Schweitzer Engineering SEL-387-0, Instruction Manual

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Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Section 1
Introduction and Specifications
Overview
Use this relay to protect two- to four-winding power transformers, buses,
reactors, generators, large motors, or other multiterminal power apparatus.
Three- or four-terminal applications permit separate connection of current
transformers from two breakers connected to the same transformer winding,
such as in ring-bus or breaker-and-a-half schemes. The relay settings permit
you to use wye- or delta-connected current transformers with virtually any
type of transformer winding connection.
The SEL-387 Differential Relay provides three differential elements with dual
slope characteristics. The second slope provides security against CT saturation
for heavy through faults. Be sure to conduct detailed analysis of CT
performance under worst-case saturation conditions to set the relay
characteristic correctly for bus protection applications. For assistance with CT
selection, obtain SEL
Application Guide 99-07 Bus Protection Using a Four-
Winding Low-Impedance Percentage Differential Relay from the SEL website
(selinc.com).