HARMONIC CORRECTION.

 

Mikano Power Solutions Division provides solutions for Eliminating/reducing Harmonics in the power systems by: 

1)  Analysis of the system for quantifying the problem 

2)  Determining the power quality objectives at various points in the system (determining the acceptance limits at each point). 

3)  Using one of the various techniques for reducing the harmonics. 

- Increasing effective source impedance
- Diverting harmonics to an alternative path
- Employing the hybrid of the above two
- Harmonic cancellation. 

No one solution is ideal for all application. 

There are some precautions available to be deployed right at the start-up phase of any power system. 

A typical harmonic correction system consists of a combination of Inductance and Capacitance arranged in series/parallel pattern to achieve the result. 

Brief theory on Harmonics 

What are Harmonics. 

Harmonics are a mathematical way of describing distortion to a voltage or current waveform. The term harmonic refers to a component of a waveform that occurs at an integer multiple of the fundamental frequency. Understanding the mathematics is not important. What is important is understands that harmonics are a steady state phenomenon and repeat with every 50 Hz/60Hz cycle. Harmonics should not be confused with spikes, dips, impulses, oscillations or other forms of transients. 

Causes. 

Harmonics are caused by non-linear loads, that is loads that draw a non-sinusoidal current from a sinusoidal voltage source. Some examples of harmonic producing loads are electric arc furnaces, static VAR compensators, inverters, DC converters, switch-mode power supplies, and AC or DC motor drives.

Potential Effects of Harmonics. 

Power system problems related to harmonics have a number of undesirable effects. High levels of harmonic distortion can cause such effects as increased transformer, capacitor, motor or generator heating, mis-operation of electronic equipment (which relies on voltage zero crossing detection or is sensitive to wave shape), incorrect readings on meters, mis-operation of protective relays, interference with telephone circuits, etc. The likelihood of such ill effects occurring is greatly increased if a resonant condition occurs. 

Resonance occurs when a harmonic frequency produced by a non-linear load closely coincides with a power system natural frequency. There are 2 forms of resonance which can occur: parallel resonance and series resonance. 

Parallel resonance occurs when the natural frequency of the parallel combination of capacitor banks and the system inductance falls at or near a harmonic frequency. This can cause substantial amplification of the harmonic current that flows between the capacitors and the system inductance and lead to capacitor fuse blowing or failure or transformer overheating. 

Series resonance is a result of a series combination of inductance and capacitance and presents a low impedance path for harmonic currents at the natural frequency. The effect of a series resonance can be a high voltage distortion level between the inductance and capacitance.

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