Wye wound motors 1

[mwimbush]

I have recently encountered a 460 volt 3 phase 200hp fan motor that was wired with 2 wye windings in parallel for across the line starting. It was wound with the centre tap of each wye being inacessible inside the motor. At the junction box there were 6 leads present, that initially led me to believe that it was a delta wound motor.

What are the issues that I need to be aware of to set up my vfd to run this motor. We have at least 100 motors in similar installations, but this is the first one I have encountered that is wound wye, I believe all the others are wound delta (I checked my readings twice and had them verified by 2 other technicians) We are using an Emmerson VFD however we also use a Sqare D VFD as a portable backup.

We became aware of this unusual motor during a breakdown situation and are attempting to determine if this was a factor. During the breakdown we had the original emmerson VFD fail, a standby Emmerson VFD fail and a standby Square D VFD fail, all with different faults. The only common element is the motor.

 

[busbar]

It may be a part-winding-start motor, which is sort of a cheeseball version of reduced-votage starting. PW-starting uses two 3-pole contactors, with one of them timer-delayed at startup.

A partial clue for NEMA standard may be leads marled T1-T2-T3/T7-T8-T9

http://www.joliet-equipment.com/terminal_markings_and_connections-part_wind_start.htm

 

[jbartos]

Suggestion: Please, post the motor nameplate data including RPM data.

 

[aolalde]

The internal three phase connection of a motor does not interferes with the external power supply.
As far as the winding is well designed and the external connection is done properly the motor could be internally wye or delta and have one or several paths in parallel.
What the driver sees is a three phase reactance that should match the current capacity of the power supply with the Volt/hertz applied. For motors of the same power, speed, voltage and frequency, the external impedance is similar (although it is not identical) for different manufacturers and winding constructions.

 

[purplepete]

Could it be a Dahlander arrangement? (ie two speed)
This might explain what appears to be two windings connected in parallel.
Cheers

 

[Marke]

Hello mwimbush

I believe that Busbar is correct, what you have there is a part winding start motor.
Connect both wyes in parallel and connect ot your drive. I do not expect to see any problems from this connection.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[jbartos]

Suggestion: Visit

http://www.sea.siemens.com/contrlbu/upld/files/p41-46.pdf

for: Figures 5 and 9

 

[mwimbush]

I assume it has been wound for part winding start, with the three leads for each winding being available at the terminal box, and the centre tap inside the motor. We have it connected with the 2 sets of windings connected in parallel. What I had expected was a delta wound motor with 2 leads per winding available at the terminal box.

Is there any difference in the torque curve charactaristics of a wye wound motor verses a delta wound motor.

We have come up with another possible wiring configuration, but are not sure how we can confirm which it may be. I originally expected a delta wound motor, as mentioned above. I then reasoned out that it must be a wye wound motor. The new possibility that has been suggested is that it is a dual winding delta wound motor with the delta connections made internally with connection wires brought out. How can we confirm this? Does it matter?

The 3 leads per winding, when ohm'd out give a reading of 8 ohms phase to phase across all 3 phases. When the windings are connected up in parallel, the reading drops to approx 1 ohm. The meter may not be 100% accurate, but it does give a consistent reading. I am using a fluke electronic VOM.

The motor has a nameplate from a local rewind shop with a reference number. I will obtain that number and post it.

Can someone recommend a reference source that can explain in beginners terms the issues to consider when setting up a drive, and how to do it.

 

[jbartos]

Comment on the previous posting. There are various principles of drives. It may be better to narrow them down to a manufacturer or a category. Also, voltage and size of the drive can make a difference.

 

[Marke]

Hello mwimbush

With a part winding start system, it is though you have two motors built in one frame. If you connect to one winding (doesn't matter if it is star or delta), you are effectiviely connecting a lower rated motor, so the start current and torque are reduced. When you connect in the second set of windings, you have effectively put the "second" motor in parallel, increaseing the torque, current and power ratings.

With both windings in parallel at start, it wil behave the same as an ordinary squirrel cage motor.

Best regards,

Mark Empson

http://www.lmphotonics.com