-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
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Real part (R) of Z in Ohms
I
m
a
g
i
n
a
r
y
p
a
r
t
(
X
)
o
f
Z
i
n
O
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Ztr
Ze
Zgen
SE
RE
Z(R,X)
R
Zline
Zone 2
relay
¬
Z-line
120°
¬
Lens is the locus
of constant rotor (power)
angle, e.g. 120°.
Lens' width determined
by the setting Pickup Angle
X
Position of the OOS
relay is the origin of
the R - X plane
Zone 1
limit-of-reach
®
circle depends on
the position of the
points SE and RE
X-line
determined
by the
®
setting
ReachZ1
ANSI10000112-1-en.vsd
ANSI10000112 V1 EN-US
Figure 203: Construction of the lens characteristic for a power system
ANSI10000113-1-en.vsd
d
Y
Generator
13.8 kV
13.8 kV
Power line
220 kV
Infinite power
system
Out-Of-Step
protection
OOSPPAM
13.8 / 220 kV
REG
ForwardZ(ForwardR, ForwardX)
ReverseR = Rg ForwardR = Rtr + Rline + Req
ReverseX = Xd’ ForwardX = Xtr + Xline + Xeq
All impedances must be referred to the generator voltage 13.8 kV
SE RE
Generator
13.8 kV
13.8 kV
Power line
220 kV
Infinite power
system
Transformer
System
equivalent
REG
Zgen(Rgen, Xgen) Ztr(Rtr, Xtr) Zline(Rline, Xline) Zeq(Req, Xeq)
ReverseZ(ReverseR, ReverseX)
ReverseR = Rg ForwardR = Rtr + Rline + Req
ReverseX = Xd’ = Xtr + Xline + Xeq
SE RE
ANSI10000113 V1 EN-US
Figure 204: Example of an actual power system
To be able to automatically construct the lens characteristic for a system shown in Figure 204, the
actual power system must be modeled as a two-machine equivalent system, or as a single
machine – infinite bus equivalent system, the following information is necessary: Zgen(Rgen,
Xgen), Ztr(Rtr, Xtr), Zline(Rline, Xline), Zeq(Req, Xeq), and the setting
PickupAngle
, for example 120
degrees. All impedances must be referred to the voltage level where the out-of-step protection
relay is placed; in the case shown in Figure
204 the relay is connected to the terminals of the
generator and, therefore, the previous quantities shall be referred to the generator nominal
voltage and nominal current. The impedances from the position of the out-of-step protection in
the direction of the normal load flow can be taken as forward.
Section 7 1MRK 502 066-UUS B
Impedance protection
382
Technical manual
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