2 Functions
82
7UM61 Manual
C53000-G1176-C127-3
Setting example:
Multiplied by a safety factor of about 1.05, the setting value 1/xd CHAR. 1 results
under address 3002.
For α1, the angle of the underexcitation limiting of the voltage regulator is selected or
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 for
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 2-22
(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, ap-
proximately between the synchronous direct reactance xd and the transient reactance
x
d
'. However, it should be greater than 1.
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 2-4.
Figure 2-24 Admittance diagram of a turbogenerator
Machine U
N, Mach
= 6.3 kV
I
N Machine
= SN/√3 U
N
= 5270 kVA/√3 · 6.3 kV = 483 A
X
d mach
= 2.47
(read from machine manufacturer's specifications in
Figure 2-23)
Current Trans-
former
I
N CT prim
= 500 A
Voltage trans-
former
U
N VT. prim
= 6.3 kV
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