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9.43
Date Code 20070117
Instruction Manual
SEL-351-5, -6, -7 Relay
Setting the Relay
Settings Explanations
Relay setting VNOM is the nominal secondary voltage connected to voltage
inputs
VA-VB
–
VC-N
. For wye-connected PTs, VNOM is a phase-to-neutral
secondary voltage value. For open-delta connected PTs, VNOM is a phase-to-
phase secondary voltage value.
For example, for a 10 kV (phase-to-phase) system with wye-connected PTs
rated 7200:120 V (PTR = 60), the setting for VNOM would be:
10000 V/ (
√
3 • 60) = 96.22 V
For a 12.5 kV (phase-to-phase) system with open-delta connected PTs rated
14000:115 V (PTR = 121.74), the setting for VNOM would be
12500 V/121.74 = 102.68 V
In the loss-of-potential logic (see
and accompanying text), setting
VNOM scales certain voltage thresholds for voltage measurement
comparisons. In
, a setting of VNOM = OFF is shown to disable/
turn-off a number of features. Effectively, setting VNOM = OFF signifies that
a full three-phase voltage source is not connected to voltage inputs
VA-VB
–
VC-N
.
Even with VNOM = OFF, voltage can still be connected to voltage inputs
VA-VB
–
VC-N
(e.g., single-phase voltage connected to voltage input
VA-N
), as
discussed in the top of
(for the undervoltage block for frequency
elements) and demonstrated in
Line Settings
Line Settings (See Settings Explanations on page 9.37) on
Line impedance settings Z1MAG, Z1ANG, Z0MAG, and Z0ANG are used in
the fault locator (see
) and in automatically
making directional element settings Z2F, Z2R, Z0F, and Z0R (see
Made Automatically on page 4.38
). A corresponding line length setting (LL)
is also used in the fault locator.
If the protected line belongs to a hybrid power system, such as shown in
, then for proper directional decision, Z0ANG
≠
Z0MTA and
E32
≠
AUTO. Z0MTA must be set to compensate for the neutral ground
resistor and is used in the Best Choice Ground Directional Logic™ to make
proper forward and reverse fault determination. Z0ANG must be set to the
Line Angle for correct fault location for forward faults.
Figure 9.12
Hybrid Power System With Neutral Ground Resistor
The line impedance settings Z1MAG and Z0MAG are set in
Ω
secondary.
Line impedance (
Ω
primary) is converted to
Ω
secondary:
Ω
primary • (CTR/PTR) =
Ω
secondary
where:
CTR = phase (IA, IB, IC) current transformer ratio
PTR = phase (VA, VB, VC) potential transformer ratio
Neutral ground
resistor
Содержание SEL-351-5
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