Input Module Circuit Description; Figure 18: Input Module Schematic - GE MiCOM P40 Agile Technical Manual

Single breaker current differential (with distance)

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Chapter 3 - Hardware Design

INPUT MODULE CIRCUIT DESCRIPTION

A/D Conversion

The differential analogue inputs from the CT and VT transformers are presented to the main input board as shown.

Each differential input is first converted to a single input quantity referenced to the input board's earth potential.

The analogue inputs are sampled and converted to digital, then filtered to remove unwanted properties. The

samples are then passed through a serial interface module which outputs data on the serial sample data bus.

The calibration coefficients are stored in non-volatile memory. These are used by the processor board to correct

for any amplitude or phase errors introduced by the transformers and analogue circuitry.

Opto-isolated inputs

The other function of the input board is to read in the state of the digital inputs. As with the analogue inputs, the

digital inputs must be electrically isolated from the power system. This is achieved by means of the 8 on-board

optical isolators for connection of up to 8 digital signals. The digital signals are passed through an optional noise

filter before being buffered and presented to the unit's processing boards in the form of a parallel data bus.

This selectable filtering allows the use of a pre-set filter of ½ cycle which renders the input immune to induced

power-system noise on the wiring. Although this method is secure it can be slow, particularly for inter-tripping. 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.

Use double pole switching on the input

Use screened twisted cable on the input circuit

8 digital inputs

A/D Converter

Parallel Bus

P54x1i-TM-EN-1

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