In the operation and maintenance of power systems, the cable series resonance test is an important high-voltage testing method. This test method can effectively detect the insulation performance of cables and ensure the safe operation of power equipment. This article will provide a detailed introduction to the wiring principle, operation steps, and precautions in practical applications of the cable series resonance test.
I. Experimental Principle and Equipment Composition
The cable series resonance test is based on the principle of series resonance of inductance and capacitance. When the inductive reactance of the test circuit is equal to the capacitive reactance, the system will undergo series resonance. At this time, the circuit impedance is the smallest, and only the resistance component remains. In the resonant state, the voltage output by the test transformer will be distributed between the reactor and the tested cable according to the impedance ratio, thereby enabling high-voltage testing of the cable.
The test system is mainly composed of the following components: 1. Frequency converter power supply: providing adjustable AC power 2. Excitation transformer: raising the power supply voltage to the required level 3. Resonant reactor: forming a resonant circuit with the cable capacitance 4. Voltage divider: measuring the test voltage 5. Tested cable: serving as the test object
II. Detailed Explanation of Test Wiring Steps
1. Preparation: First, check whether all equipment is in good condition and confirm that the two ends of the test cable have been disconnected from other devices. Measure the insulation resistance of the cable to ensure it meets the test requirements. Estimate the resonant frequency range based on the cable parameters, which is usually between 30 and 300 Hz.
2. Equipment Connection: Connect the output terminal of the frequency converter power supply to the input terminal of the excitation transformer. Connect the high-voltage output terminal of the excitation transformer to one end of the resonant reactor. The other end of the reactor is connected to one end of the tested cable, and the other end of the cable is grounded. The voltage divider is connected in parallel at both ends of the tested cable to measure the test voltage.
3. System Debugging After powering on the system, gradually increase the output voltage of the frequency converter power supply while observing the frequency changes. When the system reaches the resonant state, the voltage meter indication will show a significant change. At this point, record the resonant frequency. Adjust the output voltage to the required value for the test, which is usually 1.7-2 times the cable’s rated voltage.
4. Test Procedure: Maintain the resonant state and continuously apply the test voltage for 15 minutes. During this period, closely monitor the changes in voltage and current. If any abnormalities occur, immediately reduce the voltage and cut off the power supply. After the test is completed, first lower the voltage to zero, and then disconnect the power source.
III. Notes and Safety Requirements
1. Safety distance: A safety fence should be set up at the test site to maintain an adequate safety distance. Operators must wear insulating protective gear.
2. Grounding Protection All equipment must be reliably grounded to prevent electric shock from induced voltage. After the test, the cables must be fully discharged.
3. Parameter Matching When selecting the reactor, the capacitance parameters of the cable should be taken into account to ensure resonance can be achieved within the specified frequency range.
4. Environmental Factors: Avoid conducting tests in damp or polluted environments. If necessary, take measures to prevent moisture.
IV. Common Problems and Solutions
Failure to reach resonance state Possible causes: Inconsistent parameters of the reactor or incorrect wiring. Solution: Check the wiring and adjust the configuration of the reactor.
2. Resonance frequency shift Possible causes: Changes in cable parameters or equipment failure. Solution: Re-measure the cable parameters and inspect the equipment status.
3. Unstable test voltage. Possible causes: Power supply fluctuation or resonance point drift. Solution: Stabilize the power supply and fine-tune the frequency.
V. Practical Application Cases
During the 110kV cable commissioning test at a certain substation, a series resonance method was used for the withstand voltage test. The cable length was 1.2km and the estimated capacitance was 0.25μF. Two 50kV/50H reactors were connected in parallel, and the measured resonant frequency was 85Hz. The test voltage was raised to 128kV (1.7 times the rated voltage), and it was maintained for 15 minutes without any abnormalities. The test was deemed合格.
VI. Technical Advantages and Development Trends
Compared with traditional DC withstand voltage tests, the series resonance test has the following advantages: 1. The test voltage waveform is close to the power frequency, which is more in line with the actual operating conditions. 2. The equipment is lightweight and suitable for on-site testing. 3. It will not accumulate space charges in the insulation, avoiding damage to the cables.
Future development trends include: 1. The application of intelligent testing systems 2. Higher-precision online monitoring technologies 3. Comprehensive application with other testing methods
From the above introduction, it can be seen that the cable series resonance test is a safe and effective method for cable inspection. Mastering the correct wiring method and operation procedures is of great significance for ensuring the safe operation of the power system. In practical work, it should be applied flexibly according to specific circumstances, and experiences should be continuously summarized to improve the test quality.
Post time: Dec-18-2025