Ward Leonard Control of DC Motor 2

[thekingpin]

Hi Guys, I have a rather old (circa 1930) mine winder that uses a Ward Leonard control system. The MG set comprises 2 generators to supply armature voltage control for the Winder motor. The smaller generator supplies voltage to the motor all the time whilst the larger only supplies voltage to the motor after the controller gets to a certain point. The 2 generator armatures are connected in series to the motor armature. Prior to the main generator field being connected to the exciter its field is suicided across the armature. My question is "How important would this suicide connection be?".

Many Thanks

 

[waross]

Doesn't sound like a Ward Leonard any more.
In a Ward Leonard drive the smallgenerator generally supplies a constant field to the motor, and through control resistors, the exciting current for the large generator. The armature of the large generator should be in series with the armature of the motor. The motor field is maintained constant. As the field of the large generator is increased, the voltage output increases and so also does the speed of the motor.
I know left side, right side, bottom side and top side.
What's a "Suicide" connection?

Bill
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"Why not the best?"
Jimmy Carter

 

[edison123]

Wow, ward leonard system ? A blast from the past.

I have the same question as Bill.

 

[Skogsgurra]

A suicide connection is when you want to kill armature voltage completely. It is done by connecting the excitation directly to the armature - but with "wrong" polarity - so that any armature voltage feeds back to excitation to reduce itself. You could say that it is a negative feed-back.
Was common in many WL applications where you needed the armature voltage to stay put and not cause uncontrolled remanence induced creeping movement when the controller was at zero.
If you want your winder to stay when ordered to do so, then the suicide is important.
I see (or, rather saw) it mostly in German equipment, where it is called "Selbstmordschaltung".

Gunnar Englund

http://www.gke.org

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

 

[waross]

Thank you for the information Gunnar.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Wow, what a wealth of information you are Gunnar.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[edison123]

A LPS Gunnar. Is this equivalent to plugging ? What happens to the inrush current ?

 

[thekingpin]

Thanks Skogsgurra,

I thought that was the reson it was there, but the way it is connected prevents it being useful since the Auxiliary Generator field is not suicided.

The system is a genuine Ward Leonard but is the only one I have ever seen with 2 generator armatures connected in series with the motor armature with the small generator supplying the motor aramture when the face plate is in the minimum position and the large generator plus the small when the face plate is rotated further.

The supply for the motor field, and both generator fields is from a separate MG exciter set.

Cheers and thanks for your help.

 

[Skogsgurra]

Edison,

No, plugging is reverse braking without control over currents and torques. That would (at best) trip the protection of a Ward Leonard drive and is also not necessary since the WL is a true four quadrant system where you take the speed up or down by adjusting the armature voltage.

Gunnar Englund

http://www.gke.org

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

 

[edison123]

Thanks Gunnar. Back to the books for me.