space heater for induction motor
- Thread starter sahafi
- Start date
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- Massachusetts
Re: space heater for induction motor
You should look at 430.32.
The motor will need some kind of protection.
430.32 gives the options that can be used.
You did not provide enough info to give the specific code section that will apply.
You should look at 430.32.
The motor will need some kind of protection.
430.32 gives the options that can be used.
You did not provide enough info to give the specific code section that will apply.
Re: space heater for induction motor
I assume that by "space heater" you are referring to a heater that is rapped around the end of the stator of the motor in order to keep the motor warm when it's not running.
Just a thought which I found interesting....
Another way that I had run across in the past is to run low a low voltage DC current through one phase of the stator which actually heats the motor internally. I can't recall the voltage but it would be related to the resistance of the winding being energized and the heating watts desired. A contactor for the DC current must be interlocked with the run contactor.
I assume that by "space heater" you are referring to a heater that is rapped around the end of the stator of the motor in order to keep the motor warm when it's not running.
Just a thought which I found interesting....
Another way that I had run across in the past is to run low a low voltage DC current through one phase of the stator which actually heats the motor internally. I can't recall the voltage but it would be related to the resistance of the winding being energized and the heating watts desired. A contactor for the DC current must be interlocked with the run contactor.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: space heater for induction motor
Every motor requires "0verload" protection, by one of 4 methods. "heaters" are one method, anther common method is internal thermal protection. 430.32 is your starting point.
Every motor requires "0verload" protection, by one of 4 methods. "heaters" are one method, anther common method is internal thermal protection. 430.32 is your starting point.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: space heater for induction motor
I think the starter of this thread is confused as to what the term heater means? Space heater?
I think the starter of this thread is confused as to what the term heater means? Space heater?
- Location
- Illinois
- Occupation
- retired electrician
Re: space heater for induction motor
Wayne,
Many larger motors use some type of "space heater" to prevent condensation. It can be a built-in heating element, an external heater or as another poster stated low current DC can be passed through the winding to provide the heat.
Don
Wayne,
Many larger motors use some type of "space heater" to prevent condensation. It can be a built-in heating element, an external heater or as another poster stated low current DC can be passed through the winding to provide the heat.
Don
stew
Senior Member
- Location
- federal way,washington
Re: space heater for induction motor
If I understand the post correctly the inquiry is about sizing space heaters for motors which are operated in damp enviorionments. Some manufactures build thes embedded in the einding however there rod type heating elements and flate plate elements which can be bolted in place insude the end bell. there are 2 formulas in common use in determining the required wattage of the heater. Unfortunatly the formulas do not give the same answer. The way the heater is mounted type of motor enclosure and motor mounting all have an effect on on required but it general it is best to use a larger size rather than heaters that are too small.
The 2 formulas are H=DL/35 where
H= heat in KW
D= motor end bell diameter in feet
L= length between end bell centers in feet
W=2DL
W= heat in watts
D= outside diameter of staor laminations in inches
L= lenght of stator core laminations in inches
Using the dimensions given by some manufacturers the 2 formulas are fairly close. Formula 2 gives the higest values. A temp rise of 10 deg centigrade is the most you want to raise the winding temp without damage so some testing is required to dte4rmine actual values. For smaller frame motors the wattage seems to fall on the higher side wheas larger motors the wattages fall abouyt midway betweent the values.
For instance a Baldor 56 frame motor needs 27 watts wheras a 326 frame requires 327 watts. Hope this helps. Joe
If I understand the post correctly the inquiry is about sizing space heaters for motors which are operated in damp enviorionments. Some manufactures build thes embedded in the einding however there rod type heating elements and flate plate elements which can be bolted in place insude the end bell. there are 2 formulas in common use in determining the required wattage of the heater. Unfortunatly the formulas do not give the same answer. The way the heater is mounted type of motor enclosure and motor mounting all have an effect on on required but it general it is best to use a larger size rather than heaters that are too small.
The 2 formulas are H=DL/35 where
H= heat in KW
D= motor end bell diameter in feet
L= length between end bell centers in feet
W=2DL
W= heat in watts
D= outside diameter of staor laminations in inches
L= lenght of stator core laminations in inches
Using the dimensions given by some manufacturers the 2 formulas are fairly close. Formula 2 gives the higest values. A temp rise of 10 deg centigrade is the most you want to raise the winding temp without damage so some testing is required to dte4rmine actual values. For smaller frame motors the wattage seems to fall on the higher side wheas larger motors the wattages fall abouyt midway betweent the values.
For instance a Baldor 56 frame motor needs 27 watts wheras a 326 frame requires 327 watts. Hope this helps. Joe
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: space heater for induction motor
Thanks Don
I learned somthing new.
Thanks Don
I learned somthing new.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: space heater for induction motor
If you have condensation heaters, I suggest they be wired thru the motor started on a set of NC contacts. When the motor is running the condensation heaters are turned off, the motor does not need the extra heat when it is on. Also be sure you comply with 430 part VI on more than one source of supply to a controller, I use an aux contact on the motor controller disconnect switch to turn off the 120V circuit. AB makes a motor condensation heater that is fed from the motor controller ckt, it runs a low power tru the windings when the motor is off. This allows a motor winding heater if it can't be field installed.
If you have condensation heaters, I suggest they be wired thru the motor started on a set of NC contacts. When the motor is running the condensation heaters are turned off, the motor does not need the extra heat when it is on. Also be sure you comply with 430 part VI on more than one source of supply to a controller, I use an aux contact on the motor controller disconnect switch to turn off the 120V circuit. AB makes a motor condensation heater that is fed from the motor controller ckt, it runs a low power tru the windings when the motor is off. This allows a motor winding heater if it can't be field installed.
stew
Senior Member
- Location
- federal way,washington
Re: space heater for induction motor
Tom you are correct and thats they way I have always run them:a NC contact. On 460 volt motors I use 4 120 volt elements,2 in each end bell all tied in series. I mount them 180 degrees apart in the housing and of course they are only on when the motor is off.
Tom you are correct and thats they way I have always run them:a NC contact. On 460 volt motors I use 4 120 volt elements,2 in each end bell all tied in series. I mount them 180 degrees apart in the housing and of course they are only on when the motor is off.
Re: space heater for induction motor
Folks, dont' know if this helps much but I sometimes use a welding machine to circulate full load current through the motor winding to help dry it out. On 3 phase motors I tie 2 of the phases together and connect one of the welder leads and then connect the other welder lead to the 3rd motor phase. This puts about 1/2 current through 2 phases and full load through one phase. I try to keep the stator temperature below 200 F. Most of the motors I deal with have thermocouples or RTDs to measure winding temperature. If not you can use a rule of thumb that the resistance of copper increases about 4% for every 10 deg C or 18 deg F rise in temperature. You will note that as the temperature of the winding rises the current will drop and you have to increase the welder voltage to raise the current back to full load. You can use the current and voltage to get the new resistance and calculate the temp. NEMA and IEEE have a standard for this that gives a more accurate result. As mentioned in other posts for normal use the heaters are on when the motor is off and the wattage is only enough to keep the temperature above the dew point or about 5 to 10 deg C above ambient. Most of the large motors I deal with have the heaters and temperature detectors installed by the OEM.
If you mean overload heater instead of space heater, most OEMs furnish a chart with their motor overloads that shows what size "heater" to use based on the nameplate rating. Read their instructions carefully as you may need to compensate for motor ambient different than overload ambient or for service factor. Sometimes a heater size will need to be increased or decreased depending on motor service factor and or ambient temp.
Folks, dont' know if this helps much but I sometimes use a welding machine to circulate full load current through the motor winding to help dry it out. On 3 phase motors I tie 2 of the phases together and connect one of the welder leads and then connect the other welder lead to the 3rd motor phase. This puts about 1/2 current through 2 phases and full load through one phase. I try to keep the stator temperature below 200 F. Most of the motors I deal with have thermocouples or RTDs to measure winding temperature. If not you can use a rule of thumb that the resistance of copper increases about 4% for every 10 deg C or 18 deg F rise in temperature. You will note that as the temperature of the winding rises the current will drop and you have to increase the welder voltage to raise the current back to full load. You can use the current and voltage to get the new resistance and calculate the temp. NEMA and IEEE have a standard for this that gives a more accurate result. As mentioned in other posts for normal use the heaters are on when the motor is off and the wattage is only enough to keep the temperature above the dew point or about 5 to 10 deg C above ambient. Most of the large motors I deal with have the heaters and temperature detectors installed by the OEM.
If you mean overload heater instead of space heater, most OEMs furnish a chart with their motor overloads that shows what size "heater" to use based on the nameplate rating. Read their instructions carefully as you may need to compensate for motor ambient different than overload ambient or for service factor. Sometimes a heater size will need to be increased or decreased depending on motor service factor and or ambient temp.
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