What are Harmonics?
The mains supply in the UK and most of the rest of the world has a frequency of 50 cycles per second (50Hz). The shape of the mains waveform is sinusoidal. Harmonics are voltages and currents which have frequencies which are multiples of 50Hz, for example the 5th harmonic has a frequency of 250Hz.
What Causes Them?
Power Electronic Equipment: –
- Variable speed drives
- Rectifiers
- Some types of lighting
- Switch mode power supplies commonly fitted in computers and their peripherals
What is the Result?
It’s important to understand that there are almost always several harmonic frequencies generated and each one has a sinusoidal waveform. However, when these combine with the mains 50Hz supply, the resulting waveform is no longer sinusoidal and its amplitude may be significantly increased.
Common problems resulting from harmonics are :-
- Electrical failures
- Malfunctions in microprocessor equipment including computers
- Overloading of Cables, Switchgear and Transformers etc
- Circuit breaker trips
- Increased motor wear
The list is endless.
Effects on Neighbouring Consumers
The effects of harmonics are not confined to the site which is generating them. Some of the distortion is fed back into the mains supply and can cause problems for your neighbours.
The permissible distortion that you are allowed on the mains supply is stipulated in Engineering Recommendation G5/4. If you check your electricity supply agreement you will probably fine that it includes compliance with this document.
What’s the Cost of Generating Harmonics?
- Increased energy usage caused by increased current flow
- Repair and replacement of failed equipment
- Production loss
- And, if you cause problems ‘next door’, which can be traced to you, claims for recompense
Remember, the problems caused by harmonics won’t go away until the harmonics go away. If you exceed the G5/4 limits, your electricity supplier has the authority to withdraw supply.
What Can Be Done?
PQE can design and build harmonic filtration equipment to reduce distortion to acceptable levels, ie below G/4 limits which will eliminate failures and malfunctions and remove the liability which exists when those limits are exceeded.
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Harmonic Filters What Are Harmonics?
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