Determining Eddy Current Coupling Losses

[Steventyj]

I am trying to determine how much power a pump is using. The pump is attached to a 15HP motor through an eddy current coupling. I can find out how much power the motor is using at any given moment as well as the shaft speed on the pump side of the ECC. Is there a way to determine how much power is being lost through the ECC. There are plans in place to replace the ECC with a VFD, but at the moment we need to know how much power the pump is using.

Thanks,

Steven

 

[gcaudill]

Steventhj,

Part of your original question was "how much power is being lost through the ECC". I took this to mean how efficient is the ECC. I still contend that the ECC is very efficient and that the electrical power that is put into the clutch is converted very efficiently to mechanical power used to transmit torque from the motor to the clutch output shaft.

I agree that a running motor with the ECC idle (no voltage) is inefficient (100% to be exact). What's the point of running a motor and doing no work?

Maybe I do not understand what you are trying to determine.

 

[Steventyj]

I am trying to find stuff on a pump curve. So I want to know the HP being used by the pump. If I had the pump connected to a motor, then I could just turn the motor on, take current and speed readings and calculate the power produced by the motor (taking into account motor eff) and all of that power would be transfered along the solid shaft to the pump. However because there is an ECC in the middle, I do not know how to figure out how much power is being transfered to the pump.

 

[gcaudill]

The ECC does not generate any torque, in only enables the transfer of torque.

To determine the power being consumed by the pump:
1.) Measure voltage(E) and current(I) of the motor.
2.) Based on the current(I), determine if the motor is 25%, 50%, 75%, etc. loaded. Use manufacturer's data to estimate a PF and %Eff based on the actual load current compared to full load current rating of the motor.
3.) Calculate motor HP (IxEx1.73x%EffxPF)/746.

The calculated HP is more or less the HP that is being input to the pump. Yes, there will be some extra HP that is measured due to bearing drag, belt losses, rotor windage. But if you calculate a load of 10HP, I would bet the farm that less than 5-10% is actually due to inefficiencies in the sytem. That means the actual load HP is 9-9.5HP.

I have confidence in this because I have implemented 15HP Dynamatic motors (Induction motor with ECC) personally. In these applications I monitor motor current, voltage, and clutch RPM to calculate motor HP, torque, and finally a web tension. The calculated value has good degree of acuracy.

If you give me your current and voltage measurements, the drive type and part number (Dynamatic, Torspec, etc.) and tell me how the drive is coupled to the pump I would be willing to calcualte for you what I believe the HP is being consumed by the pump.

 

[Steventyj]

Thank you to everyone who responded, especially gcaudill. I know what I need to now to work on the rest of the problem. It actually is a 15HP Dynamatic ECC/motor. I should have all the numbers formulas I need now.

 

[jbartos]

Suggestion: Visit

http://www.abb.ch/GLOBAL/SEAPR/SEAP...10DA35B37271C1256C860030142D/$file/MWA_CS.pdf

etc. for more info on ECC losses

 

[jbartos]

Small encore: Visit

http://udl.com/pdf/p65.pdf

http://udl.com/library/p65.html

http://www.electrolink.co.nz/CC256A...012C8A6/78376DC76A4A1BAACC256A1C0082CEC8!Open

etc. for more info

 

[gcaudill]

With the issue of mechanical power being consumed by the pump put to rest, let's revisit the issue of electrical efficiency.

As compared to a motor/drive combination, the Dynamatic is not as electrically efficient as some other options. You have two issues:
1.) Power required to operate the clutch (VxI).
2.) Inherent inefficiencies in the induction motor (PF and %Eff).

With a motor/drive combination the clutch is eliminated and the PF and %Eff condition can be mitigated.

Good luck Steventyj.

 

[CB2]

Steventyj,

We seem to have been caught up in how an ECC functions and not really solving the problem on what condition your pump is in. I will assume that you have a standard centrifugal pump, end suction or horizontal split case, and have a copy of the pump curve. If you don't have the pump curve, contact the manufacture with the serial # or model #. Note that you need the impeller trim (inches)to use the curve (all should be on the nameplate).

Note, if you have the pump curve that used the ECC speed range you are good to go. However, if you have a standard curve that is based on a standard motor speed (1750 or 1160 RPM typically), you must recalculate for the maximum output speed of the ECC. This will be 150 RPM (plus/minus 30 RPM)of the motor synchronus speed.

Run the following test. Install a suitable pressure guage on the discharge side of the pump, adjust the ECC to maximum speed, have your electrician ready to take an amperage reading. Momentarily shut the discharge valve, note the discharge pressure and amperage.

Take a pressure and amperage reading at maximum possible flow (ECC again at full speed)

On the pump curve locate the first duty point (0 flow/max pressure, this will be at (but most likely below) the shutoff point on your curve. From this new duty point you can draw a new curve parallel to the original curve. This gives you a rough estimate of your pump's best performance, it's probably not that good as you move to the right on the curve.

At the maximum flow duty, the amperage reading compared to the motor FLA gives you a indication of motor loading. The ECC at full speed should have about 4% losses, or slightly less. If you have the original duty points for the pump, this will be another indicator of the pump's condition.

A quick note on retrofitting the VFD, "out of the box" it will have the motor turn at motor nameplate speed (higher than the ECC)so watch the full speed amps for possible overload condition. If this happens, adjust the VFD software to limit the speed so you don't overload.

PS. Most of todays VFDs will give you very accurate load data from their controller screen. RPM, Amp, Kw, Torque.