Page 187 - Practical Power System and Protective Relays Commissioning

Chapter 18

Protection Relays

Subchapter 18.1

Introduction

Relays are devices connected throughout a power system to detect any
unbalance or abnormal condition. There are many types of relays used to
protect power systems and these are described in this chapter.

Subchapter 18.2

Classification of Relays

18.2.1 CLASSIFICATION BASED ON FUNCTION

1. Protective relays are relays that detect abnormal conditions in the system
and issue an alarm or trip based on the severity of the fault.
2. Monitoring relays are relays that monitor the system but do not issue any
trip signal, such as synchronism verification relays.
3. Programming relays have electrical sequences, such as autoreclosing and
synchronizing relays.
4. Regulating relays, such as voltage regulator relays, regulate the trans-
former voltage by changing the on load tap changer.
5. Auxiliary relays include repeater relays and trip lookout relays.

18.2.2 CLASSIFICATION BASED ON INPUT QUANTITIES

1. Current relays;
2. Voltage relays;
3. Power relays;
4. Pressure relays;

Practical Power System and Protective Relays Commissioning.
DOI: https://doi.org/10.1016/B978-0-12-816858-5.00018-6 189
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