Harmonics Explained

Normal and Distorted Sine Wave Graph

Harmonics refers to the amount of distortion that occurs to the voltage or current sine wave and is commonly referred to as electrical noise.  In the home, this can be caused by various sources such as UPS back-up power supplies, fluorescent light ballasts, fan speed controls, halogen lights, unfiltered dimmer switches and the A/C-D/C power supplies found in various electronic devices.

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Incoming power from the utility company can also contain harmonics.  This may or may not be caused directly by the utility company. Other customers served by the same substation may be introducing electrical noise into that section of the grid which serves your home.  This is more apt to occur if you live near a large industrial complex.

This distortion occurs when a higher electrical frequency resonates with the base frequency.  In the U.S. this base frequency is 60 Hz and in Europe it is 50 Hz.  Resonance, or electrical vibration, occurs at integer multiples of the base frequency.   Each of these integer multiples define a harmonic order of magnitude, more commonly referred to as simply harmonic order.

For example, if distortion occurs at 120 Hz in the US, or 100 Hz in Europe, it would be caused by a second order harmonic (2 x 60 Hz or 2 x 50 Hz).   Likewise in the U.S., 180 Hz is the third order, 300 Hz the fifth and so forth. Some sophisticated power quality analyzers can measure beyond the 60th order.

If distortion occured across all harmonic orders out to the 41st, graphically it would look like this:

Harmonic Order Spectrum

Home energy monitoring systems are not designed to measure this phenomenon due to the excessive cost it would place on the system.  However, communications between the components of a home energy monitoring system can can be affected by this electrical noise, especially if power line carrier technology is used.

Trouble Shooting Tips

If you are having difficulty with communications in your system, make a list of all the potential sources of electrical noise in your home.   This would include everything with an AC-DC power supply such as computers, printers, fax machines, televisions, etc.  Add any UPS battery back-ups, fluorescent and halogen light circuits, low voltage transformers for outdoor lighting, dimmers and fan motor controls.

Shut all of these devices off, preferably at the circuit breaker, or with a power strip to eliminate any lingering vampire loads.  Check the communications for your home energy monitor system.  If communications are working - good!  If not, the problem is not caused by electrical noise.  Consult your energy monitor trouble shooting guide further.

If home energy system communications are working, turn each listed item back on, one at a time.  Recheck communications each time you turn another device back on.   When communication become unstable or drops off you've found the culprit. Make a note of it, turn it back off, and continue checking the rest of the items on the list to be sure the problem is not emerging from multiple sources.

To correct the situation, simply install a noise filter to absorb the electrical distortion.   Plug-in noise filters simply plug into a nearby outlet and the noisy device is plugged into the filter.  Other hard-wired filters can be installed in the circuit breaker panel to clean up the affected circuit.   Either solution will isolate the noise from the rest of the wiring in the house.

Technical Explanation

Harmonic distortion contributes to a lower total power factor by producing distortion currents that circulate through portions of the electrical distribution system, similar to reactive power currents.   The portion of total power factor that is attributed solely to these currents is called distortion power factor.  The reactive power portion of total power factor is called displacement power factor.

If we apply the concept of the power triangle to show the relationship between real and reactive currents, the hypotenuse becomes the fundamental current as shown here in gray:

Displacement Power Factor Diagram

Extending this concept into three dimensions, distortion currents are projected on to the Z-axis giving us the power cube.  Using vectors within the power cube, the relationship between displacement power factor (C), distortion power factor (D) and total power factor (T) can be shown as follows:

PowerCube Diagram

Both reactive and distortion currents swirl around the grid between the source of generation, the source of harmonic resonance and the load.  Normally, they are quite small when compared to the amount of current drawn for real power.   As a result their effect on residential electric systems is relatively insignificant, most of the time.

However, if you are having trouble with power line carrier communications or your sensitive electronic equipment is acting up, these currents may be a contributing factor.   Try the trouble shooting strategy discussed above to isolate the culprit device and install a harmonic filter.   If that proves ineffective, you may want to consider having a professional perform a study on the electrical loads in your home using a power quality analyzer.  Start with a request to your local utility as many will provide an assessment of the problem at no charge.

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