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Functions
Time Delays
112
Voltage transformer: U
1
------------ -
=
x
dsec
Multiplied by a safety factor of about 1.05, the setting value 1/xd CHAR. 1 at address
3002 results.
α
For
, the angle of the underexcitation limiting of the voltage regulator is selected or
1
the inclination angle of the machine stability characteristic is used. The setting value
ANGLE 1 is typically situated between 60 ° and 80 °.
In most cases, the machine manufacturer prescribes a minimum excitation value for
small active powers. For this purpose, characteristic 1 is cut from characteristic 2 in
case of a low active-power load. Consequently, 1/xd CHAR. 2 is set to about 0.9 ⋅
(1/xd CHAR. 1), the ANGLE 2 to 90 °. The kinked tripping limit according to figure
2-54 (CHAR. 1, CHAR. 2) results in this way, if the corresponding time delays T
CHAR. 1 and T CHAR. 2 of both characteristics are set equally.
Characteristic 3 serves to adapt the protection to the dynamic machine stability limits.
If there are no precise indications, the user must select a value 1/xd CHAR. 3
situated approximately between the synchronous direct reactance x
reactance x
'. However, it should be greater than 1.
d
A value between 80 ° and 110 ° is usually selected for the corresponding ANGLE 3,
which ensures that only a dynamic instability can lead to a pickup with characteristic
3. The associated time delay is set at address 3010 T CHAR 3 to the value suggested
in Table 2-6.
Simulated
characteristic
consists of
characteristic 1
and char. 2
B [p.u.]
1.05
Figure 2-56
Admittance Diagram of a Turbo Generator
If the static limit curve consisting of the characteristics 1 and 2 is exceeded, the voltage
regulator must first have the opportunity of enhancing the excitation. For this reason,
a warning message due to this criterion is "long-time" delayed (at least 10 s for 3004
T CHAR. 1 and 3007 T CHAR. 2).
If the excitation voltage is missing or too low, the stator criterion picks up as well,
provided that the excitation voltage request feature has been switched ON at address
3012 EXCIT. VOLT., and the voltage has dropped below the threshold Uexcit. <
set at address 3013, or the absence of the excitation voltage has been signalled to
the device by a binary input. In all these cases tripping is possible with a short delay.
= 6.3 kV
N VT prim
1
483 A
6300 V
⋅
⋅
---------- -
------------------ -
------------------ -
2.47
6300 V
500 A
ϕ
θ
Ν
1
1
⋅
------ -
------ -
x
x
d
d
=
0.39
and the transient
d
Underexcitation limitation
(controller)
G [p.u.]
I
E
------- -
U
N
I
N
------- -
U
N
Ν
C53000-G1176-C149-3
7UM62 Manual
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