However, the facts on the ground indicate that the voltage and current waveforms are not as smooth as desired. Deviations from the ideal waveform is often expressed as THD (Total Harmonic Distortion). Or THD can be used to describe large harmonics contained in the wave.
For this problem is used calculate with Fourier series. Suppose the frequency of electrical waves generated by PLN at 50 Hz, then the harmonics are the Fourier components of a value greater frequency of 50Hz.
Harmonic currents are rather low impedance to flow in, for example on the capacitor, because the capacitors have low impedance for high frequencies. Harmonics itself consists of two harmonic components like power in general. Namely harmonic voltage and harmonic currents. According to one source, the voltage harmonics is more dangerous than the harmonic currents.
Harmonics generally occur on the load side or users. Both the industry and offices and households. The effect of harmonics is very dangerous for the user. Some examples of incidents caused by the harmonics:
- Damage to electrical equipment
- Burning of the cable / conductor Conductor though it has not reached the maximum value.
Here are tips to reduce the THD (Total Harmonic Distortion of Mr. Prasetyo Roem):
a. At the time of purchasing an inverter, UPS, and all buy see specnya (optional) harmonic filters. Once installed, the commissioning time, make sure (measured himself) that harmonics filters are especially well. I once met a filter inverter from famous brands do not work.
b. Attach an additional filter (series) with and installed before the UPS, inverter.
c. Replace the 'vacuum' harmonic with a series inductor and capacitor (and resistor), mounted parallel with the load. Some harmonics sucked into heat and discharged into the atmosphere (using AC) and partly transferred into a slight increase in voltage. Inductor value and capacitornya in-tuned to the dominant harmonic frequency would sucked, for example, harmonic-5 = 250Hz. May need to set some of the 'vacuum' is harmonic for different frequencies. The dominant harmonic is usually 3, 5, 7.
What's Harmonic ?
Harmonic is a wave consisting of a sinusoidal wave with some frequency. This principle is derived from Fourier transformation described in the following formula:
This transformation could describe a waveform into components DC, cosine or sine with several different frequencies. DC component is represented (ao / 2) and n is the harmonic to the n. Therefore, there is the term harmonic to 3, 5 and so on that indicate the frequency of multiples of 3, 5, etc. of the fundamental frequency. The figure below shows how a square wave can be parsed into several sine wave with some frequency that is n = 3.5 dan7.
If there are harmonics in a power system, it is fundamental frekeuensi frekeunsi system eg 50Hz or 60Hz. Harmonics of the power system can be in the form of voltage harmonics or current harmonics.
What causes the appearance of harmonics of the power system?
The reason is the non-linear loads, eg A / VSD (Adjustable / Variable Speed Drives), SMPS (Switch Mode Power Supply) etc.. In the form of real, non-linear loads are loads that use power electronics components. What is meant by non-linear load is a load that acts as an arbitrary impedance. There are non-linear load impedance is changed periodically such as A / VSD, but there is also a non-periodic changes such as arc furnaces.
The picture beside shows the flow of a non-linear load fluctuations periodically with 10Ohm resistance value and an open circuit. Beside it shows the load current linearly with 10Ohm resistance. Voltage source, Vs, a pure sinusoidal form with frequency 50Hz. Non-linear load current during the period of sinusoidal shaped sine is positive and zero on the negative sine period. In the linear load current, always-shaped sinus. The results of an analysis using Fourier transform or the so-called harmonic spectrum is shown in the figure below. Function shows the amplitude spectrum at frequencies that were analyzed. In the voltage source and a linear load currents appears that the frequency appears only at 50Hz. While the current non-linear load there appears a DC component (frequency = 0Hz) and several components of the sine / cosine with the largest magnitude at the fundamental frequency (frequency = 50Hz). In practice, non-linear loads with current form as above can be obtained in a single phase half wave rectifier.
Another example of non-linear flow on the A / VSD (or so-called inverter drives) can be seen in the figure below with harmonisanya spectrum. The spectrum of harmonics appear at n = 5.7, 11, 13 etc. or in general 6x 6x +1 and-1 (x = bil. Original).
What are the effects of harmonics on power system?
Harmonic currents can cause the appearance of voltage harmonics on the power system. This is because the harmonic currents flow through the system impedance. Impedance can be derived from the line, transformer, etc.. The negative effects of the presence of harmonic currents are:
- Noise on the analog meter kWh
- Increased losses and abnormal heating in the transformer
- Increased losses and abnormal heating in the motor
- The possibility of explosion of the capacitor bank
- Etc.
Yet this effect does not always show up and happens when there are other conditions that support. Therefore the presence of harmonic currents are not always accompanied by the disorder. The amount of harmonic currents in the system in general increase the likelihood of interference. Presence of harmonic currents in the system should not be reduced by installing harmonic filters. Installation of filters need to be reviewed their emergence both technical and economic terms.
Hopefully useful and Good Work!
References:
- Surya Santoso, H. Wayne Beaty, Roger C. Dugan, and Mark F. McGranaghan, "Electrical Power Systems Quality," McGraw-Hill, 2002
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