Siemens SIPROTEC 7UM62, Manual

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Out-of-Step Protection (ANSI 78)
143
7UM62 Manual
C53000-G1176-C149-3
X
d
' can be calculated from the per unit reactance x
d
' as follows:
where X
d
' – Transient reactance of the machine
x
d
' – Transient per unit reactance
U
N, Gen
– Primary rated machine voltage
I
N, Gen
– Primary rated machine current
ü
ct
– Current transformer ratio
ü
vt
– Voltage transformer ratio
Dependent on the type of generator and on the secondary current, a secondary
voltage U
N
= 100 V or 120 V leads to approximately the reactance ranges listed in
Table 2-10.
As it is presupposed that the generator is connected with the network via a unit
transformer, the setting in the network direction is chosen such that the reactance
reach of characteristic 1 is approximately 70 % to 90 % of the transformer impedance,
and the reach of characteristic 2 is into the network. Thus,
Zc
at address
3506
is set
to 70 % to 90 % of the transformer impedance X
SC
. For characteristic 2, the remaining
portion of the transformer impedance is set at
3507
Zd - Zc, if necessary
complemented by the impedance of the additional line section to be monitored.
Table 2-11 shows typical values of the impedances of unit transformers X
SC
for
secondary rated currents I
N
= 1 A and I
N
= 5 A, the relationship of the values is
according to the following equation:
.
X
d
'
U
N, Gen
3 I
N, Gen
⋅
----------------------------- x
d
'
ü
ct
ü
vt
-------
⋅ ⋅
=
Table 2-10 Transient Machine Reactances (Referred to Secondary Side)
Generator Type X
d
X
d
U
N
= 100 V/ I
N
= 1 A
X
d
U
N
= 120 V/ I
N
= 1 A
X
d
U
N
= 100 V/ I
N
= 5 A
X
d
U
N
= 120 V/ I
N
= 5 A
Non-salient
pole rotor
0.13..0.35 7.5
Ω
...20.2
Ω
9.4
Ω
..24.3
Ω
1.5
Ω
...4.0
Ω
1.9
Ω
...4.9
Ω
Salient-pole rotor 0.20..0.45 11.5
Ω
...26.0
Ω
13.9
Ω
...31.2
Ω
2.3
Ω
...5.2
Ω
2.8
Ω
...6.2
Ω
X
SC prim
U
SC
3 I
N
⋅
-----------------
u
SC
U
N
⋅
100 3 I
N
⋅ ⋅
-------------------------------
u
SC
U
N
2
⋅
100 S
N
⋅
--------------------------
= = =
X
SC
X
SC prim
ü
ct
ü
vt
-------
⋅
=
Table 2-11 Per Unit Impedance Voltages and Impedances of Transformers
Transformer Type u
SC
X
SC
U
N
= 100 V/ I
N
= 1 A
X
SC
U
N
= 120 V/ I
N
= 1 A
X
SC
U
N
= 100 V/ I
N
= 5 A
X
SC
U
N
= 120 V/ I
N
= 5 A
Unit transformer 8 %...13 % 4.6
Ω
...7.5
Ω
5.5
Ω
...9.0
Ω
0.9
Ω
...1.5
Ω
1.1
Ω
...1.8
Ω
General 3 %...16 % 1.7
Ω
...9.2
Ω
2.1
Ω
...11.1
Ω
0.3
Ω
...1.8
Ω
0.4
Ω
...2.2
Ω