2 Functions
116
7UM61 Manual
C53000-G1176-C127-3
Thermal Character-
istic
A thermal characteristic is superimposed on the trip stage characteristic. For this the
temperature rise created by the overexcitation is approximately modeled. Not only the
already mentioned pickup signal is generated on transgression of the U/f induction
limit set at address 4302 but in addition a counter is set additionally which causes the
tripping after a length of time corresponding to the set characteristic.
Figure 2-36 Thermal tripping time characteristic (with presettings)
The characteristic of a Siemens standard transformer was selected as a presetting for
the parameters 4306 to 4313. If the protection object manufacturer did not provide
any information, the preset standard characteristic should be used. Otherwise any trip
characteristic can be specified by point-wise entering of parameters for up to 7 straight
segments. 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 addresses 4306 t(U/f=1.05) to 4313 t(U/f=1.40). The protection
device interpolates linearly between the points.
Limitation The heating model of the object to be protected is limited to a 150 % overshoot of the
trip temperature.
Cooldown Time Tripping by the thermal image drops out by the time of the pickup threshold dropout.
However, the counter content is counted down to zero with the cooldown time param-
etrized at address 4314 T COOL DOWN. In this context this parameter is defined as
the time required by the thermal image to cool down from 100 % to 0 %.
Transformer Adap-
tation
Any deviation between primary nominal voltage of the voltage transformers and of the
object to be protected is compensated by an internal correction factor (U
N prim
/U
N Mach
).
For this it is necessary that the relevant system parameters 221Unom PRIMARY and
1101 were properly entered in accordance with Section 2.3.
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