Overview; Introduction To Elements - GE L90 Instruction Manual

OVERVIEW

 SETTINGS
 TESTING
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5.2 Overview

5.2.1 Introduction to elements

For URs, the term element is used to describe a feature that is based around a comparator. The comparator is provided
with an input (or set of inputs) that is tested against a programmed setting (or group of settings) to determine if the input is
within the defined range that sets the output to logic 1, also referred to as setting the flag. A single comparator can make
multiple tests and provide multiple outputs. For example, the time overcurrent comparator sets a pickup flag when the
current input is above the setting and sets an operate flag when the input current has been at a level above the pickup
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setting for the time specified by the time-current curve settings. All comparators use analog actual values as the input.
An exception to this rule is digital elements, which use logic states as inputs.
Elements are arranged into two classes, grouped and control. Each element classed as a grouped element is provided with
six alternate sets of settings, in setting groups numbered 1 through 6. The performance of a grouped element is defined by
the setting group that is active at a given time. The performance of a control element is independent of the selected active
setting group.
The main characteristics of an element are shown on a logic diagram. This includes the inputs, settings, fixed logic, and the
output operands generated. The previous chapter explains how to read a logic diagram, and the abbreviations used in a
diagram are defined in the Abbreviations chapter.
Some settings are specified in per-unit (pu) calculated quantities:
pu quantity = (actual quantity) / (base quantity)
Where the current source is from a single current transformer (CT), the base quantity is the nominal secondary or primary
current of the CT. Use the secondary current base to convert per-unit settings to/from a secondary current value, and use
the primary current base to convert to/from a primary current value.
Where the current source is the sum of two or more CTs with different nominal primary current, the primary base quantity
is the largest nominal primary current. For example, if CT1 = 300 / 5 A and CT2 = 100 / 1 A, then in order to sum these, CT2
is scaled to the CT1 ratio. In this case, the base quantity is 300 A primary, 5 A secondary for CT1, and 300/(100/1) = 3 A
secondary for CT2.
For voltage elements, the primary base quantity is the nominal phase-to-phase primary voltage of the protected system
provided that the VT ratio setting is set to the nominal ratio of the VTs and the secondary voltage setting is set to the
phase-to-phase voltage seen by the relay when the voltage of the protected system in nominal. The UR uses the
convention that nominal voltages in a three-phase system are phase-to-phase voltages.
5-4
TEST MODE
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FUNCTION: Disabled
TEST MODE FORCING:
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On
 PMU
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 TEST VALUES
 FORCE CONTACT
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 INPUTS
 FORCE CONTACT
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 OUTPUTS
 CHANNEL TESTS
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Range: Disabled, Isolated, Forcible
See page 5-407
Range: FlexLogic operand
See page 5-407
See page 5-408
See page 5-409
See page 5-409
See page 5-410
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS