How to measure induction motor efficiency?
How to measure induction motor efficiency?
(OP)
Dear All,
Recently, I try to collect a set of data from PWM controller that control the speed of a three-phase induction motor. The problem is how to measure the efficiency of the motor. It's related with the electrical power input and mechanical power output. That's no clear description on how to measure.
I'm still not clear with this. Wish anyone here with experience can tell me in more detail about any equipment or alternative I can get the measurement. Thanks a lot!!
Recently, I try to collect a set of data from PWM controller that control the speed of a three-phase induction motor. The problem is how to measure the efficiency of the motor. It's related with the electrical power input and mechanical power output. That's no clear description on how to measure.
I'm still not clear with this. Wish anyone here with experience can tell me in more detail about any equipment or alternative I can get the measurement. Thanks a lot!!





RE: How to measure induction motor efficiency?
RE: How to measure induction motor efficiency?
unique and accurate proprietary method of efficiency calculation tested to
within 2% of torque cell measured efficiency at Advanced Energy Labs in
North Carolina. Utilizing nameplate information we determine the slope of
the relationship between the input power to, and output power from the
motor. From there we identify the input running characteristics at the time
of the test and calculate the output values. Once the output and input
values are known, the efficiency can be determined. PdMA motor testers Emax or MCEmax can determine the efficiency of any motor.
Visit www.pdma.com
RE: How to measure induction motor efficiency?
http://www.reliance.com/pdf/brochures/raps_913.pdf
for a Motor Efficiency Vizard
RE: How to measure induction motor efficiency?
Thread237-67726
RE: How to measure induction motor efficiency?
RE: How to measure induction motor efficiency?
"12.46 VARIATION FROM RATED SPEED
The variation from the nameplate or published data speed of alternating-current, single-phase and
polyphase, medium motors shall not exceed 20 percent of the difference between synchronous speed and
rated speed when measured at rated voltage, frequency, and load and with an ambient temperature of
25°C."
So using a 20% accurate parameter (slip), we expect to get a 2% accurate measurement? Hmmm. Makes you wonder about all those other claims those guys spew.
RE: How to measure induction motor efficiency?
http://www.reliance.com/pdf/brochures/raps_913.pdf
a Motor Efficiency Vizard?
Have you checked a source code?
RE: How to measure induction motor efficiency?
uets - I didn't mean to be disrespectful. If you are associated with a product you should identify that. If you can show where I am mistaken I would be interested to hear.
RE: How to measure induction motor efficiency?
///Please, notice that the original posting does not address the slip variable. The slip was introduced in:\\\
electricpete (Electrical) Sep 13, 2003
Estimating output power from speed using linear relationship with slip is a simple and crude method which can be done by anyone with a stobe or other means to determine speed.
///I am sorry, I do not mean to be disrespectful. However, to try to reduce the original posting topic that appears to have an answer and solution to a specific variable, i.e. slip, seems to be rather limited or misleading.\\\
RE: How to measure induction motor efficiency?
Your link:
"All electrical measurements can be made at the motor
disconnect point, without the need to open the motor conduit box. Lab tested accuracy to
within 1%....
By measuring the input power, voltage, current, speed, temperature, frequency, and
resistance at two motor load points, the Motor Efficiency Wizard provides accurate
efficiency data.."
I don't see any way that this device can estimate output power except by using speed (slip), with corrections for voltage etc. If there is a more detailed description of this or the pdma box which explains how it can be done, I would be interested to see it.
Out of curiosity, if they don't use slip to estimate output power, then why do they bother to determine speed?
RE: How to measure induction motor efficiency?
Output Power HP, Input Current, Power factor, Efficiency, Speed RPM, Output Torque.
Verifying the first line speed, hp and torque:
5.5HP x 746 Watt/HP~1199RPM x 0.105 (rad/sec)/RPM x 24.2 ft-lb x 1.356 x N-m/ft-lb
4103 Watts ~ 4131.3 N-m/sec
which is about right with .007%=100%x(4131.3-4103)/4131.3 error
This is where the calculated speed is also needed.
The nameplate speed at rated load is 1185RPM
and the calculated speed at 5.5HP is 1199RPM. This is off by 14RPM, and at about rated load, 77.5HP, the calculated speed is 1185.5RPM. This is very accurate result with respect to 1185RPM motor nameplate speed. There is no slip mentioned, and expressed explicitly. Also, I do not see any acknowledgement to EPRI there.
Generally, the efficiency EFF may also be calculated over electrical losses in the motor since:
EFF=Pout,watt/Pin,watt=1-Ploss,watt/Pin,watt
If Ploss,watt is calculated over the motor parameters, not necessarily over the motor speed, then the EFF is known.
RE: How to measure induction motor efficiency?
UETS - If the claims are true, I believe this would be a truly relevant device for the purposes of measuring efficiency. As we know, even the best dyno labs have been shown to differ up to 1 or 2 efficiency points when measuring efficiency during round robin tests. But it is logical to be skeptcial about this method. Why is it not addressed in IEEE 112 standard methods for calculating efficiency? Does the pdma device require measuring electrical parameters at two different current levels as well as shutdown (like the Reliance?)
RE: How to measure induction motor efficiency?
Assume for simplicity balanced system which can be analysed from single-phase equivalent circuit, we have unknown parameters R1,R2,L1,L2,Lmagnetizing,Rcore (Rmag represents core loss).
We measure R1 directly, so it is a known quantity.
Now we have two sets of measurements of V, I, s under two different loading conditions.
Each set of measurements gives one complex (phasor) equation, equivalent to two scalar equations.
Two complex/phasor equations are equivalent to four scalar equations... almost enough to analyse our 5 remaining unknowns (R2,L1,L2,Lmag,Rcore). Perhaps there is an assumption L1=L2 or something similar to complete the problem? Any comments on what assumption might give the last required scalar equation?
Unbalance introduces one additional complexity which can be handled. .... we would assume calculate the torque created from the positive sequence components and subtract out reverse torque created by any negative sequence components.
RE: How to measure induction motor efficiency?
Stray losses it seems are the most difficult to deal with. You can certainly establish total losses including stray losses with a dyno test. But other IEEE 112 methods allow stray losses to be estimated.
Let us focus on friction and windage: from the motor electrical and speed standpoint, there is NO way to distinguish friction and windage from actual load. If I put in a lousy grease which increase friction, the response will be identical to an increase in load.
The simple un-deniable fact is that the pdma and Reliance box cannot distinguish true mechanical load from motor friction and windage. They must rely in some manner on the nameplate data, which may be an inaccurate condition of truth at the time of motor manufacture, and even more so at some point after years of service. After all, if we believe the motor nameplate data then why do we need the testing?
RE: How to measure induction motor efficiency?
What is the size of the motor? Smaller motors and drives are more frequently tested with dyno.
Can the motor/drive be pulled out or do you have to do it in place?
There was a post very recently that discussed some kind of torque measuring devices suitable for in-place use.
RE: How to measure induction motor efficiency?
That appears to gives you a means to measure the output (torque) of the motor, which is the difficult quantity to get at.
The input power should be fairly easy to measure using suitable equipment. If you meausre input power to the drive you capture losses in the drive, cables, motor.
RE: How to measure induction motor efficiency?
RE: How to measure induction motor efficiency?