Electronics Protection - November/December 2012 - (Page 12)
Feature Mitigating Risks Through Power Distribution Design
Dave Proli, Director of Engineering Marway Power Solutions Power distribution is the backbone of any system involving sensitive electronics. Yet it is often low on the priority list of initial system design concerns. Personnel safety, equipment reliability, and system performance are all items that can be affected by power related problems. Areas of concern include emergency safety control, equipment overcurrent conditions, induced power problems such as transients and noise, facility power problems such as improper phase rotation, poor voltage regulation and dropouts, and environmental hazards. The degradation is caused by the devices using the power such as: • air conditioners and compressors • electric heating equipment • motor-driven industrial machinery • elevators, conveyors • computers, printers, copy machines • ballasts for fluorescent lights Since signal problems are introduced to power lines throughout a facility’s wiring, it is beneficial to add power conditioning at points throughout the facility. An effective place to do this is at power distribution points near the end use equipment with a power distribution unit.
When questioning the risks that can expose a system to power related problems, mitigation techniques can be implemented directly into the power distribution design – saving time, expense and most importantly, reducing safety hazards. When designing a power distribution scheme, it’s best to answer the following questions: a. What type of power conversion do I need (facility voltage/configuration vs. equipment needs)? b. What type of power receptacles do I need? c. What type of control and monitoring capabilities do need? d. What type of power conditioning do I need, including: • What kind of noise and transients are present in my facility? • How stable is the facility power (do I need to worry about brownouts and blackouts)? • How sensitive is my equipment to the issues listed above? Before selecting a PDU, it’s important to understand the variety of power challenges as this can determine what type of power distribution is needed.
Signal Conditioning Challenges
There are several problems that can affect a voltage signal. The most severe is a complete loss of power for short or long-term durations. Similarly, significant periods of excessively low or high voltage is also a problem. Solutions to these problems are generally too large or specialized to integrate within a near-point-of-use PDU and are best applied as external complements. Most other conditioning problems involve various forms of high voltage surges (a.k.a. spikes) and electromagnetic interference (EMI), also known as electrical noise, or just noise. The solutions to minimizing these signal problems are well suited to the integration within a PDU.
Electronic Systems Require Clean Power
Modern electronic equipment such as computers, communications hardware, security systems, data acquisition systems and others require clean, stable power free of noise in order to perform their functions optimally and reliably. A clean alternative current (AC) signal has a perfectly smooth sine wave (Fig.1) when viewed on an oscilloscope. Any imperfections in this signal can adversely affect electrical equipment causing poor performance, incorrect functionality or even damage to sensitive circuitry. Most electronic equipment will have some minor power conditioning capabilities built in, but there’s a basic assumpFigure1. Signal conditioning of AC tion that incoming power is power seeks to ensure as close to a pretty close to a perfectly perfect sine wave in the voltage signal as possible. The upper waveform clean signal. However, that’s has no noise, where the lower one is not always the case. Mobile quite noisy. power sources and power utilities in some developing nations, will not deliver clean signals. Even the clean power supplied by a developed nation power utility will become degraded within a facility.
Spikes are very short increases in voltage, and commonly come from power switching equipment like circuit breakers, contactors and other causes. Less common sources include short circuits, static electricity, lightning and even large electromagFigure 2. A voltage spike may have a very high voltage value, up to several netic fields. While spikes are thousand volts, but the duration is on short, the increased voltage the order of microseconds. for even that short time may be enough to damage microelectronic components and/or cause malfunctions. Counteracting voltage spikes is done with surge protection devices (SPDs, a.k.a. surge suppressors). These devices typically divert excess voltage from the power line being protected straight to ground, though there are other techniques. There are a variety of technologies to choose from, each with advantages for particular power environments.
Electromagnetic Interference (EMI)
EMI is a broad term covering multiple causes where the net effect is that electromagnetic waves of a wide spectrum of frequencies cause interference with the power signal. This interference, or noise, on an AC power line is any deviation in the signal from the desired perfect sine wave form.
Types of EMI Noise
EMI can be classified in several ways. One way is to identify how interference gets into the power line which includes conduction, capacitive coupling and induction. Another way is to address the frequencies being added to the signal. RFI, or radio frequency in-
November/December 2012 www.ElectronicsProtectionMagazine.com
Table of Contents for the Digital Edition of Electronics Protection - November/December 2012
Electronics Protection - November/December 2012
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Lowering Data Center Energy Bills: DCIM to the Rescue
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Mitigating Risks Through Power Distribution Design
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New Surge Suppression Solution to Shield Electronics from Surge Energy Let-Through
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Calendar of Events
Electronics Protection - November/December 2012