Can some one suggest where to get typical heating and cooling time constant information for large HV motors, say, 1000kW. The motors are old and manufacturer's data sheets are not available.

My plant has many large motors which are continuously monitored for winding temperature and bearing temperature.

I'll assume you are talking about winding temperature.

Two examples in the horsepower range you mention:
1 - 800hp 120rrpm vertical air-cooled motor.
Motor is initially steady state at 119F (space heaters keep it above ambient). Ambient temperature is initally 81F
12:06am motor started -  T=119F
12:11 - T=152F
12:16 - T=167
12:21 - T=177
12:26 - T=185
12:31 - T=190
12:36 - T=196
12:41 = T=201
12:46 - T=205

Getting tired of 5 minutes readings. Here are some wider spaced readings:
1:06AM - T=216
1:21 - T=220
2:06 - T=226
3:00 - T=229
4:00 = T=229F
Final ambient temperature is 82F (relatively constant).

At the moment I don't have the energy to figure out the time constant. You are welcome to if you'd like.

Electripete,

Thanks for the info. The Heating Time Constant comes to 15minutes (hope I am right).

Could you please pass the info for calculating the Cooling Time Constant for the motor.

Thanks once again,

Suggestion: The manufacturer recommends a number of starts/stops per specified time period. These are linked to cooling/heating time constants.