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Power Quality & Energy Measurement

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Power Quality & Energy Measurement

The measuring and monitoring of electric power have become more critical because of down time associated with equipment breakdown and material failures.

Until fairly recently, power quality referred to the ability of the electric utilities to supply electric power without interruption. Today, the phrase encompasses any deviation from a perfect sinusoidal waveform. Power quality now relates to short-term transients as well as continuous state distortions. Power system harmonics are a continuous state problem with dangerous results. Harmonics can be present in current, voltage, or both. It is estimated that as many as 60% of all electrical devices operate with non-linear current.

Harmonic distortion can cause serious problems for the users of electric power, from inadvertent tripping of circuit breakers to dangerous overheating of transformers and neutral conductors, as well as heating in motors and capacitor failure.

Harmonics can cause problems that are easy to recognize but tough to diagnose. It is becoming increasingly important to understand the fundamentals of harmonics, and to be able to recognize and monitor the presence of damaging harmonics. Harmonics within an electrical system vary greatly within different parts of the same distribution system and are not limited simply to the supply of the harmonic producing device.

Loads which produce harmonic currents include:

  • Electronic lighting ballasts
  • Adjustable speed drives
  • Electric arc furnaces
  • Personal computers
  • Electric welding equipment

  • Solid state rectifiers
  • Industrial process controls
  • UPS systems
  • Saturated transformers
  • Solid state elevator controls
    Medical equipment

This is by no means an exhaustive list of equipment which generates harmonics.
Due to the ever increasing use of electronics, the percentage of equipment which generates harmonic current has increased significantly. Harmonics in the electric power system combine with the fundamental frequency to create distortion. The level of distortion is directly related to the frequencies and amplitudes of the harmonic current. The contribution of all harmonic frequency currents to the fundamental current is known as “Total Harmonic Distortion” or THD. This THD value is expressed as a percentage of the fundamental current. THD values of over 10% are reason for concern.

Until recently, most loads were “linear”. With expanding markets of computers, uninterruptable power supplies, and variable speed motor drives, resulting nonlinear waveforms are drastically different. When distortion occurs, the relationship between average readings and True RMS values changes drastically.
Only a meter which measures True RMS values gives accurate readings for a non-sinusoidal waveform.

Libros Engineering have high quality power quality measurement meters that are able to accurately measure existing harmonics and Total Harmonic Distortion. Equipped with accurate measurements corrective measures can be employed to reduce the negative effects of Harmonics in an electrical installation.

Libros Engineering can also provide accurate load profiles for accurate sizing of solar PV plants or other renewable energy sources of power.

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