28-02-2010, 09:28 PM
Abstract:
The amount and complexity of household electrical equipment has increased tremendously over the last few years. Electronic ballast lighting, computer monitors and air conditioners are welcome additions to our homes but come with additional burdens. One of these is on the electricity grid, as these appliances generate more signal harmonics. This change in the end-consumer profile is a disadvantage for energy distributors which bill energy based only on active power. With the application of non-linear loads to power lines the active energy no longer represents the total energy delivered. As a response to improve billing, the measurement of reactive energy is gaining interest. For example, Italy.s leading energy distributor has decided to install more than 20 million household energy meters with active and reactive power measurements. This growing interest in measuring reactive energy leads to the question: What method should an energy meter designer implement to accurately measure the reactive energy? Although today.s electronic digital signal processing (DSP) enables reactive energy measurements to be closer to the theoretical value, there is no consensus in the field of energy metering on the methods of measurement. This article aims to explain and compare the three main methods in use, namely the Power Triangle, the Time Delay and Low-pass Filter. SYSTEM REQUIREMENTS Electromechanical meters have set a precedent in reactive energy billing. Although they are bandwidth limited and cannot take into account harmonics of the line frequency, they are supported by the international standard for alternating current static var-hour meters for reactive energy (IEC-1268). The standard defines reactive energy measurements at the fundamental line frequency, which implies that it is not mandatory to include harmonics. It also specifies additional testing conditions to check the robustness of the measurements against the third harmonic, the dc offset in the current input, and the line frequency variation.
Presented By Etienne Moulin, Applications
Engineer, Energy
Measurement Group, Analog
Devices Inc.
