Often familiar phenomena in the electrical power system are harmonics. Non-linear loads are the major contributors to this power system problem. Rectifiers, motors, non-ideal transformers, computers printers etc. are the examples of the non-linear loads. Systems, when connected with loads like these, can have both voltage and current harmonics.
SINUSOIDAL WAVE CONCEPT
A pure sinusoidal waveform is an ideal concept. Due to the various AC generator characteristics, the voltage generated tends to have distortions in its sinusoidal waveform. Such distortions may contain harmonics. Theses harmonics are integral multiples of the fundamental frequency (say 3, 5, 7,9 etc).
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| Fig 1. Pure sinusoidal wave |
CURRENT HARMONICS
Consider a circuit with a rectifier connected between the AC supply voltage and a load. As the rectifier is a non-linear load, the current drawn by it from the supply may note be purely sinusoidal. So 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.
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| Fig 2. Current waveforms with fundamental and harmonic frequencies. |
VOLTAGE HARMONICS
The current harmonics cause voltage harmonics. The harmonic currents also depend upon the impedance of the power supply source while distorting the voltage waveform. Large voltage distortions are likely to occur when there is a large amount of source impedance. Otherwise, current harmonics causes smaller voltage distortions.
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| Fig 3. Voltage harmonics |
EFFECTS OF HARMONICS IN POWER SYSTEM
- It can lead to losses.
- Increases the heating of the conductors, cables, transformers etc.
- Reduces the efficiency of the system.
- Lowering the power factor of the system
- Causes errors in the reading of metering instruments.
- Can lead to electrical equipment failure.
How can we minimize the harmonics in electrical systems?
Smoother waveform creating reactors can be used to suppress harmonics. Also, filters with the range of necessary frequencies can be used to filter out the unwanted harmonics in the electrical power systems. Also, the selection of good power supplies which are free from harmonics also helps in maintaining a power system without problems.
