Need Helpful Comments and Suggestions On Electric Motor Dynamometer Bench Build

[D.Stan]

I am new to the Dynamometer Scene. I have learned a ton from this forum and I absolutely love it.

Needs:
Test AC and DC motors
120v to 480v
single and 3 phase
10-20HP

Retrieve Amps, Torque, Vibration, Temperature, and any other bells and whistles.

Like I said I am new to this particular scene and I have to start somewhere. I have a motor and I want to use it as the Load Generator. If you could please tell me what your thoughts are about this motor and what types of motors I can test with this particular Load Motor.

Specs:

Reliance Electric
20HP
1760RPM
460V
3Phase
Code G
Insulation Class F
TEFC
24Amps
Master Duty XE
60HZ
Power Factor 84.4
Type P
Design B

Very close to the Baldor CECP2334T-4 Bit not exactly. Specs

http://www2.baldor.com/products/spe...0&voltage=460&enclosure=TEFC&winding=&rating=

I am waiting on baldor to send me a specs sheet on my motor.

I have not decided yet on a energy dissipate. I am pretty sure I will choose a electric element and water.

I thank you for your time and input. This will help me out a ton.

 

[waross]

An induction motor being run as an induction generator may not be the best load.
Consider a regenerative Variable frequency drive.
By dropping the speed of the load motor under control you will be able to load the motor under test.
The regenerative feature will return most of the power used by the motor under test to the grid.
If you are doing much testing this will reduce your energy costs.
A 15 HP motor is at 90% efficiency is about 12.5 kW. That's a lot of power to waste boiling water when it can be reclaimed by a regenerative VFD.


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

 

[iceworm]

Give us some clues on the context.
Are you looking to make money with this?
Needed for a corporate project?
School project?
What kind of money do you have to spend?


What you are suggesting is a hell of a science fair project - but maybe not so good at making money.

So with out giving up any secrets - What does this need to do? Context?

If all you wanted to do was come up with a self excited standalone induction alternator, that would be pretty neat.

ice


Harmless flakes working together can unleash an avalanche of destruction

 

[D.Stan]

This project is for making money in my business. It is a very first model to get started. (Prototype) Income is very tight right now. Currently I can only test motors not under load. I come across all kinds of equipment and a VFD is a must that I am keeping my eyes open for. This build will help me understand a lot more and then allow me to move forward. I am trying to use the items I currently have to build this and see how far I can push it before it is time to rebuild a new model.

I understand time is money and it is better to run out and purchase the best equipment for the business but I really enjoy learning things like this and that is priceless as it pays me back ten folds in the future.

As for regenerative back on the grid. I am not sure about this for now. I am in the USA and what I understand it is a lot of work to get the utility companies permissions. I think the boiled water for now is just a get me started kinda thing and then upgrade from there. I have some very large elements at my dispense to learn.

I do have a few questions that will help me understand things better.

What is the max size motor I could test with this 20HP motor?

This motor is rated at 1760RPMs. Can I test 3400 RPM motors with this Load Motor?

How many Watts of power do you think this will generate? (Trying to size the elements needed)

I thank you for all input and tour time.

 

[LionelHutz]

Using a regenerative VFD and simply lowering the frequency until the motor reaches full load is about the simplest way to load test. In an industrial application, you can connect a regenerative VFD without any special utility permission.

If you're not going to be testing for too many hours then use a VFD with a braking transistor and resistor load. A 15kW resistor is fairly simple to find so you don't need to boil water.

Applied voltage, HP and frequency of the motor need to vary linearly with speed. Knowing this, you should be able to figure out what load you can apply and at what speeds. For example, you can't run a 1800rpm motor up to 3600rpm unless you have a VFD capable of 2X the motor rated voltage.

By your questions, it would seem you know almost nothing about this, not even that 1hp = 746W. So, it will be quite a learning experience.

 

[D.Stan]

I thank you and you are correct. I know almost nothing in this area. One thing is I am a very quick learner and very determined and persistent. This is why I said I have to start somewhere. Usually I ask my questions that are specific to what I am doing and once I receive clear answers I evaluate. That helps me a ton in deciphering the knowledge in a new area. I see how what I need works and then go from there reverse engineering it. Thanks for your patience and knowledge. Any and all input is good. If something downright isn't going to work please let me know.But most of please explain why it won't work. Thanks!

 

[waross]

With a 20 HP, 460 Volt motor, a 460 Volt VFD and 460 Volts applied, You will be able to develop or absorb 20 Hp at 3600 RPM.
The torque drops off above 1800 RPM as the frequency and speed increase. However HP is related to Torque times speed so that 20 HP is available at over speeds.
If the 20 HP motor may be reconnected for 230 Volts, you may develop or absorb 40 HP at 3600 RPM.
Regeneration:
The motor under test will draw energy to drive the load and to supply the losses of both motors and the VFD.
The losses of the driven motor and the VFD will be part of the load on the motor under test.
The balance of the power drawn in excess of the losses will be returned to your system.
In effect your test rig is supplying most of its own power.
The regenerated power reduces your plant load but never actually returns to the grid through the revenue meter.

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

 

[D.Stan]

Ok I thank you very much for that. I am sorry for my ignorance but I may have had this all backwards and that is where most of my confusion has came from. Please clear the air for me.

***Warning this may sound completely off but we all start somewhere. Please let me know if this is correct or wrong..

Load Generator Motor = ML1
Testing Motor = MT2

VFD is connected to ML1. The VFD drives ML1 while being coupled to MT2.

ML1 is the Main Point of electricity being used. As in just like driving an everyday motor in the factory.

ML1 Spins MT2 causing MT2 to generate electricity which has to be dissipated. (Back into the grid, Boiling Water, Etc...)

If back into the grid is chosen then the Regen VFD will recoup most of the electricity that ML1 and the VFD is using.

***

If this is correct then this makes alot more sense. I was under the impression you drive with the VFD MT2 and use some kind of stopping brake on ML1 to create a load just like when MT2 is working hard.

I thank you guys for this. It can help me out tremendously.


Waross you stated "If the 20 HP motor may be reconnected for 230 Volts, you may develop or absorb 40 HP at 3600 RPM."
First I am waitng on Baldor for complete specs of this motor to see what voltages I can use.

Do you mean If I am able to drive this motor with 230V and reconnect back to the 230V grid
OR
Drive it with 460V and reconnect back to a 230V Grid??

 

[waross]

I am not sure about ML1 and ML2.
Lets call the 20 HP motor the dyno and the motor being tested the motor.
The motor being tested drives the dyno at about 1760 Rpm (or 3560 RPM).
The VFD is fed with 480 Volts and is connected to the dyno. The dyno motor is connected for 230 Volts.
The VFD is set for a speed of 1720.
The motor under test will spin this up to 1760 RPM and the dyno will regenerate back through the VFD.
The motor under test is connected to the normal voltage, not to the VFD.
This is slower than the motor under test so it loads the motor under test.
The load may be adjusted by adjusting the VFD frequency.
The proper parameters must be set on the VFD to use maximum HP at 3600 RPM.
Out of time just now.
I will explain later about over voltage use of a motor and VFD.

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

 

[D.Stan]

Ok So the power to the motor is just like when ran at the factory. Wired straight into the power source.
The motor runs at free spin speed usually 1760RPM or 3560RPM.
The VFD to the Dyno is set to slightly slower RPM than the Test Motor.
This is where the Test Motor Speeds up the Dyno while the Dyno is trying to slow down the Test Motor and this creates the fightback force load (Brake)....

The slower you set the VFD RPMs on the Dyno the more of a Brake Load it puts on the Test Motor until the Test Motor stalls if lowered to much...

Please let me know if this is correct.

By the way you guys rock! Thanks for the help and making things clear. I got word back from Baldor and I don't believe the motor can be wired to 230V. I have uploaded the specs they sent me here if you would like to look them over.

http://files.engineering.com/getfil...0c4-39bb96d2fd6d&file=Motor_Specs_6843214.txt

 

[LionelHutz]

The VFD goes on the load motor or dyno and either dumps the absorbed energy back into the grid or into a heater.

Using a VFD and a constant output voltage above 60Hz, I couldn't get a 10hp, 1760rpm motor to run at 3000rpm without a shaft load. So, I wouldn't expect a general purpose motor to work acceptably as a 20hp load at 3600rpm. In theory it works, but not necessarily in practice.

Follow what I posted before. For example, if you use this motor and test at 1200rpm then you can only apply 13hp of load. So, you need to define what HP range you want to test for each synchronous rpm.

 

[itsmoked]

A regenerative VFD is not a common VFD it's 'special'. Rare, but certainly available. You just don't want to run out and buy a VFD if that's the way you want to go with your dyno. It is the best way to go if you plan to run long load tests or test frequently. You'd want a regenerative if your tests are over, say, 5 minutes on up to hours. Or, if you will be running a LOT of tests.

The regenerative VFD puts the energy back into your building supply, as waross said, to be reused (up to an extent) by your ongoing test.

A standard half-that-cost VFD cannot do this but it can provide the same exact testing only the energy used in the test must entirely be paid for by you and every watt of it will be deposited in your work-space via a large "braking resistor" as Lionel mentions. This means you will roast the place if you try to do long or frequent tests.

Recapping.
On the one hand:
The regenerative VFD costs about twice as much
Energy costs will be minimized
You can do frequent or long tests

On the other,
The VFD costs half as much
You will also have to purchase a braking resistor and a fan to help it
And you cannot do frequent or long tests unless you go to extraordinary efforts to get the heat out of the workspace and you don't mind large power bills.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[davidbeach]

Regenerative VFD is also known as a four quadrant VFD.

 

[iceworm]

Hummm -
At 20Hp, .9 eff, $0.10/kwh >> $1.70/hour

4Q 20hp VFD >> $6,000 I only looked up one, an ABB.

That's a lot of test hours

Harmless flakes working together can unleash an avalanche of destruction

 

[iceworm]

Lionel (and others)
I see the connection\physics for a 4Q vfd dumping the energy back into the grid. I'm not seeing on how one would dump the energy back into a heater.

Are you thinking a braking resistor that is part of the VFD?

Harmless flakes working together can unleash an avalanche of destruction

 

[cswilson]

david:

I have a lot more experience with servo drives than VFDs, but I believe the terminology distinctions are the same for both. A 4-quadrant drive can apply torque in the opposite direction from the velocity, turning the motor into a generator, with the generated energy charging up the DC bus capacitors.

But in the common terminology, a regenerative drive can take this energy and invert it back to the AC lines, dumping energy into the lines. Many (most!) 4-quadrant drives do not have this capability, as it requires a second power stage almost as expensive as the one driving the motor.

iceworm:

If a 4-quadrant drive cannot regenerate to the line, it often has a "shunt" resistor between the DC bus and neutral that can be turned on when the bus voltage exceeds a certain threshold. Many drives have a small shunt resistor internal that can handle occasional power dumps, but if it will be used often (or continuously) a large external resistor is required.

Curt Wilson
Omron Delta Tau

 

[itsmoked]

iceworm!! You couldn't have come up with a more expensive one..

I found a 20HP 460V one that's new for:
Delta Industrial Automation - VFD150C43A
AC Drive, 20hp, 460V, 3 Phase, High Efficiency and Performance, Built-In PLC
$1,452.00


Used on ebay they're around ~$700

That's a lot less testing hours.

BTW that's an awsome looking drive too. I'd like to mess with one.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[iceworm]

Curt -
Yes, that is about what I had in mind.
I'm somewhat familiar with regen drives - pretty good sized ones anyway. And yes, the front end looks just like the inverter end - except the frequency is fixed.

Not so familiar with braking resistors. What I envision is an inverter section that can be gated to send power back to the DC bus. Then a GTO type device that monitors the DC bus voltage, and pulls power from the DC bus and sends it to the braking resistor.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[davidbeach]

Thanks Curt, learned something new.

 

[iceworm]

Keith -
I don't doubt I picked a poor example. I've never fooled with a regen drive smaller than 1000hp. And none of them were set up to use the regen feature. Makes one wonder why the regen feature was specified. Definitely leaves me short of experience/knowledge in this area. I'm learning here.

I am much more interested in an SEIG running wild on frequency, caps for excitation, dumping to a resistive load bank. But that is just because I'm still fooling with the idea of a one-lung Listeroid for a remote access cabin.

However, at $700 for a 20hp regen VFD, that looks a lot better for the OP's project.

ice


Harmless flakes working together can unleash an avalanche of destruction