Input Module; Transformer Board; Input Board; Universal Opto Isolated Logic Inputs - GE MiCOM P40 Agile Technical Manual

P44x/EN FD/Hb6
(FD) 8-10
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 consists of two PCBs;
the main input board and a transformer board. The 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 110 V.
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 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.
Firmware Design
MiCOM P40 Agile P442, P444