It can be very frustrating for a business owner who just lost thousands of dollars from random equipment shutdowns and an electrician who spent hours troubleshooting the problem to get a system back up and running. You could simply attribute the problem to random chance, but that won’t work the next time it happens. Power quality is a broad discipline that provides useful theory and research to understand the causes of equipment shutdowns. Of all the topics in power quality, one stands above the others — voltage sags.
External voltage sags are the leading cause of equipment shutdowns. External voltage sags are caused by various problems on the electrical grid. Faster than the blink of the human eye, sensitive electrical equipment will shut down. The flicker of the lights may not even be noticed. The most obvious cause of voltage sags is inclement weather, such as wind, ice and lightning. Did you know that curious squirrels, large birds, and metallic balloons are the leading causes of power interruptions and voltage sags? When they make contact with high-voltage conductors, a phase-to-ground or phase-to-phase fault occurs, resulting in a voltage sag on adjacent circuits. In some instances, the fault is so significant that the voltage on all three phases may drop to 30% of nominal voltage for 6-120 cycles.
Unless you have power quality monitoring equipment installed on the system, you would not be able to correlate and determine that voltage sags are the cause. Permanent power quality monitoring is always recommended for facilities adversely affected by shutdowns. Without a power quality monitoring system, the electric utility will need to be contacted to assist in identifying the cause. The date and time of the event will be needed in order for the Distribution Engineer to identify the actual cause. It’s important to ask the engineer to evaluate adjacent circuit faults fed from the serving substation. Most likely, the event was not on your distribution circuit. Identifying the cause is not always easy after the fact. Plan ahead and install a power quality monitor system to capture future events. Once you understand the cause, you can plan for the proper mitigation technology to allow the equipment to ride through future events.
Glenn is a power quality consultant for EC&M. He can be reached at [email protected].
