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How to judge whether the temperature change of the transformer is normal or abnormal?

1. How to judge whether the temperature change of the transformer is normal or abnormal?

During the operation of the transformer, the losses in the core and windings are converted into heat energy, causing heat in various parts, and causing the temperature to rise. The heat is radiated to the surroundings, diffused by conduction, etc. When the heating and heat dissipation reach a balanced state, the temperature of each part tends to The iron loss is constant due to stability, while the copper loss changes with the load. When inspecting the transformer, the external temperature, top oil temperature, load, and oil level height should be recorded, and compared with previous values to analyze and determine whether the transformer is operating normally.

If it is found that the oil temperature is more than 10°C higher than usual under the same conditions, or the load remains unchanged but the temperature continues to rise, and the cooling device operates normally, it is considered that an internal fault has occurred in the transformer (pay attention to whether the thermometer has errors or malfunctions). Generally, The main insulation of the transformer (winding insulation) is Class A insulation (paper insulation), and the maximum operating temperature is 105°C. Generally, the winding temperature is 10~15℃ higher than the soil surface temperature. If the oil surface temperature is 85℃, the winding temperature will reach 95~100℃.

2. Causes of the abnormal temperature of the transformer

① Internal fault causes temperature abnormality

Internal faults of the transformer such as inter-turn short circuit or inter-layer short circuit, coil discharge to the surrounding screen, internal lead joints heating, multi-point grounding of the iron core causing eddy current increase and overheating, zero sequence unbalanced current and other leakage flux forming a loop with the iron tank to generate heat When the temperature of the transformer is abnormal due to factors such as gas or differential protection, it will also be accompanied by gas or differential protection action. When the fault is serious, the explosion-proof pipe or pressure relief valve may inject oil. At this time, the transformer should be stopped for inspection.

② Abnormal temperature caused by abnormal operation of the cooler

The abnormal temperature may be caused by improper operation or malfunction of the cooler, such as submersible pump outage, damaged fan, fouling in the heat dissipation pipe, poor cooling efficiency, or failure of the radiator valve to open. The cooling system should be maintained and flushed in time or a backup cooler should be put in, otherwise the load of the transformer must be adjusted.

③ If the temperature indicator has an error or indicates a malfunction, the thermometer should be replaced.

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