How to Measure Mains / Line Voltage and Harmonic Distortion

How to Measure Mains / Line Voltage and Harmonic Distortion

Postby VirtinsTech » Mon Aug 31, 2015 10:30 am

This video demonstrate three methods to measure the voltage and harmonics of an AC power supply using a USB oscilloscope with passive probes. The three method are: (1) Earth-Grounded Single-Ended Measurement (2) Earth-Grounded Differential Measurement (3) Floating-Ground Differential Measurement.


Method 1
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Method 2
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Method 3
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Re: How to Measure Mains / Line Voltage and Harmonic Distort

Postby retika » Mon Feb 18, 2019 4:35 pm

Power quality in the context of ac lines usually refers to how closely the ac line comes to approximating the ideal sinusoidal wave. Real-world factors such as electrical noise and the tolerance of a voltage and frequency all affect power quality. Thus it is often important to measure the degree to which ac lines depart from the ideal sinusoid.

Perhaps the simplest way of determining power quality is to measure the ac mains voltage with two different kinds of voltmeters, one an averaging type of unit (such as an electromechanical movement meter), the other a true-RMS type of unit (such as a high-quality digital meter). Averaging- type meters are calibrated so their scales indicate RMS volts, assuming the measured ac voltage is sinusoidal.

However, if the ac voltage is a distorted sinewave, the averaging meter will not register the proper value, but the true-RMS meter always will, regardless of waveshape. So the greater the difference between the two-meter readings, the worse the power quality, and the greater the harmonic content.

Unfortunately, the comparison of meter readings is somewhat of a blunt instrument as far as assessing power quality. When there are issues with power quality, it’s nice to have a way of isolating the source of the problem. That’s where an oscilloscope comes in, particularly a modern scope able to double as a spectrum analyzer.

First, we’ll list some properties of electrical power as supplied by a utility and modified at the customer’s facility, which impacts power quality:

• Unreliability – Frequent and/or prolonged outages. Utilities take the position that they will endeavor to maintain continuous service, but the fact is that at times there will be interruptions in power, most often due to violent weather events, equipment failure, or when intoxicated or texting drivers take out a power pole. Whatever the cause of a power loss, the utility is not generally liable for consequential damages unless negligence can be shown.
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