Included in this category are static and rotary UPSs, isolation transformers, transient suppressors, and voltage regulators, along with CAD/CAM systems and draining equipment.
Computers and other sensitive electronic equipment make up a growing and extremely vulnerable portion of the load served by the electrical industry. In addition, computers have become significant tools in the design, engineering, and installation of electrical systems. Computers, programmable logic controllers (PLCs), process controls, communications equipment, and similar electronic apparatus are sensitive to fluctuations, disturbances, and interruptions in their power supply. Because malfunctions and failures in this type of equipment can be extremely costly, a wide variety of power conditioning and protection equipment has been developed to counter these problems.
Power conditioning devices are available in a wide variety of types, configurations, and designs, depending on the application. This variety ranges from simple transient and surge suppressors, through constant voltage and isolation transformers, voltage regulators, motor generators, and combination units, to static, rotary, and hybrid uninterruptible power supplies (UPSs).
Transient surge suppressors eliminate the effects of brief high-voltage spikes. Filters remove spurious high-frequency signals (noise), harmonics, and other electrical pollution from power and data systems. Isolation transformers prevent noise in the power supply from reaching computers and other sensitive equipment. Constant-voltage transformers or voltage regulators deliver the required rated voltage to the loads in spite of wide voltage fluctuations in the supply. Motor-generators create a new output, using the input power simply as a source of energy; they completely isolate the output from the input and can provide an output voltage the same as or different from the input voltage.
Combination units can merge several types of conditioners to provide protection against all power problems, except sustained outages. Computer power centers (CPCs) provide local power distribution panelboards and grounding provisions in a computer area, and often contain some combination of power conditioning technologies, usually with an isolation transformer, all in a self-contained floor-mounted unit.
The only full protection against all input power disturbances, including a sustained power outage, is a true UPS. Static and most rotary UPS systems use batteries as a source of energy when the normal supply is interrupted; some rotary units, however, do not require batteries. Since battery power is costly, it is ordinarily limited to periods of from 5 min to 1 hr, and typically 15 min. This limited time period is normally used to facilitate an orderly shutdown of computers or other sensitive electronic equipment. Backup generators are commonly used to supply power before the battery time has expired.
Static UPSs consist of a rectifier (AC-to-DC converter), a DC bus with floating (continuous connected) battery, a DC-toAC inverter, and a solid-state bypass switch. The bypass switch transfers power to another source in less than 4 ms, with the output overlapping, so there is no break in the continuity of power. Static UPS units range from a few hundred VA for microcomputers to 750kVA and higher for larger installations, with larger capacity achieved by using parallel units. They are available for online, offline, and lineinteractive service.
Rotary UPS systems vary more in concept and design than static UPSs. The one thing most rotary UPS systems have in common is that the output to the load is supplied by a M-G set during normal operation and on loss of normal power. The output of an M-G set is a clean, low distortion sine wave, completely isolated from disturbances in the input power supply to the motor. Many rotary systems are quiet enough to be installed right in the computer room.