P54x/EN FD/La4 Firmware Design
(FD) 9-8
MiCOM P543, P544, P545 & P546
FD
The calibration non-volatile memory holds the calibration coefficients which are used by the
processor board to correct for any amplitude or phase errors introduced by the transformers
and analog circuitry.
The other function of the input board is to read the state of the signals present on the digital
inputs and present this to the parallel data bus for processing. The input board holds 8
optical isolators for the connection of up to eight digital input signals. The opto-isolators are
used with the digital signals for the same reason as the transformers with the analog signals;
to isolate the relay’s electronics from the power system environment. The input board
provides some hardware filtering of the digital signals to remove unwanted noise before
buffering the signals for reading on the parallel data bus. Depending on the relay model,
more than 8 digital input signals can be accepted by the relay. This is achieved by the use
of an additional opto-board which contains the same provision for 8 isolated digital inputs as
the main input board, but does not contain any of the circuits for analogue signals which are
provided on the main input board.
2.4.3 Universal opto isolated logic inputs
The P54x is f
itted with universal opto isolated logic inputs that can be programmed for the
nominal battery voltage of the circuit of which they are a part i.e. thereby allowing different
voltages for different circuits e.g. signaling, tripping. They can also be programmed as
Standard 60% - 80% or 50% - 70% to satisfy different operating constraints.
Threshold levels are as follows:
Standard 60% - 80% 50% - 70%
Nominal
battery
voltage
(Vdc)
No operation
(logic 0) Vdc
Operation
(logic 1) Vdc
No operation
(logic 0) Vdc
Operation
(logic 1) Vdc
24/27 <16.2 >19.2 <12.0 >16.8
30/34 <20.4 >24.0 <15.0 >21.0
48/54 <32.4 >38.4 <24.0 >33.6
110/125 <75.0 >88.0 <55.0 >77.0
220/250 <150.0 >176.0 <110 >154
This lower value eliminates fleeting pickups that may occur during a battery earth fault, when
stray capacitance may present up to 50% of battery voltage across an input.
Each input also has selectable filtering which can be utilized. This allows use of a pre-set
filter of ½ cycle which renders the input immune to induced noise on the wiring: although this
method is secure it can be slow, particularly for intertripping. This can be improved by
switching off the ½ cycle filter in which case one of the following methods to reduce ac noise
should be considered. The first method is to use double pole switching on the input, the
second is to use screened twisted cable on the input circuit.
The P543 has 16 opto inputs
The P544 has 16 opto inputs
The P545 has 24 opto inputs (or 32 by certain ordering options)
The P546 has 24 opto inputs
2.5 Power supply module (including output relays)
The po
wer supply module contains two PCBs, one for the power supply unit itself and the
other for the output relays. The power supply board also contains the input and output
hardware for the rear communication port which provides an EIA(RS)485 communication
interface.
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