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7UM62 Manual
C53000-G1176-C149-3
"Response
circle"
–0,8
–0,6
–0,4
underexcited
Figure 2-55
Power Diagram of a Salient-Pole Generator, Indicated per Unit
The primary setting values can be read out directly from the diagram. The related
values must be converted for the protection setting. The same conversion formula can
be used if the protection setting is calculated with the predefined synchronous direct
reactance.
1
------------ -
=
x
dsec
with
x
Secondary per unit synchronous direct reactance,
dsec
x
Per unit synchronous direct reactance of machine,
d mach
I
Rated machine current
N mach
U
Rated machine voltage
N mach
U
Primary rated voltage of the voltage transformers
N VT prim
Primary rated current of the current transformers
I
N CT prim
Instead of 1/x
the approximate value I
d mach
current at no-load excitation).
Setting example:
Machine:
Current transformers:
Underexcitation (Loss-of-Field) Protection (ANSI 40)
P/S
N
1,4
1,2
Limit of the stator
winding heating
1,0
0,8
0,6
0,4
Phase
angle
0,2
0
–0,2
0
0,2
0,4
I
U
1
Nmach
N VT prim
⋅
⋅
---------------- -
------------------ -
------------------------- -
x
U
I
dmach
Nmach
N CT prim
/I
K0
U
= 6.3 kV
N mach
I
= S
/√3 U
N mach
N
x
= 2.47 (= machine manufacturer's indication
d mach
= 500 A
I
N CT prim
U = U
I = I
S
N
f
= 50.0 Hz
N
n
N
cos ϕ = 0.800
x
d
x
q
Measuring point
Limit of the stator
winding heating
0,6
0,8
overexcited
can be used (with I
N
K0
= 5270 kVA/√3 ⋅ 6.3 kV = 483 A
N
in Fig. 2-55)
.
= 6300 V
N
N
= 5270 kVA
= 1500 RPM
= 2.470
= 1.400
Q/S
N
= short-circuit
111
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