Time Synchronization Using Irig-B - ABB Relion 670 Series Application Manual

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1MRK 505 382-UEN E

IEC10000203 V1 EN-US

Figure 10: Setting the GPS clock

At synchronization start, the internal clock is adjusted to have the correct global time in

seconds with only integers set. The remaining fractional parts, milliseconds (ms) and

microseconds (μs), to reach global time, are used to slowly synchronize the internal clock to

global time.

Synchronizing the internal clock to global time is done at a rate of 1 ms/s. When the internal

clock is within 16 μs from global time, the protection function is enabled. If time deviation

between the internal clock time and global time is more than 16 μs, GPS timing is deactivated

and the differential protection is either blocked or changed to Echo mode depending on the

setting for LDCM (

After the protection function is enabled, soft calibration is performed to have the internal

clock remain within 1 μs from global time for < 1 hour. This reduces the restart time after a

short GPS interruption. If time deviation after the interruption is less than the set

MaxtDiffLevel , the protection function can be enabled directly.

In the case of GPS interruption, the protection function is disabled or echo timing is enabled as

a back-up synchronization method. Enabling echo timing has a delay which depends on how

long the GPS system has been in service after start. Inaccuracy of the internal clock starts at 16

μs and goes down to ±1μs after some minutes.

In telecommunication networks with unspecified route switching, echo timing can only be

used with unchanged time delay in both directions. As soon as the time delay is outside the set

limits, the protection function gets blocked. Some additional features are available to increase

the performance of echo timing:

•

If redundant or alternative routes are available, they are also supervised for changes in

time delay. If no time delay difference is observed in these routes, echo timing continues

to use the reserve channel.

•

In telecommunication networks with unspecified route switching, time deviations below

the set limits are accumulated to handle multiple route switching, and these accumulated

deviations can reach the set time deviation limit.

3.3