Schweitzer Engineering Laboratories SEL-700G Series, Инструкция по эксплуатации

Страница: 237 / 824

4.131
Date Code 20170814 Instruction Manual SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
If the system in Figure 4.91 is a solidly-grounded system (mostly inductive;
presume uniform system angle) with load-connected line to neutral, the
impedance plot (in the R + jX plane) would appear as in Figure 4.92a, with
resultant Z0F and Z0R settings as in Figure 4.92b. The zero-sequence line
angle noted in Figure 4.92a (

Z0MTA) is the same angle found in
Figure 4.78 and Figure 4.80 (in the equation box with the Enable line). Note
that the Z0MTA shown in Figure 4.78 and Figure 4.80 should be set
(calculated) accordingly taking into account the system grounding (solidly
grounded, low or high impedance).
The preceding method of automatically making settings Z0F and Z0R (where
both Z0F and Z0R are positive values and Z0R > Z0F) usually suffices for
mostly inductive systems—Figure 4.91 and Figure 4.92 just provide a
theoretical background.
Figure 4.91 Zero-Sequence Impedance Network and Relay Polarity
Figure 4.92 Zero-Sequence Impedance Plot for Solidly-Grounded, Mostly
Inductive System
Z0MTA—Zero-Sequence Maximum Torque Angle.
If enable setting
EDIR := AUTO, then Z0MTA is set equal to Z0ANG and Z0MTA is hidden.
Note that ORDERX := U cannot be set when EDIRX := AUTO and vice-
versa. If enable setting EDIR := Y and ORDER contains a V or U setting,
Z0MTA should be set.
If the protected line belongs to a hybrid power system, such as shown in
Figure 4.93, then for proper directional decision, Z0ANG does not equal
Z0MTA. Z0MTA must be set to compensate for the neutral-ground resistor
and is used in the Ground Directional Logic to make proper forward and
reverse fault determination.
Figure 2.25 shows a specific application where multiple high-impedance
grounded generators are connected to a common bus. The grounding
resistance value in the secondary of the grounding transformer is typically
I
0
V
0
Z
N
Z
M
Forward
Reverse
Zero-Sequence Reference Bus
SEL-700G
(a) Impedance Plot (b) Z0F and Z0R Settings
ZN = RN + jXN (Reverse)
–ZM = —RM — jXM (Forward)
R
jX
Reverse
Forward
Z
Z0F
0
Z0R
ZN
— ZM
ZN > Z0R
Z0F > — ZM
Z0R > Z0F
Zero-Sequence
Maximum Torque Angle
Z0MTA