MV Motors

[DrPhils]

Seeking some basis guideline for the selection of fuses for protection of large medium voltage motors. We are a manufacturer of medium voltage motor control, but have encountered some large motor that exceed our database. Seem fuse manufactures have been reluctant to supply this data in recent years.

 

[electricuwe]

I wouldn't rely on a fuse to protect a large MV motor...

 

[JERRYROBINSON]

General Electric supplies MV fuses in their combination starers for MV. Their application engineers have a check sheet to help apply these fuses based upon your starting conditions. I am certain that Siemens, ABB, and other suppliers of MV motor starters can help you. These fuses all have time current curves available. As electricuwe stated, these are not for the main protection

 

[davidbeach]

Fuses will provided faster fault interruption than can be achieved otherwise. Beyond that a contactor or breaker controlled by a relay will provide better (tighter) protection for your motor than a fuse.

 

[LionelHutz]

Knowing what a "large motor" is could help.

 

[waross]

I would check your data base to determine the percentage of full load current is used for the fuses for smaller motors. You may also check the time current characteristics and attempt to match that also. Also check your codes for the acceptable range of fuses.
If these motors are larger than your data base, and in the medium voltage group, the fuses are for short circuit protection of the conductors feeding the motors.
Protection of the motors will be by overload relays, and possibly by thermal modelling, differential protection and temperature monitoring.
If, despite the motor protection, the motor burns up, or if there is physical damage to the motor circuit conductors the fuses will interupt the fault current.
respectfully