System accuracy test of LPIT-based metering systems

This paper presents the results of an accuracy testing procedure for LPIT-based metering systems. It emphasizes on experimental linearity verification tests on LPITs (Low Power Instrument Transformers) and uncertainty calculations for the test system. The system accuracy test is generally based on four stages: type, routine, commissioning, and on-site accuracy verification tests. Current IEC standards demand system accuracy tests for energy meters including LPIT, but because of impractical system tests at high voltages and currents, smaller test amplitudes are needed – especially for on-site accuracy verification tests with mobile test devices. By verifying the linearity of LPITs before installation and consideration of an additional uncertainty contribution due to amplitude dependencies or nonlinearities, the metering system's accuracy can be assessed effectively with lower test magnitudes.