Measuring Losses of an Air-Core Shunt Reactor with an Advanced Loss Measuring System

Losses of low-loss inductive components like power transformers and reactors are difficult to measure accurately because of the very low power factor. Low power factor means that accuracy of the measurement of the phase angle is a crucial factor in the measurement uncertainty. In this paper we introduce an advanced loss measurement system for measuring the losses of an air-core reactor under high voltage. The system consists of a capacitive voltage divider, a current sensor and two sampling multimeters. The high-voltage arm of the used capacitive divider is a gas-compressed reference capacitor. The low-voltage arm consists of ceramic capacitors on the feedback loop of a buffer amplifier, which enables a load independent output and very small phase error in power frequency. A well-characterized Rogowski coil is used as the current sensor. The outputs of the voltage and current sensors are measured using 8½ digitsampling multimeters, which are synchronized using an external trigger generator. The developed loss measuring system was used to measure losses of an air-core reactor during 16-hour temperature rise tests according to IEC 60076-6. The test object was an air-core shunt reactor with nominal inductance of 11.7 mH. The tests were performed with 1200 A, while the feeding voltage was a few kilovolts. Results show the losses of the air-core reactor as function of time during the heating. Measured losses were also compared to the temperature compensated loss calculation, where the losses measured on cold coil are corrected to the reference steady state temperature according to IEC 60076-1.