VFD Traction Applications Discussion

[itsmoked]

1) Has anyone run a VFD from a battery bank?

2) Will the system likely suffer from DC bus under-voltage faults during moderate acceleration demands?

3) Can the battery bank be utilized successfully as a 'load'?

4) Will the system likely suffer from DC bus over-voltage faults during dynamic braking?

5) What drawbacks exist when using a 60Hz 3ph ~1050RPM motor in 400Hz service?(7000RPM)

Positioning is not required.
6) Is a vector drive suggested or would a scalar drive be adequate?

Any recomendations of other points to consider?[/color #006600]

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[DickDV]

I would think the battery source issues, undervoltage and overvoltage etc. are manageable by choice or design of the VFD to tolerate these conditions.

As to Vector/Scalar, a lot depends on the application. Certainly, for maximum starting torque, vector would be the choice.

Your question about the motor is really a motor issue, not a VFD issue. Operating a motor at over four times its base speed requires a motor specifically designed for that service, both as to electrical and mechanical aspects.

My concern with a traction application would be with the shock forces and general vibration levels if the VFD is mounted in the vehicle. Railroad locomotive designers really had their work cut out for them building VFD's for the new generation of AC traction locomotives but they seem to have succeeded. I would think that fork trucks, luggers, mining tuggers, etc. would all have the same mechanical issues.

 

[Drivesrock]

Dear itsmoked. I supply some answers;

1. I have come across battery fed VFDs for use in emergency hoisting when the mains has failed.

2. The batteries will have a maximum current discharge rating which will determine the fastest aceleration rate.

3. I don't think the batteries will make a good load. The battery charging characteristics will be much longer than the discharge.

4. Because of above you will most likely have DC bus overvoltages.

5. As mentioned above you will need a special motor for 400Hz. I believe that over 2 x base speed is not recommended for standard motors.

6. Scalar or Vector will depend on your application.

Drivesrock

 

[itsmoked]

DickDV,Drivesrock; Yes, I understand the shock considerations as I have built and constantly work on railroad equipment. I have often found bolted-on-the-wall items converted to laying-on-the-floor devices.. The locomotives have it a little better as they are sooo heavy. The cars they run into suffer far more.


Thanks Drivesrock for the battery info.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[DickDV]

Or, itsmoked, in railroad vernacular:

2 cars
1 car
half a car
BANG
that will do

 

[itsmoked]

zzacktly! I was standing 5 feet from a caboose in when it was coupled. It jumped twice it's length faster than my eye could follow... The switch-man jumped on as the train pulled forward it took him three car lengths before he got the brakes released enough so the wheels could start to turn. As they say; "We don't care, we don't care.." (sung to a lilting tune)

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[DickDV]

Well, Keith, I've been a railfan and industrial rail facility consultant for many years. We've got plenty we could talk about but it would be way off topic.

Be interesting to do that sometime off the board.

 

[UKpete]

Hello Keith, I'm a railfan too!

I have done performance calculations on battery-electric shunting locomotives, you need to ask the battery supplier for the internal resistance characteristic (versus load and depth of discharge), as well as the regular discharge characteristic.

On the question of vector and scalar, well all rail technology is scalar as far as I know, with a simple speed sensor on the motor or gear. The difference with traction being that you are also concerned with road speed as well as wheel (or motor) speed, as spin or slide may be occuring. Hence a doppler sensor is sometimes used to get road speed. Maximum tractive effort at low speed being achieved in the slow creep condition i.e. the wheel moving slightly faster (doesn't fit with static friction being higher than dynamic friction, I know).

I don't think dynamic braking was offered on battery, which were lead-acid, only rheostatic i.e resistors were fitted. But it is in hybrid road vehicles of course, but that is with ... whatever battery the Toyota Prius uses (forgotten!).

 

[waross]

Attention rail fans; Many of the forum members will enjoy an exchange of anectdotes and experiences relating to railways.
Pat's Pub would be a great venue, but it may not be open to all who wish to post. Can anyone suggest a place where such a discussion may be conducted?
Can it continue in this forum?
respectfully

 

[itsmoked]

The traction app I'm referring to is an electric vehicle (auto) not rail. As the OP of this thread it would be fine with me as I am here to learn and share.

This week we had a rail problem with a SuperScenicCruiser dome car. They have a tremendous solar gain. Truly insane actually. Requiring large refrigeration systems(Note: these are not air conditioning but refrigeration as air conditions just doesn't cut it under the required loads and other constraints.) Anyway the car was loaded, staffed and customer'ed when the generator went down.

The non-technical car steward was walked thru myriad scenarios and quizzed. It was finally determined that the diesel fuel pump was at fault and a 'technical' was dispatched to Idaho. As is typical, it wasn't the fuel pump but was certainly fuel related. The Woodward governor recently installed and working like a dream at keeping the power from ever sagging detectably, was not allowing any fuel to be injected. A short troubleshooting episode revealed that the Woodward's speed sensor was dead, dead, dead, as was any hope, for the the people baking like pheasants under glass.

The governor takes it's speed signal from a magnetic "generator" that is a permanent magnet and a fixed armature whose relationship to the the ring gear teeth rapidly closes/opens the magnetic circuit thereby generating a 1.5V AC signal that the governor uses. The BIG downside is that the sensor needs to be located approximately "0.040" or less from the ring gear teeth. Something, a tooth burr, or pebble, or run-out, or thermal expansion, or? had reduced the clearance to less than 0.00" and the face of the sensor had been spontaneously removed. Signal gone.. governor commands zero fuel.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[davidbeach]

Ouch, not good. Good thing about the old partial domes was that there was someplace else for the passengers to go if the AC went out in the dome.

 

[ScottyUK]

ItSmoked,

Those speed sensors are pretty typical of what is used for shaft speed indication and vibration sensors in much larger (multi-MW) machines. 40 thou gap seems quite generous - our closest ones run about half that! The biggest problem we have is the locknut on the threaded barrel working loose allowing the sensor body to rotate. I'm not sure which law of physics ensures that rotation always causes the probe to touch the shaft though. Scott's Law? We also occasionally see tip damage which looks like a foreign body has gotten between the probe tip and the shaft, but have never found any fragment of debris. The lube oil system is heavily filtered, so in theory there is nothing of any significant size in the oil system which could affect a probe. Theory is great!

----------------------------------

Sometimes I only open my mouth to swap feet...

 

[itsmoked]

Scotty; Sounds like you've had the exact same ream job..

Maybe I should design a probe that puts out the same signal but can run from 1/2 an inch away..

The voltage they put out is a function of the distance. The Woodward needs at least 1.5V = ~ 0.04" They go up to something like 15V if you get them reallllly close.



Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com