[logik-uebererregungsschutz-einfach-040603-st, 1, en_GB]
Figure 2-101
Logic diagram of the overexcitation protection (simplified)
The thermal replica is realised by a counter which is incremented in accordance with the value U/f calculated
from the measured voltages. A prerequisite is that the U/f value has exceeded the pickup value U/f > of the
warning stage. If the counter reaches a level corresponding with the set trip characteristic, the trip command
is given.
The trip signal is cancelled as soon as the value falls below the pickup threshold and the counter is decre-
mented according to the set cooldown rate.
The thermal characteristic is specified by 8 value pairs concerning the U/f value (referred to nominal value)
and the associated trip time T. In most cases, the default characteristic for standard transformers provides for
sufficient protection. If this characteristic does not correspond to the actual thermal behaviour of the object to
be protected, any desired characteristic can be implemented by entering user-specific trip times for the speci-
fied U/f overexcitation values. Intermediate values are determined by a linear interpolation within the device.
The counter can be reset to zero by means of a blocking input or a reset input. The internal upper limit of the
thermal replica is 150 % of trip temperature rise.
Setting Notes
General
A precondition for use of the overexcitation protection is that measured voltages are connected to the device
and that a 3-phase protected object has been selected during configuration of the protection functions. Addi-
tionally, the overexcitation protection can only operate if it has been configured under address 143 OVEREXC.
PROT. = Enabled.
In address 4301 OVEREXC. PROT., the overexcitation protection can be switched ON or OFF. The option
Block relay allows to operate the protection but the trip output relay is blocked.
2.11.2
Functions
2.11 Overexcitation Protection
SIPROTEC 4, 7UT6x, Manual 219
C53000-G1176-C230-5, Edition 09.2016
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