Series winding

[astroid]

A separately excited 185 kW DC motor has an optional series winding. Manufacturer says it is to be used to enhance speed regulation in a Master application and speed drooping in a slave, but only when both motors are fed from one converter, otherwise there is no distinction. In single drive application the series winding may or may not be used depending on process requirement. Please explain.

 

[Skogsgurra]

The series winding is situated on the main poles and enhances or reduces the total magnetic field in the motor. It enhances field when current flow is such that main excitation and armature current work in the same direction.

If several motors are fed from one rectifier (or WL set, as it used to be in the dark ages) and if these motors are mechanically coupled (like in a press section or wire in a paper machine), then it is important that the motors share load in a controlled manner. Using a series winding, a motor that tends to draw more current will also gets its field enhanced and thus produce more counter-EMF, which reduces current to an equilibrium that is stable and easily controllable.

In some cases, where a motor speed droop is excessive, the opposite can be used to keep speed constant. If the series winding reduces main field, an increased load (that causes the speed droop) will also reduce excitation so that the counter-EMF is reduced. That will, in its turn, make tha motor draw more current and speed up until most of the droop is compensated. Overcompensation leads to unstable operation or runaway.

The use of a series winding is often called "compounding". It is a forgotten technique and the series winding shall usually not be used when running a DC motor from a thyristor rectifier. Especially not when four quadrant operation is used.

Do not confuse series winding and compensation winding. They are two different things.

Gunnar Englund

http://www.gke.org

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

 

[astroid]

Thankyou Skogsgurra,
Does this summerise the issue
1.In sections like Wire, Couch, and Press that are mechanically coupled, but each motor is fed from individual Drive panels, the master drive speed is controlled by Tacho and the slave drives share the load by controlling the current ref limit to the current regulator. USE THE SERIES WINDING TO AID THE MAIN FIELD IN THE MASTER AND THE SLAVE MOTORS FOR BETTER MOTOR PERFORMANCE.
2. In case of Drives like Dryer, USE THE SERIES WINDING TO AID THE MAIN FIELD TO OBTAIN BETTER DYNAMIC RESPONSE. If not required, leave it unconnected.
3. In case of a Master and slave fed from common Drive panel, USE THE SERIES WINDING TO AID THE MAIN FIELD IN THE SLAVE TO OBTAIN DROOPING, AND LEAVE IT UNCONNECTED IN THE MASTER.
Hope I got it right. Please comment.
Thanks
Astroid

 

[Skogsgurra]

Hello,

Your text in {{xxx}}. My comments in [[yyy]]

{{1.In sections like Wire, Couch, and Press that are mechanically coupled, but each motor is fed from individual Drive panels, the master drive speed is controlled by Tacho and the slave drives share the load by controlling the current ref limit to the current regulator. USE THE SERIES WINDING TO AID THE MAIN FIELD IN THE MASTER AND THE SLAVE MOTORS FOR BETTER MOTOR PERFORMANCE.}}
[[If the motors have individual drives, do not use series winding on any of them. The load sharing is done in the drives, either by using droop or torque control - or a combination]]

{{2. In case of Drives like Dryer, USE THE SERIES WINDING TO AID THE MAIN FIELD TO OBTAIN BETTER DYNAMIC RESPONSE. If not required, leave it unconnected.}}
[[Dryers rarely need better dynamic response. But they may need more torque to start. The series winding may help. But a compensated motor is much better. Also, the series winding can cause problems (excessive EMF) when regenerating. I would not use it here either.]]



{{3. In case of a Master and slave fed from common Drive panel, USE THE SERIES WINDING TO AID THE MAIN FIELD IN THE SLAVE TO OBTAIN DROOPING, AND LEAVE IT UNCONNECTED IN THE MASTER.}}
[[Correct. Use series winding in this case. But only in this case]]

Where are you situated?

Gunnar Englund

http://www.gke.org

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

 

[astroid]

Dear Skogsgrra,
thanks a lot. I am situated in a remote factory in Java, Indonesia. We have TOYO DENKI drives and motors from Japan. They use series winding in ALL drives of the wet section. One last point. If a motor fitted with series winding is required to be connected without using the series winding, should the series winding terminals be left open or shorted. I am reffering to induced voltages and currents.
best regards
Astroid

 

[Skogsgurra]

Hi again!

I have visited a few paper mills in Indonesia. Malaysia and S. Korea. But not yours.

I do not know much about the TOYO DENKI drives (have worked with Toshiba DC drives, though). Is there a reason why ALL the drives have series windings? I mean, the master (couch, probably) should not have a series winding. It may work, but it is not good.

It is better to leave the series winding open. There will not be any high voltages induced. And, besides, if there were any voltages, it is better not to let them create any currents - which they would do if you short the winding.

If you are thinking of CT secondaries and high voltage if left open; this is not at all like that.

Gunnar Englund

http://www.gke.org

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

 

[astroid]

Thank you friend. Best regards
astroid