Issue
Harmonic distortion values are observed on a power meter installed at a utility feed. Is there a method to determine whether these harmonics originate from the utility or from the facility side? In other words, can the meter indicate the source direction of the harmonic distortion?

Product Line
Power logic and Power Quality Meters

Environment
Harmonic Distortion

Cause
The meter does not directly indicate the direction or source of harmonic distortion (whether it originates from the utility or the facility).

Resolution

A practical way to determine whether a facility or the utility is imposing harmonics on the system, compare the percentage of each harmonic relative to the main (fundamental) voltage and current.

If the utility is the source of harmonics

The relative magnitude of the harmonic current will generally be less than or equal to the relative magnitude of the harmonic voltage.

Example:
If the 3rd voltage harmonic is 3.1% and the 3rd current harmonic is 2.8%, this suggests that the harmonic current is primarily caused by the harmonic voltage present on the utility’s line. This occurs because most loads have reactive (inductive) components, which increase impedance for higher frequencies, making the load behave like a low-pass filter. As a result, current harmonics tend to be smaller than voltage harmonics when expressed as percentages.

If the facility is the source of harmonics

The relative magnitude of the harmonic current will be greater than the relative magnitude of the harmonic voltage.

Example:
A current harmonic of 22% with a voltage harmonic of 3.9% strongly indicates that the facility’s load is generating harmonics. This is because the utility’s line impedance is typically much lower than the facility’s load impedance, especially for lower-order harmonics.

Important considerations

• Resonance effects:
  Resonance can occasionally amplify certain harmonics, which may distort conclusions about the source. Therefore, always analyze harmonics as a group, focusing on the lower-order odd harmonics (typically 3rd through 11th), where line impedance effects are less pronounced.

• Meter capability:
  Not all meters support individual harmonic measurements. Verify meter capabilities before performing this analysis.