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