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2.22.2 Setting Hints
General
Independent
Stages
7UM62 Manual
C53000-G1176-C149-3
Figure 2-75 illustrates the logic diagram of the overexcitation protection. The counter
can be reset to zero by means of a blocking input or a reset input.
4302 U/f >
U
U/f heating
U/f cool down
U/f
f
4304 U/f >>
FNo. 05357
>RM th.rep. U/f
FNo. 05353
>U/f BLOCK
Figure 2-75
Logic Diagram of the Overexcitation Protection
The overexcitation protection is only effective and accessible if it has been set during
the configuration of the protective functions at 0143 OVEREXC. PROT. = Enabled.
Set Disabled if the function is not required. Address 4301 OVEREXC. PROT. is
used to switch the function ON or OFF, or to block only the trip command (Block
Relay).
The overexcitation feature serves to measure the voltage/frequency quotient
proportional to the B induction. The overexcitation protection must pick up when the
induction admissible for the protected object (e.g. power station unit transformer) is
exceeded. The transformer is endangered, if, for example, the power station block is
switched off at full-load operation and the voltage regulator does not respond at all or
does not respond fast enough to avoid the related voltage increase.
Similarly, a decrease in frequency (speed), e.g. in island systems, can endanger the
transformer because of increased induction.
In this way, the U/f protection monitors the correct function both of the voltage
regulators and of the speed regulation in all operating states.
The limit-value setting at address 4302 U/f > is based on the induction limit value
relation to the nominal induction (B/B
be protected.
A pickup message is transmitted as soon as the induction limit value U/f set at address
4302 is exceeded. A warning message is transmitted subsequent to the
corresponding 4303 T U/f > time delay.
Overexcitation (Volt/Hertz) Protection (ANSI 24)
FNo. 05370
U/f> picked up
4303 T U/f >
&
1
t(U/f)
2
Reset
counter=0
OR
4305 T U/f >>
&
FNo. 05373
U/f>> pick.up
FNo. 05362
U/f> BLOCKED
) specified by the manufacturer of the object to
N
FNo. 05367
U/f> warn
Tripping
matrix
&
FNo. 05372
U/f> th.TRIP
FNo. 05371
TMin
U/f>> TRIP
TRIP CMD
FNo. 05369
RM th.rep. U/f
161
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