GPS Standard
If GPS -> Standard is selected, the time alignment of the current data is performed by using the values of
propagation delay times (tp1, tp2) that were calculated and stored prior to the GPS failure. Each terminal continues
to measure the overall propagation delay (tp1+tp2). If the overall propagation delay remains unchanged, the
differential protection will continue to use the stored values until the GPS synchronisation is restored.
A communications delay tolerance setting (Comm Delay Tol) is provided. If the overall propagation delay changes
but by an amount less than this setting, the differential protection will continue to use the stored values of tp1 and
tp2 until GPS synchronisation is restored. If the overall propagation delay changes by an amount more than this
setting, the differential protection will be blocked until GPS synchronisation is restored.
GPS Inhibit
With GPS -> Inhibit selected, if the propagation delay times are equal when the GPS synchronisation is lost,
the product reverts to the ping-pong method of time alignment. If the propagation delays are not equal when the
GPS signal is lost, the product performs in the same way as if GPS -> Standard had been selected, using the
stored propagation delay times.
If the propagation delay changes by more than the Comm Delay Tol setting, the differential protection is blocked
until GPS synchronisation is restored.
GPS Restrain
If GPS -> Restrain is selected in the GPS Sync setting, the supervision applied to the Current Differential
function is the same as that for Switched Communications Paths Supervision described previously, and based on
increasing the bias quantity if path switching is detected.
In this case, if GPS has failed, and if the difference between successive propagation delay time measurements
exceeds the user settable Comm Delay Tol value, the device asserts the Comm Delay Alarm DDB signal and
initiates the temporary change in the bias characteristic managed by the Char Mod Time and Char Mod RstTime
settings.
2.4.1
PROPOGATION DELAY MANAGEMENT
When GPS synchronisation is used, there are some settings that are provided to control the behaviour of the
product according to the propagation delay times between terminals. These are described, together with some
related settings in the table below:
Setting Description.
Prop Delay Equal
This applies if the device is using GPS synchronisation. If the GPS signal is lost and there is a switch in the
protection communications network, the differential protection is inhibited. When the GPS is restored, the
differential protection will return to service. Using this setting you can return the differential protection to
service in the absence of the GPS signal. Before activating this setting you must be sure that the
communication receiver and transmitter path delays (go and return) are equal, otherwise false tripping may
occur.
The setting is invisible when GPS Sync is disabled.
Prop Delay Stats
This setting enables (activates) or disables (turns off) the alarms of Maximum propagation delay time described
by the MaxCh1 PropDelay and MaxCh2 PropDelay settings
MaxCh1 PropDelay
When the protection communications are enabled, the overall propagation delay divided by 2 is calculated for
channel 1. The maximum value is determined and displayed in the MEASUREMENTS 4 column. The value is
compared against the MaxCh1 PropDelay setting. If the setting is exceeded, an alarm MaxCh1 PropDelay DDB
is raised.
MaxCh2 PropDelay
When the protection communications are enabled, and where used, the overall propagation delay divided by 2
is calculated for channel 2. The maximum value is determined and displayed in the MEASUREMENTS 4 column.
The value is compared against the MaxCh2 PropDelay setting. If the setting is exceeded, an alarm MaxCh2
PropDelay DDB is raised.
TxRx Delay Stats
This is used to enable (activate) or disable (turn off) the alarms of absolute difference between the
Transmission and Reception propagation delay. This setting is not visible if GPS Sync is disabled.
Chapter 18 - Supervision P543i/P545i
468 P54x1i-TM-EN-1
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