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Tackling power concerns in the digital age

Posted: 06 Oct 2015 ?? ?Print Version ?Bookmark and Share

Keywords:data centres? Google? power surge? switch-mode power supplies? SMPS?

When lightning struck the local power grid supplying one of Google's data centres in Belgiumfour timesseveral of the discs stored there got completely wiped. Data centres have to ensure there is additional protection to defend against power disruptions such as surges or shortages. However, it just goes to show that even when these measures are in place, as they were at the Google data centre, they can't protect your electronic systems from everything.

However, it's not just data centres that need to take power quality into consideration. These days you'd be hard pressed to find a business that does not rely on electronic systems and electronic data and, while you may think you've got everything covered, if you're not thinking about power quality you could be leaving your business vulnerable.

It's easy to picture how disruptions to, or caused by, power can cost your manufacturing, automation or industrial business time and money. A power surge or shortage can cause expensive downtime, damage to parts being manufactured, or damage to equipment. But power quality is also a threat to the business side of business; it's not just large scale operations that rely on consistent power anymore.

Banks, accountancy firms, telecommunications, retail outlets, designers and pretty much any business you can think of now operate based on electronic systems and rely on electronic equipment, devices and data.

Power surges
A power surge occurs when a system receives more electricity than it should for more than three nanoseconds. While there are several reasons this would happen, lightning strikes are the most common cause.

At the extreme end of the spectrum, a power surge can wipe data from hard drives, as it did at Google's data centre. However, there are more subtle problems a power surge can cause. For instance, frequent power surges can reduce the physical life span of your hard drive.

Upon power loss the read/write head of the drive will jump back to its starting position. This abrupt motion can lead to the formation of minute imperfections that accumulate over time until they cause a head crash, where the drive head scrapes the disc surface and destroys the hard drive.

Compact power supplies in electronic devices and controlled motors are possible thanks to switch-mode power supplies (SMPS) in both personal usage and variable speed drives (VSDs) in commercial and industrial settings. This is achieved by manipulating the mains power supply using components in rectifier and chopper circuits in a process of high frequency switching or pulse width modulation (PWM).

Although PWM achieves very low power losses, the process introduces harmonic currents into the power supply. Harmonics are essentially multiples of the fundamental 50Hz frequency and are responsible for numerous problems, particularly in industrial environments.

Harmonics can lead to increased energy consumption and noticeable component damage. In addition, the electromagnetic interference (EMI) that is generated as a result of harmonics, can begin to affect telecommunication equipment and metering apparatus. High levels of harmonics also contribute to voltage distortion.

Voltage distortion
Internal SMPSs that draw a nonlinear current waveform can cause voltage distortion. While linear loads produce a sine wave current, an SMPS draws current pulses at one portion of the applied voltage waveform, which increases with every device added to the system.

The nonlinear current and impedance of circuit conductors and the power source creates a visible voltage drop, the greater the loading demands of a system, the greater the voltage drop. A little distortion isn't going to grind your business to a halt, but where the distortion is in high enough levels, there is the risk of decreased efficiency of the power system.

In addition, localised power distortion such as voltage ripples can be reintroduced into the mains supply. This is can be especially problematic in industrial settings where SCADA and DCS systems are in use over wide geographic areas.

Sharing responsibility
The quality of electricity provided by any power grid operator in Europe has to be in compliance with the parameters laid out in the EN 50160. However, users of this power can have a negative effect on the quality of power in the grid for other users.

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