What correction factor for - 4 deg C motor rating?

[druck]

Anyone can suggest what correction factor should be used for -4 deg C ambinet while selecting the AC motor?

 

[dpc]

What are you trying to correct?

 

[druck]

well i want to make sure that the torque is sufficient for clod start of the pump controlled by VFD?

 

[dpc]

I don't think a low ambient will reduce motor torque much, other than what is caused by the thicker bearing grease (assuming anti-friction bearings).

-4 deg C isn't all that cold anyway. Any if you a have motor space heater, it wouldn't be -4 in the motor.

But I await correction from the motor experts.

 

[druck]

Acutally the inside ambient temperature is -4 deg C and the motor should be rated ot -40 deg C. This is winter time and i think i should have high torque available for the motor for cold start?

 

[itsmoked]

Should be no problem. You do need to worry about condensation on both the VFD and the motor or you could have zero starting torque.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[dpc]

Is your concern actually that the torque requirements of the **load** will increase in cold weather? That's a different question than the one you are asking.

 

[aolalde]

Standard NEMA MG1 Part 14 defines USUAL SERVICE CONDITIONS.

Environmental Conditions
Machines shall be designed for the following operating site conditions, unless other conditions are specified by the purchaser.
a. Exposure to an ambient temperature in the range of –15°C to 40 °C or, when water cooling is used, an ambient range of 5°C ( to prevent freezing of water) to 40 °C, except for machines rated less than ¾ HP and all machines other than water cooled having commutator or sleeve bearings for which the minimum ambient temperature is 0°C.

 

[druck]

Thanks Guys,
Yes as indicated by "dpc" torque is a concern do you suggets me to double the torque for cold start of pump?
becuase i have to select the motor for pump operating temperature in winter condition is -4 to -40 deg C?

 

[controlsdude]

this sounds like a freezer job

-20 degree F conditions
in my industry it is always standard practice to mulitply any hp requirments by 1.25 on top of any hp calc for motors. This was due to things never worked at that low of temperature as they did above freezing.

Of course you have all the thin gear box oil that you need. Then of course avoiding the use of compressed air unless you could gaurentee the dewpoint down to -20f.

 

[druck]

hi controldude,
thanks very much for your reply. Finally i worked with factor 2 to be on more safer side.

 

[controlsdude]

forgot about the thin grease you need also, but I think other responses pointed this out.