I don't know much of hormonics in motor testing. How important is this? Should i start thinking about it? How do i measure it? Please advise.

 

I don't know much of hormonics in motor testing. How important is this? Should i start thinking about it? How do i measure it? Please advise.

I'm not familiar with "harmonics" when it comes to motor testing. Are you perhaps referring to resonance?

 

I was seeing some of the online videos in which they were referring to 3rd harmonics etc. I am not sure what it means?

 

https://www.google.com/url?sa=t&rct...thefacts.pdf&usg=AOvVaw2_fB-qiV4rMKUge0PIHKcx

https://www.google.com/url?sa=t&rct...ts-part1.pdf&usg=AOvVaw0KXIexpsZzrUylLbnRyV5y

Regards, Dana.

 

A "harmonic" is just an integral multiple of a "fundamental" frequency. Frequency can relate to pendulums, motors, and electronic circuits. For a motor it might be vibrations associated with the speed of revolution. As an example suppose that the shaft speed is 600 RPM. Further suppose that the 3rd harmonic of 600 RPM corresponds to a mechanical resonance of the motor/shaft/load combination. Let us further suppose that the vibrations are so severe that the system will destroy itself without some corrective action. To counteract this situation, you might try to determine if changing the speed up or down by a few RPM will reduce the tendency toward oscillation. Is that what you had in mind?

 

Because motors cannot be perfectly wound they can generate harmonics in the motor current.
This is unrelated to any mechanical resonance.

Harmonics in the voltage from external sources feeding the motor can cause heating in the motor and lower motor efficiency.

 

Because motors cannot be perfectly wound they can generate harmonics in the motor current.
This is unrelated to any mechanical resonance.

Harmonics in the voltage from external sources feeding the motor can cause heating in the motor and lower motor efficiency.

I guess it would have helped if the original question had been more explicit.
Mechanical resonance is an integral part of life with stepper motors.

 

I think he wants to know what are harmonics for and what are they in general.

 

can i know the project first? what do you want to do with a motor to start thinking about harmonics. the question seems to vague to me.

 

I am driving the motor using the trapezoidal switching. To improve the torque performance i wanted to know if harmonics play any role. If they do then how to reduce them?

 

I was seeing some of the online videos in which they were referring to 3rd harmonics etc. I am not sure what it means?

In power systems that feed nonlinear loads, which includes a lot of electronics, the current throughout the cycle is not proportional to the voltages. The result is that there is distortion in the waveform in the power system, this distortion is in the form of harmonics, at frequency multiples of the basic line frequency. At higher power levels this can lead to reduced efficiency, meaning more heat, which is usually a problem.
The whole explanation is much longer and fairly tedious, this is the very short explanation.

 

I am driving the motor using the trapezoidal switching. To improve the torque performance i wanted to know if harmonics play any role. If they do then how to reduce them?

Generally speaking a trapezoidal waveform will have less harmonic content than a square wave. You can show this by computing the Fourier Series for both.

 

Generally speaking a trapezoidal waveform will have less harmonic content than a square wave. You can show this by computing the Fourier Series for both.

Can i measure the harmonics and fourier series using oscilloscope at run time while motor is rotating.

 

I don't know much of hormonics in motor testing. How important is this? Should i start thinking about it? How do i measure it? Please advise.

Depends on the magnitude. Each utility has it’s own specs as to what you can put back onto the line. Within a local supply, it will depend on the needs of the other devices on that supply. Arresting the source is the most practical and is commonly done with inductive filtering. All VFD suppliers that I am familiar with, spec an appropriate filter. Tektronics supplies a scope that provides harmonic info.

 

Can i measure the harmonics and fourier series using oscilloscope at run time while motor is rotating.

A DSO (Digital Sampling Oscilloscope) should have more than sufficient capability to do a harmonic analysis.

 

You should certainly be able to see the harmonics, measuring them accurately will depend on both the scope and your skills. I recommend caution with the scope connections because connecting a scope to three-phase power is not a minor task. There is a very real hazard with the voltages involved, both for the user and for the equipment. So please be sure to use the correct equipment and also follow the right safety procedures.