Measurement Journal Issue 6

E Ensuring a stable and reliable supply of electrical power is essential to the successful operation of any city. Stability is especially critical when a city expects that its maximum power supply will be exceeded, such as during the 2008 Beijing Olympic Games (see the sidebar, Powering the 2008 Olympic Games). However, the production of high-quality electrical power requires more than simply providing the proper voltage and sufﬁcient current. It also requires the proper shape of the voltage waveform. One critical speciﬁcation of wave shape is total harmonic distortion (THD). The delivery of low-distortion electrical power is important since too much distortion can cause tripping of overcurrent protection devices. It can also cause overheating and reduced reliability of equipment such as capacitors, transformers and motors. Higher-order harmonics can even couple into communication systems, thereby generating interference. For these reasons it is important to measure AC power THD as it provides a means of verifying that power quality is within an acceptable range. This article describes a method of measuring power-generation THD that allows for remote data monitoring from a local-area network (LAN) or wide-area network (WAN). Deﬁning THD THD is deﬁned as the ratio of the root-mean-square (RMS) value of the harmonically-related signal components to the fundamental frequency (not including the fundamental frequency). Mathematically, we square the amplitudes of harmonics 2 through N, sum them, take the square root, and then divide by the amplitude of the fundamental. It is usually expressed in terms of a percent. For example, if 100 harmonics are to be considered, then THD is calculated in Equation 1 as: Equation 1. THD Sa 100 i=2 2 i a1 In practice, measurements are either made by monitoring taps (electrical connections in power lines that provide low-voltage monitoring points) in power-generation facilities or directly on line power at customer premises. While a digital multimeter (DMM) can offer a convenient method to measure the AC voltage of the line, until recently this type of instrument did not have the capability to measure THD. Also, it is difﬁcult to conﬁgure a traditional DMM to be monitored remotely. New generations of DMMs now provide the ability to digitize waveforms with sufﬁcient bandwidth to calculate THD. Some of these DMMs also offer remote monitoring and control using a LAN or WAN connection. Such capabilities enable technical personnel in a central location to evaluate the operation of power-grid components over a wide area. Agilent Measurement Journal 48

Table of Contents Feed for the Digital Edition of Measurement Journal Issue 6

Measurement Journal Issue 6 Using a Few Words to Convey a Deeply-Held Spirit Charting a Unique Path to Technology Innovation Contents Announcing First Commercial GC/MS Metabolites Library Assessing Nonlinear Behavior Testing Combines Form and Function Testing Multiplay Networks Higher Sensitivity LC/MS Easing Military Radio Test Stepping Up Calibration Accuracy Increasing Spectrum Analyzer Bandwidth 3GPP Tool Supports TS 36 Standards The Olympic Story Spotlights Agilent's Continuing Contribution to Technology Innovation Ensuring a Level Playing Field in Competitive Sports GPS: Coming of Age Resolving Design Issues in HSPA Mobile Devices Achieving Accurate Results with Oscilloscope-Based Jitter-Analysis Software RF Handheld Testers Guarantee Traffic Stability Under Olympic-Sized Stress Conditions Utilizing LAN-Based Instrumentation to Measure Total Harmonic Distortion in Remote Facilities IMT-Advanced: 4G Wireless Takes Shape in an Olympic Year EPO Doping: A Speed Engine, Turbo-Charged by Chemistry

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