In the field of high-voltage tests in power systems, the series resonance withstand voltage test device has been widely used due to its unique advantages. This device adjusts the resonant state of the reactor and the capacitance of the test sample to generate high voltages under a lower power supply capacity, thereby enabling the withstand voltage test of power equipment. Among them, the calculation of the voltage division ratio is a key link to ensure the accuracy of the test, directly affecting the measurement accuracy of the test voltage and the reliability of the test results.
I. The basic principle of the series resonance withstand voltage test device
The series resonance withstand voltage test device mainly consists of a variable frequency power supply, an excitation transformer, a variable reactor, a voltage divider, and the test sample. Its working principle is to utilize the inductance of the reactor and the capacitance of the test sample to undergo series resonance at a specific frequency. At this point, the circuit impedance is at its minimum, with only the resistance component remaining, thereby generating a relatively high test voltage with a smaller power supply capacity. The voltage divider serves as a voltage measurement device, and the accuracy of its voltage division ratio directly affects the measurement result of the test voltage.
II. Definition and Importance of Pressure Ratio
The voltage ratio refers to the ratio of the voltage of the high-voltage arm to the low-voltage arm of the voltage divider, usually denoted by K. In the series resonant withstand voltage test, accurately calculating the voltage ratio is of great significance: Firstly, it determines the measurement accuracy of the test voltage; Secondly, it affects the reliability of the test results; Finally, it is related to the safe operation of the test equipment. If the voltage ratio is calculated incorrectly, it may cause the test voltage to deviate from the set value. In the mild case, it may affect the test results; in the severe case, it may damage the test sample or the test equipment.
III. Calculation Method of Pressure Ratio
1. Theoretical calculation method: The theoretical calculation of the voltage ratio is based on the equivalent circuit model of the voltage divider. For capacitive voltage dividers, the voltage ratio K can be expressed as: K = (C1 + C2)/C1, where C1 is the capacitance of the high-voltage arm and C2 is the capacitance of the low-voltage arm. In practical applications, the influence of distributed capacitance and stray capacitance needs to be considered, so correction calculations are required.
2. Actual Measurement Method Due to the inherent errors in theoretical calculations, it is usually necessary to conduct actual measurements to determine the voltage ratio. The commonly used measurement methods include: (1) Low-pressure calibration method: Measure the output of the voltage divider at low pressure and calculate the voltage ratio; (2) Comparison method: Measure and compare with a standard voltage divider; (3) Frequency response method: Determine the voltage ratio by measuring the response characteristics of the voltage divider at different frequencies.
3. Temperature Compensation Calculation Changes in environmental temperature will affect the parameters of the voltage divider components. Therefore, temperature compensation needs to be considered. The temperature compensation coefficient α can be determined through experiments. The corrected voltage division ratio is: K’ = K × (1 + αΔT) where ΔT is the temperature change amount.
IV. Factors Affecting the Accuracy of Pressure Ratio Calculation
1. Frequency influence: The voltage division ratio of the divider will change with frequency, especially at non-resonant frequencies; 2. Temperature influence: As mentioned before, temperature variations will cause parameter drift of the components; 3. Humidity influence: High humidity environment may alter the insulation performance of the divider; 4. Electromagnetic interference: Strong electromagnetic fields may affect the accuracy of the measurement system; 5. Connection line impedance: The distributed parameters of the connection line will affect the results of high-voltage measurement.
V. Pressure Ratio Calibration and Verification
To ensure the accuracy of the voltage ratio, calibration needs to be carried out regularly. The calibration methods include: 1. Standard voltage source method: Calibrate using a traceable standard voltage source; 2. Standard voltage divider comparison method: Compare with a more precise standard voltage divider; 3. Power frequency withstand test method: Verify under actual power frequency conditions; 4. Partial discharge detection method: Indirectly verify the voltage ratio by detecting partial discharge signals.
VI. Notes for Practical Application
1. Before each test, the working condition of the pressure divider should be checked.
2. The pressure ratio should be calibrated regularly, and it is recommended to do so once every six months.
3. Pay attention to the influence of environmental conditions changes on the pressure ratio.
4. Record the pressure ratio data of each test and establish a historical archive.
5. If any abnormalities are found, the cause should be promptly investigated. If necessary, the calibration should be redone.
VII. Analysis of Instance for Calculation of Partial Pressure Ratio
Take a certain type of series resonant withstand voltage test device as an example. The high-voltage arm capacitor of the divider C1 in this device is 100 pF, and the low-voltage arm capacitor C2 is 1000 pF. The theoretical voltage division ratio is: K = (100 + 1000) / 100 = 11. Considering the temperature compensation coefficient α = 0.001/℃, when the ambient temperature rises by 10℃, the corrected voltage division ratio is: K’ = 11 × (1 + 0.001 × 10) = 11.11. The actual measured value is 11.05, and the error is within the allowable range.
VIII. Future Development Trends
With the advancement of technology, the calculation of the voltage division ratio in the series resonant withstand voltage test device will develop in the following directions: 1. Intelligence: Automatic calculation and compensation of the voltage division ratio; 2. Digitization: Utilizing digital signal processing technology to improve measurement accuracy; 3. Multiplicity: Integrating more measurement and protection functions; 4. Miniaturization: Reducing the equipment size and enhancing portability; 5. Networking: Achieving remote monitoring and data sharing.
The calculation of the voltage division ratio in the series resonance withstand voltage test device is a complex and important task, which requires comprehensive consideration of both theoretical calculations and actual measurements. Through scientific methods and strict management, the accuracy of the voltage division ratio can be ensured, thereby enhancing the reliability and safety of the entire test system. In the future, with the application of new technologies, the calculation and measurement of the voltage division ratio will become more precise and convenient, providing stronger guarantees for the safe operation of power equipment.
Post time: Dec-08-2025