Motor Starting Duty

[Shells]

Can anyone explain what this motor starting duty means? I never quite understood it...is it 3 consecutive starts in an hour ?? And what is the additional start after/cooling period refer to? This is for a 2.4kV motor.

Starting Duty:
Number of consecutive starts
3 starts cold
2 starts hot
Coolinq Period:
Additional start after:
45 minutes, motor shutdown
30 minutes, motor running at full load.
15 minutes, motor running at no load.

Thanks

 

[Jraef]

At 250HP Low Voltage and below, NEMA has specific guidlines on motor design that dictate what people should expect from a motor. The ratings vary greatly by size, larger motors usually being rated for fewer starts per hour than smaller ones.

In MV motors (and above NEMA LV motors), the motors are usually made for specific tasks, so each one will come with a design rating from the manufacturer as you see on yours. There is no "standard" though.

So in the data for your motor, it means that you can start it 3 times consecutively in an hour (so every 20 minutes) if it is "cold" meaning room temperature up to about 40degC. Think of those as "unsuccessful" starts, i.e. the motor never was fully engaged with the load so it didn't heat up very much. Once it's "hot" from too many starting attempts (or hot from external sources), you must not attempt to start it more than twice consecutively as per the cooling off periods described below.

After it has been running, and trips off line (Motor Shutdown) from the Overload Relay or other protective device, you must wait 45 minutes for it to cool off before re-starting. If was running under full load but did not trip off-line (normal shutdown), then you can restart after 30 minutes. If it was running unloaded, you can restart in just 15 minutes.