Number of Start per Hour

hi! folks

I would like to know if there is a standard calculation of Number of Start per hour of a motor? could it was affected by the number of poles, duty cycle, applied voltage, etc?

How about if the machine was fitted to electrical braking modes such as plugging, dynamic braking, or frequent reverse-stop modes? how can we apply the Number of start per hour regulations?

Anyone could specify on AC and DC machines. Much better if anyone could provide substantial reference and or manuals on calculations).


thanks,

fbjavier

 

[electricpete]

For NEMA frame induction motors there is very clear guidance provided in NEMA MG-1.

http://www.joliet-equipment.com/allowable_starts.htm

Columns A and B give max number of starts per hour on average over life of the motor to prevent excessive long-term degradation.

Column C gives miniumum rest time between starts to prevent short-term degradation from insufficient cooling between starts.

The tables are dependent on speed and horsepower as expected. Regarding the minimum time between starts, one thing which they don't give is the status run or off between starts which makes a difference. Machine will cool faster if running for most of the time between starts.

NEMA MG-1 also has some words about 2 starts cold or one start hot. For large motors, we ask the OEM to provide us starting duty specific to each motor.

 

[Mendit]

Note to remember, Starts, are normal starts. Stops are noraml stops with coasting to a stop. A coast to stop is typically 5 min on 4 pole and 7-8 min on 2 pole. This coasting is required to cool the shorting rings. Failure to cool the shorting rings and then restarting could cause the rotor to be damaged.

 

[electricpete]

I'm not sure I understand the comment about coast to stop times. Typically if attached to a pump I see the machines coast to a stop in under a minute. Uncoupled coast-down time is much longer of course but not revelant to field applicaitons.

Is there something to suggest a certain coast down time is built into the standard NEMA MG10 limits? As I mentioned I feel there is lacking any info about whether time between starts is run or idle and coast-down would play a role as well.

 

[jbartos]

Suggestion: Please, notice that the plugging duty motors are designed for relatively fast rotation reversals in a specified time.
Visit

http://www.reliance.com/mtr/flaclcmn.htm

for motor plugging duty at the end