Ground Quadrilateral Characteristics - GE LPS-D Instruction Manual

1.2 INTRODUCTION
When both phase and ground distance functions are used for a zone of protection, six individual measuring
functions are available: three for phase distance and three for ground distance. The algorithm that implements
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the variable-mho measuring functions is derived from designs that have evolved through several different fam-
ilies of static analog and digital relay systems which have accumulated decades of dependable and secure in-
service experience.
An instantaneous overcurrent tripping function (50G) provides direct tripping for severe phase-to-ground faults.
A time-overcurrent tripping function (51G) provides time-delayed backup tripping for phase-to-ground faults.
Either or both of these ground-overcurrent functions can be controlled by the NT negative-sequence directional
trip unit, at the customer's discretion.
The LPS-D relay has been modified to include the option to use either quadrilateral characteristics or variable
Mho characteristics for all zones of ground distance protection. The model numbers affected by this modifica-
tion are: LPSDB xxxxxxxxx (where x represents any valid character) with firmware version V0005.00AA00 or
higher. A new version of ALPS-Link may be required to access the new settings via remote communications (it
must be version 3.5 or higher). If required, the updated version of ALPS-Link may be downloaded from the GE
Power Management website at www.ge.com/indsys/pm.
Many protective relay engineers prefer to use a quadrilateral (polygonal) characteristic for ground distance
functions, as it provides more fault resistance coverage than the circular Mho characteristic. A typical quadrilat-
eral characteristic is shown in Figure 1–1: GROUND DISTANCE QUADRILATERAL CHARACTERISTIC. The
characteristic is comprised of four straight lines; the trip zone is the area bounded by all four characteristic
lines. The upper boundary (the reactance characteristic) may also be used with a variable Mho function. The
variable Mho provides both directional supervision for reverse faults and resistive limits to prevent operation on
load.
Figure 1–1: GROUND DISTANCE QUADRILATERAL CHARACTERISTIC
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LPS-D Line Protection System

1.2.4 GROUND QUADRILATERAL CHARACTERISTICS

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GroundQuad.CDR
1 PRODUCT DESCRIPTION
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GE Power Management