Harmonic braking coefficient verification (for transformer differential protection) test wiring
Connection method 1 (Applying current to both high and low voltage sides simultaneously):
The microcomputer relay protection calibration instrument IA is connected to the A phase on the high-voltage side, IB is connected to the a phase on the low-voltage side. The neutral lines of the high-voltage and low-voltage sides are short-circuited and then connected to the calibration instrument IN.
Connection method 2 (applying current only to the high-voltage side):
The microcomputer relay protection calibration instrument IA is connected to the A phase on the high-voltage side, and the neutral line of the high-voltage side is connected to the IN terminal of the calibration instrument for the test method.
Test steps:
Start the experiment
After confirming that the connection is correct, click the “Start Test” button or press the F2 shortcut key on the keyboard to start the test.
If the “manual control” option is selected in the test operation mode, then the “output increment” and “output decrement” buttons can be used.
The pre-set test data before the experiment may have variations in amplitude and phase during the experiment. After the experiment, by selecting the “Operation” option in the menu and then choosing “Restore Set Values”, the data can be restored to its initial value before the experiment, which greatly facilitates repetitive experiments.
Click the “Exit Experiment” button or press the F3 key on the keyboard to exit the experiment.
Here, we take connection method 2 as an example (applying current to both the high-voltage and low-voltage sides simultaneously):
Suppose the second harmonic braking coefficient of a certain transformer is 20%.
First, in the “Harmonic Calculation Method” menu, select “Calculate by Base Wave Percentage”. Then, select IA, set the base wave amplitude to 2A (note: this value must be greater than the action threshold value of the differential protection). In the harmonic parameter table, set the second harmonic to 25% (greater than the harmonic braking coefficient of 20%, so that the protection does not act at the beginning of the test). Then, set the amplitude step size to 1% and select the “Manual Control” mode.
Start the test, and the protection should be in the locked state. Gradually reduce the variable step by step until the protection activates. Compare the second harmonic value of the action with the set braking coefficient.
The test results indicate
When conducting the test using method 1, the option “Calculate based on fundamental wave percentage” cannot be selected.
Post time: Mar-28-2026