Programmable Scheme Logic; Event And Fault Recording - GE MiCOM P40 Agile Technical Manual

Firmware Design
MiCOM P40 Agile P442, P444
3.4.3

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.
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, 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 MiCOM S1 Agile.
3.4.4

Event and Fault Recording

A change in any digital input signal or protection element output signal causes an event
record to be created. When this happens, the protection and control task sends a message
to the supervisor task to indicate that an event is available to be processed and writes the
event data to a fast buffer in SRAM which is controlled by the supervisor task. When the
supervisor task receives either an event or fault record message, it instructs the platform
software to create the appropriate log in battery backed-up SRAM. The operation of the
record logging to battery backed-up SRAM is slower than the supervisor's buffer. This
means that the protection software is not delayed waiting for the records to be logged by the
platform software. However, in the rare case when a large number of records to be logged
are created in a short period of time, it is possible that some will be lost if the supervisor's
buffer is full before the platform software is able to create a new log in battery backed-up
SRAM. If this occurs then an event is logged to indicate this loss of information.
3.4.5 Disturbance recorder
The disturbance recorder operates as a separate task from the protection and control task. It
can record the waveforms for up to 8 analogue channels and the values of up to 64 digital
signals. The recording time is user selectable up to a maximum of 10 seconds (the maximum
storage capacity is 84 s). The disturbance recorder is supplied with data by the protection
and control task once per cycle. The disturbance recorder collates the data that it receives
into the required length disturbance record. It attempts to limit the demands on memory
space by saving the analogue data in compressed format whenever possible. This is done
by detecting changes in the analogue input signals and compressing the recording of the
waveform when it is in a steady-state condition. The disturbance records can be extracted by
MiCOM S1 Agile that can also store the data in COMTRADE format, thus allowing the use of
other packages to view the recorded data.
3.4.6 Fault locator
The fault locator task is also separate from the protection and control task. The fault locator
is invoked by the protection and control task when a fault is detected. The fault locator uses
a 12-cycle buffer of the analogue input signals and returns the calculated location of the fault
to the protection and control task which includes it in the fault record for the fault. When the
fault record is complete (i.e. includes the fault location), the protection and control task can
send a message to the supervisor task to log the fault record.
P44x/EN FD/Hb6
(FD) 8-19