Harmonic direction, inflow or outflow 1

[tem1234]

Here is the case,

I measure harmonic with a power analyser at some motors and looking for the direction of the harmonics.

When i look at motor without drive or capacitor, the harmonics are going inflows, i.e. in the same direction of the fundamental. It's ok since motor and capacitor will not create harmonics, they'll just filter a little bit of them.

When i look at motor with drive, the harmonic are going mostly outflow, the drive are injecting harmonic in the network.

BUT... for some drive, harmonic are going inflow! Sometime all the harmonic are inflow, and other time only a couple are inflow. There a lot of other drives which are injecting harmonic in the network near theses drives.

So is it normal? Can a drive filter harmonic like this? or it is more like a bug of the power analyser? There's a drive (little compare to the other) which have 50% of 5th harmonic going inflow.

If you have a good reference on this phenomenal it would be very appreciate.

If you are asking how i determine the direction of the harmonic, look at "case study 12" of the attachement.

thanks

 

[dpc]

I'm not sure there is much relevance in terms like "inflow" and "outflow" when looking at harmonics. Harmonic currents and voltages are ac phasors, so they might have a phase angle relative to something else.

Drives cause harmonic currents by drawing current in a non-linear way. The harmonic currents cause voltage harmonics on the system due to the voltage drop created by the harmonic currents.

But maybe I'm missing the point. Can you explain what you mean by "direction" of the harmonics?

Dave

 

[jghrist]

I don't believe that measurements of inflow vs outflow of harmonics are often accurate or useful. Often, the angle between the voltage and the current is close to 90°, which makes a small angle error critical in determining direction of flow. The voltage harmonics are often low, particularly if the nonlinear load is small and the source is stiff. The angle error when using CTs and VTs can be quite high. See thread238-213812.

When you think about what is causing the current and voltage harmonics, the concept of using the voltage-current angle to measure inflow/outflow may not make sense. For example, consider a switched mode power supply. The harmonic current is a result of the current only being conducted during a short part of the power cycle. The harmonic voltage resulting from each harmonic current is the current times the source impedance. If the source impedance is mostly inductive, the angle will be close to 90°. If there is any background voltage harmonic, that is, voltage distortion caused by some other source, the voltage angle will be completely unrelated to the measured switch mode source.

 

[tem1234]

Hi, thanks for your reply

dpc, when i talk about direction, i mean if the load is an harmonic source or an harmonic sink. Capacitors (specially filters) are an harmonic sink (inflow), drives are an harmonic source (outflow). But, as i said in the first post, i found drives which were harmonic sink!!!

Maybe these angle aren't accurate as you said jghrist. But when you do a harmonic flow analysis and you want to know how much harmonic current will be injected into utility network, it's useful to know the angle of the different harmonic source, because:

"Harmonic distortions with similar phase angle will superimpose, raising the harmonic level, while those with opposite phase angles will compensate each other, thereby lowering the harmonic level."

I don't know if with measurement take directly at the drives, this can be accurate?

 

[tem1234]

Maybe an example tells more.

The only thing i change from the 2 power flow is the angle of the 5th harmonic current of 1 drive. The 2 motor have the same FLA.

 

[jghrist]

I agree that the current angle is important when adding multiple sources of harmonic current. It is the relationship to the harmonic voltage that I have a problem with. I don't think the angle between the harmonic voltage and the harmonic current has any real importance.

See On the Assessment of Harmonic Pollution, by A.E. Emanuel, IEEE Transactions on Power Delivery, Vol. 10, No. 3, July 1995.
Abstract
This paper analyses the interactions between the incremental changes of current harmonic phasors injected by a power system NL (nonlinear load) and the resulting variations of harmonic voltages and powers. It proves that it is not always possible, following simple measurements of individual harmonic powers, to decide if a certain harmonic current is harmful or useful. It is suggested that the NL “distortion” be evaluated with the help of a quantity called non60 Hz (nonfundamental) apparent power.

 

[Senselessticker]

Hop in your boat... Find a good place to bounce waves off a flat surface. Make a couple runs back and forth, and, if you feel froggy, introduce a "variable" speed... take note of the direction (or change in direction) of some of reflected wave flows as the energy is transferred...

Or... simply spend WAY too much time wakeboarding and trying to get the maximum pop avialable with variable-speed-short-radius Mastercraft turns with years of driver/skier combined experience... (beware of of the monster waves headed "towards" you when they double up while you are trying to reach max speed).... yeee-ha

http://www!!!!

 

[tem1234]

By thinking about it a little more, i agree pretty much with you jghrist. But this isn't a simple subject.

thanks