Frequency of voltage sags at industrial and commercial sites in Canada

The occurrence of voltage sags (i.e. undervoltage conditions) on the primary and secondary sides of industrial facilities often disrupt continuous and noncontinuous industrial computer processes, a costly issue for society. Prior to 1990, very little information was available on the frequency of these incidents and their origins (i.e. did the voltage sag originate on the utility's system or within the industrial facilities electrical system?). In 1991, the Canadian Electrical Association took a proactive approach to power quality problems and initiated a three year "Canadian National Power Quality Survey" involving twenty-two utilities. This paper presents some of the survey results of the frequency of voltage sags at industrial sites monitored at their utilization voltage levels (e.g. 120, 347 V) and on the utility primary side of their facilities and discuss the implications as to the origins of voltage sags. The survey results provide a basic knowledge base for designing and utilizing voltage sag mitigating technologies.