The DC withstand voltage test and the DC leakage current test of the stator winding of the internal water-cooled generator are carried out under two conditions without external water blowing or water flow. The advantages and disadvantages of each are as follows:

1. Experiment with water blowing

Advantages: general DC high voltage tester can be used for testing (such as 60kV/10mA type), the equipment is light, easy to operate, accurate readings and not affected by water quality.

Disadvantages: Due to the structure of the generator unit, it is difficult to dry the water accumulated at the bottom. Therefore, it is very time-consuming, and the blowing time can even be more than a week. Extends downtime for major repairs. If the water is not completely blown, it will not only cause measurement errors, but also in case of arcing in the coil during the test, there is a danger of damaging the winding.

2. Test under water supply

Advantages: No water blowing equipment is needed, saving the time of blowing water.

Disadvantages: At present, AC test transformers (or resonance transformers) are combined with silicon stacks and capacitors, and additional devices are required to compensate for polarization of water collection pipes. The equipment is bulky, scattered, and wiring is complicated. The test result is affected by the water quality, the microammeter fluctuates greatly, and the reading is difficult.