1. The setting of balance coefficient: If the setting of balance coefficient is not correct, it will cause a large deviation between the test curve and the setting curve. The balance coefficient should be selected correctly according to the protection setting value.

2. Selection of calculation formula: Incorrect selection of differential current and braking current formulas will cause large deviation or even complete error between test results and setting values, and should be correctly selected according to the formula provided by the protection manufacturer.

3. Selection of current phases on both sides: Incorrect selection of current phases on both sides will make the test result completely wrong. If the difference current is equal to the sum of the currents on both sides, the phase difference on both sides is 180 degrees; if the difference current is equal to both sides Current difference, the phase difference between the two sides of current is 0 degrees,

4. When using three-phase current for differential test, if no compensation current is added, the test result will also be incorrect, because the three-phase current can only be used for differential test in phases, and due to the different wiring of the transformer, the current on both sides There will be a certain phase difference, so the protection device must perform phase compensation on the software, so that when we do a phase differential test, the differential of other phases will preemptively move, and a compensation must be added to the phase of the snapping The current makes the phase differential unable to operate, so that the test result can be correct.