Answer / kn afridi

Heating and cooling time constants are generally given by the motor manufacturer.

This is the time required by the motor to reach 63.2% of its steady state temperature T when run with full load.

Heating time constant (t) is given by the formula (1-1/e) T= (1-1/2.718) T= 0.632T

If the steady temperature T attained by the motor is 90 degree C (say) when started from cold condition, the heating time constant in minutes will be the time required by the motor to reach 57 degree C. This can be noted during the heat run test on the motor under rated condition.

Answer / thabo

A motor with a time constant of 120 minutes is rated at 40 kW continuously .compute the half hour rating for the same temperature if it starts from room temperature every time.

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