| Zugriffsnummer | 36293 |
| Dokumenttyp | Zeitschriftenartikel |
| Sprache | Englisch |
| Titel | Assessment of the behaviour of digital power comparators with harmonically distorted signals |
| Autor(in); Institution |
Mohns, Enrico; 2.3, Elektrische Energiemesstechnik, PTB-Braunschweig
|
| Quelle/Jahr | ZERA Newsletter:(2009), 40 S. |
| ISSN | NO-ISSN |
| Verlag | Königswinter: ZERA GmbH |
| Zusammenfassung | It is becoming increasingly important for ac power measurements to determine the electrical ac power P as well as the voltage URMS and the current IRMS under distorted conditions. This is due to the increasing distortions in electrical grids that result from non-linear loads. The measurement accuracy of electricity meters must therefore also be assessed under such conditions. This is done worldwide in specially equipped and certified laboratories with reference meters traceable to power comparators. The comparators are calibrated from time to time to national standard in the respective national metrology institutes (NMI). This calibration is usually performed under sinusoidal conditions, as the number of possible harmonically distorted waveforms (HDWFM) is unlimited and tests would have to be restricted to specific HDWFMs. However, the measurement bandwidth of digital power comparators (DPC) is sufficiently high to determine even the highest required 40th harmonic [1] with sufficient small measurement uncertainty. This report describes a method to specify the error limits of DPCs for any HDWFM. This is done by using "worst case" test signals that are more distorted than the waveforms used when testing electricity meters [2] (leading edge or half-wave rectification). Equations in general form for determining the error limits for URMS, IRMS and P are provided. They can be used for retrospective calculation of the error limits of DPCs that were previously only calibrated under sinusoidal conditions. Finally, the deviations of a DPC determined with these test signals and other but standardised test signals are compared. |
