Prototype Field Calibration System for Coupling Capacitor Voltage Transformers (CCVTs). Final Report

摘要

In recent years, the coupling capacitor voltage transformer (CCVT) has come into wide use for 0.3% accuracy extra-high voltage (EHV) revenue metering in interties between utilities, a function performed for many years by the inductive potential transformer (PT). Whereas the PT has been thoroughly proven in this application, the CCVT has not. Considerable user experience has raised very reasonable doubts as to its adequacy and suggested the need for periodic calibration. Since the CCVT is permanently installed in the substation, this calibration must be done on-site. A prototype field calibration system for CCVTs has been developed. The system consists of (1) CCVT capacitor modules; (2) a high voltage (100 kV) capacitor standard; (3) a current comparator bridge; and, (4) a resonant power supply, all of which are transported in a closed truck. At the substation site, the capacitor modules are removed from the truck and stacked up to form a capacitive divider with a rating that matches the system voltage for calibrating purposes. This divider is used as a transfer standard since it is first calibrated against the high accuracy, high voltage capacitor standard (2) located in the truck. Then it is connected to the high voltage bus to calibrate the substation CCVTs. The mobile unit is compact and comparatively easy to use. Only a two-man crew plus a minimum of support from the local utility are required to assemble and operate the modular system at the test site. System accuracy is 0.05% and 0.3 milliradians. It has successfully undergone two complete field tests in which a total of six CCVTs and six PTs were calibrated. Feasibility of a considerably simpler and less costly system has been demonstrated in a project extension. (ERA citation 03:044631)