Alstom MiCOM P846, Technical Manual

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P846/EN FD/D Firmware Design
(FD) 9-14
MiCOM P846
P4091ENa
Figure 5: Frequency response of the DLO Kalman filter
1.4.6 Fourier filtering
All backup protection and measurement functions use one cycle fourier digital filtering to
extract the power frequency component. This filtering is performed on the main processor
board.
1.4.6.1 Programmable scheme logic
The purpose of the programmable scheme logic (PSL) is to allow the relay user to configure
an individual protection scheme to suit their own particular application. This is achieved
through the use of programmable logic gates and delay timers.
FD
The input to the PSL is any combination of the status of the digital input signals from the
opto-isolators on the input board, the outputs of the protection elements, e.g. protection
starts and trips, control inputs, function keys and the outputs of the fixed protection scheme
logic. The fixed scheme logic provides the relay’s standard protection schemes. The PSL
itself consists of software logic gates and timers. The logic gates can be programmed to
perform a range of different logic functions and can accept any number of inputs. The timers
are used either to create a programmable delay, and/or to condition the logic outputs, e.g. to
create a pulse of fixed duration on the output regardless of the length of the pulse on the
input. The outputs of the PSL are the LEDs on the front panel of the relay and the output
contacts at the rear.
The execution of the PSL logic is event driven; the logic is processed whenever any of its
inputs change, for example as a result of a change in one of the digital input signals or a trip
output from a protection element. Also, only the part of the PSL logic that is affected by the
particular input change that has occurred is processed. This reduces the amount of
processing time that is used by the PSL. The protection and control software updates the
logic delay timers and checks for a change in the PSL input signals every time it runs.
This system provides flexibility for the user to create their own scheme logic design.
However, it also means that the PSL can be configured into a very complex system, and
because of this, setting of the PSL is implemented through the PC support package MiCOM
S1.