Rectivar drop voltage when connecting to motor

[wilsoncalma]

I have this situation:
Dc motor is not running continuously, it only run one quarter at a time.
When I remove the motor and check the voltage of my Dc drives (Rectivar), i was getting 480vdc into A1-A2 terminal and 240volts into F1-F2 terminal. when i connect the motor again and start, i can get only 8vdc into A1-A2 and 240vdc into F1-F2. The supply voltage is correct which is 415 vac. Is it the motor or the drives is faulty?

 

[Skogsgurra]

It definitely sounds like your motor is either mechanically blocked or running without excitation current.

Check that excitation current is there. Use a DC clamp to measure current. Voltage alone will not tell the truth.

If no excitation current, check field winding resistance.

If excitation is there and armature current is nominal, then the motor is most likely mechanically blocked.

More details would help solving your problem. For instance: Is this a new drive that never has run before? Or is it an old one that just stopped working?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[wilsoncalma]

The motor is not blocked, and even I replaced the drives with a new one, its the same problem. I'm getting 8 amps. What I dont understand is when I pull-out the motor and taken to the rewinding workshop, the motor (without the drives) is working there. I order a new motor and will see what will happen next.

 

[Skogsgurra]

So, what excitation current do you have?

When you say "it only run one quarter at a time", does that mean a 90 mech degree turn and then stop?

Or is it something else you describe?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[wilsoncalma]

Yes, the motor only turn quarter at a time then stop and then turn quarter again and then stop. the motor can turn freely by hand when no power applied. the armature current is playing between 7.5 to 8 amperes.

 

[edison123]

Have you checked the drive to armature supply cables for any loose contact/semi-broken connection at the cable lugs ?

 

[wilsoncalma]

All the connection are tighten properly and even all the relays and thermal protector before the motor has been by-pass and yet the same problem.

 

[Skogsgurra]

This start/stop motion puzzles me. Does it just turn 90 degrees and then stop? Do you have to start again to make it turn another 90 degrees? Or is it doing it all the time? Like a relaxation oscillator?

In the latter case, it is probably only the fact that you are running the motor without load and haven't tuned the speed control properly.

What happens when you turn up the speed reference? What happens when you brake the shaft? When you say that current is between 7.5 and 8 amps - does that mean that the current stays between those values continuously? Or that it hits those values when motor is rotating? Or at standstill?

We are trying to help you, but you do not give us much information. The excitation current is something you still haven't told us. Nor the nameplate data.

What does the commutator look like? Do you have any sparking?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[wilsoncalma]

I just receive the new motor and fixed it. The machine is now working without any problem. Now I know that the problem was from the Motor. Thanks to all of you guys.