How To Eliminate Harmonic In Electrical System?

What Is Harmonics in Electrical System?

Harmonic define as any Non-Linear Current or Voltage in an electrical distribution system.

The presence of harmonics in electrical systems means that current and voltage are distorted and deviate from sinusoidal waveforms.

Harmonic shouldn’t be thought of as an acoustic or vibration harmonic, but simply any electrical device that draws current unpropotionally to voltage.

Harmonic currents are currents circulating in the networks and which frequency is an integer multiple of the supply frequency.

Cause of Harmonic.

Harmonic currents are caused by non-linear loads connected to the distribution system. A load is said to be non-linear when the current it draws does not have the same waveform as the supply voltage. The flow of harmonic currents through system impedances in turn creates voltage harmonics, which distort the supply voltage.

Harmonic are commonly produced by non-linear loads or devices that rectifies AC Voltage into DC Voltage. The most common non-linear loads generating harmonic currents are power electronics equipments such as variable speed drives, rectifiers, inverters, lighting and computer.

Other loads such as inductors, resistors and capacitors are linear loads and do not generate harmonics.

Why Harmonic Need To Be Eliminate?

One of the major effects of harmonics is to increase the current in the system. This is particularly the case for the third (3^rd) harmonic, which causes a sharp increase in the zero sequence current, and therefore increases the current in the neutral conductor. This effect can require special consideration in the design of an electric system to serve non-linear loads.

In addition to the increased line current, different pieces of electrical equipment can suffer effects from harmonics on the power system.

Despite the reason above, there are numbers of other reasons why harmonic need to be eliminate. The tabulation below shows the effect of harmonic to the electrical equipments that will be the main reason for eliminating the harmonic.

Equipment	Effect of Harmonic
Motor	Overheating, production of non-uniform torque, increased vibration
Transformer	Overheating and insulation failure, noise
Switchgear and cables	Neutral link failure, increased losses due to skin effect and overheating of cables
Capacitors	Life reduces drastically due to harmonic overloading
Protective Relays	Malfunction and nuisance tripping
Power electronic equipment	Misfiring of Thyristors and failure of semiconductor devices
Control & instrumentation Electronic equipment	Erratic operation followed by nuisance tripping and breakdowns
Communication equipment / Computer	Interference
Neutral cable	Higher Neutral current with 3rd harmonic frequency, Neutral over heating and or open neutral condition
Telecommunication equipment	Telephonic interference, malfunction of sensitive electronics used, failure of telecom hardware

How to Eliminate Harmonic?

To ensure a good and proper operation of the electrical installation, both harmonics (Current Harmonic and Voltage Harmonic) need to be eliminated.

Current Harmonic can be eliminated by adding Line Choke or by installing Isolating Transformer to the harmonic producing equipments.

Voltage Harmonic can be eliminated by installing Tuned Capacitor.

Other than the above method, you might consider equipments with a low Current Total Harmonic Distortion (THD).