# Ward-Leonard control



## paulengr (Oct 8, 2017)

The state legislature building in NC, at least a couple of them at Duke University, and of all places a Doubletree hotel in the Chaoel Hill area. I’d say the majority of dragline excavators still use it even if it is digitally controlled, over 300 machines worldwide.


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## Wirenuting (Sep 12, 2010)

They also made Motor Starters that last forever.


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## 460 Delta (May 9, 2018)

paulengr said:


> The state legislature building in NC, at least a couple of them at Duke University, and of all places a Doubletree hotel in the Chaoel Hill area. I’d say the majority of dragline excavators still use it even if it is digitally controlled, over 300 machines worldwide.


Well if that’s the case, @Dennis Alwon should post a video for us motor control nerds.


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## micromind (Aug 11, 2007)

One of the casinos I used to do a lot of work in had an old (60s) elevator that had an MG set and clapper relays. It was 3 or 4 floors but everyone said it was the most reliable one they had. 

Kinda makes ya wonder about all this fancy electronic stuff.............


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## paulengr (Oct 8, 2017)

460 Delta said:


> Well if that’s the case, @Dennis Alwon should post a video for us motor control nerds.


What does he have to do with it? Southern Ekevator mostly maintains them. They just call me if they get into an actual motor or generator or loop control problem.

Ward Leonard itself is super simple, just lots of moving parts.

Start with a DC motor. You can do field weakening but let’s stick with basic control and just run strong field. So we use resistors or rheostats and diodes to make the field voltage (SiC rectifiers came out in the 1920s) or use a compound wound motor. Now the next problem is the armature which could be hundreds of Amos (up to 6,000 amps on a dragline MD824). So the secret is first use an AC motor. Really advanced systems use a synchronous motor because the system is more stable and can be 1.0 power factor or even leading. Now mechanically couple this to a DC generator (alternator). The input control voltage supplies generator excitation but at roughly up to 1000:1 gain via the generator. So a couple amps can control thousands. If necessary and on larger systems it is, you can also connect another much smaller DC generator to the same motor, called an exciter. The controls feed the exciter excitation (now in fractions of an Amp) whose armature in turn feeds the bigger generator.

Need more HP or multiple motors? No problem. Put the armatures of two generators and two motors in series so you have G1-M1-G2-M2-back to G1. Feed the fields in parallel. The voltage across the lower current motor will increase keeping them in sync with each other.

I’ve worked on these for years. The biggest trick at this point is everything is so old that documentation, let alone anyone who ever knew about it, is often long gone. Retired or even passed away. So unless it’s obvious troubleshooting turns into reverse engineering. DC motors and generators are super simple compared to AC but there are a lot of rules of thumb you forget if you don’t do this every day and lately I’m down to maybe every few months.


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## 460 Delta (May 9, 2018)

paulengr said:


> What does he have to do with it? Southern Ekevator mostly maintains them. They just call me if they get into an actual motor or generator or loop control problem.
> 
> Ward Leonard itself is super simple, just lots of moving parts.
> 
> ...


What does he have to do with this? He's from Chapel Hill and presently retired, and maybe needs to get out of the house, and I just wanted to mention him possibly.
BTW, I understand how the W-L system works, and started building a small model in the 80's to find the sweet spot RPM on a 4 bearing shaker screen at the stone plant I first worked at, as I was finishing it up I was transferred to another division.


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## Dennis Alwon (May 9, 2009)

The last elevator we did was based on a pneumatic vacuum elevator like the old air tubes they use at banks.









Homepage


Home Elevators For Residential Applications Homepage




www.vacuumelevators.com





@460 Delta thanks but I think I'll stay at home and try avoid getting the covid virus. I found out that the maintenance chemo I take has left me with no antibodies for the virus even after getting both vaccines.


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## paulengr (Oct 8, 2017)

Dennis Alwon said:


> The last elevator we did was based on a pneumatic vacuum elevator like the old air tubes they use at banks.
> 
> 
> 
> ...


Next time Burlington calls you should go along. They have a wound rotor slip recovery drive make it variable speed wound rotor vertical pumps! It makes Ward Leonard pretty tame.


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## JRaef (Mar 23, 2009)

I once interviewed for a job at Chevron that I thought was an EE job, because a friend of mine was already working there and was getting me an inside track for an open position. So when I got the call from their HR department to come in for an interview, I thought it was for that job. Turned out it was for an Elevator Mechanic job, because my resume showed that I had been an electrician before I got my Engineering degree, so they thought that was perfect because they needed someone to deal with the controls. So since I was there, I took the tour of their 40 story high-rise building in down town San Francisco with the manager of the elevator dept.

In the mechanical penthouse elevator room, it was full of dozens and dozens of clickity clackity open style DC relays on a wall, There were also 6 x 500HP DC motors (plus a spare) and Ward Leonard controllers in there, something I had seen at the steel mill I had worked at, so the guy was really excited that I knew what it was. I asked them how they serviced those motors, he said that each year, at least one of them would be lifted out of the roof by helicopter and flown to a motor shop in Oakland for PM work, so essentially every one of them was PMd every 7 years minimum. I looked at that task, then I looked down the elevator shaft (just a chain safety fence around it). This was in 1981 and at THAT TIME, I could have made around $60k per year with mandatory OT (which would be like $180k now). My brain and wallet wanted me to take it, but I got vertigo when I looked down that open shaft and my testicles pulled up into my throat, making the words come out as "No thank you."

Turned out that 3 years later, Chevron sold the building and moved their HQ to the suburbs, so I probably would have lost the job, or had to work for a building management company, which I have heard is usually crappy.


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## paulengr (Oct 8, 2017)

Good elevator mechanics get paid pretty well. I doubt the pay would go down.

But today the number of people in this country that still truly understand Ward Leonard is probably less than what you can count on both hands.


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## CAUSA (Apr 3, 2013)

paulengr said:


> What does he have to do with it? Southern Ekevator mostly maintains them. They just call me if they get into an actual motor or generator or loop control problem.
> 
> Ward Leonard itself is super simple, just lots of moving parts.
> 
> ...


paulengr

what would be the vector angle and voltage ratio on the lower current motor? any notes or prints on the controls ?

I am very interested in this setup. as you described. I am no means a elevator teck, just interested in the excitation field generation and circuit's interconnections.

Thanks


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## paulengr (Oct 8, 2017)

CAUSA said:


> paulengr
> 
> what would be the vector angle and voltage ratio on the lower current motor? any notes or prints on the controls ?
> 
> ...


Except for the AC motors it’s all DC so angles don’t apply. On draglines a large portion of the dig cycle is a static pose. So while you are swinging for instance drag and hoist aren’t moving very fast once the bucket clears the cut. So without sync motors average power factor is about 0.60. In addition line lengths from the sub tend to be an issue so running leading PF helps. Most mines run 0.85 leading so the machine is also a synchronous condenser and counteracts low PF of the rest of the mine for free:

I have some prints but no need most of the time. GE makes them span 30+ pages but if you understand what it is prints are not needed.

Almost all the elevators just run straight induction motors or fixed voltage synchronous adjusted to name plate with little PFC. Running a DC voltage control loop adjusting based on a watts bar transducer is certainly possible pre 1960s but I’ve never seen one. Today we just use a servo style drive like a Siemens 6RA80 and do ir in software.

Starting in the 1950s one of the first power electronics was a 16 A SCR. You were limited to discrete transistor circuits by then. And they are large. A GE DOM. Very expensive. Google the Amplidyne and Amplistat. Those were the height of DC tech before the DOM II and then digital drives.

Keep in mind a DC system is just as much mechanical as it is electrical. People that work on them blend skills with magnetics, mechanical, and electrical. The only school left in the country teaching it is Wyoming Tech. The work is grubby, greasy, and the equipment is very field customized. It is a far different world from prepackaged VFDs that are UL Listed with engineering drawings. Even the engineered systems took significant field testing and calibration just to make them operational. If you like having lots of pots to tweak and get grubby covered in carbon dust in overalls and playing with really fussy systems this is your thing. Commissioning Ward Leonard’s can take days. It’s a far cry from the hour most VFD systems take.

The Ward LeonRd loop itself is rarely an issue. But with AC most of the time things either work or they don’t. With DC often you are facing performance issues…it’s still working but because some component is out of tolerance it doesn’t work right.

As an example Google neutral setting by the voltage drop method or if you don’t mind the safety issue pencil point method. A lot of motor shops just put AC on the comm to set neutrals. Often they are way off and you get a 2 or higher sparking score. Voltage drop gets you within a quarter bar safely.


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## Gavin R (11 mo ago)

paulengr said:


> What does he have to do with it? Southern Ekevator mostly maintains them. They just call me if they get into an actual motor or generator or loop control problem.
> 
> Ward Leonard itself is super simple, just lots of moving parts.
> 
> ...


Hi @paulengr 
Thanks for this explanation. Can you explain the purpose of trimming resistors for the Swing Motor fields on a Dragline please? If you had a loop unbalance when the machine is plugging, would you adjust the resistors for the loop with the higher or lower current?


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## paulengr (Oct 8, 2017)

Gavin R said:


> Hi @paulengr
> Thanks for this explanation. Can you explain the purpose of trimming resistors for the Swing Motor fields on a Dragline please? If you had a loop unbalance when the machine is plugging, would you adjust the resistors for the loop with the higher or lower current?


Neither. It depends on your controls (Amplidyne, Amplistat, DOM II, various PLC clones of the DOM II design). In strong field adjust to match name plate. In field weakening you can increase speed below peak power but do not go under 50% or you will get dangerously close to overspending. 50% is a safe minimum. This is for the master loop. Be sure you know which is which. The slave loops should be adjusted to match the master loop.

With draglines the correct way to adjust things is to match the performance spec. Adjusting things just so it works can work but then you get lousy performance. GE was many things but they were amazingly detailed in documenting exactly what the performance specs and tuning procedures are. The DOM II regulator “schematics” is a treasure trove of data. Modern PLC upgrades are really just digital simulations (with upgrades) of the DOM II design.

One issue to be aware of if you haven’t seen this or are aware of this. When swing gears get worn and loose they can vibrate from the wear (washboard effect). This spills over into the control loops causing wild oscillations that then in turn make it worse with torque oscillations in a nasty electromechanical resonance. Many draglines have cross resistors to prevent this. The output of say both motors is connected (should theoretically be zero Volts) with a resistor. This forms an LR low pass filter across each MG set with a fairly low 3 dB point that effectively shunts and blocks the resonance.


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