Power Quality, Problems & Solutions

By: Alison Campbell

Businesses and organisations are now totally dependent on electricity to run their data and voice processing systems. Power failures - short or long - can be devastating if they are not protected by UPS (uninterruptible power supplies).

However, a lesser-known threat - but equally troublesome - is that of power quality and problems in supply.

The causes of power quality issues are usually environmental: weather phenomenon (local lightning strikes and electrical storms), heavy loads being switched into and out of the supply; load shedding; cable and switchgear faults and sometimes interference from radio transmission equipment. They can cause hardware to lock, fail or re-boot resulting in equipment wear-and-tear and lost or corrupted data.

Power Problems

Sags are common: short-duration voltage reductions below the mains supply level that can last for several seconds. One of the most common causes is switching heavy loads (air-conditioners, motors, industrial machinery) into and out of the local electricity circuit.

Conversely, the same issues can cause surges, which are short-duration voltage increases above the mains power level, which can also last for several seconds. When voltages rise above the acceptable input window of a PSU (power supply unit), for example, built-in cut-out protection activates resulting in a system crash.

Brownouts are less common now but may become more frequent as demand for electricity continues to increase. They are classified as long-term reductions in mains power supply that can typically last for several days and compromise the effectiveness of other equipment, such as lighting.

Spikes and Transients are fast-moving, high-energy bursts (some in excess of 6kVA) lasting only a few milliseconds, superimposed onto a normal mains power supply. Their intensity can cause damage to circuit boards, processors, memory loss and data corruption. Possible causes are lightning strikes, electrical storms, local load shedding, relay-based thermostats and inductive motor loads.

Electrical Noise, which is a high-frequency sound, can be caused by flickering lights, cable and switchgear faults and occasionally interference from electronic equipment such as radio transmitters.

Harmonic pollution is a growing problem. Within the UK it is addressed by Engineering Recommendation G5/4-1, published by the Energy Networks Association. Harmonics are current and voltage waveforms, the frequencies of which are not in harmony with the fundamental which in Europe is 50Hz. Harmonics will create multiples of the fundamental and can cause wiring circuits and other electrical equipment to overheat and occasionally ignite.

An effective UPS solution should contain filters and frequency conditioners that shield and protect upstream equipment and attached loads from power quality problems. But power protection should always begin with a power quality review to asses the actually quality of mains supply and the level required. This should also include future demands, sources of alternative power on site and priority-based load shedding and shutdown.

For more information on power quality issues and how they can be addressed through the strategic use and implementation of UPS, see The Power Protection Guide , written by Robin Koffler and Jason Yates of Riello UPS and published by entiveon, or visit .

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