1. Introduction to dielectric loss ultra-low frequency products

This product is used for multifunctional testing of cables. Can measure the dielectric loss, capacitance, insulation resistance of cables, and also perform AC and DC withstand voltage tests. And obtain the cable insulation quality report. Adopting an integrated structure. Due to the built-in dielectric loss measurement unit in the ultra-low frequency booster, the device is small in size, light in weight, easy to connect, and convenient to use.

2. Technical indicators for dielectric loss ultra-low frequency

2.1 Rated voltage: 30KV, 40KV, 50KV, 60KV, 80KV

2.2 Test frequency: 0.1Hz-0.01Hz

2.3 Dielectric loss measurement range: 0.01 × 10-3-655.35 × 10-3. For values greater than 655.35 × 10-3, a prompt of>655.35 × 10-3 will be given

2.4 Dielectric loss measurement accuracy: 1x10-3

2.5 Dielectric loss resolution: 1x10-4

2.6 Capacitance measurement range: 0.001 μ F -10 μ F

2.7 Capacity resolution: 0.001 μ F

2.8 Capacitance measurement accuracy 3%

2.9 Insulation resistance measurement range: 1M Ω -65535M Ω. For values greater than 65535M Ω, a prompt of>65535M Ω will be given.

2.10 Insulation resistance resolution: 1M Ω

2.11 Insulation resistance measurement accuracy 3%

2.12 Voltage accuracy: 3%

2.13 AC current range: 0-20mA

2.14 AC current resolution: 0.1mA

2.15 AC current accuracy: 3%

2.16 DC current range: 0-2000 μ A

2.17 DC current resolution: 1 μ A

2.18 DC current accuracy: 3%

2.19 RS232 (or USB) communication interface

2.20 Volume: 50 * 28 * 45 (cm)

2.21 Weight: 30kV and 40kV products weigh 32gk, 50kV, 60kV, and 80kV products weigh 40kg.

3. Ultra low frequency operation method

After connecting the on-site testing system as described above, the power can be turned on to enter the testing process. The homepage of the control box touch screen is for selecting the wiring diagram. Click on the wiring diagram to enter the parameter setting interface. Modify the test time and voltage according to the test requirements. Click on the data to be modified, a numeric keypad will pop up, and enter the desired data. In order to ensure safety, the system has limited the input data: the test voltage range is 1kv to the rated value; The experimental time ranges from 1 to 99 minutes. Continuous dielectric loss test is a continuous measurement of dielectric loss at a set voltage, which can also be used as an AC withstand voltage test. The national standard dielectric loss test is to perform eight data tests on three-phase cables under three-point voltages (0.5U0, U0, 1.5U0) according to regulations, and calculate the average value, variation, and stability of dielectric loss, automatically determining the insulation quality of the cable according to regulations. Please refer to section 3.7 below for an introduction to the automatic ultra-low frequency dielectric loss test procedure according to the regulations. After the experiment is completed, the parameters will be automatically saved as the default values for the next experiment. Dielectric loss testing program: The instrument first enters self-test, which is a pre-test of the test sample and calibration of the instrument itself. The length of the self-test time is related to the length of the cable, and the longer the cable, the longer the self-test time. If it takes about one to five minutes, patience is required. After the self check is completed, it automatically enters the continuous dielectric loss test, which can simultaneously measure the dielectric loss, capacitance, and insulation resistance values, and update the data once every cycle. Our company's technology is designed to be more stable and accurate with each measurement. After a few measurement cycles, the data will become very stable and can be read. The system provides intelligent protection for the testing process, including protection actions such as overvoltage, overcurrent, voltage and current transients, and discharge. The shutdown process will automatically discharge the test sample. After shutdown, the current data can be printed or saved, and the selected data records can also be printed in the historical data query on the homepage. The top line of the screen is the working status prompt of the instrument, which includes some fault information of the instrument. Because there are touch key prompts and help information, users can follow the prompts to operate. Before dismantling the wire, the test sample should be discharged with a discharge rod, followed by short-circuit discharge, and then the dismantling operation should be carried out. If the length of the tested cable is less than 100 meters and the instrument cannot output a smooth sine wave voltage, a compensation capacitor can be connected in parallel at the end of the test sample, and "Add Compensation Capacitor" can be selected on the parameter setting interface. This way, the test results will deduct the influence of the compensation capacitor. The compensating capacitor must be the one included in this product, as the parameters of this capacitor are pre-set in the instrument. The four main operating interfaces are as follows (the form of product interfaces has changed in different periods).

4. How to eliminate the influence of cable surface leakage current on dielectric loss

When the air humidity is high or there is dirt on the surface of the cable end, leakage current will form on the surface of the cable end, which will increase the dielectric loss value and affect the judgment of the dielectric loss of the cable body. So when conducting dielectric loss tests, it is necessary to eliminate this influence. The method is to wrap a shielding ring with bare copper wire in the lower half of the cable head, and lead it to the shielding terminal of the control box with a wire. Because there is surface leakage current at both ends of the cable, theoretically both sides need to be measured. The method is to use an unmeasured phase line to connect the remote shielding ring, and then connect the shielding ring signals at both ends in parallel to the shielding terminals of the instrument. This method is called double ended shielding. This method of connecting shielded wires is obviously inconvenient on site. To simplify this problem, we approximate the leakage current at both ends as being the same, only measuring the leakage current at the near end, and deducting twice the leakage current during dielectric loss testing. This method is called single ended shielding. The wiring method is shown in the on-site wiring diagram of the dielectric loss above. So in the parameter settings page, the corresponding shielding connection method should be selected. If the air humidity is low and the surface of the cable end is clean, shielded wires can be omitted.