Siemens SIPROTEC 7RW80 Manual page 105

The 4304 24-2 PICKUP, 4305 24-2 DELAY trip element characteristic serves to rapidly switch off particularly
strong overexcitations.
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 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.
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 char-
acteristic 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). 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 %.
SIPROTEC, 7RW80, Manual
C53000-G1140-C233-1, Release date 10.2010
Thermal tripping time characteristic (with presettings)
2.8 Overexcit. Protection (Volt/Hertz) 24
Functions
105