AC Motor 3 Phase

U

unknow54

Member
Location
Huntsville, AL USA
Occupation
Maintenance Tech
Today at work, we had a 3 phase 480VAC pump motor that was going in the wrong direction. The Maintenance Tech switched legs L1 and L2 to allow the motor to go in the forward direction. After, switching both phases and renergizing the motor, the motor would not start. Another Maintenance Tech said to swape L1 and L3, instead of L1 and L2. Once the Tech changed L1 and L3, the motor was renergized and began to run normal.
Any idea what would cause the motor to not run when swaping legs L1 and L2?
 
unknow54 said:
Today at work, we had a 3 phase 480VAC pump motor that was going in the wrong direction. The Maintenance Tech switched legs L1 and L2 to allow the motor to go in the forward direction. After, switching both phases and renergizing the motor, the motor would not start. Another Maintenance Tech said to swape L1 and L3, instead of L1 and L2. Once the Tech changed L1 and L3, the motor was renergized and began to run normal.
Any idea what would cause the motor to not run when swaping legs L1 and L2?
Click to expand...
Luck.
 
Sounds like a loose connection. How could a 3 phase motor not run in either rotation if properly connected and the motor is ok?

What caused it to run in the wrong rotation in the beginning? New Install?????

I have seen a 3 phase motor run in the wrong rotation when the starter or contactor is pushed in by hand and only two poles of the contactor or started "make" and the othe pole does not make contact.

I would check the starter contacts.

Or is this motor on a vfd?
 
Yes, it was a new install and had not been tested. The motor is not currently on a VFD... Also, someone on our team mentioned that the motor was on Y phase and not Delta phase. Would this make a different in the phase order for the wires?
 
If there was a "lost phase" the motor will run if there is any flow pushing the pump and would do so in either direction. It won't have rated torque available and likely won't be running at full speed. If rotor is not turning at startup it should just sit there drawing high current between the two legs that do have voltage.

This happens easier with fans when there is some air flow spinning the fan before you start it but would also be a possibility with some pumps.

Wye vs delta wound motor or even wye vs delta wound source won't matter.
 
I'm with @Eddie702 , I think there was a poor connection. And you might still have the problem.

A three phase motor supplied through only two terminals is called 'single phased' (you need 2 terminals to supply single phase power and 3 terminals to supply 3 phase power).

A single phased induction motor can continue to rotate if it is already spinning, and might even accelerate if given a nudge to get going. But it doesn't have any direction to its (0) starting torque. If a single phased motor starts spinning it is because of some additional influence. If a single phased motor spins, and the direction of spin can be a matter of luck.

When L1 and L2 were swapped, it would have to switch direction of rotation, IF all 3 phases were present. If you then swap L1 and L3 this should restore the original rotation direction. Unless you put L2 back to its original position, which is not clear from the description....

From the somewhat random direction of rotation or even starting, there is a real chance that one phase is missing and you still have a problem.

Check current flow on all 3 supply legs.

Jonathan
 
Eddie702 said:
Sounds like a loose connection. How could a 3 phase motor not run in either rotation if properly connected and the motor is ok?

What caused it to run in the wrong rotation in the beginning? New Install?????

I have seen a 3 phase motor run in the wrong rotation when the starter or contactor is pushed in by hand and only two poles of the contactor or started "make" and the othe pole does not make contact.

I would check the starter contacts.

Or is this motor on a vfd?
Click to expand...
Thank you for your help!
 
winnie said:
I'm with @Eddie702 , I think there was a poor connection. And you might still have the problem.

A three phase motor supplied through only two terminals is called 'single phased' (you need 2 terminals to supply single phase power and 3 terminals to supply 3 phase power).

A single phased induction motor can continue to rotate if it is already spinning, and might even accelerate if given a nudge to get going. But it doesn't have any direction to its (0) starting torque. If a single phased motor starts spinning it is because of some additional influence. If a single phased motor spins, and the direction of spin can be a matter of luck.

When L1 and L2 were swapped, it would have to switch direction of rotation, IF all 3 phases were present. If you then swap L1 and L3 this should restore the original rotation direction. Unless you put L2 back to its original position, which is not clear from the description....

From the somewhat random direction of rotation or even starting, there is a real chance that one phase is missing and you still have a problem.

Check current flow on all 3 supply legs.

Jonathan
Click to expand...
Thank you for help!
 
kwired said:
If there was a "lost phase" the motor will run if there is any flow pushing the pump and would do so in either direction. It won't have rated torque available and likely won't be running at full speed. If rotor is not turning at startup it should just sit there drawing high current between the two legs that do have voltage.

This happens easier with fans when there is some air flow spinning the fan before you start it but would also be a possibility with some pumps.

Wye vs delta wound motor or even wye vs delta wound source won't matter.
Click to expand...
Thank you for your help!
 
You must log in or register to reply here.
Top