Functions
2.24 Overexcitation (Volt/Hertz) Protection (ANSI 24)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
187
Figure 2-77 Logic Diagram of the Overexcitation Protection
2.24.2 Setting Notes
General
Overexcitation protection is only effective and available if address 143 OVEREXC. PROT. is set to Enabled
during configuration. If the function is not required, it is set to Disabled. Address 4301 OVEREXC. PROT.
serves to switch the function ON or OFF or to block only the trip command (Block relay).
Overexcitation protection measures the voltage/frequency quotient which is proportional to the induction B. The
protection must intervene when the limit value for the protected object (e.g. unit transformer) is exceeded. The
transformer is for example endangered if the power station block is switched off at full-load operation and the
voltage regulator does not respond fast enough or not at all to avoid related voltage increase.
Similarly a decrease in frequency (speed), e.g. in island systems, can lead to an inadmissible increase in in-
duction.
In this way the U/f protection monitors the correct functioning both of the voltage regulator and of the speed
regulation, in all operating states.
Independent Stages
The limit-value setting at address 4302 U/f > is based on the induction limit value relation to the nominal in-
duction (B/B
N
) as specified by the manufacturer of the object to 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 after expiry of the corresponding 4303 T U/f > time delay.
The 4304 U/f >>, 4305 T U/f >> trip stage characteristic serves to rapidly switch off particularly strong
overexcitations.
The time set for this purpose is an additional time delay which does not include the operating time (measuring
time, drop-out time).
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