The effect of particulate and water contamination on the dielectric strength of insulating oils

The dielectric strength of insulating oils is influenced by particulate and water contamination. The deleterious effect of moisture on the dielectric strength is well known in the industry and is reflected in the manufacturing, commissioning and maintenance practices for oil wetted electrical equipment. The deleterious effect of solid contaminants on the dielectric strength is also well known but most often there are no specifications for the oil contamination level and it is not monitored. The subject study was undertaken to quantify the influence of naturally occurring particulate contaminants with various amounts of moisture on the dielectric breakdown voltage of serviced oil from a circuit breaker. The paper also discusses dielectric oil filtration and automatic particle counters and their use in the control of particulate contaminants in oil wetted electrical equipment.