Power Quality Measurement

Key role in ensuring reliable supply

Power systems have evolved with time and so have consumers. Today, consumers across the domestic, commercial and industrial categories have installed sophisticated electrical and electronic equipment devices that require uninterrupted, reliable and “good quality” power. Meanwhile, utilities are faced with challenges relating to the grid integration of renewables and decentralised power, which cause voltage fluctuations and harmonic currents, and result in “bad power” supply, if unchecked.

Power quality issues range from fast transient overvoltages to long-duration outages as well as harmonic distortion and voltage flickers. These issues have a significant impact on consumers and utilities. For instance, voltage spikes can often lead to equipment failure in facilities with microprocessor-based devices. It can also lead to the failure of insulators in an industry/utility, loss of vital information or hampering of processes in data centres, and halting of operations in a manufacturing facility equipped with automated control equipment.

These issues can, however, be avoided by adopting advanced tools for power quality measurement and testing, waveform correction devices, and condition monitoring, which help maintain the power quality for consumers as well as utilities.

Measurement and testing tools

A wide range of testing equipment is available to detect and analyse power quality issues. These include multimeters, harmonic meters, oscilloscopes and power quality analysers, which record the complete spectrum of power quality variables. Lately, utilities and consumers have been moving towards multifunction power quality measurement equipment that monitors the maximum variables at a relatively lower cost than instruments that record only specific variables. Another growing trend is a reduction in the size of equipment and ease of application.

An oscilloscope is handy when performing real-time tests for power quality. Distortions in power supply can be inferred from the voltage and current waveforms provided by the device. Digital oscilloscopes also have data storage and analysis capabilities, and a communication system to transfer data to other devices (such as computers and laptops) for further interpretation.

Power quality analysers are also used to get real-time readings and collect data regarding power supply. While some analysers are permanently installed in the distribution system, hand-held analysers are used for applications such as troubleshooting. Hand-held power quality analysers measure a variety of parameters including voltage, amperage, frequency, power factor, harmonic currents, inrush current values and light flicker. Today, analysers are getting smaller and easier to use but still provide information based on voltage events. The analysers also incorporate load and power analysis, which is crucial for a large segment of users.

Portable data loggers monitor similar parameters as the power quality analyser; however, they are meant for long-term recording (days to several weeks). Unlike power quality analysers, data loggers do not typically provide real-time values on screen.

Additional test equipment such as scopemeters and recording digital multimeters also find specific use applications. Multimeters can be used to check voltage or current levels in a facility. Overloading of circuits, undervoltage and overvoltage issues, and circuit imbalances can be detected using multimeters.

Troubleshooting a power system for a suspected harmonics problem also includes voltage and current measurements made with true root mean square digital meters. By using such meters, the voltage and current amplitudes can be accurately determined in the presence of non-sinusoidal loads.

Another key aspect of power quality measurement is flicker measurement. Flicker meters measure the  magnitude of voltage fluctuations and the corresponding frequency of fluctuation. Further, digital cameras are used during field measurement and are crucial for documenting the data.

Conclusion

The effects of bad quality power may not be visible immediately but they can be severe in terms of production and revenue loss. It can also result in highenergy costs, decreased life of equipment, and frequent equipment failures. In addition, as utilities and consumers are increasingly moving towards energy efficiency, it is important to optimise electricity use for any given load and power quality management plays a crucial role in it.

 

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