Power measurements as an aid to energy efficiency

By Hafeez Najumudeen, Yokogawa Europe & Africa



Manufacturers are increasingly focusing their efforts on energy conservation. This trend is reflected in the growing emphasis on both renewable energy and energy efficiency measures to reduce the amount of energy consumed. Governments and regulatory authorities are establishing new standards for the energy consumption of various types of equipment, which has to comply with complex and stringent specifications, and in many cases have to carry energy efficiency labels to show that they meet these requirements. Standby power consumption Typical of this trend is the demand for a lower threshold in standby power consumption. This is an important area for a number of reasons. For example, it is estimated that between 5% and 15% of residential electricity used in the OECD countries can be attributed to the power consumption of appliances in standby mode: equivalent to about 240 million tonnes of carbon dioxide emissions every year. Moreover, by 2020 it is expected that approximately 4.6 billion products will be featuring a standby option, contributing around 50 TWh of electricity consumption per year. This amount is equal to the total electricity consumption of a country like Greece or Portugal. The International Energy Agency (IEA) has launched a 1 W standby initiative, and it is expected to decrease this threshold to 0.5 W by 2013. The scale of the challenge presented by these limits is illustrated by the fact that 18.5% of all household appliances in "off" mode and 31% in standby mode failed to comply with the 1 W initiative. The proposed reduction to 0.5 W will result in 41.5% in "off" mode and 66.4% in standby failing to comply. If an item of equipment has power consumption between 0.5 W and 1.0 W, it is estimated that electricity consumption in standby/off mode by 2020 will be about 15 TWh. This represents a saving of around 35 TWh of electricity: equivalent to the total electricity consumption of Denmark User requirements In order to meet these regulatory requirements, equipment suppliers will need to measure the actual power consumption of their products, often at very low power levels. They require accurate and reliable power measurement over a range from milliamperes to dozens of amps. Accuracy and reliability are essential to develop and produce products which not only comply with standards but also guarantee consistency. There is also a need to carry out measurements other than the standard electrical parameters of voltage, current and power, because of the increased regulatory emphasis on power quality which demands measurements in areas such as harmonics and frequency-based parameters. Equally important, particularly in the production environment, are ease and flexibility of use, to ensure that employees with all skill levels are able to operate the instruments. Production testing also requires a communications interface so that the measuring instrument can interact with PCs and other instruments to create an automatic test system for improving productivity and enhancing quality assurance. Digital power meters One example of how these challenges are addressed can be found in Yokogawa's latest generation of digital power meters (Fig.1), which offer a basic accuracy of 0.1% of reading, guaranteed accuracy over the entire measurement range (from 1% to 130%), a wide measurement range from standby power levels of a few milliamperes up to 40 A, and the flexibility to enable users to target different technical and commercial applications. In addition to standard power measurements, these instruments incorporate a wide range of harmonic measurement capabilities, including the ability to carry out simultaneous measurement of normal power parameters such as RMS, mean or DC power along with measurement of harmonics up to the 50th order. As a result, overall measurement times are reduced, allowing users to allocate their effort and time to other tasks. Other features of the new instruments include a bandwidth of DC and 0.5 Hz to 100 kHz (up to 20 kHz for 40 A on the WT310HC), plus an auto-range function for measurement and integration. Software is also available for testing equipment compliance to industry energy-saving standards such as IEC62301 Ed2.0 and IEC62018 for standby mode equipment or for dealing with waveforms having a crest factor of 5 or more. Quality assurance and production line testing of electrical devices: The instruments' compact half-rack mounting size plus the choice of interfaces makes it easy to integrate into a customised production test system. In addition to the USB, RS232 or GPIB and Ethernet capability, a D/A output function is also available for data recording. Test times are minimised via the ability to make simultaneous power and harmonic measurements, and the communication interfaces make it possible to capture measured data remotely. It is also easy to create a test program using sample program and LabVIEW drivers. Power consumption and efficiency measurements on industrial motors: This application benefits from the ability to make accurate measurements on fundamental power parameters over a broad bandwidth (DC to 100 kHz) and to make long-term energy measurements using the integration capability. The user can also save the measurement data and monitor the results along with other parameters using the D/A interface and an external waveform recorder. Measurements on distorted waveform including both DC and AC components and simultaneous measurement: The digital power meters can measure DC components and distorted waveforms including rectified and half/full waves without changing the measurement mode. A line filter (cut-off 500 Hz) can eliminate unnecessary components. The broadband capability allows the instrument to measure the RMS value of distorted waveform like rectified half wave without any change in measurement mode. Evaluation of equipment against international standards: International standards such as SPEC Energy Star and IEC62301 specify limits on parameters such as crest factor and total harmonic distortion. The high resolution of 5 mW and low current range of 5 mA are ideal for these applications. PC-compatible free software is also available to make measurements to the IEC62301 standard. The ability to carry out simultaneous normal and harmonic measurements results in a low-cost test solution. Evaluation of uninterruptible power supplies (UPS): It is possible to evaluate a UPS against the IEC62301 standard using the integration feature for energy measurement and the integrated auto-range function. For a UPS that complies with the performance test of IEC standards, the power meter can calculate and measure the efficiency and the strain rate and the frequency and output level between the input and output at the same time. A global concern Energy efficiency has become a global concern over the past decade, and evolving national and international standards will help to ensure that power efficiency is incorporated into all the key stages of the design and manufacture of electrical appliances. Ensuring compliance with these standards requires accurate measurement. This will not only help manufacturers achieve energy efficiency goals, but will also benefit the consumers, the economy, and the environment.