Availability of hardware in substations

The software and hardware in the substation are designed in a way that they meet high availability requirements. The means high reliability ( Long mean-time-to fail MTTF) and short down time ( Short mean-time-to recover MTTR). MTTF means statistical time until component need a repair.Short down times can be achieved by extensive diagnostic functions, modular hardware designs, fast reconfiguration and automatic restart after a power supply failure.

The redundancy recomended:

• Repair faulty parts in process and bay level in less than two hours and less than 4 h for station level.
• Standby hardware exist physically connected and per-configured.
• Warm standby - standby HW constantly supervise active HW, automatically takes over in a failure. Time stamped events may be lost. commands are reusable after 10-30 sec
• Host standby -  standby HW constantly supervise active HW, it takes over in a failure. No Time stamped events  lost. commands are reusable after 1-5 sec. at bay level switch over time is less than 100ms.

Self supervision of IEDs

• Insensitive against EMI
• A/D conversion may subjected to aging should be supervised by a reference signal
• Watchdog should supervise the response time from processing algorithms
• Checksums are used detect failure in mamory
• Loss of power should be checked

Supervision of communication:

• All communication devices ( Star couplers, routers, switches) are subjected to self supervision
• Detection of errors, check the response time and counting lost messages