By hvhipot 
With the continuous development of China’s power industry, the application of high-voltage and large capacity cross-linked polyethylene cables (hereinafter referred to as XLPE cables) is becoming increasingly widespread, especially in urban power grids, where using XLPE cables instead of overhead lines has become a trend. Cables are factory tested, and during transportation, storage, construction, and installation of accessories, mechanical damage or installation process defects may occur. Therefore, it is necessary to complete on-site voltage cable line acceptance testing before operation.
Test method for series resonant frequency withstand voltage
The resonant frequency pressure test method is a cable insulation pressure test method that uses an adjustable series inductor and capacitor to form series resonance in high-voltage cables. The series resonant frequency voltage testing equipment requires high weight, poor maneuverability, and difficulty in matching inductance and capacitance, making it suitable for laboratory applications and not suitable for on-site testing of high-voltage, high-capacity, long-distance cross-linked cables.
Test method for series resonant frequency
The principle of the series resonant frequency test method is basically the same as that of the resonant frequency withstand voltage test method, and both are based on the cable series resonant voltage test method, except that: the series resonant frequency voltage test is conducted at a frequency of 50 Hz, by adjusting the reactor of the resonant inductance of the test circuit, and the series resonant frequency test method is to use a fixed reactor and the main circuit composition of the sample high-voltage series resonance, by adjusting the frequency of the inverter output voltage test circuit to produce resonance, and then adjust the voltage regulator, the pressure value reached under the cable test meets the requirements of the high-voltage XLPE cable voltage test. For series resonant frequency voltage testing equipment, which has the advantages of light weight, high quality factor, and detachable performance, only suitable reactors with fixed inductance values can achieve AC voltage testing of cables at different lengths (10m~10km).
Experimental plan, reactor inductance L=16.2H; Cx test cable; As an excitation transformer, Tr directly resonates in series with the test reactor.
Due to the negligible voltage division of the capacitor relative to the tested cable capacitance, when the series resonance frequency of the main circuit is f=1/2VLCx=28.9HZ. In the equation, L=16.2H, Cx=1.873 uF. At this time, the primary current of the test circuit is I=UoCx=76A.
Testing security measures: Conduct on-site testing before implementing security measures in the testing terminal area to prevent staff from being diverted to other testing locations; Set up warning lines and post warning signs within the safety zone, and send people to travel outside the warning zone. Conduct tests inside tunnels or terminal towers, and assign dedicated personnel to be responsible for them; When replacing the test lead, it is necessary to confirm the dismantling of the power supply and ground during on-site testing, and it is prohibited to throw out the measuring line during dismantling; The experimental phase is currently underway, and the cables are grounded in two stages. Please assign a dedicated person to handle this.
Experimental plan implementation: The output current of the system excitation transformer and the gear selected for this experiment are selected a 315kva substation as the test power series resonance. There is a case study in a return section of a fHV Hipot Electric Co., Ltd. circuit line: the first section measures the insulation resistance of the phase high voltage conductor to ground, and without exception, connects the phase high voltage conductor to a reactor. In terms of power supply, the output frequency of the inverter power supply is adjusted to 29Hz. When the maximum voltage is measured and displayed, the test circuit reaches the resonance point; Adjust the output voltage of the frequency power supply to 216kV for 60 minutes until the voltage drops to zero, disconnect the power supply, and discharge after the test is completed.