A Simple Calibration Procedure for an LPIT plus PMU System Under Off-Nominal Conditions

This work deals with two paramount devices when Smart Grids are concerned: phasor measurement units (PMUs) and low-power instrument transformers (LPITs). In particular, a simple calibration procedure to test the measurement chain PMU + LPIT has been developed. The procedure involves steady-state conditions of the grid and off-nominal input signals for testing current, voltage, frequency, and rate of change of frequency (ROCOF). In addition, the procedure includes a preliminary testing of the PMU without the LPIT to understand the influence of the latter. The procedure is then applied to a specific case study: a low-cost PMU developed by the authors and one of the most common LPITs adopted in Italian medium voltage networks. The obtained results are promising for two reasons. First, the low-cost PMU works correctly even in off-nominal conditions of the grid; second, the presented calibration procedure demonstrated to be effective and applicable to very common equipment, using a rather simple test setup.