Remote Measurement Calibration

Power system reliability and economy of operation require accurate measurements of current, voltage, real and reactive powers. These measurements are telemetered to a central location for monitoring, display, and use in power system application programs. Typically in an Energy Management System (EMS), the number of measurements is in the thousands. Routinely field technicians must calibrate transducers and/or determine other sources of metering errors. Due to the large number of measurements and the time required to check each individual measurement, field calibration procedures are impractical, expensive, and not timely. There has been a need for a more efficient approach to measurement calibration and identification of the defective instruments. This paper describes a novel approach which meets the need. Repetitive measurements are used to determine errors due to the instrument transformers, transducers, secondary leads between these devices, analog-to-digital convertors, and the scaling procedure. The amperes, volts, watts and vars scales are then adjusted to compensate for these errors, thus providing more accurate measurements. The remote measurement calibration (RMC) method has been implemented on the EMS of Potomac Electric Power Company (PEPCo) for several 230kV substations with excellent results.