Technical FAQs

# Is there any way to determine the direction of the source of the harmonic distortion using a power meter?

Issue
The customer sees some value of harmonic on a power meter which is installed at a utility feed. Is there any way determine if this harmonic comes from the utility or it comes from the facility side? In other words, is there any way to determine the direction of the source of the harmonic distortion with the meter?

Product Line
ION8800, ION8650, ION7650, ION7550, CM4000T, PM8000, PM870, PM850, PM820, PM810, PM800, ION7350, ION7330, PM750, PM710, PM5500, PM5300, PM5100, PM3000

Environment
Harmonic Distortion

Cause
The "direction" of the source of the harmonic distortion is not given directly by the meter itself.

Resolution

A useful means of detecting whether a customer is imposing harmonics on the system is to look at the relative magnitude of the harmonics, as a percentage of the fundamental voltage and current. If the customer is experiencing harmonics imposed upon him by the utility, then the relative magnitudes of the harmonic current will be less than or equal to the relative magnitude of the harmonic voltage.

For example, if the third voltage harmonic was 3.1% and the third current harmonic was 2.8%, then we would expect that the harmonic current was the result of the harmonic voltage on the utility's line. Since the customer's load is likely to have some reactive (inductive) component which will cause the impedance to be higher for harmonics (making his load act somewhat like a low pass filter), we would expect the current harmonic to be smaller than the voltage harmonic when expressed in percent.

If, however, the reverse is true - the relative magnitude of the current harmonic is greater than that of the voltage harmonic - then the customer's load is probably imposing the harmonic on the utility. This is because the line impedance is likely to be much less than the load impedance, although this effect diminishes at high frequencies as discussed above. Especially at the lower harmonics, this is expected to be true, and it is quite possible, for example, to see a current harmonic of 22% with a voltage harmonic of 3.9%.

Because of resonance, it is possible for occasional harmonics to have exaggerated effects, either reinforcing challenging the conclusion you would draw about who is imposing harmonics on whom. Therefore, you should always look at the harmonics as a group, with special emphasis placed on the first few harmonics (typically the odd ones, say 3rd through 11th) where line impedance effects are likely less exaggerated.

Note: Not all meters are able to provide individual harmonic information.