Detect and eliminate harmonics: why?

Disturbances caused by harmonics

Harmonics flowing in distribution networks downgrade the quality of electrical power. This can have a number of negative effects:

• Overloads on distribution networks due to the increase in rms current
• Overloads in neutral conductors due to the cumulative increase in third-order harmonics created by single-phase loads
• Overloads, vibration and premature ageing of generators, transformers and motors as well as increased transformer hum
• Overloads and premature ageing of power-factor correction capacitors
• Distortion of the supply voltage that can disturb sensitive loads
• Disturbances in communication networks and on telephone lines

Economic impact of disturbances

Harmonics have a major economic impact:

• Premature ageing of equipment means it must be replaced sooner unless oversized right from the start
• Overloads on the distribution network can require higher subscribed power levels and increase losses
• Distortion of current waveforms provokes nuisance tripping that can stop production

Increasingly serious consequences

Only ten years ago, harmonics were not yet considered a real problem because their effects on distribution networks were generally minor. However, the massive introduction of power electronics in equipment has made the phenomenon far more serious in all sectors of economic activity.

In addition, the equipment causing the harmonics is often vital to the company or organisation.

Which harmonics must be measured and eliminated?

The most frequently encountered harmonics in three-phase distribution networks are the odd orders. Harmonic amplitudes normally decrease as the frequency increases. Above order 50, harmonics are negligible and measurements are no longer meaningful. Sufficiently accurate measurements are obtained by measuring harmonics up to order 30.

Utilities monitor harmonic orders 3, 5, 7, 11 and 13. Generally speaking, harmonic conditioning of the lowest orders (up to 13) is sufficient. More comprehensive conditioning takes into account harmonic orders up to 25.