An AC power amplifier for testing instrument transformer test equipment

This paper describes the design and setup of analogue power amplifiers for generating calibration signals for test equipment for instrument transformers. Two amplifiers have been set up for a rating of 600 VA and 70 VA, respectively. The 600 VA version is used for testing standard burdens, while the other one is used as a source for a calibrator for testing test sets for conventional and non-conventional current or voltage transformers. The amplifiers offer the possibility to switch between a voltage mode and a current mode. The bandwidth of the amplifiers covers the range from 16.7 Hz to at least 3 kHz. Different ranges between 80 V to 280 V in the voltage mode, and 2 A to 10 A in the current mode are realized with a transformer-coupled output stage. The gain accuracy is in the order of 1 %, while the stability is better than 0.01 %. The smaller amplifier will be used to set up future measurement systems in the EMRP project "Non-conventional voltage and current sensors for future power grids".