Voltage limits on motor terminals ?

[Mongao]

Dear all,

I am in search of information related to voltage operating limits in North America, more specifically switchgears and motor terminals.

ANSI C84.1 separates voltage limits in two categories, "service" and "utilization" voltages; but these refer to the voltage levels in buses throughout the system/industry (e.g.; switchgears); there is no mention of criteria for motor terminal voltages.

Please, is anyone aware of these ?

Thanks a lot,

Andre

 

[waross]

[tt]Nominal system voltages. Nominal motor voltages.
120V ------------------------- 115V
240V ------------------------- 230V
480V ------------------------- 460V
2300V ------------------------ 2400V
4160V ------------------------ 4000V
In Canada
600V ------------------------- 575V[/tt]


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Mongao]

Thanks Waross,

Please, do you have info about the voltage sag limit at the motor terminal bus when it starts ?

Thanks,

Andre

 

[7anoter4]

The minimum voltage at induction motor start has to assure a minimum motor torque -mainly the motor pull-up torque. Since the current decrease slowly from start up to breakdown torque the motor windings temperature will raise then the start duration has to be limited.
So, the acceleration torque-the difference between active torque the motor produces and the load torque-has to be enough to limit the starting time. The induction motor torque is- approximately- direct proportional with the supply voltage then the minimum voltage has to assure a limited start time.
Then the minimum starting voltage depends on starting type: D.O.L., delta-star, VFD or else [the starting current could be 6-8 times the rated for D.O.L. and close to rated for VFD]; load torque type: fan, centrifugal pump, compressor, lift, conveyor and other; the inertia moment of the motor and of the load and other parameters. Usually in low-voltage world the small motor permits dip voltage drop but big one less [usually up to 30% for small one and 10% for a big motor].