Areva MiCOM P441, Technical Manual

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Relay Description P44x/EN HW/E33
MiCOM P441/P442 & P444 Page 9/44
2.4 Input module
The input module provides the interface between the relay processor board and the
analogue and digital signals coming into the relay. The input module consist of two PCBs;
the main input board and a transformer board. The P441, P442 and P444 relays provide
three voltage inputs and four current inputs. They also provide an additional voltage input for
the check sync function.
2.4.1 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 nominal voltage input is 110V.
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
secondaries provide differential input signals to the main input board to reduce noise.
2.4.2 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 analogue-to-digital conversion for the analogue signals. Hence it
takes the differential analogue 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 analogue signals are passed through an anti-alias
filter before being multiplexed into a single analogue-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.
2.4.3 Universal opto isolated logic inputs
The P441, P442 and P444 relays are fitted 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. signalling, tripping. They
nominally provide a Logic 1 or On value for Voltages
≥
80% of the set voltage and a Logic 0
or Off value for the voltages
≤
60% of the set voltage. 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 utilised. 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. (See also section 6.2 chapter P44x/EN AP for the hysteresis values of universal
optos).