Part 2 – Potential Power Quality Problems | UPS System

This the second part of the “IT Professional’s Guide to Standby Power, draws to your attention the many power quality problems that are contained in mains electricity as drawn direct from the grid.

Incoming mains electrical current contains many aberrations that affect the smooth running of sensitive electrical equipment.

Everyone is aware of the potential for mains power failure. Many of these breaks in power only last for a few milliseconds although it is always possible to experience an extended loss of power which is often referred to as a blackout, or sometimes an outage.

Even very short breaks can cause sensitive electronic equipment such as personal computers, servers, printers, modems, hubs and routers, to crash lock up or reboot.

This problem is widely understood but there are also many more power quality problems that can also result in malfunction or equipment failure.


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Surges and Spikes

Surges and spikes are very short bursts (a few milliseconds at most) of very high energy voltages.

They cause wear or acute damage to electronic equipment and can be very damaging over extended periods.

Surges in excess of 6kVA are not unknown. They are caused by electrical storms or disturbances created by inductive motors such as those found in equipment like refrigeration units, lifts or escalators. Fluorescent lighting can also be responsible for shorter duration spikes.

If a surge voltage rises above the tolerance level of the power supply unit, the PSU will activate its built-in cut out in order to protect itself, causing an IT system crash. Surges can lead to gradual degradation of electronic components, such as printed circuit boards, processor damage, memory loss and data corruption.


Sags are one of the more common forms of poor power quality. Sag is experienced when the mains power voltage drops below the normal supply level, typically for several cycles.

This can cause data processing hardware to fail, lock up or reboot. Power supply units can also be stressed as they attempt to deliver the required power and can experience a higher running temperature which can then lead to other problems at a later date.

A common cause of sags is when electrical devices which have a high demand are on the same local circuit. These can include industrial machinery and air conditioning units.


Brownouts are caused by an extended reduction in mains power below the normal power supply voltage. This situation can sometimes persist for a period of days. The effect on sensitive electronic equipment is very much the same as for sags, and power supply units will be affected far more due to the extended nature of the fault.

The name originates from the lowering of artificial lighting levels in areas where demand for electricity sometimes exceeds supply.

Electrical Noise

Electrical noise is a high-frequency disturbance which can disrupt electrical circuits and potentially damage them. Some possible causes of electrical noise are radio transmitters, flickering lighting, faulty cabling and switchgear.


Harmonics are voltage or current multiple waveforms, of the basic frequency. It can cause distortion of the mains supply voltage, overheating of switchgear, transformers and wiring circuits within the fabric of the building. It can also cause problems and failures to equipment being fed by the same supply..

Using a UPS to ‘clean’ the incoming power

By placing a double conversion UPS between the incoming mains and sensitive electrical equipment, the UPS will ‘clean’ the power and remove any threat of malfunction.

With so many power quality issues having the potential to cause substantial problems, the UPS performs a double function. Firstly, it cleans the power, but it is also there, should the power fail completely, to supply backup power. This provides for an orderly shutdown of the electrical equipment that it is protecting or bridging the gap between power failure and the generator taking up the load.

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