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EETE MAY 2014

Power management: are you doing enough? By Rob Morris when the power suply to critical equipment fails, companies are at risk of losing out. In a retail environment, this can result in tills breaking down and lost customer orders; in manufacturing, power outages can mean downtime, wasted manhours and failure to deliver on time. We all know how annoying a power cut at home can be, but in a business environment this frustration is magnified many times over with damage incurred to reputation, customer satisfaction and to the bottom line. However, the fact is that, while potentially catastrophic, blackouts and power outages are relatively rare events. In fact they are only one small, but very visible, part of a wider power problem. Poor quality power events such as spikes, surges and electrical noise often unnoticed and, worryingly, can be more damaging to a business in the long term. Power disturbances have the ability to erode electrical components, scramble computer systems and cause sudden failures in critical equipment. But what exactly is poor quality power and what can be done to prevent it? What is poor quality power? In simple terms, poor quality power is any irregular variation in the voltage magnitude of a power source or in an electrical circuit. This can include things like surges, spikes, transients, electrical noise, electrical pollution and brownouts. It can be caused by many different factors – both internally and externally. A lightning strike, for example, can have a current as high as 100,000 Amps, which can cause irreparable damage to internal circuits. Lightning strikes increase the ground voltage, inducing electromagnetic fields, which subsequently cause surges in voltage and current in the power supply. Equipment inside buildings can also create pollution within a circuit, sending potentially damaging spikes and transients to other equipment. For example, lifts in office buildings or flashfreezers in restaurants can send massive spikes around the circuit when being turned on and off. Most businesses are alive to the problem of power outages and blackouts and often take action to prevent them from damaging their business, installing uninterruptible power supplies (UPS) which provide backup power in the event of failure. However, UPS do not always safeguard against poor quality power and therefore don’t offer full protection against power problems, despite what many business owners believe. All of these disturbances, from the problems in the power supply coming from the grid to the pollution introduced by electrical equipment, can cause serious problems for a business, both immediately and in the long-term. These power quality problems can be defined by the 3 D’s: The three D’s • Destruction occurs when a disturbance is so significant that it causes a component to fail instantly. This sort of problem Fig. 1: A blown chip due to an uncontrolled power surge. is easily identifiable by the charred remains of the part • Low amplitude disturbances affect semiconductors within electronic equipment by causing degradation of the material over time. When power disturbances exceed the low voltage tolerance of a semiconductor junction, the material erodes over time, eventually causing the failure of the component. • Some power disturbances can mimic genuine signals, causing disruption. Disruption can also be a result of a secondary fault created when surge diverters shunt excessive voltages to ground. This sort of problem is difficult to identify and is often diagnosed as a software bug. The best guard against the 3D’s is to use a combination of components in one overall power conditioning system, providing full overall protection from poor quality power. The optimal combination will include the following components: • Surge diverter to shunt any high voltages away from sensitive equipment. • Low-impedance isolation transformer to protect against the common-mode caused by a surge diverter. This is the biggest problem modern computers face and is the one which leads to lockups and data losses • Noise filter to remove any low amplitude disturbances that pass through the surge diverter. Low amplitude noise can affect the operation of digital systems by causing the circuit to misinterpret the noise as a signal • V oltage regulator to remove any dips or swells • Frequency regulator for occasions when the frequency is not stable. This is especially problematic in electricity in developing countries or from generators • Uninterruptible power supply to provide backup power in the event of a power outage • Ground loop control technology prevents the formation of current loops when a circuit has more than one ground. Rob Morris is UK Country Manager at Powervar – www.powervar.com www.electronics-eetimes.com Electronic Engineering Times Europe May 2014 29


EETE MAY 2014
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