Electrical Industry Canada Power Quality Issue - 5

Flickering is a voltage variation with a lighting load that causes the light output to visibly flicker. This can be caused by the input in function of
electro-domestic loads; however, it is mostly due to industrial loads (ex.: motor start up or speed variation)
Blackouts can last from a few microseconds to hours or even days. These total losses of current normally occur due to damaged equipment or
electrical lines.
Power Factor is the ratio between the apparent power (VA) and the real power (W). Energy suppliers deliver electricity with a sine voltage wave at
60 Hz. If the current and voltage waves are not aligned, the system's efficiency is diminished and the apparent power is greater than the real power.
In an inductive system, the voltage wave is ahead of the current wave. In a capacitive system, it is the current sine wave that is ahead of the voltage
sine wave. In order to compensate for the inductive effect of motors, correction is achieved using capacitors to align the two waveforms. There are
now two causes that contribute to the deterioration of the power factor: inductive loads, which influence the displacement power factor, and
non-linear loads when the current harmonics are not aligned with the voltage source. Utilities measure the total power factor and consider both of
these causes.
Knowing the cause for the deterioration of the power factor will help choose best way to correct it. In some cases, correcting harmonic problems
can rectify the power factor.
Power Factor Calculations: The power factor ratio measures the relative amounts of work-producing active power measured in kW versus the total
apparent power (kVA). Power factor is defined as the cosine (cos) in the following equations:
Power factor = COS
Power = Vrms Irms COS
PF = kW / kVA
Power factor is based on the 60 Hz fundamental frequency. Harmonic currents drawn by UPS's, E.V. chargers, adjustable speed drives, electronic
ballast and electronic office equipment are increasing in the modern facility. As a result, power factor must now be viewed in reference to harmonic
frequencies of the 60 Hz fundamental. Conventional power factor is now called displacement power factor to relate it to the displacement between
the system current and voltage waveforms.
Distortion power factor, on the other hand, takes into account the harmonic currents that do not contribute to the real work produced by the load.
Distortion power factor is defined as the ratio of the fundamental component of the line current to the total line current. The total power factor is a
combination of both displacement and distortion power factors. This relationship is represented as a three-dimensional vector with the kVA value
illustrated as the diagonal of a box. Total power factor is always equal to or less than conventional displacement power factor.
Power Factor Measurements
A facility can sometimes determine its power factor by examining its power bill or asking for the information from its Utility. Power factor may be
measured or calculated from other measurements such as kW, kVA, or kVAR measurements.
Measurement techniques that consider only the 60 Hz fundamental frequency determine the displacement power factor. This is simply the phase
shift between the current and voltage waveforms. Measurement techniques that include current and voltage root-mean-square (RMS) values take
into account the effects of harmonic currents to reflect both displacement and distortion power factors. Many solid-state power monitors are
available to sample voltage and current waveforms and calculate the electrical parameters. These devices usually indicate both displacement and
total power factor.
You can find more information on Power Quality from Hammond Power Solutions HERE
ELECTRICAL INDUSTRY CANADA

VOLUME 1, ISSUE 2

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Electrical Industry Canada Power Quality Issue

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