Harmonic management PDF download

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 b 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.

Harmonic emissions are subject to various standards and regulations:

• Compatibility standards for distribution networks
• Emissions standards applying to the equipment causing harmonics
• Recommendations issued by utilities and applicable to installations

In view of rapidly attenuating the effects of harmonics, a triple system of standards and regulations is currently in force based on the documents listed below.
Standards governing compatibility between distribution networks and products
These standards determine the necessary compatibility between distribution networks and products:

• The harmonics caused by a device must not disturb the distribution network beyond certain limits
• Each device must be capable of operating normally in the presence of disturbances up to specific levels
• Standard IEC 61000-2-2 for public low-voltage power supply systems
• Standard IEC 61000-2-4 for LV and MV industrial installations
• Standards governing the quality of distribution networks
• Standard EN 50160 stipulates the characteristics of electricity supplied by public distribution networks
• Standard IEEE 519 presents a joint approach between Utilities and customers to limit the impact of non-linear loads. What is more, Utilities encourage preventive action in view of reducing the deterioration of power quality, temperature rise and the reduction of power factor. They will be increasingly inclined to charge customers for major sources of harmonics

Standards governing equipment

• Standard IEC 61000-3-2 or EN 61000-3-2 for low-voltage equipment with rated current under 16 A
• Standard IEC 61000-3-12 for low-voltage equipment with rated current higher than 16 A and lower than 75 A

Maximum permissible harmonic levels
International studies have collected data resulting in an estimation of typical harmonic contents often encountered in electrical distribution networks. Figure M1 presents the levels that, in the opinion of many utilities, should not be exceeded.