Advanced uses of disturbance recordings for verifying transmission system performances and triggering conditional maintenance

Disturbance recordings are used together with sequence of events (SOE) data to document and understand a power system fault; to manually verify the behaviour of digital protection relay; and nowadays, to perform automatic fault analysis (AFA) for the sake of fast and accurate fault location and to assist fault analysis engineers in their task. This paper focuses on two additional uses of the disturbance recordings. The general purpose is to gain insight into the condition of the monitorable assets using information from recorded signals. The authors suggest that each significant power system event provides an opportunity to verify that key processes behave within their design limits.The first field of application is circuit breaker monitoring. If sampled currents are recorded, it is shown that a system can monitor virtually all switching events, provide some alerts in near real-time if some critical conditions are found, and produce history data that are usable for long-term statistics in asset management systems.The second area of interest is automatic monitoring of protection schemes. The paper presents a literature survey about this topic, then it describes a methodology to verify major protection scheme automatically, on the occasion of every recorded short-circuit fault occurring in the grid, provided that enough event-related data are collected. The verifications consider essential design targets like maximum fault clearance time, phase-segregated tripping, maximum allowable time delay of teleprotection signals, pick-up for back-up protection of distant lines, etc.This process may issue some alerts or warnings for immediate consideration by fault analysts, drawing their attention on potential weaknesses of the protection system that may have severe consequences on security. But the main use of the presented technology is to generate statistical inputs for off-line verification of the protection behaviour on a large scale, since utilities routinely manage thousands of protection relays. Monitoring of their field performance complements routine protection testing very nicely. As an example, a relay that picked up recently and correctly hardly requires testing, except a verification of the tripping circuit. On the other hand, a distance relay that failed to pick up in protection zone 3 or 4, to provide back-up protection of a remote line, may be considered for an early inspection even if its self-check functions indicate that the device is operating.The paper discusses methodologies for circuit breaker and protection monitoring for transmission systems and underlines the main operational uses of these monitoring tools by transmission system operators.