Schweitzer Engineering Laboratories SEL-351A, Руководство пользователя

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4.46
SEL-351A Relay Instruction Manual
Date Code 20080213
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Directional Control Settings (Not in SEL-351A-1)
Z0F—Forward Directional Z0 Threshold
Z0R—Reverse Directional Z0 Threshold
Setting Range:
–128.00 to 128.00
Ω
secondary
(5 A nominal phase current inputs,
IA
,
IB
,
IC
)
–640.00 to 640.00
Ω
secondary
(1 A nominal phase current inputs,
IA
,
IB
,
IC
)
If preceding setting ORDER does not contain V or S (no zero-sequence
voltage-polarized directional element is enabled), then settings Z0F and Z0R
are not made by the user or displayed.
Z0F and Z0R are used to calculate the Forward and Reverse Thresholds,
respectively, for the zero-sequence voltage-polarized directional elements (see
Figure 4.10 and Figure 4.12 ).
If enable setting E32 = Y, settings Z0F and Z0R (zero-sequence impedance
values) are calculated by the user and entered by the user, but setting Z0R
must be greater in value than setting Z0F by 0.1
Ω
secondary.
Z0F and Z0R Set Automatically
If enable setting E32 = AUTO, settings Z0F and Z0R (zero-sequence
impedance values) are calculated automatically, using the zero-sequence line
impedance magnitude setting Z0MAG as follows:
Z0F =
Z0MAG/2
(
Ω
secondary)
Z0R =
Z0MAG/2 + z
(
Ω
secondary; “z” listed in table below)
If setting ORDER = U (ungrounded or high-impedance grounded system; see
Figure 4.14 ), the following settings are made internally and hidden:
Z0F =
–0.10
Ω
secondary
Z0R =
0.10
Ω
secondary
Deriving Z0F and Z0R Settings
Figure 4.25 shows the voltage and current polarity for an SEL-351A in a zero-
sequence impedance network (the same approach can be instructive for
negative-sequence impedance analysis, too). For a forward fault, the
SEL-351A effectively sees the sequence impedance behind it as:
Z
M
= V
0
/(–I
0
) = –(V
0
/I
0
)
V
0
/I
0
= –Z
M
(what the relay sees for a forward fault)
For a reverse fault, the SEL-351A effectively sees the sequence impedance in
front of it:
Z
N
= V
0
/I
0
V
0
/I
0
= Z
N
(what the relay sees for a reverse fault)
Relay Configuration z (
Ω
secondary)
5 A nominal current, 300 V voltage inputs 0.2
1 A nominal current, 300 V voltage inputs 1.0
NOTE:
If the calculation of Z0F and
Z0R exceeds the setting range, the
quantity is set to the upper limit of the
setting range.
NOTE:
Z0F and Z0R (
Ω
secondary)
are set in reference to the phase
current channels
IA , IB , and IC , as are
settings Z2F and Z2R. However,
settings Z0F and Z0R are applied to
Figure 4.12 , and Figure 4.14 , where
neutral current I
N
, from neutral
current channel I
N
, is also applied.
Settings Z0F and Z0R are adjusted
internally (with CT ratio settings) to
operate on this IN current base, when
needed (effectively, Z0F • CTRN/CTR
and Z0R • CTRN/CTR). See
Internal
Enables on page 4.30 .
Courtesy of NationalSwitchgear.com