Abnormal sound

During normal operation, transformers will emit a continuous and uniform buzzing sound. If the generated sound is uneven or there are other special noises, it should be considered as abnormal operation of the transformer, and the fault can be identified and dealt with in a timely manner according to the different sounds. There are several main faults: overvoltage in the power grid.

When a single-phase grounding or electromagnetic resonance occurs in the power grid, the sound of the transformer is sharper than usual. When this situation occurs, a comprehensive judgment can be made based on the indication of the voltmeter.  

Transformer overload operation. The load changes greatly, and due to harmonic effects, there is an intermittent sound of "wow wow" or "giggle" in the transformer, and the monitoring and measuring instrument pointer swings with high pitch and volume.  

Loose transformer clamps or screws. When the sound is louder than usual and there is obvious noise, but there is no obvious abnormality in the current and voltage, it may be due to the loosening of internal clamps or screws that press the iron core, resulting in increased vibration of the silicon steel sheet.  

Partial discharge of transformer. If the drop out fuse or tap changer of the transformer has poor contact, there will be a "squeaking" discharge sound; If the transformer bushing is dirty, with enamel peeling off or cracks on the surface, a "hissing" sound can be heard; If there is partial discharge or poor electrical connection inside the transformer, it will make a "squeaking" or "crackling" sound, which will vary with the distance from the fault. At this time, the transformer should be immediately stopped for testing.  

The transformer winding has a short circuit. If the sound is mixed with the sound of boiling water, and the temperature changes rapidly with an increase in oil level, it should be judged as a short circuit fault in the transformer winding.In severe cases, there may be a loud roar, followed by a possible fire. At this point, the transformer should be immediately stopped for inspection. Transformer shell flashover discharge. When the high voltage of the transformer winding causes flashover discharge between the outgoing lines or between them and the casing, this sound will occur.

Explosion proof film rupture of explosion-proof tube: The rupture of explosion-proof film of explosion-proof tube can cause water and moisture to enter the transformer, resulting in emulsification of insulation oil and a decrease in insulation strength of the transformer.  

Sleeve flashover discharge can cause heating, aging, insulation damage, and even explosions.  

Abnormalities caused by overheating at the leads (connectors) and wire clips; Loosening of the fastening part at the end of the conduit or sliding teeth of the lead wire nose can cause severe oxidation of the contact surface, resulting in overheating, darkening of color and loss of luster, and damage to the surface coating.  

Abnormalities caused by casing fouling; The contamination of the casing can cause corona and flashover, resulting in ozone odor. Cooling fans and oil pumps that burn out can emit a burning smell.  

In addition, excessive moisture absorption, damaged gaskets, and excessive water entering the oil chamber can cause the moisture absorbent to discolor.  

Abnormal oil temperature

If the oil temperature is found to be more than 10 degrees Celsius higher than usual under normal conditions, or if the load remains unchanged and the temperature continues to rise (under normal operation of the cooling device), it can be determined that there is an abnormality inside the transformer. Mainly for:

Internal malfunction causing abnormal temperature. Internal faults, such as winding breakage or interlayer short circuit, coil discharge to the surrounding screen, heating of internal lead joints, increased eddy current caused by multiple grounding points of the iron core, overheating, zero sequence unbalanced current and other leakage magnetic flux that forms a circuit with the iron oil tank and heats up, can cause abnormal transformer temperature. When these situations occur, they will also be accompanied by gas or differential protection actions. When the fault is severe, it may also cause the explosion-proof pipe or pressure relief valve to spray oil. In this case, the transformer should be immediately stopped for maintenance.        

Abnormal temperature caused by abnormal operation of the cooler. Abnormal operation or malfunction of the cooler, such as shutdown of the submersible pump, damage to the fan, accumulation of scale in the radiator pipeline, poor cooling effect, failure to open the radiator valve, malfunction of the thermometer indication, etc., can cause temperature rise. The cooler system should be maintained and flushed to improve its cooling effect. Abnormal oil level

Abnormal oil level and oil leakage are common phenomena during the operation of transformers, which should be inspected and checked irregularly. The main manifestations include the following two aspects.        

1. False oil level: clogged oil gauge tube; The oil pillow suction tube is blocked; Explosion proof pipeline air hole blockage.        

2. Low oil level: The transformer is severely leaking oil; The staff failed to replenish the oil in a timely manner due to work needs; The temperature is too low and the oil level is insufficient, or the capacity of the oil pillow is too small to meet the operational needs.