One for the Older Ones

Probably for infinitely variable speed control combined with smooth torque control. It's basically a high gain closed loop control system that was originally built before the advent of vacuum tubes and solid state devices. It's why elevators have such smooth transitions from starts to stops. Same for your mine winches. Here's more.... http://en.wikipedia.org/wiki/Ward_Leonard_control.

It's the dual rating for the components that confuses me.

I've worked on Ward Leonard systems for over 30 years but I've never found drives rated like this.

Thanks for the clarification. Having failed at my first attempt I'm going to venture the guess that this is some form of a "universal" or "multi-use" MG set that is wound with pairs of symmetrical windings that depending upon the application allows for running them either in series or parallel depending on the voltage available and/or the horsepower desired.

This is an ole time rock crusher, still in service? Is it direct or pendulum?

On Winder motors in the Paper industry we often get NP ratings like:

300/300/300Hp 250/340/1200 RPM 652/480/480Amps 368/500/500VDC

O/L 200/200/100% 60 seconds

Field 20/20/3 Amps

The motor is run below base speed at 250 RPM, but is allowed a higher current to produce the 300 hp required. As the motor exceeds the base speed of 340 rpm the field is reduced to achieve the higher speed. But the current commutation is limited at week field and tapers to 100% NP at 1200rpm.

I do not have the data sheets for your motor, but would not be surprised if they have similar envelopes of operation defined. The NP's get pretty cryptic for some of the special applications.

I was thinking Strong field / weak field, but on rereading the values I think it might be continuous rating / short time rating . Traction motors often have a short time rating far higher than their CMR. Are the motor and generator both compound wound, (the series component of of the generator may be in the form of busbars)?

Is the motor a slip ring induction motor or a synchronous motor? Synch motors are more common on MG sets. They can look a bit confusing with a large squirrel cage in the rotor too. The cage is the amortisseur winding which also doubles as a squirrel cage on DOL starting. The easy way to tell is a Synch motor will have 2 slip rings and wound rotor induction motor 3 rings.

I would guess two speed and load settings. One for stuff and one for men.

That makes sense for the generator and final drive, there were two speeds for men and coal. They weren't that different though. But I'm still puzzled why the generator set has a dual rating for the drive motor. The motor it's self is a weird set up, slip ring with a liquid slip controller so resistance was always in the rotor circuit and a flywheel. It's allowed to slip by 15% giving up power from the flywheel when accelerating the cage drum.

I'm gleaning a bit more from the accident report, but it's like wading through porridge, heavy going.

Hi,

I am not entirely sure about this, but the Coal Board generally used reverse power braking on the coal skips and dynamic dc braking on personnel winders, with variable liquid resistance control. I think the rating must be due to the short term braking forces.

Most of these had dual operating ranges. One for materials and one for men.

Re: Most of these had dual operating ranges. One for materials and one for men.

Were these two different speeds? (I ask because the ratings on this motor both appear to be at the same speed (53.7 r.p.m).)

Or maybe it was for two different loads?

I'm not really arguing with you, I'm just puzzled. I guess I'm thinking that it had a lot to do with two different loads and the Ward Leonard control system. I'm guessing that the Ward Leonard system could put out anywhere between 2,260 and 4,000 amps, varying based on the load, and the motor could handle that same 2,260 and 4,000 amps, varying based on the load, maintaining the same speed with either load.

Maybe somebody has said this already, or at least in essence. I'm just trying to get my head around it. I guess I'm thinking it's sort of like a PID control loop, trying to maintain a constant speed (53.7 rpm) in the face of varying loads, and varying the current to do that.

???

It may be a little misleading to dual rate the motor that way, it seems like the rating on the motor might mention only the highest rating--just like any other motor, it uses less current at lower loads... It seems like the dual current rating would be more appropriate to the generator in the Ward Leonard m-g set.

RPM depends on the pole configuration. E.g. switched 3, 6, etc.

Men require longer 'ramping' than material, or lesser g rates. Materials 'up' higher torque. Materials 'down', higher breaking (regeneration).

It's not a simple 'star delta' system.

Yes, thanks, you're right about different acceleration rates required.

I still think thinking of it as something like a PID controller is useful and not far off the mark.

Considering acceleration, the Ward Leonard system is the (PID?) controller to achieve and maintain the required acceleration under the various conditions, by outputting a varying current.

I am starting to recall in some instances the motors were given a 1 hour rating and an 8 hour rating. It also depended on the cooling supplied to the motor.

On some old mill motors we were even given a 5 minute rating. We could get extreme torques and currents for the short time, but then we had to have a cool down period. The alternative if the motor was going to be used continuosly then we had to have the rms current below the 8 hour level.

I suspect you have an 8 hour rms rating, and a short duty high load rating.

The manuals for the machine should spell it out. If it is a GE machine they will probably still be able to dig out the info from the serial #. The old Harland and Westinghouse machines may pose a bigger research problem.

If anyone wants to have a look at the report:

http://www.dmm-pitwork.org.uk/html/brookhouse.htm