Monitoring ageing CCVTs practical solutions with modern relays to avoid catastrophic failures

Abstract

Ageing coupling capacitor voltage transformers (CCVTs) can pose safety problems and possibly restrain system operations. Catastrophic failure of a CCVT could start a widespread fault in the substation and/or endanger personnel working in a close proximity. The latter becomes a real danger when inspecting a suspicious CCVT or when live line work is being performed. CCVT monitoring becomes more and more important as the installed population of CCVTs ages with sporadic incidents of catastrophic failures alerting both field personnel and dispatching managers regarding safety and liability. Microprocessor-based protection relays facilitate cost-efficient and broad deployment of CCVT monitoring functions across the organization. First, modern relays allow programming a number of indicators that alone, or in combination, are reliable enough to raise alarms and initiate an in-depth engineering analysis. Second, these relays can provide data recording and remote access. This data includes high-resolution data such as oscillography, and long-term trending such as the magnitude profiling. Third, relay-based CCVT monitoring schemes can be retrofitted in the existing installations. In many cases with a simple wiring and setting changes, existing relays could provide a solid CCVT health indication. The combination of reliable alarming via protective relays with remote access yields a cost- efficient, easy to implement, and safe to operate, solution. This paper presents a number of CCVT health indicators that could be programmed on modern relays via logic and simple math operands in order to monitor the CCVTs with a minimum material and labor investment.