Alstom MiCOM P846, Technical Manual

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P846/EN FD/D Firmware Design
(FD) 9-6
MiCOM P846
FD
1.3.2 Co-processor board
The processor used on the second board is the same as that used on the main processor
board. The second processor board has provision for fast access (zero wait state) SRAM for
use with both program and data memory storage. This memory can be accessed by the
main processor board via the parallel bus, and this route is used at power-on to download
the software for the second processor from the flash memory on the main processor board.
Further communication between the two processor boards is achieved via interrupts and the
shared SRAM. The serial bus carrying the sample data is also connected to the co-
processor board, using the processor’s built-in serial port, as on the main processor board.
The co-processor board also handles all communication with the remote differential relay(s).
This is achieved via optical fibre communications and hence the co-processor board holds
the optical modules to transmit and receive data over the fibre links.
1.3.3 Internal communication buses
The relay has two internal buses for the communication of data between different modules.
The main bus is a parallel link that is part of a 64-way ribbon cable. The ribbon cable carries
the data and address bus signals in addition to control signals and all power supply lines.
Operation of the bus is driven by the main processor board that operates as a master while
all other modules within the relay are slaves.
The second bus is a serial link that is used exclusively for communicating the digital sample
values from the input module to the main processor board. The DSP processor has a built-in
serial port that is used to read the sample data from the serial bus. The serial bus is also
carried on the 64-way ribbon cable.
1.3.4 Input module
The input module provides the interface between the relay processor board and the analog
and digital signals coming into the relay. The input module consists of two PCBs; the main
input board and a transformer board.
1.3.4.1 Transformer board
The transformer board holds up to four voltage transformers (VTs) and up to five current
transformers (CTs). The current inputs will accept either 1A or 5A nominal current (menu
and wiring options) and the voltage inputs can be specified for either 110V or 440V nominal
voltage (order option). The transformers are used both to step-down the currents and
voltages to levels appropriate to the relay’s electronic circuitry and to provide effective
isolation between the relay and the power system. The connection arrangements of both the
current and voltage transformer secondary’s provide differential input signals to the main
input board to reduce noise.
1.3.4.2 Input board
The main input board is shown as a block diagram in Figure 2. It provides the circuitry for
the digital input signals and the analog-to-digital conversion for the analog signals. Hence it
takes the differential analog signals from the CTs and VTs on the transformer board(s),
converts these to digital samples and transmits the samples to the processor board via the
serial data bus. On the input board the analog signals are passed through an anti-alias filter
before being multiplexed into a single analog to digital converter chip. The A - D converter
provides 16-bit resolution and a serial data stream output. The digital input signals are opto
isolated on this board to prevent excessive voltages on these inputs causing damage to the
relay's internal circuitry.