POWER QUALITY: MEASUREMENTS OF SAGS AND INTERRUPTIONS

摘要

Good power quality refers to the condition where a uniform constant magnitude sinusoidal fundamental frequency voltage is seen by the customer. Poor power quality takes on some notably different concepts: a) harmonic content of the system voltages, as well as the currents, b) voltage interruptions and sags and the related concept of flicker, and c) voltage surges. This paper will focus on issue b. Over time, small home electronics devices have gradually improved in their ability to withstand the short duration interruptions or sags that lead to blinking clocks and lost microcontroller programming, but including good versions of this feature competes with consumer demand for low price, so the matter will never be perfected. Further, if the home electronics requires any substantial power to run, such as computers, lighting, or entertainment equipment, the customer will need a small UPS to maintain operation. The industrial customer also faces rapid shutdown of a process for interruptions or sags. While a UPS is needed for high power equipment or longer events, most issues could be resolved if the facility could ride through outages of a second or less in duration. The usual worst source of problems is with the control system's motor and lighting contactors which, in typical design, drop out if voltage drops below around 50-75% for more than 1-2 cycles. Other culprits that can lead to shutdown for short voltage sags and interruptions include computers, PLCs, and miscellaneous support equipment such as the electronics associated with some sensors and gauges.