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Functions
2.8 24 Overexcit. Protection (Volt/Hertz)
Thermal Characteristic
A thermal characteristic is superimposed on the trip element characteristic. For this purpose, the temperature
rise created by the overexcitation is approximately modeled. Not only the already mentioned pickup signal is
generated on transgression of the V/f induction limit set at address 4302, but in addition a counter is activated
additionally which causes the tripping after a length of time corresponding to the set characteristic.
[thermische-ausloesekennlinie-020827-ho, 1, en_US]
Figure 2-30
The characteristic of a Siemens standard transformer was selected as a default setting 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 entering parameters point-
bypoint over a maximum of 7 straight lengths. To do this, the trip times t of the overexcitation values V/f =
1.05; 1.10; 1.15; 1.20; 1.25; 1.30; 1.35 and 1.40 are read out from predefined characteristic and entered at
the addresses 4306 24-t(V/f=1.05) to 4313 24-t(V/f=1.40) 24-t(V/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.
Cooling 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 parametrized at address 4314 24 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 %.
Voltage Transformer Adaptation
Any deviation between primary nominal voltage of the voltage transformers and of the object to be protected
is compensated by an internal correction factor (V
parameters 202 Vnom PRIMARY and 1101 FullScaleVolt. have been entered correctly in accordance
with Section
2.1.3.2 Setting Notes
94
Thermal tripping time characteristic (with presettings)
and
2.1.6.2 Setting
/V
). For this it is necessary that the relevant
Nom prim
Nom Mach
Notes.
C53000-G1140-C233-4, Edition 07.2018
SIPROTEC 4, 7RW80, Manual
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