What’s the harm in harmonics?

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Harmonics are a by-product of non-linear loads, a load which draws a non-sinusoidal current.

In our increasingly technology-reliant society, harmonics are a growing concern with managing electrical systems in both industrial and commercial sites.

Despite the ubiquity of harmonics, there’s a general lack of understanding around them, particularly in terms of how best to mitigate them.

It is something that engineers and electricians must be mindful of.

Not only is it important in order to optimise the performance of devices, but also with a view to energy efficiency and changing electrical environments.

Power tripping

The presence of harmonics in electrical systems means that current and voltage are distorted and deviate from sinusoidal waveforms. Put simply, they place added strain on electrical networks.

This can lead to the potential damage of – often crucial and costly – equipment.

Harmonics threaten to disrupt the regular functioning of devices, which leads to increased operating costs, namely through downtime and the cost of ongoing maintenance.

Additionally, harmonic currents increase the RMS current and compromise the quality of the supply voltage. This, in turn, causes power supply failures, such as tripping of circuit breakers or causing fuses to blow.

Harmonics not only cause plant downtime, but can also lead to financial penalties for failure to comply with utility provider harmonic limits and, in extreme cases, being disconnected from the network.

Non-linear loads and distortion

So where does the problem arise? Essentially it boils down to the inherent difficulty with equipment, such as switched-mode power supply (SMPS) equipment or variable speed drives, otherwise known as non-linear loads, of which there is an increasing amount.

A linear load is one where voltage is applied across a constant resistance resulting in a sinusoidal current.

In contrast, non-linear loads occur when the resistance is not a constant and changes during each sine wave of the applied voltage waveform, resulting in a series of positive and negative pulses.

Equipment such as computers, printers, variable speed drives, chargers and TVs etc. tend to make up a significant percentage of non-linear loads in most electrical distribution systems.

There are two types of non-linear loads: single-phase and three-phase.

Single-phase non-linear loads are most commonly found in office buildings, whereas three-phase non-linear loads feature more often in factories and industrial plants.

SMPS systems draw their current in short, high amplitude pulses. This kind of pulse creates harmonic distortion that flows back into the power source, affecting any devices connected to the same point.

This process has been likened to the function of water pipes if you were to take a shower while someone turns cold and hot water on repeatedly at the sink, alternately burning or freezing you.

The principle of harmonic distortion is the same, causing significant stress and interference to the equipment involved.

Filtering the harm out of harmonics

The challenge comes in being able to mitigate the issues created by harmonics and distortion against a backdrop of vastly increasing numbers of non-linear loads in commercial and industrial buildings, such as variable speed drives and UPS systems in industrial buildings and office equipment like computers and photo copiers in commercial environments.

And the simple answer lies with harmonic filters. Harmonic filters remove harmonics, thus converting non-linear loads into linear loads.

There are two types of harmonic filter – passive and active.

Passive filters are designed to remove harmonic currents by diverting them through low impedance paths whereas active harmonic filters cancel out harmonics by generating an equal and opposite harmonic current.

Control Logic

Control Logic, a leading supplier of industrial, electrical and automation products, services and solutions, has a comprehensive range of active harmonic filters including both the smallest and largest current rating modules of any active filter on the market.

It also provides an entire range of ABB active harmonic filters.

These have the ability to:

• Link multiple modules together to increase power and build in redundancy.

• Operate in ambient temperature of up to 50 degrees Celsius which not all the competitors can do.

• Preset the desired harmonic levels for each individual harmonic, allowing the user to freely decide which harmonics they want to filter and by how much.

• Be used to perform load balancing and to provide reactive power compensation where required, as well as their primary purpose of mitigating harmonics.

 

Image: http://www.abb.ie/