Influencing factors of transformer winding deformation test results

Transformer winding deformation testing is an important means of evaluating mechanical displacement or deformation of windings, and its test results are influenced by various factors. The following are the main influencing factors and their analysis:
The impact of stray capacitance:
The ground stray capacitance of transformer bushing busbars is often not fixed, and the repeatability of three-phase results leads to more accurate diagnostic results. Testing should be conducted in a state where the transformer is completely isolated from the power grid. Before testing, all leads connected to the end of the transformer bushing should be removed, and the removed leads should be kept as far away from the tested transformer bushing as possible to reduce the impact of stray capacitance.
The position of the tap changer affects:
The frequency response characteristics of transformer windings are related to the position of the tap changer, and the position of the tap changer should be checked and recorded during testing. It is recommended to measure at the highest tap position to include the graph information of the entire winding; Alternatively, it should be ensured that the tap changer is in the same position (usually the rated tap) for each measurement, in order to compare the test results before and after.
The influence of electrostatic charges:
To avoid damage to the testing system caused by static charges stored in the winding, transformer winding deformation measurement needs to be conducted before the DC test project. If the tested transformer has just completed the DC test project, the transformer winding must be fully discharged before connecting the test circuit.
The impact of connectivity:
Due to weak measurement signals, the measurement terminals for excitation and response signals should be reliably connected to the transformer winding terminals to reduce contact resistance. The stray capacitance of the measuring lead itself can also affect the test results of frequency response characteristics. During testing, specially configured measuring cables and connecting leads should be used, and these leads (including injection units and detection units) should be kept as far away as possible from the bushing of the tested winding.
The impact of grounding:
The grounding wires of the input unit and monitoring unit should be connected together at the grounding point of the transformer core, and the grounding wires should be as short as possible and should not be tangled.