Harmonics - Its Generation & Effect on Power System

Harmonics

• The harmonics are defined as the component of signal whose frequency is integral multiple of fundamental frequency.

Fundamental frequency and harmonics

Fundamental frequency	Third harmonics	Fifth harmonics	Seventh harmonics	Ninth harmonics
50 Hz	50 × 3 = 150 Hz	50 × 5 = 250 Hz	50 × 7 = 550 Hz	50 × 9 = 450 Hz

Generation of Harmonics by Non Linear Load

• Inverters
• Television
• Variable speed drives
• Furnaces
• Choke coil
• Semiconductor kit
• Single / three phase rectifiers
• Discharge lamps
• Single phase converters
• Computer / IT load
• Switch Mode Power Supply

Effect of Harmonics

( 1 ) Power electronics kit  

• Mal functioning

( 2 ) Power Capacitors

• High current, failure due to load

( 3 ) Transformer / Switchgear equipment

• Power losses
• Over heating
• Higher power consumption
• Neutral overloading due to triple harmonics

( 4 ) Rotating machines

• Higher power losses
• Pulsating torque due to negative phase sequence current
• Higher frequency current increase cable resistance due to skin effect , finally it increases over heating

( 5 ) Relays

• False tripping

Types of harmonics

• Current harmonics
• Voltage harmonics

How to reduce harmonics or harmonics mitigation?

The harmonic mitigation is done by harmonic filters. There are following types of harmonic filters

• Active filter
• Passive filter
• Hybrid filter

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