I. Abnormal sounds
During operation, the alternating magnetic flux causes the silicon steel sheets in the transformer core to vibrate, producing sound. Under normal operation, this sound is clear and regular. However, if the transformer load changes significantly or the operating condition becomes abnormal, the sound will be louder than usual, and may include intermittent noise or a harsh sound, collectively referred to as abnormal noise.
II. Analysis and Treatment of Abnormal Noises
1. The sound is noticeably louder, but relatively uniform. This abnormal noise is usually caused by excessive load.
The overload can be determined by measuring the load or touching the temperature of the transformer casing. Identify the cause of the overload and reduce the load exceeding the allowable range. If it is a severe overload, the possibility of transformer insulation degradation and damage should also be considered, and further necessary tests should be performed.
2. The transformer is subjected to impact loads, such as frequent starting of large motors or intermittent operation of welding machines, which cause the sound to increase or decrease suddenly and change irregularly.
A clear judgment can be made by measuring the load. As long as it does not exceed the allowable load standard or the allowable voltage fluctuation, no action is needed. If it exceeds the allowable range, responsibility should be identified and action taken. If the user's equipment is used with approval, the power supply department should consider increasing the transformer capacity. If the user's equipment is used without approval, not only should it be stopped immediately, but necessary penalties should also be imposed.
3. If the system is short-circuited or grounded at a distance and the fuse fails to blow in time (due to the short-circuit current not being too large or the fuse having an excessively large capacity), strong and uniform noise will occur due to the severe imbalance of the magnetic flux under the action of the short-circuit current.
4. If the internal core or clamps of the transformer are loose, the noise will increase and there will be intermittent noise. If the load current is not large, the temperature is not high, and the secondary no-load voltage is basically balanced, and the operation is not monitored; if the noise continues to increase, the transformer should be replaced for maintenance.
When there is a short circuit between 5 turns, the short-circuited turns generate severe local overheating, causing the transformer oil to boil locally, producing a "gurgling" sound like boiling water. Poor contact of the tap changer or insulation breakdown will produce a "crackling" sound of discharge.
In such cases, a severe imbalance will be observed in the secondary no-load voltage of the distribution transformer, and the oil temperature will also rise. If the oil filler hole is opened, a burnt smell will be detected. The distribution transformer should be shut down and sent to a repair shop for maintenance.
6. When encountering abnormal noise during transformer inspection, if testing is not possible without the necessary instruments, after confirming reliable grounding of the transformer casing, touch the casing to check its temperature and observe whether the oil level in the oil tank has risen. Then, disconnect the secondary load on the transformer to allow it to run under no-load conditions. If the noise returns to normal, the problem is likely caused by an external fault. If the abnormal noise persists during no-load operation and the casing temperature is high, it is very likely an internal fault in the transformer. After shutdown, further measurements should be taken with instruments to determine whether to resume operation.
