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Power Quality: Problems and Solutions

Key Points
  • Power quality problems can threaten critical data, reduce productivity and lead to costly repairs.
  • A variety of power quality protection devices are available.
  • A strategic approach to power protection requires planning and record-keeping.

Source: http://www.sxc.hu/
Circuit breaker
Facilities of all types rely on electrical equipment. Power quality problems—such as outages and voltage sags—can reduce productivity, threaten critical data and lead to costly repair or replacement of damaged equipment. The following are descriptions of the most common power quality problems, as well as potential solutions:

Transients—also known as impulses, transients are sharp, rapid rises in voltage that typically last a few microseconds. Causes include capacitor bank switching, welding machines, as well as lightning strikes. Surge protection devices (SPD) can provide protection against most transients. Make sure the SPD has an adequate short-circuit current rating.

Sags and swells—are sudden changes in voltage that last from a few milliseconds up to three seconds or more. Longer changes are called under voltages or over voltages. The starting or stopping of heavy equipment is the most common cause of sags and swells, but they may also be the result of undersized circuits. Voltage restorers and compensators can maintain a constant voltage within a limited range, while uninterruptible power supplies (UPS) provide clean power regardless of the status of the incoming electricity.

Momentary outages—are a complete loss of power lasting up to five minutes. These outages are caused by a breaker or fuse reacting to abnormal electrical conditions. Common solutions include a UPS or a backup generator.

Harmonic distortion—is a change in the supply voltage waveform caused by interaction with distorting equipment, such as computers and adjustable speed drives. Adverse effects include overheated motors and transformers, as well as data loss and burned-out computer circuit boards. Harmonic filters, phase-shifting transformers and power conditioning equipment can block or reduce harmonic distortions, while isolation transformers provide limited harmonic control.

Line noise—occurs in the form of electromagnetic interference (EMI) or radio-frequency interference (RFI). It is caused by interference from radio and television broadcasts, as well as wireless electronic devices. Typical solutions include proper grounding, separation of power and signal cables, use of shielded cable and EMI filters.

Establish a plan

By developing an understanding of the electrical environment in which your equipment operates, you can learn ways to improve uptime and increase overall productivity. When a power quality disturbance occurs, locate the source of the problem and fix it, and then take steps to adjust equipment to survive the disturbance. 

While fixing problems as they occur is important, a thorough power protection system requires a more strategic approach. Start with a thorough investigation of the reason behind any power quality problems you have been experiencing. Has new equipment been added? Does the problem occur at certain times or only once in a while? Keep a log to help track problems in more detail. Armed with this information, you can make more informed decisions about designing a power protection system that meets your needs.


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