motor cool time constant
motor cool time constant
(OP)
Hi guys,
i'm trying to set the correct cool time constant motor running and motor stopped on a GE multilin 469.
On the motor data sheet, the info is:
Thermal copper time constant (short time altern.) : 3.6 min.
Thermal time constant (long time load altern.): 20 min.
Thermal time constant for cooling down (standstill): 140 min.
As i see it, the cool time constant stopped is 140 min, but i'm not sure about the running. What's "long time load altern." standing for?
We often set the running constant 1/2 of the stopped constant where info is missing.
Any idea?
Thanks
i'm trying to set the correct cool time constant motor running and motor stopped on a GE multilin 469.
On the motor data sheet, the info is:
Thermal copper time constant (short time altern.) : 3.6 min.
Thermal time constant (long time load altern.): 20 min.
Thermal time constant for cooling down (standstill): 140 min.
As i see it, the cool time constant stopped is 140 min, but i'm not sure about the running. What's "long time load altern." standing for?
We often set the running constant 1/2 of the stopped constant where info is missing.
Any idea?
Thanks





RE: motor cool time constant
The temperature drops at an exponential rate. The time constant is based on temperature (rise) dropping to 1/e of the total rise. The time for drop in pre-defined level of temperature rise may be reverse calculated. With elapsed time, the temperature changes per the following:
Tt = Th * e(-t/(tau))
where, Th = total temperature rise
t = elapsed time
tau = cooling time constant
Tt = remaining temperature rise
Following typical cooling time constants, regardless of the motor size, can be used.
Running cooling time constant is 45 minutes (10 minutes for 20% drop in temperature rise).
Stopped cooling time constant is 100 minutes (22 minutes for 20% drop in temperature rise).
RE: motor cool time constant
So the mass of the motor is not a factor at all? That surprises me.
David Castor
www.cvoes.com