How to Test the Temperature Rise of Oil-Immersed Transformer?

I. Overview of Transformer Temperature Rise Testing Methods 

In the process of transformer testing, the temperature rise test is often the most time-consuming procedure with the largest workload. Currently, the primary methods used to test the temperature rise of a transformer include:

• Direct Load Method

• Mutual Load Method

• Circulating Current Method

• Zero-Sequence Current Method

• Short-Circuit Method

Among these, the short-circuit method requires the lowest test voltage and the smallest power capacity. Moreover, for oil-immersed transformers, international and national standards stipulate the short-circuit method as the standard method for temperature rise testing.

Below, we share how to carry out the temperature rise experiment for an oil-immersed transformer using this method.

II. Step-by-Step: The Oil-Immersed Transformer Short-Circuit Method (H2)

The execution of the short-circuit temperature rise test is divided into two core phases:

1. Phase A: Applying Total Loss 

Connection: Short-circuit the outgoing terminals of the low-voltage (LV) side of the tested transformer.

Power Supply: Apply the calculated total loss to the high-voltage (HV) side of the transformer to begin the test.

Monitoring & Recording: During the test, regularly monitor and record critical temperature values every half hour, including:

-Ambient temperature of the surrounding environment

-Top oil layer temperature

-Inlet and outlet temperatures of the radiator

Duration & Stability: The typical test time is 3 hours. When the temperature rise variation of the monitored parts is less than 1°C per hour, the temperature rise is considered stable. We average the values of the last 1 hour of testing to use as the final result.

2. Phase B: Applying Rated Current 

Winding Current: Adjust the input current of the winding until it reaches the rated current.

Stabilization: After continuous monitoring for 1 hour, record the ambient temperature, top oil temperature, and the inlet/outlet radiator temperatures.

Resistance Measurement: Cut off the power supply immediately, minimize the current, and measure the thermal resistance value to calculate the temperature rise of the winding group.