Checking Disturbance-Voltage Suppression in the Load Resistor with a System Ground Fault
DANGER
Touching live parts or reaching into rotating machines will result in death or serious injury.
²
Perform primary measures only when the machine is at standstill and the system components are de-
energized and grounded.
²
With the primary system de-energized and grounded, insert a 1-pole ground fault bridge on the high-
voltage side of the unit transformer.
CAUTION
Material can be damaged during the test if there is a neutral-point grounding at the transformer and simul-
taneously a grounding on the high-voltage side.
²
Neutral grounding at the transformer must be interrupted during the test.
²
Start the machine and excite it slowly up to 30 % of the rated machine voltage.
²
Read the zero-sequence voltage V
0, measured value
from the operational measured values.
²
Extrapolate the zero-sequence voltage to 100 % of the machine voltage (V
0, fault
).
²
Calculate the safety margin by dividing the calculated fault value by the set threshold value.
If the result is less than 0.5, the safety margin is sufficient. If the fault voltage is lower, you can increase the
sensitivity of the protection function.
EXAMPLE:
V
0, meas.
= 0.75 V
V
threshold value
= 5.68 V
V
0, fault
= 0.75 V * 100 % / 30 % = 2.5 V
Safety margin = 2.5 V / 5.68 V = 0.44
The calculated safety margin of 0.44 is sufficient because it is below 0.5.
²
Shut the machine down and de-excite it. Remove the ground-fault bridge.
²
Restore neutral-point grounding if you require grounded operation of the neutral on the high-voltage
side of the unit transformer.
When using the function for startup ground-fault protection on a busbar connection, carry out the same check
as for the unit connection, but only the part Test during machine ground fault.
Functional Tests
11.11 Functional Test for Overvoltage Protection with Zero-Sequence Voltage/Residual Voltage
1390 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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