1. Introduction of oil-immersed transformer

Distribution transformer is one of the important equipment in the power supply and distribution system of industrial and mining enterprises and civil buildings. It reduces the 10(6)kV or 35kV network voltage to the 230/400V busbar voltage used by users. This type of product is suitable for AC 50 (60) Hz, three-phase maximum rated capacity of 2500kVA (single-phase maximum rated capacity of 833kVA, single-phase transformer is generally not recommended), can be used indoors (outdoor), and the capacity is 315kVA and below It can be installed on the pole, the ambient temperature is not higher than 40℃, not lower than -25℃, the maximum daily average temperature is 30℃, the maximum annual average temperature is 20℃, the relative humidity does not exceed 90% (ambient temperature 25℃), the altitude not more than 1000m. If it does not conform to the above conditions of use, appropriate quota adjustments should be made in accordance with the relevant provisions of GB6450-86.

2. Classification of oil-immersed transformers (according to the shell type of oil-immersed transformers)

1. Non-enclosed oil-immersed transformers: There are mainly S8, S9, S10 and other series products, which are widely used in industrial and mining enterprises, agriculture and civil buildings.

2. Enclosed oil-immersed transformers: There are mainly S9, S9-M, S10-M and other series products, which are mostly used in places with many oil pollution and chemical substances in the petroleum and chemical industries.

3. Sealed oil-immersed transformers: mainly include BS9, S9-, S10-, S11-MR, SH, SH12-M and other series products, which can be used for power distribution in various places such as industrial and mining enterprises, agriculture, and civil buildings.

Three, oil-immersed transformer operation prevention

1. Prevention of oil leakage: The oil-immersed transformer is filled with transformer oil in the oil tank, and the oil-resistant rubber element is pressurized and sealed by fasteners during assembly. Insufficient sealing is the main reason for oil leakage of transformers, so special attention should be paid to maintenance and maintenance. Whether the small bolts are loosened by vibration, if they are loose, they should be tightened. The tightening degree should be appropriate and should be consistent everywhere. Whether the rubber is broken or severely deformed. At this time, when replacing the rubber parts that can be updated, attention should be paid to whether the model and specifications are consistent, and the sealing surface should be kept clean.

2. Prevent the transformer from getting wet: The transformer is a high-voltage equipment, and its insulation performance is required to be kept good. Oil-immersed transformers are very susceptible to moisture, and preventing moisture is one of the main measures to maintain transformers. For this reason, users are required to pay attention to the following matters: After purchasing the transformer, the power supply bureau should be asked to do a handover test immediately; As soon as the transformer is transported to the site, a moisture absorber should be installed immediately to prevent the internal body from getting wet.

Monitor the silica gel in the dehumidifier and replace it immediately when wet. The silica gel in the moisture absorber absorbs moisture and protects the transformer. After the moisture is fully absorbed, the color of the silica gel changes, and a new dry silica gel needs to be replaced at this time.

When ordering, it should be noted that the storage time of the transformer before power transmission should be minimized. After the transformer is manufactured, it is very easy to get wet during storage. The longer the storage time, the more serious the moisture will be. Therefore, the plan should be arranged to shorten the storage time as much as possible.

Small transformers with a capacity of 100 kVA and below, without a dehumidifier device. The oil in the oil pillow is easily damp, and the oil pillow accumulates water. If it has been stored for more than six months without power transmission, or has been put into operation for more than one year, the oil in the transformer oil pillow has been seriously damp. If you want to carry out lifting and transportation, maintenance and refueling, oil valve draining, lifting core, etc., you should first drain the dirty oil in the oil pillow through the oil drain plug under the oil pillow, and wipe it with a dry cloth and seal it well to avoid Let the dirty oil in the oil pillow enter the oil tank.

During the operation of the transformer, always pay attention to the changes of oil level, oil temperature, voltage and current. If there is any abnormal situation, it should be analyzed and dealt with in time. When installing the transformer, it is strictly forbidden to use aluminum stranded wire, aluminum row, etc. to connect with the copper guide rod of the transformer to avoid corrosion of the guide rod.

3. Transformer oil change and drying treatment: The transformer has been idle for a long time, the operation time is too long or other natural and human factors, resulting in the phenomenon of transformer insulation decline, internal water or oil quality deterioration, etc., the transformer must be replaced at this time. and drying process.

Transformer oil change: first lift out the body, drain the dirty oil and clean the oil tank. If there is oil on the body, it should also be washed. After the body is dry, inject new oil and replace all oil-resistant rubber seals. After passing the test, it can be connected to the network and run. Transformer drying treatment: There are many methods of drying the body.

Users can use zero-phase sequence drying method, eddy current drying method, short-circuit drying method, oven drying method, etc. when drying by themselves. For transformers with larger capacity and voltage of 35 kV, it is best to send them to the manufacturer for vacuum drying. In this way, the insulation of the transformer can be guaranteed to be completely dry, and the insulation will not be aged.

Fourth, the aging method and life evaluation method of the transformer

In the long-term operation of the transformer, the insulation will be aged due to many effects such as electric field, moisture, temperature and mechanical force. The degree of polymerization (DP) of transformer insulating materials is the most accurate, reliable and effective criterion for the degree of insulation aging. According to the average degree of polymerization of the insulating paperboard to judge the standard of the aging degree of the transformer, we adopt the following judgment standard.

Evaluation standard for average degree of polymerization of insulating paper