Although standard power supply methods are normally sufficient for handling most commercial or industrial applications, electrical disturbances can sometimes harm the performance of sensitive equipment or interrupt vital operations. Interferences in power supply can be particularly harmful in computerized systems, which require stable, continuous electrical power to reduce the risk of data loss and distortion of control signals. For these reasons, electronic power supplies manufacturers offer protection from certain unwanted conditions. In this sense, uninterruptible power supply (UPS) units may provide significant benefits to performance stability and cost-efficiency by decreasing industrial system downtime, lowering the rate of equipment malfunction, and reducing the potential for process interruptions.
Total power outage from an electrical source is a rarity under most conditions, but even mild power fluctuations and brief breaks in supply current can prove harmful, especially if they occur during a critical processing stage. Disruptive electrical interference, such as surges, can result from a variety of different causes, including power switching operations, the presence of other electrical equipment in the vicinity of the operating system, and natural phenomena such as lightning and thunderstorms. Understanding the various kinds of electrical interference and their effects on power supply systems can be helpful in developing strategies to safeguard vulnerable industrial processes.
One of the most common and unpredictable sources of sudden power spikes is atmospheric lightning, which can severely affect an electricity supply network. A lightning strike into a power line, overhead line, or cable can generate a high-voltage spike that disrupts current transmission. Similarly, switching operations, particularly those in the vicinity of other sensitive electrical equipment, can also produce spikes. Switchgear that operates on heavy current and certain fuses may yield transient spikes even under standard performance conditions. Major electrical system faults can produce high-amplitude transient spikes ranging up to hundreds or thousands of volts, although they are of brief duration and usually have a short rise time. Other common sources for spikes in electrical power supply include:
The switch starting and stopping of induction motors, like the ones found in driving pumps and fans, can lead to comparable spiking effects. Random electrical spikes usually have amplitudes not in excess of 800 volts and with rise times as short as several nanoseconds.
Dips and Surges
Unintended surges in an electrical power supply are most often the result of switching off large electric loads, while electrical dips occur from switching on. The most important factor in both surges and dips is the size of the load being switched relative to the transformer rating at the power supply source. The duration of a surge or dip can vary from a single half-cycle of the supply waveform to several half-cycles, while the variation from the standard voltage often exceeds 6 percent above or below the optimal range. Large fluctuations in a high-voltage supply network can be caused by system faults or load switching in an industrial power plant, and the frequency and scale of voltage disturbances beyond an initial power supply source depends on the quality of the local electrical distribution network.
In some industrial processes, the potential for surges and dips can be a significant concern. Applications that involve high power loads, such as arc furnaces used in steel working or reversing mill motor drives, can produce severe voltage fluctuations. Through transmission along the supply network, these fluctuations can cause performance interference or flickering. A flicker is a more minor disturbance, usually only a few hertz in strength and characterized by a voltage amplitude with a relatively small deviation from the standard range.
Harmonics are another common cause of electrical interference among power supplies. In most alternating current power systems, voltage variations occur along a sine wave frequency, but a non-linear electric load can generate a different frequency for the current waveform. These harmonics changes may cause an increase in system current that can lead to excess heating and component malfunction. Typical sources for harmonics include solid-state semiconductors, current rectifiers, discharge lamps, and variable speed and induction motors. While the harmonic variation will usually be no greater than 2 to 5 percent on most distribution systems, in some cases a higher degree of harmonic fluctuation may occur. The Department of Energy’s Office of Scientific and Technical Information provides more information on harmonics measurements.
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