When investigating a power quality issue, most investigations start by using a multimeter that only displays the voltage amplitude as a root-mean-square (rms) value. When trying to narrow the search down to a piece of equipment, some investigators only observe and analyze the rms voltage when an electrical device is turning on and off. This can be time-consuming and inaccurate if a facility has many devices operating in tandem with one another.
Generally, the rms value only describes the amplitude of a waveform and does not include important information, such as transient characteristics and waveform distortions. To perform a power quality investigation, it is important to review the entire voltage waveform and not just the amplitude. This requires understanding what the fundamental waveform looks like. In other words, what is the point of reference?
The fundamental voltage waveform is a sinusoidal shape that has an amplitude and time period. The period can be described as one waveform cycle. A multimeter measures the amplitude and mathematically converts it to an RMS value, by taking the waveform peak and dividing it by 1.414 or √2. In most all cases here in the United States, the electrical system operates at 60 Hz or 60 waveform cycles per second. In a 3-phase system, the individual waveforms are shifted in relationship to one another in what is commonly described as 120 electrical degrees apart. The fundamental voltage waveform is the basis for power quality studies. Power quality definitions describe any deviations from this waveform.
Using a monitoring device that has the capability to capture waveforms will support your efforts to troubleshoot and find the root causes of electrical equipment misoperations. Power quality events or deviations from the fundamental waveform, such as voltage sags, transients, harmonic distortions, and other types of events can be used as a “fingerprint” to pinpoint the device causing the problem. Poor power quality can be caused by a power factor capacitor bank switching, which generates transient voltages on the lines. It could also be associated with a variable frequency drive that creates harmonic distortions.
The best way to identify power quality problems on a system is to capture voltage waveforms and compare it to the fundamental voltage waveform, which is the initial point of reference.
