Section 1: Introduction; Current Transformer Circuits; External Resistors; Fibre Optic Communication - Siemens 7SR21 Manual

Section 1: Introduction

This manual is applicable to the following relays:
•
7SR21 Multi-Function Non-directional Overcurrent and Earth Fault Relay
•
7SR22 Multi-Function Directional Overcurrent and Directional Earth Fault Relay
The 7SR21 and 7SR22 relays integrate the protection and control elements required to provide a complete
overcurrent based protection.
The 'Ordering Options' Tables summarise the features available in each model.
General Safety Precautions
1

Current Transformer Circuits

The secondary circuit of a live CT must not be open circuited. Non-observance of this precaution can result in
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injury to personnel or damage to equipment.
2

External Resistors

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Where external resistors are fitted to the circuit, these may present a danger of electric shock or burns, if touched.
3

Fibre Optic Communication

Where fibre optic communication ports are fitted, the lasers are Class 1 devices but recommend they should not
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be viewed directly. Optical power meters should be used to determine the operation or signal level of the device.
4

Front Cover

The front cover provides additional securing of the relay element within the case. The relay cover should be in
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place during normal operating conditions.
©2010 Siemens Protection Devices Limited
7SR21 & 7SR22 Argus Description of Operation
Chapter 1 Page 6 of 71