I. Core Components of the Device
A standard set of power frequency withstand voltage test equipment consists of core functional components, protective and auxiliary components, which work together to perform a complete operation of high-voltage insulation strength tests.
(1) Core Functional Components
Test Transformer
As the core component of the device, its main function is to step up the mains power (220V/380V) to the required high voltage level for the test (such as 50kV, 100kV, 200kV, etc.). According to the insulation method, it can be divided into three types:
Oil-immersed: Large capacity, excellent heat dissipation performance, suitable for fixed laboratory scenarios with high power and high voltage requirements;
Dry-type: Light weight, easy to move, no leakage risk, suitable for on-site test scenarios, with generally smaller capacity;
Gas-filled: Internal filled with inert gases such as SF6, excellent insulation performance, small equipment volume, and more environmentally friendly, is currently the mainstream application type. Pressure regulator
It is used to smoothly and continuously adjust the input voltage on the primary side of the test transformer, thereby precisely controlling the output voltage on the high-voltage side. The main types include:
Self-coupled voltage regulator: Simple structure, good economy, suitable for small-capacity test equipment;
Electric column-type voltage regulator: Wide voltage adjustment range, small voltage waveform distortion, large carrying capacity. It is the preferred type for most complete sets of equipment;
Electronic voltage regulator (thyristor voltage regulator): No mechanical contacts, fast voltage regulation speed, supports remote precise control, relatively higher in cost, and may introduce harmonics during use.
Measurement System
Its core function is to accurately measure the high voltage applied during the test process. It is mainly divided into two measurement methods:
High-voltage measurement circuit (direct measurement): Connect a standard high-voltage divider resistor or capacitor in series at the end of the high-voltage winding of the test transformer, measure the voltage on the low-voltage arm, and convert it proportionally to obtain the actual high-voltage value. It is a relatively accurate measurement method;
Low-voltage measurement (indirect measurement): Measure the voltage on the primary side of the test transformer, combined with the equipment transformation ratio to estimate the high-voltage value. This method has lower accuracy, and the measurement result is affected by the transformer load and magnetization characteristics. It is generally used only for reference. Control system
As the core control unit of the device, it is usually integrated into the control box or console, integrating various control, display, and protection functions of the test process, specifically including:
The start-stop control module for the pressure regulator motor;
Voltage and current monitoring and display instruments (digital / pointer type);
Multiple protection circuits such as overcurrent, overvoltage, and zero position protection;
The timer for setting and monitoring the test time;
The sound and light alarm device for indicating the test operation status.
(II) Protective and Auxiliary Components
Protective resistor: Connected in series in the high-voltage output circuit, its core function is to limit the short-circuit current when the test specimen breaks down, protecting the test transformer and measurement system;
Ball gap device: Overvoltage protection device, with a preset breakdown threshold slightly higher than the test voltage, when unexpected overvoltage occurs during the test, the ball gap breaks down and discharges, achieving protection for the test specimen;
Limiting resistor: Used in series with the ball gap device, to limit the discharge current of the ball gap;
Grounding system: Ensures reliable grounding of all device enclosures and non-electrified parts, fundamentally protecting the safety of the test personnel and the operation safety of the equipment.
II. Device Selection Principles
The selection of the power frequency withstand test complete device needs to comprehensively consider the test requirements, usage scenarios, equipment parameters, etc., to ensure the effectiveness, safety, and economy of the test process. The core selection basis is the following key parameters and requirements:
1. Rated output voltage (kV)
The rated output voltage is the core parameter for device selection. The device’s higher output voltage must be higher than the required higher voltage value for the test.
Standard basis: According to national standards (such as GB/T 16927, DL/T 474, etc.) or industry-related standards, determine the standard value of the power frequency withstand test for the tested equipment;
Safety margin: It is recommended to reserve 15%-20% safety margin when selecting, to avoid the influence on the test results due to voltage fluctuations during the test.
2. Rated capacity (kVA)
Rated capacity determines the load-carrying capacity of the device, which is particularly crucial for tests of capacitive test specimens such as cables, long busbars, and large generators.
Calculation formula: P = U² × ω × Cx × 10⁻³ (kVA)
Where, P is the required rated capacity of the device (kVA), U is the test voltage (kV), ω is the angular frequency (2πf, power frequency f=50Hz), Cx is the capacitance of the test specimen (μF), which can be obtained from the equipment factory report or measured in practice;
Estimation method: If it is impossible to obtain the more accurate capacitance of the test specimen, you can refer to the experience values of similar equipment, and for test specimens with large capacitance, the capacity must be calculated precisely using the formula to avoid the inability to raise the test voltage to the predetermined value due to insufficient capacity;
General selection reference: For small capacitance test specimens such as switches and insulators, a device of 1-5kVA can be selected; for large-capacity test specimens such as long cables, GIS, and transformers, a device of 25kVA or above specification is required.
3. Power supply type
Selected according to the power supply conditions at the test site, it is divided into single-phase (220V) and three-phase (380V) input types. Large-capacity test devices usually require three-phase power supply.
4. Usage environment
Determined based on the usage scenario of the device, considering mobility and performance:
Fixed laboratory: Oil-immersed or gas-filled equipment can be selected, as such equipment has a large capacity and can meet the long-term test requirements of high power and high voltage in the laboratory;
Field mobile test: Prioritize dry or gas-filled portable power frequency withstand test devices, as such devices are lightweight and small in size, suitable for complex usage environments in the field, and convenient for transportation and operation.
5. Function and Intelligent Demand
Select the device of the corresponding functional level according to the frequency, standard requirements, and efficiency requirements of the test:
Basic type: Equipped with manual pressure adjustment, pointer meter display, and mechanical timing function, it can meet the basic requirements of power frequency withstand voltage tests, suitable for scenarios with lower test frequencies and relatively simple requirements;
Intelligent type: Based on microcomputer control, equipped with a color touch screen, supporting automatic voltage increase, timing, and voltage reduction, it can automatically record and judge test results, has the function of storing and printing test reports, and integrates complete protection and safety interlock functions; suitable for laboratories with high test frequencies and strict standards, which can effectively improve test efficiency and the reliability of test results.
Post time: Jan-30-2026