The quality issues of power supply will result in difficulty to the electrical consumers. Several electrical based standards are employed to maintain the supply voltage within the standards based tolerable values. This article deals with the most common power quality problems, their causes, and consequences.
VOLTAGE IMBALANCE
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The differences in the magnitudes of R, Y, and B phases of the three phase supply is called voltage unbalance. The voltages of the three phases should be nearly, if not exactly, equal in voltage to each other. If the voltages are too far out of balance, the loads like motors and compressors supplied from these imbalanced three phase voltage will start overheating. This, in turn, will reduce the life of the equipment. The most affected loads of voltage imbalance are three phase induction machines.
VOLTAGE SAG
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| Fig 2. Voltage sag |
The reduction in the RMS voltage for a duration of a one-half cycle to one minute is called voltage sag. The sag would reduce the RMS voltage between 10%-90% of the nominal voltage. Faults on the power transmission and distribution networks, starting of an electrical motor and furnace fans, sudden load changes, etc. can result in voltage sags. Voltage sag could result in malfunction of microprocessor based systems.
VOLTAGE SWELL
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| Fig 3. Voltage swell |
Voltage swell is the momentary rise in RMS voltage for a duration of more than one cycle. It is basically the opposite of voltage sag. It happens due to the start/stop of heavy loads, use of unregulated transformers etc. It results in data losses and flickering of lighting devices.
HARMONIC DISTORTIONS
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| Fig 4. Harmonic distortion |
The connection of non-linear loads in power system tends to draw non-sinusoidal current from the supply voltage. Thus the overall current in the circuit may have distortion and deviation from its sinusoidal waveform. These distortions also depend upon the load connected to the circuit. These distortions in the current waveform are termed as current harmonics. By proper mathematical analysis, these complex waveforms are seen with integral multiples of the fundamental frequency of the power system. Current harmonics cause voltage harmonics in power systems. Harmonic distortions reduce the efficiency and power factor of a power system. Also, it will result in equipment failure.
NOISE
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| Fig 5. Noise |
Undesirable electric signals that can distort the original signal are called noise signals. Noise causes the superimposition of high frequency signals on the normal supply voltage waveform. Improper grounding, use of electronic equipment and arc furnaces, etc cause the electrical noise. Noise signals in the systems cause data losses and data processing errors.
VOLTAGE SPIKE
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| Fig 6. Voltage spikes |
Voltage spikes are sudden and short duration electrical transients in the supply voltage. It is basically the very fast variation of voltage magnitude for a minute fraction of seconds. Sudden stopping of heavy loads, lightning, etc causes voltage spikes. Data processing errors, malfunction of electronic equipment are sometimes as a result of voltage spikes.
