Alstom MiCOM P846, Technical Manual

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Firmware Design P846/EN FD/D
MiCOM P846
(FD) 9-11
FD
1.3.6 Mechanical layout
The case materials of the relay are constructed from pre-finished steel that has a conductive
covering of aluminum and zinc. This provides good earthing at all joints giving a low
impedance path to earth that is essential for performance in the presence of external noise.
The boards and modules use a multi-point earthing strategy to improve the immunity to
external noise and minimize the effect of circuit noise. Ground planes are used on boards to
reduce impedance paths and spring clips are used to ground the module metalwork.
Heavy duty terminal blocks are used at the rear of the relay for the current and voltage signal
connections. Medium duty terminal blocks are used for the digital logic input signals, the
output relay contacts, the power supply and the rear communication port. A BNC connector
is used for the optional IRIG-B signal. 9-pin and 25-pin female D-connectors are used at the
front of the relay for data communication.
Inside the relay the PCBs plug into the connector blocks at the rear, and can be removed
from the front of the relay only. The connector blocks to the relay’s CT inputs are provided
with internal shorting links inside the relay which will automatically short the current
transformer circuits before they are broken when the board is removed.
The front panel consists of a membrane keypad with tactile dome keys, an LCD and 12
LEDs mounted on an aluminum backing plate.
1.4 Relay software
The relay software was introduced in the overview of the relay at the start of this manual
(P846/EN FD). The software can be considered to be made up of four sections:
•
The real-time operating system
•
The system services software
•
The platform software
•
The protection & control software
This section describes in detail the latter two of these, the platform software and the
protection & control software, which between them control the functional behavior of the
relay. Figure 4 shows the structure of the relay software.