Table of Contents
Advertisement
7UM62 Manual
C53000-G1176-C149-3
The following relation allows to estimate the rate of change:
dZ t ( )
dR t ( )
Xπf
≈
------------- -
--------------
---------------------------- -
=
dt
dt
2
2sin
Meaning:
X
Reactance between the sources of the power swing
f
Power swing frequency
p
δ
Power swing angle
Figure 2-64 shows an example of how the rate of change evolves as a function of the
power swing angle. The rate of change is smallest at an angle of 180°, but increases
proportionally with the angle considered.
Ω /s
300
dZ( δ )
250
200
150
100
50
0
Figure 2-64 Evolution of the Rate of Change (f
For this reason, the setting value dZ/dt must also be coordinated with the impedance
jump occurring at the start of a short-circuit.
To do so, you determine the minimum operating impedance (Z
ence to the setting of the impedance zone (e.g. Z1) and calculate the impedance gra-
dient, taking into account the one-cycle measuring interval.
Example:
U
= 0.9 U
, I
= 1.1 I
min
N
max
U
= 100 V, I
= 1 A
N
N
,
u ⋅
⋅
0 7
U
K
N
-------------------------------------- -
Z1
=
⋅
⋅
100 %
3 I
N
Xπf
Ω
p
p
---------------------- - in
--- -
=
δ
s
(
πf
)
æ ö
2
t
2sin
-- -
p
è ø
2
50
100
150
= 1 Hz; X = 10 Ω)
p
= 10 %, ∆t = 20 ms
, u
N
K
4 04 Ω
,
=
Impedance Protection (ANSI 21)
200
250
300
350
δ
), form the differ-
L, min
400
Degrees
133
Advertisement
Table of Contents
