Functions
162
7UM62 Manual
C53000-G1176-C149-3
The
,
trip stage characteristic serves to switch off
particularly strong overexcitations within a short time.
The time set for this purpose is an additional time delay which does not include the
operating time (measuring time, drop-out time).
Thermal
Characteristic
A thermal characteristic is superimposed to the trip stage characteristic. For this
purpose, the overtemperature created by the overexcitation is approximately
modeled. Not only the already mentioned pickup signalization is generated on
exceeding the protection U/f induction limit value set at address
but a counter is
tripped additionally. Depending on the set characteristic, this counter provokes the
tripping after the specified time.
Figure 2-76
Tripping Time Characteristic of the Overexcitation Protection – Presettings
The characteristic of a Siemens standard transformer was selected as a presetting for
the parameters
to
. If the manufacturer of the object to be protected did not
include any instructions on this subject, the preset standard characteristic should be
used. Otherwise, any trip characteristic can be specified by point-wise entering of
parameters by maximally 7 straight lengths. To do this, the trip times of the
overexcitation values U/f = 1.05; 1.10; 1.15; 1.20; 1.25; 1.30; 1.35 and 1.40 are read
out from the predefined characteristic and entered at the addresses
to
. The protective relay executes a linear interpolation
between the points.
Limitation
The model of the heating of the object to be protected is limited to a 150 % trip
temperature overrange.
Time for Cool Down
The tripping by the thermal image drops out by the time of the pickup threshold
dropout. However, the counter content is reset to zero with the cool-down time
parameterized at address
. In this context, this parameter is
defined as the time required by the thermal image to cool down from 100 % to 0 %.
U f
⁄
U
N
f
N
⁄
-----------------
t [s]
