a source from external 1 phase utility. I have no intention of disassembling new motor to install flexable strip heater.
 
puckman said:
These heaters are for the inside of motors not for overload protection. Im trying to find out how and why they are used . Anything they are used for.
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How

They are turned on when the motor is turned off.

Why

They keep the motor warm which keeps moisture in the air from condensing inside the motor which can lead to premature winding failure.
 
puckman said:
Can someone tell me about heaters inside of 3 phase motors and what they are doing in there and how they are powered. Anything the know about them. Thanks
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Space heaters installed in enclosed motors internal cavity to prevent condensate forming as the motor cools down after stopping and draws outside air in. The heater circuit is activated by the NC auxiliary contact of the main contactor. If the power is derived from the CPT of the motor, it should be oversized and obviously when the motor is locked out the space heater does not function. Auxiliary power source can be used.

TEFC motors employ small metallic cartridge heaters. They have a tendency to corrode and fail. On critical equipment you may want to monitor the current of the heater and alarm on failure. It is expensive to replace, since usually it is employed on larger motors and to remove and disassemble a motor to install a $25 heater can exceed the cost of the heater multiple times.

Another alternative is the AB type winding heater, where upon stopping the motor an electronic circuit will circulate reduced voltage through two phase connections, utilizing the existing wiring. So it saves the separate wiring required for the space heater and provides more uniform heating throughout the motor cavity. (There are some claims that it accelerates the aging of the insulation, but I have not seen data backing up this claim.)

MV motors can not utilize winding heaters and it is advisable to utilize 240V heaters and operate them at 120V to prolong their life and also ask for dual space heaters so when the first one fails the 'spare' can be put in service. I have seen flexible silicone embedded heater cables strapped against the coil 'heads' on MV motors. It should lasts longer than the metal cartridge heaters.
 
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