The protection relay has a disciplined RTC in hardware with a resolution of one millisecond. The clock can be either free-running or synchronized to an external source. The RTC is used to time-stamp events, recorded data, disturbance recordings, sampled measured values and various other system services.
The protection relay supports SNTP to synchronize the RTC. The accuracy is ±5 ms with SNTP.
Real-time clock at power off
During power off, the system time is kept in a separate capacitor-backed RTC. This RTC provides a millisecond resolution and digital temperature compensation for the crystal oscillator. Typical accuracy is 10 ppm which means the time may drift maximum 1 second per day. This RTC runs on a stored charge in a supercapacitor at least for 48 hours. After the capacitor has been discharged, the time is lost.
Real-time clock at power-up
At startup, the initial system time is recovered from the capacitor-backed RTC or set to 01-01-2010 if the RTC time was lost. The clock is free-running until the selected synchronization source becomes available. The first synchronization message sets the time to an accurate value and later synchronization messages additionally discipline the clock so that the time drift between synchronization messages is minimized. If the synchronization source is lost, the drift can be 0.25 ppm if the external clock source was a high-quality clock and the surrounding temperature is constant.
The setting Synch source determines the method for synchronizing the RTC. If it is set to "None", the clock is free-running and the settings Date and Time can be used to set the time manually. In this mode the typical accuracy is 10 ppm and the time may drift maximum 1 second per day.
Other setting values activate a communication protocol that provides the time synchronization.