1MRS755225
Transformer Terminal
Technical Reference Manual, General
RET 54_
83
Communication inputs acts as holding registers, they preserve the last received
value until next update is received. When a relay has been started, initially all inputs
will be zero and all invalidity flags will be TRUE. If an input is bound, the first
network variable update received will update the input and the corresponding
invalidity flag will be set to FALSE.
If the network variable connection is created using NV poll support, then the
receiving device can query the value from the sending device. This occurs at relay
startup and when open/close control of an object (for example COCB1) is selected or
executed. An input invalidity flag indicates the status of the poll. When the poll is
initiated, all input invalidity flags (with NV poll support) are set to TRUE. After
each successful NV poll the corresponding invalidity flag is set to FALSE. After all
polls are complete, the control command is allowed to be completed.
Communication outputs are prioritized by the number of the output. If multiple
output values need to be transmitted at the same time, the output with the lowest
number will be sent first. The relay configurations should be designed so that the
most time critical and least often changed signals are assigned to outputs with the
lowest numbers.
Communication outputs shall not change too frequently, otherwise outputs with a
low priority may not be sent to the network at all, or the updates may be delayed. The
maximum transmission rate is 50 updates per second for all communication outputs
together. If the limit is exceeded, loss of data will occur. The system is however
designed to always send the latest value when there is communication bandwidth
available. It may be necessary to use a data latch with timer mechanism in the relay
configuration to limit the update rate of an output.
Network variable connections are not supervised by the relay system software. For
example, a broken fibre will not be detected by the relay.
For further information about horizontal communication, refer to the Protection &
Control Terminals REF 54_, RET 54_, REM 54_, REC 523 Configuration
Guideline .
5.1.13.12.
Secured object control
Secured object control refers to the two-step select-execute process in order to exe-
cute open and close commands for controllable switching devices of the switchgear.
Which communication protocol, SPA or LON, is used to transfer the remote select-
execute commands affects the flow of actions in secured object control. It is the
command time-out parameter (F001V019) that determines which scheme is used for
secured object control.
In case of SPA communication, the command time-out parameter has to be shorter
than 1.5 sec. The default is 0.5 seconds. Also when parallel communication is used,
where LON is used for horizontal communication and SPA for control commands,
the command time-out parameter has to be shorter than 1.5 sec.
In case of LON communication, the command time-out parameter has to be longer
than or equal to 1.5 sec. A longer time-out is needed because the time for horizontal
communication to take place needs to be taken into account.
