Industrial-Grade Uninterruptible Power Supplies (UPS)

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Another common type of power supply used in industrial applications is called an uninterruptible power supply (UPS). The UPS has become important in industrial and commercial power supplies because it provides a means of supplying power to computers and programmable logic controllers (PLCs) in applications where a power failure can't be tolerated. In most parts of the U.S., weather conditions such as lightning storms and ice storms may cause the power company to loose power for a period of time. The amount of time the power is disrupted may last from 10 seconds to several hours. If the power outage occurs while a computer or PLC is running, it will cease operating and may loose the information in active memory. The outage condition will also cause the systems to be restarted, which may take additional time.

The UPS combines a power supply with a battery to provide a circuit that can provide output power while the power company's incoming power is down. This is accomplished through a rectifier section in the system that converts the ac voltage into dc voltage. The major difference in the UPS is that the power from the rectifier section is used to charge a battery. The battery acts as a buffer for the voltage because the battery supplies dc voltage to the inverter part of the system. Here dc voltage is turned back into ac voltage with a set frequency that matches the power system of the equipment connected to it. This means that some of the dc voltage may go through the battery to keep it charged. The battery is sized so that it's large enough to continue providing dc voltage to the inverter even when the ac incoming voltage has been interrupted. The battery is rated for the amount of time the UPS system is supposed to provide the voltage during an outage. Since, most computers and PLCs don't use a large amount of voltage, even very small UPS systems can provide dc voltage for up to an hour. Larger UPS systems are designed to provide backup power to complete buildings such as hospitals or for control rooms for nuclear power plants. Fig. 1 shows images of two industrial UPS models; Fig. 2 shows an electronic block diagram of models like or similar to these.

An industrial uninterruptible power supply (UPS) An industrial uninterruptible power supply (UPS)

Above: Fig. 1: Varoius industrial-grade uninterruptible power-supply (UPS) models from Liebert Inc.

An electronic block diagram of an uninterruptible power supply (UPS).

Above: Fig. 2: An electronic block diagram of an uninterruptible power supply (UPS).

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