Schweitzer Engineering Laboratories SEL-167D, Instruction Manual

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HARDWARE DESCRIPTION
Figure 2.1 illustrates the major parts of the relay. Current and voltage inputs are isolated by
input transformers. The signals are low-pass filtered, sampled by sample/hold amplifiers, and
multiplexed to a programmable-gain amplifier. Its output drives an analog-to-digital
converter. Each analog channel is sampled four times per power-system cycle.
The microcomputer consists of an eight-bit microprocessor, ROM (read-only memory) for
program storage, RAM (random-access memory) for data storage, and EEPROM (electrically-
erasable programmable ROM) for storing the relay settings. The EEPROM saves settings
even during power loss. Input/output (I/O) devices connected to the microcomputer bus
provide for the control of the output relays, targets, and monitor inputs such as the state of
the breaker 52A contact. Other I/O devices provide communications for setting, reporting
fault location, and other purposes. The relay includes an input for time code which allows
users to synchronize the internal time clock with an external source of time code.
Figure 2.1: Hardware Block Diagram
Date Code 920326
Specifications
SEL-267D/167D Instruction Manual
2-5