Harmonics Testing

With today’s rapidly changing technologies and electrical environments, many "side effects" are created.  Harmonics are one of the most potentially troublesome and unpredictable problems affecting the smooth operation of today’s modern facilities.  Harmonics is a term used to describe distortion in an electrical distribution system and can be applied to both voltage and current.

How to Find Out if Your Business is Affected by Harmonics:

There are a number of steps that can be taken to confirm the presence of harmonics in the electrical system:

  1. As a first step, tour the facility to determine the types of equipment that are connected to low voltage systems.  If this inventory includes adjustable speed drives for motors, solid state lighting and any equipment using switching power supplies such as computers, fax machines, copy machines and most other modern office equipment, or electronic ballasts, harmonics are likely present.

  2. Locate the low-voltage power transformers that feed these non-linear loads and check for excessive heating. Remember that the harmonics will increase the transformers’ losses and cause them to overheat at loads below nameplate ratings.

  3. Third order, zero sequence harmonic currents may also result in the overloading of the transformers' neutral terminals.  Neutral currents may exceed phase currents under these harmonic conditions which will also create excessive heat.

  4. Using a "True-RMS" meter, measure the phase and neutral currents and phase to neutral voltage at the low voltage power transformers’ secondary terminal.  Again, under zero sequence harmonic conditions, the neutral current will exceed the vector addition of the three phase currents.

  5. Repeat step 3 with an "Average Responding" meter. Since this type of meter is only accurate under pure sine wave conditions, any distortion of the wave form will cause the average responding meter to read lower.  By dividing the result of the "Average Reading" to the "True-RMS" reading, one may obtain an "A/R" Ratio.  A Ratio of 1 would indicate little or no harmonics while a 0.5 ratio would indicate a significant amount of harmonics.

Measuring Harmonics

In order to develop an engineered solution to this problem, it is necessary to measure the harmonics with a Harmonics Analyzer. This is the unit we at NRG, Inc. utilize in our Harmonics Testing Service.  This instrument provides detailed information on the spectrum of harmonic currents and voltages including:

  • Total and individual harmonic distortion values.

  • Fundamental and individual harmonic RMS voltage and currents.

  • Power flow and phase angle for each harmonic.

This type of testing should be performed by an experienced person familiar with the use of the type of equipment.  The results of the testing is what is used to determine the best possible solution to the problem.  The accuracy of the test results are critical to the success of the project.

As with any mitigation technique, a detailed system study must be undertaken in order to predict a result.  Moreover, the misapplication of any device intended to correct any electrical problem can have serious safety implications.  There is, in fact, no "off-the-shelf" solution to harmonic problems.

Northeast Resource Group, Inc. is an experienced team of power quality experts.  Advanced software as well as advanced testing equipment provided by NRG Inc. is used to analyze the power system at all frequencies to optimize the application of various types of harmonic mitigation devices.

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