Siemens SIPROTEC 4 7UT6 Series Manual page 220

Functions
2.11 Overexcitation Protection
Definite Time Stages
The limit-value setting at address 4302 U/f > is based on the continuously permissible induction value
related to the nominal induction (B/B
setting determines the pickup of the warning stage as well as the minimum value for the thermal stage (see
below).
After the time T U/f > address 4303 has expired (approx 10 s) alarm is output.
Strong overexcitation endangers the protected object after short time. The high-set stage U/f >>, address
4304 should, therefore be only shortly delayed (approx. 1 s) by the time T U/f >>, address 4305.
The set times are additional time delays which do not include the inherent operating time (measuring time,
drop-out time) of the protection. If you set a time delay to , the associated stage does not trip; nevertheless,
a pickup indication is output.
Thermal Stage
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Figure 2-102
The thermal characteristic is intended to simulate the temperature rise of the iron core due to overflux. The
heating-up characteristic is approximated by 8 time values for the 8 predefined induction values B/B
(reduced U/f). Intermediate values are gained in the device by linear interpolation.
If no instructions of the manufacturer are available, the preset standard characteristic should be used; this
corresponds to a standard Siemens transformer
220
) specified by the manufacturer of the object to be protected. This
N
Thermal tripping characteristic (with preset values)
(Figure 2-102).
C53000-G1176-C230-5, Edition 09.2016
NObj
SIPROTEC 4, 7UT6x, Manual