An International Comparison of Power Measurements at 120 V, A, and 60 Hz

An international comparison of ac power measurements between metrology laboratories at the Physikalisch-Technische Bundesanstalt¿Institut Berlin, (PTB(IB)), the Electrosystems Division of the National Bureau of Standards (NBS), and the Division of Electrical Engineering at the National Research Council of Canada (NRC(EE)) is described. The three calibration systems, each of different design and developed independently, are discussed, and estimates of the systematic uncertainties are given. The transfer standard was a recently developed thermal wattmeter of high stability. No laboratory differed by more than ±15 parts per million (ppm) from the average, with reference to apparent power at unity and 0.5 power factors, lead, and lag. This is consistent with the error limits estimated by each of the participants.