# Maintenance Windows

Scheduled maintenance windows for the northern grid substations are planned
quarterly and published to the operations calendar.

- **Halden substation:** first Tuesday of each quarter, 02:00–05:00 local time.
- **Skjold substation:** second Tuesday of each quarter, 02:00–05:00 local time.

During a maintenance window the substation runs on its backup feeder. Operators
should confirm the failover has completed cleanly before starting any work and
should never begin maintenance on a substation still carrying primary load.

Authorization codes and failover procedures are documented separately in the
substation emergency procedures; this calendar covers timing only.
