Lightweight high-voltage test transformers (also commonly known as oil-immersed / dry-type test transformers, high-voltage withstand testers) are the core equipment for conducting power frequency AC withstand tests and DC withstand leakage tests on power equipment, electrical materials, and insulation components. Their “lightweight” feature stems from the application of new materials and new technologies, enabling the reduction of volume and weight while ensuring the performance of the equipment, making them more suitable for on-site mobile operations and test procedures.
I. Core Selection Principles
To select an appropriate lightweight high-voltage test transformer, multiple core factors need to be comprehensively considered, following a systematic selection process to ensure that the equipment closely matches the test requirements.
II. Core Parameter Determination
1. Rated Output Voltage (kV)
This parameter is the primary consideration factor for selection. Its value must be higher than the highest test voltage of the tested equipment.
Reference basis: Strictly follow the voltage regulations specified in national or industry standards (such as GB 50150, DL/T 596, etc.) for the交接 tests and preventive tests of various power equipment. For example， when conducting withstand tests on 10kV cables， the AC test voltage is generally 2-2.5 times the rated phase voltage (i.e.， 21.75-28.75kV). At this time， the rated output voltage of the transformer should be at least 50kV or above， leaving sufficient test margin.
Common specification grades： 50kV， 100kV， 150kV， 200kV， 300kV， etc.
2. Rated Capacity (kVA)
This parameter determines the ability of the transformer to avoid excessive voltage drop when driving capacitive loads (such as long cables， large motors)， and is a key indicator for adapting to large-load tests. Calculation formula:
P = Cx × U2 × ω × 10−3 (kVA) Among them,
P
For the required transformer capacity (kVA), Cx
For the capacitance (in microfarads) of the tested item, U
For the test voltage (kV),
ω
is the angular frequency (2πf, in the case of power frequency) f=50Hz
）。
Experience-based estimation method: If it is impossible to accurately measure the capacitance of the tested item Cx
It can be estimated based on the experience of the test scenarios. For the tests of conventional equipment such as switch cabinets, transformers, and transformers, selecting equipment with a capacity of 3-5 kVA usually meets the requirements; for tests of large-capacity loads such as long cables and large generators, equipment with a capacity of 10 kVA, 20 kVA or higher is required.
Selection principle: Capacity selection follows the principle of “preferably larger rather than smaller”. If the capacity is insufficient, when testing large-capacity loads, it is prone to a situation where the voltage cannot rise to the set value, resulting in the inability to conduct the test normally.
3. Power input (V/A)
The power input of the lightweight high-voltage test transformer is usually single-phase 220V or 380V. When selecting, it is necessary to first confirm the available power type at the test site; at the same time, the input current can be calculated based on the rated capacity of the transformer (calculation formula: I=P/U
), ensure that the on-site power supply lines and switches can withstand this current value, and guarantee the stability of the test power supply.
III. Equipment Type Selection
Light-duty high-voltage test transformers are mainly divided into three types: oil-immersed, dry-type, and gas-filled. Each type of equipment has its own performance, advantages, and disadvantages, as well as specific application scenarios. The selection should be based on the usage requirements.
1. Oil-immersed Test Transformer
Advantages: Excellent insulation and heat dissipation performance, capable of achieving large-capacity design, with economic price, and is the most widely used type.
Disadvantages: Compared to dry-type equipment, it has a larger volume and weight, and there is a potential risk of oil leakage.
Applicable Scenarios: Laboratory, factory workshops, substations, and most fixed or semi-fixed test sites.
2. Dry-type Test Transformer (Epoxy Casting Type)
Advantages: Small volume, light weight, oil-free design enables maintenance-free operation, and no pollution, with fireproof and flame-retardant properties, suitable for mobile operations.
Disadvantages: The design capacity is usually smaller, and the heat dissipation capacity is not as good as that of oil-immersed type. The equipment price is relatively higher.
Applicable Scenarios: For occasions with high requirements for equipment weight and environmental protection, such as frequently mobile on-site tests, high-rise buildings, mines, ships, etc.
3. Gas-filled Test Transformer (SF6)
Advantages: Excellent insulation performance, the smallest volume and weight among the three types of equipment, suitable for strict mobile and space requirements.
Disadvantages: The equipment is expensive, and the SF6 gas used is a greenhouse gas. If leakage occurs, it will have an impact on the environment.
Applicable Scenarios: Special test occasions with extreme requirements for equipment volume and weight.
IV. Selection of Supporting Equipment
Light-duty high-voltage test transformers are usually put into use in a system form, and need to be matched with appropriate supporting equipment to form a complete test system. The functions and selection requirements of each supporting equipment are as follows:
Control Box / Operating Console: The core function is to adjust the test voltage, control voltage rise and fall, test timing, and protect the equipment. Its output capacity must match the rated capacity of the test transformer.
Protection Resistor: Used to limit the short-circuit current when the tested item breaks down during the test, protecting the test transformer and measurement system from damage.
Voltage Divider: Used to precisely measure the high-voltage side test voltage, with a measurement accuracy far higher than that obtained through conversion from the low-voltage side.
Ball Gap: As an overvoltage protection device, used to set the protection threshold to prevent accidental overvoltage damage to the tested item during the test.
V. Summary of Selection Process
Clarify test requirements: Sort out and determine the type of the tested item, the corresponding test voltage standard, and the core basic information such as the capacitance of the tested item.
Precisely calculate parameters: According to the test requirements, calculate and determine the rated output voltage and rated capacity of the test transformer and other core parameters.
Select equipment type: Based on the usage environment of the test (such as mobility requirements, fireproof and environmental protection standards, space limitations, etc.), choose oil-immersed, dry-type, or gas-filled test transformers.
Configure complete system: According to the transformer parameters, select compatible control boxes, protection resistors, voltage dividers, etc., to form a complete high-voltage test system that meets the test requirements.
Post time: Jan-26-2026