Determining Eddy Current Coupling Losses
Determining Eddy Current Coupling Losses
(OP)
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
Thanks,
Steven





RE: Determining Eddy Current Coupling Losses
RE: Determining Eddy Current Coupling Losses
However, using a strobe to determine actual speed will introduce appreciable error. Therefore, use a strobe synch-ed to line frequency and "count" slip rotation for a reasonable time period, i.e., 1 minute, with the approprate correction for the number of pole-pairs of the motor. Also note, motor output will include ECC loss!
Before hi-tech was discovered it was done with a fluorescent lamp, and the slip rotation was divided by the number of poles!
RE: Determining Eddy Current Coupling Losses
RE: Determining Eddy Current Coupling Losses
I recall Eaton supplying loss data based on its operating temperature-rise above ambient.
RE: Determining Eddy Current Coupling Losses
IFF the motor is running less than 75% loaded (compared to FLT or HP) the losses in the clutch will be negligble compared to the costs incurred by 1.) reduced induction motor efficiency 2.) reduced induction motor power factor.
You may be looking at the problem from the wrong angle.
RE: Determining Eddy Current Coupling Losses
IFF the motor is running less than 75% loaded (compared to FLT or HP) the losses in the clutch will be negligble compared to the costs incurred by 1.) reduced induction motor efficiency 2.) reduced induction motor power factor.
In any case, I'm certain the losses in the clutch are very small.
You may be looking at the problem from the wrong angle if you are tyring to determine a payback for switching to a VSD.
RE: Determining Eddy Current Coupling Losses
RE: Determining Eddy Current Coupling Losses
You could measure the clutch supply DC voltage and DC current to calculate the power being consumed by the clutch, this is the input power. The output power = 12HP.
If the DC drive/controller has considerable ripple the clutch efficiency could be reduced. But still, the clutch efficiency should be relatively high compared to that of the motor.
For a 15HP AC induction motor the with an attached 12HP load the motor is only 80% loaded. The Efficiency is probably around 90% and the PF is probably around 0.80. In this condition the motor is pulling more reactive power from the line than it would at rated load (15HP).
Is this a Dynamatic drive by chance?
RE: Determining Eddy Current Coupling Losses
ECC's are notorious power wasters. If you run this pump more than a couple hours a day, then almost guarantee you will save money by buying an inverter and new motor. MAKE SURE THAT THE MOTOR YOU USE WITH THE INVERTER IS INVERTER-RATED.
RE: Determining Eddy Current Coupling Losses
We are planning on replacing the ECC but this pump fails often and it may not be correct for the application so before we size a new VFD and motor we plan to find the correct pump for the application.
Thanks
RE: Determining Eddy Current Coupling Losses
Eaton Corp. sold the Dynamatic division off about 5 years ago, it still exists in Wisconsin I think.
RE: Determining Eddy Current Coupling Losses
Dynamatic is still in business, but is no longer owned by Eaton as CB2 indicated. I forget who the new owner is, I think Dynamatic is now owned by the same people that own Torspec.
RE: Determining Eddy Current Coupling Losses
However...
If your pump is not working right, it seems to me that this excersise is pointless. What you really need to do is re-engineer your pump requirement from the bottom up. Start with head, flow and pressure, then pick a pump curve that works for you, then determine maximum BHP, then select a motor based on that, then buy a VFD for that motor. Who cares what the old system did if it was failing?
Quando Omni Flunkus Moritati
RE: Determining Eddy Current Coupling Losses
Is it correct to say that an ECC can change the RPM, while keeping the power transfered constant by also changing the torque?
- Thanks
Steven
RE: Determining Eddy Current Coupling Losses
The ECC controls the torque transferred from the motor to the clutch output shaft (load). You should refer to the manufacture's torque-speed curve for the clutch output torque at varying voltages at different slip RPMs (% excitation vs. slip RPM ==> torque output). Unless you are using a speed controller on the clutch the load actually determines the speed at the given output HP.
RPM = (HP x 5252)/(torque)
If you know motor kW (V and I, hence HP) and RPM you can calculate motor torque. If you know the clutch output shaft RPM you can calculate the load HP attached to the clutch shaft.
I stick by my original claim that the ECC is more efficient than the motor by many times over due to the Eff. and PF ratings. If you know the motor HP you essentially know the load HP.
In my opinion the only negatives of the motor/ECC combination are:
1.) Poor PF and Eff. at light motor loads.
2.) Speed (pump volume/velocity/pressure) control without the correct clutch controller. I do not know what kind of pump or process you have.
RE: Determining Eddy Current Coupling Losses
In the last two paragraphs of your post I feel you are ignoring the efficiency of the ECC. The ECC has a linear Eff. curve, 50% speed = 50% Eff. The motor HP would be the sum of the pump BHP plus the ECC losses at a given speed.
RE: Determining Eddy Current Coupling Losses
Are you suggesting that if I have a motor that turns at 1800 RPM and I want to turn my load at 900RPM then the motor is going to have to provide twice the needed horsepower of the load because half of that will be lost in the ECC?
RE: Determining Eddy Current Coupling Losses
The torque output of the ECC is proportional to the voltage and current applied to the coil terminals. The coil does not operate at full voltage continuously. The voltage is adjusted to vary the torque that is transmitted from the motor shaft to the output shaft of the clutch. The current will vary up and down with the voltage. Zero voltage = zero current = zero clutch output torque.
If the motor is running at full RPM and the clutch (ECC) voltage is zero, the current will be zero and the clutch speed will be zero. Where is the loss? It is in the AC motor running at less than rated load. Do you follow me CB2?
RE: Determining Eddy Current Coupling Losses
If you look at that example then the loss is 100%. The efficiency of the system is power in/power out right? We are looking at the entire system from motor to ECC to pump, so if the 100 HP motor is using 10 HP of electrical power to stay at 1800 RPM without a load, and the pump is not using any power to move liquid than your power in is 10 and out is 0. I am not concerned with how much power the ECC is using to control the speed of the output shaft, just in the power transfered to the pump.
RE: Determining Eddy Current Coupling Losses
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.
RE: Determining Eddy Current Coupling Losses
RE: Determining Eddy Current Coupling Losses
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.
RE: Determining Eddy Current Coupling Losses
RE: Determining Eddy Current Coupling Losses
http://www.abb.ch/GLOBAL/SEAPR/SEAPR035.NSF/viewunid/DB7610DA35B37271C1256C860030142D/%24file/MWA_CS.pdf
etc. for more info on ECC losses
RE: Determining Eddy Current Coupling Losses
http://udl.com/pdf/p65.pdf
http://udl.com/library/p65.html
http://www.electrolink.co.nz/CC256A1C0073A9F5/DCB530D95C0C8EBFCC2569280012C8A6/78376DC76A4A1BAACC256A1C0082CEC8!Open
etc. for more info
RE: Determining Eddy Current Coupling Losses
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.
RE: Determining Eddy Current Coupling Losses
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.