1. Introduction

The DC withstand voltage test and DC leakage current test of the water-cooled DC high-voltage generator are conducted under two conditions: blowing water or passing water. Their respective advantages and disadvantages are compared as follows:

1. Conduct experiments while blowing water

Advantages: It can be tested using a general DC high-voltage generator, with lightweight equipment, simple operation, accurate readings, and is not affected by water quality conditions.

Disadvantage: Due to the structure of the generator unit, it is difficult to dry the accumulated water at the bottom. Therefore, it is very time-consuming, and the water blowing time can even last for more than a week. Extended the downtime for major repairs. If water is not blown properly, it will not only cause measurement errors, but also pose a risk of damaging the winding if it causes internal arcing in the coil during testing.

2. Conduct experiments under water conditions

Advantages: No need for water blowing equipment, saving time for blowing water.

Disadvantages: Currently, AC trial transformers (or resonant transformers) are used in combination with silicon stacks and capacitors, and additional devices are required for polarization compensation of the water collection pipes. The equipment is bulky, scattered, and the wiring is complex. The test results are affected by water quality, and the microampere meter fluctuates greatly, making it difficult to read.

Considering the above situation, in order to overcome both shortcomings, it is necessary to solve the problem of using a complete set of specialized equipment for testing under the premise of being lightweight, simple, and accurate when water is flowing. The "water-cooled DC high-voltage generator" developed by our company based on the principle of "low-voltage shielding method" basically meets this requirement. Its main features are:

1) The entire device consists only of a control box and a voltage multiplier, and the wiring is very simple.

2) Adopting electronic control and tuning, easy and comfortable operation; Voltage, current, etc. are directly read on the panel meter without the need for conversion.

3) One minute timer and prompt function, set according to the requirements of the test procedure.

2、 Working principle (principle of low-voltage shielding method)

The low-voltage shielding method is suitable for motors with weak insulation to ground in the water collection pipe, and its wiring is shown in Figure 1. Connect the water collection pipe to the tail end of the high voltage side winding of the high voltage test transformer BS through milliampere meter 1, and connect microampere meter 2 in series with the tail end of the high voltage side winding of BS and ground. This separates the current Ik flowing through the water pipe from the pressurized phase to ground and the other two-phase insulation leakage Ix. Like air-cooled or hydrogen cooled motors, the stator insulation status can be determined from the leakage value.

When using the low-voltage shielding method for wiring, due to the correlation between microampere meter 2 and the ground resistance R3 of the water collection pipe, the reading I'X on the microampere meter is actually less than Ix. Therefore, to accurately obtain the value of the leakage Ix, it needs to be converted into the following formula:

Ix=I’X（1+RA）

R3

In the formula, RA represents the internal resistance of the microampere meter; R3- Insulation resistance of the water collection pipe to ground.

R3 can be measured with a multimeter after the test wiring is completed under water conditions. The positive and negative polarities should be measured once each, and the average value should be taken. During measurement, it is necessary to temporarily disconnect microampere meter 2 to avoid burning out the meter head and measuring values that are too small. Due to the polarization potential generated during the water test, there is an indication in the microampere meter before pressurization. At this time, an equal and opposite potential can be connected for compensation. The specific method is shown in the dashed box diagram in Figure 1. Adjust the size of Rb and use microampere meter 2 to indicate zero, achieving full compensation.

D - High voltage diode; R - Current limiting resistor, 1 ohm/volt; 1. 2- Inlet and outlet valves used during operation;

C1- stabilizing capacitor, approximately 1 microfarad; V - Static voltmeter 3, 4- Inlet and outlet valves for charging and washing;

C2- capacitance that suppresses AC components; R2- Water resistance 5. - Pressure gauge; 6- Water collection pipe;

L - inductance that suppresses AC components; 7. - Stator winding

Ra, Rb -100 kOhm and 500 kOhm potentiometers;

K1, K2- Open; DC-1.5V dry battery;;

To reduce the impact of stray currents, the grounding terminal of microampere meter 2 must be directly connected to the generator casing.

Experimental experience has shown that improving water quality during testing can not only reduce the capacity of the testing equipment, but also improve the DC voltage waveform.

After the new machine is put into operation and major repairs, testing and production are often delayed due to poor water quality. At this point, the method shown in Figure 2 can be adopted by changing the water supply to "filling water". First, close the inlet and outlet valves used in the operation of valves 1 and 2, and disconnect the flanges connecting these two valves to the external water pipe (for those equipped with insulated flanges, only remove the grounding wire to ensure that the insulation of valves 1 and 2 to the ground is greater than a few megohms). Open valves 3 and 4 again, use clean insulated pipes to draw condensate water with lower conductivity from other units, pass it into the stator winding, wait for the water to fill, and then use compressed air to flush the water out of the drainage ditch. Repeat this process several times until the water quality that flows out is qualified (3-5 μ m/cm). Then adjust the No. 4 drainage valve appropriately to keep a small stream of water flowing out. When the pressure difference between the inlet and outlet is very small (the inlet and outlet pressure is the same as during operation), the test can begin. The experiment showed that there was no significant change in leakage current and temperature after a long period of time after pressurization.

The water-cooled generator DC high voltage generator is a new generation of LCD screen display and intelligent specialized testing instrument developed by our company based on the principle of "low voltage shielding" on the basis of the previous generation product. It adopts the core technology of high-power DC high voltage generator, replacing a series of single component combination test tools such as traditional test transformers, high voltage silicon stacks, stabilizing capacitors, rectifying capacitors and inductors, DC high voltage dividers, regulators, mA meters, μ A meters, and polarization potential compensation devices. It integrates them all into one high voltage (generating) unit and one control box, significantly reducing the number of single components in the complete test device, greatly reducing the weight of the test equipment, reducing the workload of the test personnel, simplifying the test wiring, making the test more convenient, efficient, and reliable. At the same time, it has electronic voltage regulation, automatic polarization compensation, and rich protection functions, making the test operation easier and safer; The use of intermediate frequency voltage doubling makes the test voltage more ideal, the test data more accurate and stable, and the results more reliable.

3、 Main technical performance

60/20060/30080/20080/30090/20090/300100/300100/500

Output voltage (kV)606080809090100100

Output current (mA)200300200300200300300500

Output power (kW)1218162418273050

Chassis weight (kg)3538383939404045

Double pressure weight (kg)10+2414+3715+3815+3815+3915+3717+3917+50

Height of pressure doubling cylinder (mm)750750105010501050105010501050

Voltage measurement error1.0% ± 2 words

Total current measurement error1.0% ± 2 words

Leakage current measurement error± 2.0% (full degree)

Overvoltage setting error≤1%

Voltage stability1.0% (random fluctuations, power supply voltage changes ± 10%)

working methodRated load, continuous operation for ≤ 5 minutes

ambient temperature-10℃~40℃

relative humidityWhen the temperature is 25 ℃, it should not exceed 90% (no condensation)

altitudeBelow 2000 meters