Transformer test transformers, although both based on the principle of electromagnetic induction



“Test transformers” and the ordinary “power transformers” we commonly see in the power grid, although both are based on the principle of electromagnetic induction, their purposes, operating conditions, and internal designs are vastly different. Simply put, power transformers are for “using electricity,” while test transformers are for “testing electricity.”

To help you understand the differences more intuitively, I have compiled the following core differences for you:

Table

Feature Dimension    Power Transformer    Test Transformer

Core Purpose    Transmission and distribution of electrical energy (e.g., grid step-down power supply)    Conduct high-voltage insulation tests to assess equipment withstand voltage levels

Operating Condition    7×24-hour long-term continuous operation    Short-term or intermittent operation (typically lasting only 1 minute)

Load Characteristics    Loads are mostly inductive (motors) or resistive (lights)    Load is capacitive (e.g., cable and capacitor ground capacitance)

Output Voltage    Fixed voltage level, requiring extremely high stability    Needs smooth, continuous adjustment from zero to very high voltage

Capacity and Size    Large capacity, severe heating, bulky size, and complex cooling systems    Smaller capacity, less heat generation, relatively compact and lightweight

Specific classifications and characteristics of test transformers:

Test transformers are basic equipment used by power plants, power supply bureaus, and research institutions for AC or DC withstand voltage tests. Based on differences in internal insulation media and structure, they are mainly divided into the following types:

Oil-immersed test transformers: This is currently the mainstream product. They have large capacity, easy maintenance, and relatively low price, but they are bulky and heavy, with higher maintenance costs in the later stages.

Dry-type test transformers: Made by casting with materials such as epoxy resin, they are maintenance-free, lightweight, compact, and can even be placed upside down. However, their manufacturing cost is higher.

Gas-filled test transformers: Typically filled with gases such as sulfur hexafluoride (SF6), they have advantages like good arc extinguishing performance, low partial discharge, and light weight, making them very suitable for field use.

Series-excited (cascade) test transformers: To meet higher voltage requirements, multiple transformers are connected in cascade. They have the characteristics of small capacity, high voltage, and easy transportation, but the wiring is relatively cumbersome.