How Power Quality is Measured?
Several types of instruments are available for power quality measurement, each serving their own unique purpose. Power quality analyzers are the most commonly used tools to observe real-time readings and also collect data at high speeds for downloading to computers for analysis, opposed to a power recorder or “data logger” which is mainly used for simple voltage and current measurements.
Often times power interruptions are unpredictable and of short duration, which can only be captured using a power quality meter (PQM) installed over a period of days, weeks or months. Each phase in the system has a voltage probe and current sensor applied to monitor the magnitude and polarity of each channel over the specified period.
Image#1: Several types of instruments are available for power quality measurement, each serving their own unique purpose.
The place where the PQM is connected is called the measurement plane, everything to the right of the plane is considered part of the load and everything to its left is considered the source. The measurement plane can be any point within the power system, not necessarily at the incoming service.
A cycle is the time that the waveform takes to travel from the zero line up to its positive peak, back down to its negative peak, and then back to zero. Power quality meters can be extremely high speed devices designed to capture events down to the sub-cycle level.
In an ideal 60Hz system, one cycle takes 16.7 milliseconds, or 0.0167 seconds. This is called the period of the wave, and is represented by the letter T. Frequency is equal to the inverse of the period, f = 1/0.0167 = 60Hz.
Image#2: Power Quality Analyzer Connection Example.
The type of meter to install will depend on the data to be captured. For example, a simple ampere load evaluation or utility bill audit would require a far less sophisticated meter than trying to pinpoint the cause of a nuisance trip or other power interruption.
The most important factor to consider when performing power quality analysis is safety. Often times meters are applied live with equipment in service which can be an extremely dangerous task.
This type of work should only be performed by qualified personnel while observing all appropriate safety precautions. A local power outage at the monitoring location is always the safest way to install and remove a power quality meter.
Image#3: The most important factor to consider when performing power quality analysis is safety.