ABB RELION REX640, Техническое руководство, Страница: 1042 / 1960

4.7.5.6 Application
The directional negative sequence impedance function is normally used on
incoming line or feeder connected to the busbar, which is made to operate in the
specified direction for secured operation. The fault direction can be either referred
as forward or reverse of the relay.
There are different directional elements used to determine the direction of
faults, one such element is negative sequence impedance. The calculated negative
sequence impedance is sensitive enough to identify fault in power system networks
with strong source where less negative-sequence voltage and current will be present
during faults.
By using suitable restraint factor, it is also possible to avoid false tripping with
systems having un-transposed lines where some default negative sequence current
will be present during normal operation.
Application example
Relay setting calculation for the DNZPDIS function is shown with below application
example of parallel lines with two end sources of power system network.
G
G
Line 1
Line 2
DNZPDIS
CB1
CB3 CB4
CB2
Forward fault
Reverse fault
3
Figure 580: Power system network with parallel line and two sources
Setting value calculation
Line parameters:
Resistance = 0.126 ohm/km
Reactance = 0.600 ohm/km
Line length = 100 km
Total impedance (Z
1
tot) of line1 or line2 is calculated below
= 12.6 + j60.1 in ohm
Z
1
tot = (0.126 + j0.60 ohm/km) * 100 km
(Equation 279)
Magnitude of positive sequence impedance (Z
1
tot) = 60.4 ohm. The following
settings are obtained to set the relay located at circuit breaker 1(CB1).
Protection functions 1MRS759142 F
1042 REX640
Technical Manual