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Every organisation needs to ensure that their data processing and communications equipment is protected from interruptions in the mains power supply.  Alan Luscombe, director at Uninterruptible Power Supplies, a Kohler company, looks at the many different types of electrical disturbance that can pose a threat to IT operations

All business-critical data processing systems are at risk from electrical disturbances that may disrupt or damage IT operations. From data centres to industrial process control systems, medical equipment, point of sale terminals and security and alarm systems, a comprehensive power protection strategy based on a UPS is essential to maintain a stable and continuous supply of electricity.

But not everyone is aware of all the many ways the power supply can be compromised. The most obvious threat is a blackout, when the mains supply fails totally – rare, but potentially devastating to equipment without adequate protection. But there are other forms of electrical disturbance that can cause disruption or damage.

A spike, for example, is a very short pulse of energy containing a high voltage (up to 6000V), typically caused by thermostats or other devices switching heavy electrical currents, or by power companies’ load switching. Localised lightning strikes can cause particularly dramatic spikes. Spikes will damage any sensitive electronics they reach, burning out circuit boards and corrupting software and data.

A surge is similar to a spike, except the raised voltage lasts fractionally longer. This occurs when heavy electrical equipment is turned off, or after load switching at a substation. Unprotected computers may experience memory loss or data errors, and may shut down altogether. Conversely, a sag is a brief drop in the mains supply, a common occurrence that is usually the result of switching on a large load or heavy rotating machinery. It can trigger an automatic computer reboot.

Brownouts are sags that last much longer and are generally more serious. They occur when the utility mains supply can’t cope with current demand and the generating company reduces the network voltage. In extreme circumstances brownouts can last for several hours.

Electrical noise is, simply, any kind of electrical signal that interferes with the normal signal, and can be temporary or constant. It might arise from disturbances between the supply line and the ground or it might be caused by lightning strikes, load switching, cable faults, or nearby radio-frequency equipment. Electrical noise can cause computers to ‘hang’, leading to data corruption.

Equipment that includes a switching action and therefore draws power from the mains in a non-linear fashion can cause harmonics. Put simply, the current is distorted by multiples of the fundamental 50Hz frequency. Computers, photocopiers, laser printers and variable-speed motors, or any loads containing controlled rectifiers, switched-mode power supplies or rotating machines, are all known to generate harmonic interference. Harmonics disproportionately increase current and raise temperatures, leading to component failures and general equipment overheating.

These are the kinds of risk that require a comprehensive power protection strategy. Some computer equipment has a built-in ability to tolerate a short-term loss or reduction of power, while others may have enough latent energy stored within their circuitry to maintain essential DC levels during sags and other short interruptions. But only a UPS with a high level of battery autonomy can ensure a continuous supply of power that is clean and stable enough to protect sensitive loads.

Risk can be further mitigated through use of supplementary equipment such as surge suppression filters and isolation transformers, and by installing proper cable screening and earthing arrangements. Externally connected components also reduces the risk from surges. FMs should seek advice from experienced UPS suppliers able to carry out site surveys and tailor their advice to the individual customer’s specific power protection needs.

About Sarah OBeirne


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