With the upgrowing use of semi-conductors in the industry, it greatly improved the efficiency and the precision of electrical equipments.  Therefore, semi-conductors are changing the nature of the sinusoidal and generate harmonic currents.

Harmonic currents create disruption on the distribution network and can cause breakage of certain types of electrical equipment such as capacitors, motors and transformers.
 

1-  Those harmonic currents which are the dominant harmonic orders created by three phases nonlinear loads - 5th, 7th, 11th, 13th and higher odd harmonics which are not multiples of 3.

2-  Those harmonics created primarily by single phase nonlinear loads - 3rd order harmonics and higher multiples of 3.  These are sometimes referred to a "triplen" or "zero-sequence" harmonics and are usually accompanied by some 5th, 7th, and other higher order harmonics.
 

The impedance of the network is inductive, it proportionally increases with the frequency while capacitor's frequency decreases.  Consequently, at higher frequencies than the fundamental one, currents will circulate through capacitors.  In addition to this, harmonics can cause an important raise in tension in the cap. terminals and can cause domage.

Resonance frequency is reached when the network's impedance is equal with capacitor's frequency.  When capacitors are used to correct power factor and there are existing converters and/or rectifiers, there is a chance, at a given frequency, that the network's impedance goes in resonance with the capacitor's impedance.  This phenomenon create intensive currents that circulate between the capacitor and the network and can occur serious breakages of capacitor and of its protection devices.  The 5th, 7th, 11th and 13th are the most important resonance frequencies and the ones that interests us most.
 

ELIMINATE RESONANCE:

To avoid capacitor's impedance to go in resonance with the network's impedance, we add a serial reactor to the capacitor.  We normaly choose a reactor which the combination capacitor/reactor is capacitive at fundamental frequency and inductive at critical frequencies.

In addition to this, we make sure that the resonance frequency is lower than the currents that circulate through the network.  Moreover, when we add a serial reactor to the capacitor, it is primordial to be certain that the fundamental tension will never exceed operating nominal tension.
 

REDUCE HARMONIC DISTORTION:

Harmonic currents can be eliminated by using harmonic filters.  A filter is composed of a serial inductor with a capacitor.  Inductors and capacitors are dimensioned in a way so they resonate at an undesirable frequency, pushing the harmonic currents through the filter.

Power Survey Equipments Ltd possesses the necessary expertise to measure and efficiently analyze the intensity of harmonic currents and voltages.

following these meas, we offer a package of services and complete analysis:

• Computer assisted simulation.
• Calculation of harmonic currents after installation of capacitors.
• Dimensioning of anti-resonance inductors.
• Conception of harmonic filters.