tZ2: Zone 2 trip time delay in seconds. T
ime delay should be provided in order to
coordinate with zone 1 element provided for the outgoing line.
Zone 3
Zone 3 in ZGVPDIS function has offset mho characteristic and it can evaluate three
phase-to-phase impedance measuring loops or EnhancedReach loop
OpModeZ3: Zone 3 distance element can be selected as Disabled, PP Loops or
EnhancedReach. It is recommended to select EnhancedReach setting.
Z3Fwd: Zone 3 forward reach in percentage. It is recommended to set zone 3 forward
reach to coordinate with the longest time delay for the transmission line protection
connected to the generating substation bus. Alternatively it can be set to 80% of the
load impedance considering maximum short time over load of the generator.
Z3Rev: Zone 3 reverse reach in percentage. It is recommended to give limited reverse
reach to ensure operation for close in faults and to minimize area covered in R-X plane.
A setting of 8%. is recommended.
tZ3: Zone 3 operates time delay in seconds. Time delay is provided in order to
coordinate with slowest circuit backup protection or slowest local backup for faults
within zone 3 reach. A safety margin of 100 ms should be considered.
8.21.3.2 Load encroachment
GUID-EF64E2B4-2B84-421A-B719-2DCA6883D21A v2
The settings involved in load encroachment feature are:
LdAngle: Angle in degrees of load encroachment characteristics
RLd: Positive sequence resistance in per unit
The procedure of calculating the settings for load encroachment consists basically of
defining load angle LdAngle and resistive blinder RLd. The load encroachment logic
can be enabled for zone 2 and zone 3 elements. For zone 2, the load encroachment can
be enabled or disabled using the LoadEnchModZ2 setting by selecting either Enabled
or Disabled. Similarly for zone 3 load encroachment can be enabled or disabled using
the LoadEnchModZ3 setting by selecting either Enabled or Disabled.
The load angle LdAngle is same in forward and reverse direction, so it is suitable to
begin the calculation of the parameter setting. The parameter is set to the maximum
possible load angle at the maximum active load. A value larger than 20° must be used.
The blinder RLd can be calculated according to the equation
414
1MRK 504 163-UUS A Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 509
Application manual
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