Crane duty squirrel cage motor type Motor classification

DUTY TYPE :
Crane duty applications can be classified into duty types S2 to S5
Short time duty (duty type S2) : Operation at constant load during a given time, less than that required to reach thermal equilibrium, followed by a rest and de-energised period of sufficient duration to re-establish machine temperatures within 2°C of the coolant.
The recommended values for the short time duty are 10,30,60 and 90 minutes.

Intermittent periodic duty (duty type S3): A sequence of identical duty cycle, each including a period of operation at constant load and a rest and de-energised period. These periods being too short to attain thermal equilibrium during one duty cycle. In this duty type, the
starting current dose not significantly affect the temperature rise. Unless otherwise specified, the duration of the duty cycle is 10 minutes. The recommended values for the CDF are 15, 25,40 and 60 percent.

Intermittent periodic duty with starting (duty type S4): A sequence of identical duty cycles, each cycle including a significant period of starting, a period of operation at constant load and a rest and de-energised period. These periods being 100 short to attain thermal equilibrium during one duty cycle
In this duty, the stopping of the motor is obtained either by natural deceleration after disconnection of the supply or by means of braking such as a mechanical brake which does not cause additional heating of the windings.

Intermittent periodic duty with starting and braking (duty type S5) : A sequence of identical duty cycles, each cycle consisting of a period of starting, a period .of operation al constant load, a period of rapid electric braking and rest and de-energised period. The operating and rest and de-energised periods being too short, to attain thermal equilibrium during one duty cycle.