Technical informationCaution of corona discharge test of transformer and coil

Well, this time we will explain the wiring that you make mistakes when using the corona discharge tester. If you start measuring partial discharge or corona discharge, we think that it will be helpful if the results are unstable and strange.

Ⅰ. Test between core and coil

In Figure 1-1, a high voltage is applied to one side ① of the winding and the other ② side is not connected. Perhaps a lot of people think that ② will have the same potential as ①.

(Figure 1-1) Frequently Mistaken Connection

However, as shown in gray in Figure 1-1, the distributed capacitance exists in the coil. Because distributed capacitance exists, frequency and phase change with respect to ① in ②. And as a result, the measured value becomes inaccurate. In order to stabilize this, short ① and ② as shown in Figure 1-2

(Figure 1-2) Correct connection

① and ② are in phase and the measurement result is stabilized.

Ⅱ. Transformer test

In the case of the transformer test, connect the primary coil ② and secondary coil ③, after that connect H (high voltage) ④ and L (return) ③.

(Figure 2) Normal connection

Furthermore, it is better to adjust the measurement frequency to the actual use condition. In addition, the core may be grounded.

(Figure3) When the core is grounded

Generally, the high frequency transformer floats the core, the low frequency transformer is grounded and used. Please connect according to the actual use condition.
By the way, although the temporary side is separated in Figure 4, this is an unstable connection.

(Figure 4) Do not detach the primary side

Because the both ends ① ② of the primary coil are floating, the potential between the primary coil and the secondary coil is not determined and the measured value becomes unstable.
It will become different from the actual use state. Perhaps ② and ③ are supposed to be connected in actual use state. Please connect ② and ③ as shown in Figure 2.
In Figure 5 H (high voltage) is connected to ③ on the side close to the primary coil, and L (return) is connected to ④.

(Figure 5) H (high voltage) to be misconnected in the direction closer to the primary

In this connection, since high voltage is applied to the side close to the primary coil , the potential difference between the primary coil and the secondary coil becomes steep, resulting in a dangerous condition. Perhaps it is not the actual usage state.
In Figure 5, it is usually mostly a misconnection. Please check the actual use condition again.