Harmonics: Cause of Pollution of the Electrical Power Systems
Harmonics, in today’s scenario, is the first and fore most cause of pollution in the electrical power systems. Now having known this, let us now try to understand what harmonics are. Harmonics are the waveforms, that have frequencies in multiples of the fundamental frequency. For example, the fundamental frequency of our power system is 50Hz. So the 3<sup>rd</sup> harmonic frequency will be 150Hz (50 X 3), 5<sup>th</sup> harmonic frequency will be 250hz and so on. These harmonic frequencies get superimposed on the fundamental SINE waveform and thus distort it.
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The cause of these harmonics are the non linear loads used in the industries and even at our houses. Non linear loads are those which do not give a sinusoidal current output waveform for a sinusoidal input. Examples are CFLs, Air conditioners, SCRs, modern electronic circuitry etc. These loads draw distorted currents from supply, thus distorting the original waveforms. These non-sinusoidal currents flowing through the system impedance create distorted voltage drops across these impedance. The generated voltages are usually pure sinusoidal. Now as the system voltages are pure sinusoidal and the voltage drops across the impedance (due to non sinusoidal currents) are distorted, the final waveform gets distorted. As a consequence, the output is poor (due to increased losses) and hence the efficiency decreases.
The consequences of the increased harmonics are the unnecessary tripping of the protective instruments like fuses, MCCBs, ELCBs etc. For instance, a recent case which I witnessed was that a group of 5 factories were connected to one system bus and one of the factories used a large number of non linear loads. This lead to the tripping of all the protective elements in rest of the factories. This was because of the harmonics injected in the system bus by the first factory due to the use of large number of nonlinear loads. This shows how dangerous the harmonics are.
These harmonics should be eliminated by the minimum use of the nonlinear loads or by using HARMONIC FILTERS to filter out the harmonics. The active and the passive filters can be used to do the job. These filters are made up of inductors and capacitors. They can also be called as high- pass and low pass filters meaning that the filters which allow high and low frequencies respectively.
Recently M.S.E.B. (Maharashtra State Electricity Board) has sent a notice to many big factory owners to restrict their TOTAL HARMONIC DISTORTION (THD) within 3% as per the electricity act 2009. though the complete rules and regulations are yet to be formulated but this is a step in the direction of eliminating harmonic pollution. Penalty will be imposed on those who will not follow the norms as in the case of power factor control.
The transmission losses are already high and we cannot afford to increase the losses. So the harmonic pollutions needs to be controlled in order to ensure efficient working of the electrical power systems.
The cause of these harmonics are the non linear loads used in the industries and even at our houses. Non linear loads are those which do not give a sinusoidal current output waveform for a sinusoidal input. Examples are CFLs, Air conditioners, SCRs, modern electronic circuitry etc. These loads draw distorted currents from supply, thus distorting the original waveforms. These non-sinusoidal currents flowing through the system impedance create distorted voltage drops across these impedance. The generated voltages are usually pure sinusoidal. Now as the system voltages are pure sinusoidal and the voltage drops across the impedance (due to non sinusoidal currents) are distorted, the final waveform gets distorted. As a consequence, the output is poor (due to increased losses) and hence the efficiency decreases.
The consequences of the increased harmonics are the unnecessary tripping of the protective instruments like fuses, MCCBs, ELCBs etc. For instance, a recent case which I witnessed was that a group of 5 factories were connected to one system bus and one of the factories used a large number of non linear loads. This lead to the tripping of all the protective elements in rest of the factories. This was because of the harmonics injected in the system bus by the first factory due to the use of large number of nonlinear loads. This shows how dangerous the harmonics are.
These harmonics should be eliminated by the minimum use of the nonlinear loads or by using HARMONIC FILTERS to filter out the harmonics. The active and the passive filters can be used to do the job. These filters are made up of inductors and capacitors. They can also be called as high- pass and low pass filters meaning that the filters which allow high and low frequencies respectively.
Recently M.S.E.B. (Maharashtra State Electricity Board) has sent a notice to many big factory owners to restrict their TOTAL HARMONIC DISTORTION (THD) within 3% as per the electricity act 2009. though the complete rules and regulations are yet to be formulated but this is a step in the direction of eliminating harmonic pollution. Penalty will be imposed on those who will not follow the norms as in the case of power factor control.
The transmission losses are already high and we cannot afford to increase the losses. So the harmonic pollutions needs to be controlled in order to ensure efficient working of the electrical power systems.
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