GE D90 Plus Instruction Manual page 237

Line distance protection system

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Table of Contents

CHAPTER 7: PROTECTION

Table 7-1: IEEE curve trip times (in seconds)

Current (I / I

IEEE extremely inverse

IEEE very inverse

LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL

other relays, such as most static relays, which set the energy capacity directly to zero

when the current falls below the reset threshold. The timed method can be used where the

relay must coordinate with electromechanical relays.

The IEEE time overcurrent curve shapes conform to industry standards and the IEEE

C37.112-1996 curve classifications for extremely, very, and moderately inverse curves. The

IEEE curves are derived by the operate and reset time equations.

The terms in the above equations are defined as follows.

represents the operate time in seconds.

TDM represents the multiplier setting.

I represents the input current.

represents the pickup current setting value.

A, B, and p are constants and are defined in the table below.

represents reset time in seconds, assuming the energy capacity is 100% and the

reset mode is timed.

represents the characteristic constant and is defined in the table below.

Table 13: IEEE inverse time curve constants

IEEE curve shape

Extremely inverse

Very inverse

Moderately inverse

GROUPED PROTECTION ELEMENTS