Calibrating Instrument Transformers with Phasor Measurements

Abstract

Power systems measurements are often performed with current and voltage signals derived from instrument transformer secondary circuits. Errors introduced by these transformers are a recognized component of input data errors in supervisory control and data acquisition and phasor measurements. Correcting these errors by {in situ} calibration is an expensive option; hence, it is seldom employed except in a few special cases. This article proposes a new method for calibrating instrument transformers utilizing phasor measurements by estimating instrument transformers' ratio correction factors and phase angle correction factors. The method focuses on the fundamental frequency component of phasor measurements, and, in contrast with some of the techniques proposed in the literature, it does not require accurate instrument transformer models and can be executed as often as needed to keep the calibration up to date. Two alternative calibration techniques are introduced along with the simulation results to prove the feasibility.

Keywords:

• instrument transformers
• power system instrumentation
• phasor measurement units
• phasor measurements
• state estimation
• calibration