8.21.3 Setting Guidelines
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8.21.3.1 General
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The settings for the underimpedance protection for generator (ZGVPDIS) are done in
percentage and base impedance is calculated from the VBase
and IBase settings. The
base impedance is calculated according to equation
413.
ANSIEQUATION14000027 V1 EN-US (Equation 413)
ImpedanceAng: The common characteristic angle for all the three zone distance
elements
IMinOp: The minimum operating current in %IBase.
Zone 1
ZGVPDIS function has an offset mho characteristic and it can evaluate three phase-to-
phase impedance measuring loops.
OpModeZ1
: Zone 1 distance element can be selected as Disabled or PP Loops.
Z1Fwd: Zone 1 forward reach in percentage. It is recommended to set zone 1 forward
reach to 75% of transformer impedance.
Z1Rev: Zone 1 reverse reach in percentage. It is recommended to set zone 1 reverse
reach same as Z1Fwd.
tZ1: Zone 1 trip time delay in seconds.
Zone 2
Zone 2 in ZGVPDIS function has offset mho characteristic and it can evaluate three
phase-to-phase impedance measuring loops or Enhanced reach loop.
OpModeZ2: Zone 2 distance element can be selected as Disabled, PP Loops or
EnhancedReach.
Z2Fwd: Zone 2 forward reach in percentage. It is recommended to set zone 2 forward
reach to 125% of transformer impedance.
Z2Rev: Zone 2 reverse reach in percentage. It is recommended to give limited reverse
reach to ensure operation for close in fault and to minimize area covered in R-X plane.
A setting of 8%. is recommended.
Section 8 1MRK 504 163-UUS A
Impedance protection
508 Transformer protection RET670 2.2 ANSI
Application manual
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