Effects of nonsinusoidal supply on voltage tolerance of equipment

Abstract

This letter shows the effects of harmonics in the voltage supply on the voltage tolerance of equipment. Several laboratory tests have been made to obtain the voltage tolerance curves of a personal computer using a pure sinusoidal voltage supply and under different nonsinuoidal conditions. The analysis shows that the voltage tolerance of the equipment used in the test depends on both the voltage harmonic distortion magnitude and the phase difference between harmonics, with the equipment being more sensitive to low order harmonics. Introduction: Voltage sag is a sudden decrease in the voltage am- plitude followed by a return to the initial level after a short time. Voltage sags are produced by faults in the supply network, both permanent and transitory, rapidly varying loads or equipment taking high current at starting. Voltage sags are important power quality problems to many in- dustrial customers because of the sensitivity of electrical and electronic equipment, such as process controllers, adjustable speed drives, pro- grammable logic controllers, or personal computers to voltage sags. A way to characterize the behavior of equipment to voltage sags is to use voltage-tolerance curves. The first voltage-tolerance curve, the CBEMA curve—which was initially applied to data processing equipment—shows that the sensitivity of equipment is very dependent on the duration of the voltage sag. This voltage-tolerance curve is an important part of IEEE standard 1346 (1). Recently, a revised CBEMA curve has been introduced by the Information Technology Industry Council. This curve, referred to as the ITIC curve, has introduced stricter requirements than the CBEMA curve, because power quality monitoring has shown a large number of voltage sags under the