I. Overview
The oil-immersed test transformer (hereinafter referred to as the "test transformer"), also known as a step-up transformer, serves as essential testing equipment for a wide range of users, including power generation stations, power transmission and distribution systems, and scientific research institutions. It is utilized to conduct insulation strength tests on various electrical products, electrical equipment, and insulating materials under specified voltage levels. Its purpose is to assess the insulation integrity of the products, detect insulation defects within the test specimens, and evaluate their capability to withstand overvoltages.
II. Structure
The AC-type test transformers and the lightweight AC/DC dual-purpose high-voltage test transformers are constructed using high-quality cold-rolled silicon steel laminations. The coils feature a concentric, pagoda-shaped, multi-layer cylindrical design, with the low-voltage coil positioned on the inside and the high-voltage coil on the outside. The housing is designed for portability, offering advantages such as compact size, light weight, aesthetic appearance, and ease of mobility.
III. Working Principle
A 220V power supply at industrial frequency (380V for units rated above 10 kVA) is connected to the control box (or console)—an accessory unit supplied with the test transformer; for detailed information, please refer to the control box/console user manual. An autotransformer within the control unit regulates the voltage input to the primary winding of the test transformer within a range of 0–220V (or 0–380V). Based on the principle of electromagnetic induction, a corresponding amplified voltage—specifically, an industrial-frequency high voltage—is generated in the secondary (high-voltage) winding, with an amplitude proportional to the turns ratio between the secondary and primary windings. This industrial-frequency high voltage can be converted into a high-voltage DC output through rectification by a high-voltage silicon stack and subsequent filtering by a capacitor; the amplitude of this DC output is equal to √2 times the RMS value of the industrial-frequency high voltage.
This product series is categorized into three main types: AC-only, AC/DC dual-purpose, and—for units equipped with a 200V tap—units that can be configured as cascaded (series-excited) test transformers.
