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Functional Tests
10.7 Functional Test of Thermal Overload Protection
10.7
Functional Test of Thermal Overload Protection
Secondary Test
For the secondary test for the overload protection, note that all setting parameters refer to primary variables
of the protected object. The protection device extracts the current transformer ratio from the power-system
data and internally performs the adjustments to device nominal variables. Take these characteristics into
account for the test.
Reset the thermal memory before you repeat the test. This is possible, for instance, via the binary input
²
indication >Reset thermal replica. If the function is reparameterized or is switched off, the
thermal replica will also be reset.
Test without Previous Load
Test the operate time at 1.5 I/I
²
In the example, the following power-system data are assumed:
I
= 483 A
rated, obj
I
rated, transf.prim
I
rated, transf.sec
The primary test current is 1.5 * 483 A = 724.5 A. This results in a secondary current of 724.5 A *1A/750A =
0.966 A. A secondary current of 0.966 A must therefore be supplied.
Calculate the operate time with the following formula. Enter only primary variables here.
²
Set I
²
previous load
time constant (for example, 600 s or 10 min).
Test from the cold state.
²
[foauslpr-190309-01.tif, 2, en_US]
At a current of 0.966 A supplied on the secondary side, the protection function must trip after 463 s.
²
Test with Previous Load
The object rated current (I
²
Supply 483 A *1 A/750 A = 0.644 A in this case.
²
After a finite time (greater than 5 τ
K-factor
If you abruptly increase the supplied secondary current from 0.644 A to 0.966 A (1.5 I/I
²
load protection will trip in the following time.
[foauslpr-190309-02.tif, 2, en_US]
1072
rated, obj.
= 750 A
= 1 A
= 0. The setting parameters reveal the K-factor (for example, 1.1) and the Thermal
= I
previous load
rated, obj
), the stationary previous load sets in.
th
) flows at a previous load of 1 (100 %).
SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
), the over-
rated, obj
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