Abolition of leap seconds moved to 2027 to protect smart grid time synchronisation

International metrology authorities at the General Conference on Weights and Measures have decided to bring forward the introduction of continuous Coordinated Universal Time to 20 May 2027. The formal justification explicitly highlights the requirements of energy distribution networks and smart power grids, where ultra-precise time stamping and synchronisation are paramount. Historically, leap seconds have been inserted periodically to keep atomic time aligned with astronomical solar rotation. However, injecting an irregular leap second introduces significant systemic vulnerabilities to computerized infrastructure.

Modern electrical substations depend heavily on coherent, high-precision timing reference signals. Time-stamped data streams underpin wide-area monitoring, digital protective relays, disturbance fault recorders, and synchrophasor measurements across transmission corridors. Synchronised phasor monitoring demands sub-microsecond precision across vast geographic footprints to calculate phase angles and assess system stability.

When a leap second occurs, network time protocol servers and satellite-synchronised master substation clocks must handle an irregular minute containing an extra second. In practice, software implementations vary widely: some systems repeat a second, some freeze timestamps, and others attempt gradual frequency smearing. Such timing anomalies can cause protection relays to interpret temporary time slips as communication losses, triggering telemetry lockouts or false trips. For transmission and distribution operators managing interconnected transformer substations, uncoordinated timing errors complicate sequence-of-events analysis following grid faults, obscuring whether an initial transformer trip was caused by an external line fault or an internal bushing breakdown. Moving to a continuous time scale eliminates the operational overhead of preparing automated substations for leap second events.

What this means for asset owners in Europe, the Middle East and Africa: Utilities across Europe and the UK should conduct comprehensive reviews of substation master clocks, protective relays, and supervisory control software before the compliance date of 20 May 2027. Ensuring that satellite receivers and station timing modules can transition to continuous universal time without applying unexpected time-step corrections will eliminate outage risks and false alarm events during future grid disturbances.