Date Code 20171021 Instruction Manual SEL-421 Relay
Instruction Manual
Preface
This manual provides information and instructions for installing and operating
the SEL-421 Relay. This manual is for use by power engineers and others experi-
enced in protective relaying applications. Included are detailed technical descrip-
tions of the relay and application examples. While this manual gives reasonable
examples and illustrations of relay uses, you must exercise sound judgment at all
times when applying the relay in a power system.
SEL-421 Versions and Supported Features on page 1.7 shows the relay features
supported by versions SEL-421-4 and SEL-421-5. Throughout the manual, we
provide margin notes next to the text explaining a feature to specify the availabil-
ity of that feature in different versions of the relay. Note that, unless otherwise
indicated, SEL-421 refers to the SEL-421-5.
Manual Overview
The SEL-421 Relay Manual set consists of two volumes:
➤ SEL-421 Instruction Manual
➤ SEL-400 Series Relays Instruction Manual
The SEL-421 Relay Manual set is a comprehensive work covering all aspects of
relay application and use. Read the sections that pertain to your application to
gain valuable information about using the SEL-421. For example, to learn about
relay protection functions, read the protection sections of this manual and skim
the automation sections, then concentrate on the operation sections or on the
automation sections of this manual as your job needs and responsibilities dictate.
An overview of each manual section and section topics follows.
SEL-421 Instruction Manual
Preface
. Describes manual organization and conventions used to present
information, as well as safety information.
Section 1: Introduction and Specifications
. Introduces SEL-421 Relay features,
summarizes relay functions and applications, and lists relay specifica-
tions, type tests, and ratings.
Section 2: Installation
. Discusses the ordering configurations and interface
features (control inputs, control outputs, and analog inputs, for example).
Provides information about how to design a new physical installation and
secure the relay in a panel or rack. Details how to set relay board jumpers
and make proper rear-panel connections (including wiring to CTs, PTs,
and a GPS receiver). Explains basic connections for the relay communi-
cations ports and how to install optional communications cards (such as
the Ethernet Card).
Section 3: Testing
. Describes techniques for testing, troubleshooting, and
maintaining the relay.
Section 4: Front-Panel Operations
. Describes the LCD display messages and
menu screens that are unique to the SEL-421.
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