When and Where to Install a Power Quality Monitor

Having and using the proper tool for the job is always the tradesperson's main objective when working a project. Power quality (PQ) monitoring is no different.

When I began my career in this field, it was easy to set up a PQ monitor and let it record for two weeks, hoping to capture data. However, it is possible to have too much of a good thing — data, that is. I’d like to share some basic guidelines on how to quickly pinpoint electrical problems with and without PQ monitors.

Tip No. 1. Inspect the electrical installation for damage, wear, equipment installation mistakes, and NEC wiring violations. All of these problems can manifest as a PQ anomaly, causing equipment misoperations. Wiring violations to be on the lookout for are downstream neutral-to-ground bonds past where the NEC allows and grounding errors in separately derived systems. These two specific violations likely cause many types of equipment misoperations. Repairing all wiring problems before monitoring will save countless hours of data analysis.

Tip No. 2: If the customer only had one equipment misoperation in the last year, setting a monitor may not provide you with the data to understand equipment sensitivity because you would need another event to occur. The most beneficial first step is to contact the serving electric utility to investigate the date and time of the past event. Most electric utilities have all circuit breaker operations logged, and they know the speed of the circuit breaker opening. For example, a distribution circuit breaker may open in 30 cycles, whereas a transmission circuit breaker may open in six cycles. (Note: These are only examples; each electric utility has different protection settings.) Mitigation can be selected based on how sensitive the equipment was to that event, either at the distribution or transmission level.

Tip No. 3: Ongoing problems are the most ideal for setting PQ monitors and getting the most out of the tool. It is always helpful to set multiple PQ monitors to collect data. The two best locations are at the main service and the equipment. By using two monitors, you will be able to isolate internal and external problems quickly. Set the monitor to record long enough to capture a few events. Remember that when you set a monitor, it will record many different events. Most events may not even cause a problem with the equipment so don’t get bogged down by data. This is why a log must be kept near the equipment to record the time and date of each misoperation. Using that log, look for PQ events or low/high voltage that correlates with the misoperations to identify the best correction or mitigation type.

These basic tips should save you many hours of mind-numbing data analysis and help identify the problem faster.