I. Composition of the Power Frequency Withstand Voltage Test Device
A complete power frequency withstand voltage test device is mainly composed of the following core components and optional parts:
Test Transformer
As the core unit of the device, its function is to increase the input low voltage to the required high voltage level for the test. The structural form is usually single-phase and can be divided into oil-immersed or dry types.
Voltage Regulation Control Device (Control Console)
Used for stable and continuous stepless regulation of the voltage applied to the primary side of the test transformer, thereby precisely controlling the output voltage on the high-voltage side. Common types include autotransformer, electrically controlled voltage regulator, and electronic voltage regulation system.
Protective Resistor
Connected in series to the high-voltage test circuit, its function is to limit the short-circuit current generated in the circuit when the test specimen has flashover or breakdown faults, thereby protecting the test transformer and the measurement system.
Measurement System
The core function is to accurately measure the high voltage applied to the test specimen. The traditional measurement method uses high-voltage electrostatic voltmeters or measurement windings; modern devices generally adopt a measurement scheme of capacitance divider combined with low-voltage instruments, featuring both safety and high accuracy.
Compensation Reactance Transformer (Optional)
Suitable for tests of capacitive specimens (such as long cables, gas-insulated switchgear). The capacitive current of such specimens will significantly increase the capacity requirement of the test transformer, and the parallel compensation reactance transformer can provide inductive current to cancel the capacitive current, thereby effectively reducing the requirements for the test power supply capacity.
II. Main Technical Routes of Power Frequency Withstand Voltage Test Devices
Traditional Power Frequency Test Transformer Devices
Composed of the test transformer, voltage regulation control device, protective resistor, and measurement system. This technical route has a simple structure and clear principle, but when conducting tests on large-capacity specimens, there are limitations such as large equipment size and heavy weight.
Series Resonance Withstand Voltage Test Device
Mainly consists of variable frequency power supply, excitation transformer, adjustable reactor, and capacitance divider. Its working principle is to adjust the output frequency of the variable frequency power supply to generate resonance in the test circuit under the power frequency condition. In the resonant state, only the power supply capacity required to meet the active power loss of the circuit is needed to obtain the huge output capacity meeting the test requirements.
This technical route is currently the mainstream and recommended solution for conducting withstand voltage tests on large-capacity power equipment (such as power cables, generators, gas-insulated switchgear) in the field, featuring small size, light weight, and low requirements for the test power supply.
III. Selection Method of Power Frequency Withstand Voltage Test Devices
The core principle of selecting power frequency withstand voltage test devices is to ensure that the output capacity and safety performance of the device meet the test requirements of the specimen. Specific steps can be followed as follows:
Clarify the parameters of the specimen and test standards
Higher test voltage (U): Determine according to the corresponding technical standards or preventive test procedures of the specimen.
The larger earth capacitance of the specimen (C): Can be obtained from the equipment nameplate, factory test report, or measured through professional testing methods. This parameter is the most critical and easily overlooked core indicator in the selection process.
Calculate key electrical parameters
Larger test current (I): The test current of the specimen is the capacitive current, and the calculation formula is:
I = ω × C × U = 2πfCU
Where f is the power frequency f
Set to 50Hz.
The required minimum device capacity (P): The calculation formula is: P=U×I
For example: When conducting a 21.75kV withstand test on a 10kV cable with an electrical capacity of approximately 0.5μF, the calculation yields:
I ≈ 2 × 3.14 × 50 × 0.5 × 10−6 × 21.75 × 103 ≈ 3.4A
P ≈ 21.75kV × 3.4A ≈ 74kVA
In this scenario, if the traditional test transformer solution is adopted, a device with a capacity of at least 75kVA is required, and the equipment is large in size and heavy; if the series resonance solution is used, the required power input capacity is only about one-tenth of that of the traditional solution.
Matching and determining device specifications
Rated voltage: The rated output voltage of the device should be slightly higher than the higher test voltage of the test sample. U
Ensure there is sufficient margin for adjusting the test voltage.
Rated capacity: The rated output capacity of the device should be greater than the calculated minimum device capacity. P
。 To ensure the quality of the test voltage waveform and to reserve safety margins for the equipment operation, it is recommended to select a device with a capacity of 1.2-1.5 times the calculated value.
Special requirements verification
Short-circuit current: The device should have sufficient short-circuit current output capability. Generally, the short-circuit current should be greater than 0.1A.This indicator can ensure that when the test sample experiences surface flashover failure, the voltage meter indication drops significantly, facilitating the test personnel to observe the fault status in time.
Altitude and environment: If the device needs to be used in high-altitude areas, it is necessary to confirm the high-altitude correction coefficient of the equipment in advance to ensure that the equipment’s performance and safety are maintained under specific environmental conditions.
Post time: Jan-16-2026