Classification and causes of common fault phenomena of low frequency transformers

　　What are the chances of the low frequency transformer being damaged?

　　The probability of failure varies from site to site.

　　Use a multimeter to measure the quality of low-frequency transformers

　　1. Direct detection with capacitive gear

　　Some digital multimeters have the function of measuring capacitance, and their ranges are divided into five ranges: 2000p, 20n, 200n, 2μ and 20μ. When measuring, the two pins of the discharged capacitor can be directly inserted into the Cx jack on the meter board. After selecting the appropriate range, the displayed data can be read and the transformer can be judged.

　　2. Detection with resistance gear

　　Using a digital multimeter can also observe the charging process of the capacitor, which is actually a discrete digital quantity to reflect the change of the charging voltage. Assuming that the measurement rate of the digital multimeter is n times per second, while observing the charging process of the capacitor, n independent and sequentially increasing readings can be seen every second. According to this display feature of the digital multimeter, the quality of the capacitor can be detected and the size of the capacitance can be estimated.

　　Note: Whether it is a high frequency transformer or a low frequency transformer, the detection principle and method are the same.

　　Troubleshooting of low frequency transformers

　　Classification and causes of common fault phenomena in transformers

　　(1) The transformer itself has problems when it leaves the factory. Such as loose ends, loose pads, poor welding, poor core insulation, insufficient short-circuit strength, etc.

　　(2) Line interference. Line disturbance is the most important of all factors that cause transformer accidents. Mainly include: overvoltage when closing, voltage peaks at low load stage, line faults, flashovers and other abnormal phenomena. Such faults account for a large proportion of transformer faults. Therefore, it is necessary to carry out an impulse protection test on the transformer regularly to detect the strength of the transformer against excitation inrush current.

　　(3) The speed of transformer insulation aging due to improper use is accelerated. The average life span of a general transformer is only 17.8 years, which is much lower than the expected life span of 35 to 40 years.

　　(4) Overvoltage caused by lightning strike.

　　(5) Overload. Overload refers to the transformer whose power exceeds the nameplate power for a long time. Overload often occurs when the power plant continues to slowly increase the load, the cooling device does not operate normally, the internal fault of the transformer, etc., eventually causes the transformer to run overloaded. The resulting excessively high temperatures can lead to premature aging of the insulation. When the insulating paperboard of the transformer is aged, the paper strength decreases. Therefore, the impact force of the external fault may cause the insulation to be broken, and thus the failure may occur.

　　(6) Moisture: if there is flood, pipeline leakage, top cover leakage, moisture intrusion into the oil tank along the casing or fittings, and moisture in the insulating oil, etc.

　　(7) Correct maintenance is not carried out.