What are the points for dry-type transformer operation and maintenance?

The epoxy resin cast dry type transformer has many advantages such as flame retardancy, self-extinguishing, moisture resistance, high mechanical strength, small volume, light weight, and strong short-circuit capability, and has been widely used. However, the dry type transformer also has some disadvantages, such as the heat dissipation performance is not as good as that of the oil immersed transformer in the case of poor ventilation. The operation and maintenance of dry transformers are summarized as follows:

  1) Do a good job of cleaning regularly

  If excessive dust accumulation is found, it must be removed immediately to ensure air circulation. Dry-type transformers are cleaned at least once every six months in places with large dust. For dust in the air duct. Use a vacuum cleaner or compressed air to remove it. If it is not removed in time, it will affect the heat dissipation of the transformer, which will also reduce the insulation of the transformer and even cause insulation breakdown. For example, the 35kV station in a 220kV Zhuang transformer station of a company is used in a power outage test. The 2500V optical euro meter is used to measure the insulation resistance of the dry-type transformer core. The insulation resistance of the core is reduced to 3mΩ, which is much lower than the previous test data of 100mΩ. The main reason is that the dust in the air duct of the transformer is not cleaned, and the insulation resistance of the core rises to 100mΩ after cleaning.

  2) Strengthen the operation and maintenance of ventilation equipment to ensure smooth ventilation of the transformer

  Make sure that the ventilation equipment is normal, mainly to ensure the normal operation of the fan. If the load is small, and prove that the transformer does not have a special hot spot (this can be detected by the infrared thermometer and its own temperature controller), it can reduce the running fan, but must ensure the normal operation of the fan, because dry Once the transformer is thermally damaged, it will seriously damage the internal winding, and the consequences are unimaginable. Generally, the heat loss of 1 kW is dissipated, and the amount of ventilation should be 4 m3/min. For the transformer without a casing, the isolation and shielding shall be installed around the door. The doors and vents of the transformer room shall have measures to prevent the entry of rain, snow, small birds such as birds and snakes.

  3) Strengthen temperature monitoring

  It is usually necessary to strengthen the observation of the temperature controller to see if the displayed three-phase temperature is balanced, and whether the temperature display value of a certain phase has a sudden change. At present, the connector between the thermostat and the internal thermistor (measuring temperature) of the transformer is a pin plug. If the contact is poor, the thermostat will be misjudged, but if the monitoring is strengthened, the thermostat will be found. In case of abnormal working condition, take measures in advance to avoid the occurrence of malfunction. For large-capacity transformers and transformers in important places, transformer manufacturers can be required to install one thermistor per phase to achieve dual configuration of the thermostat, so that it can avoid such failures. .

  4) Actively carry out dehumidification and dehumidification work to ensure the degree of dryness

  In some humid places (such as rainy, dark places), if you have turned off the dry transformer, you should check for abnormal humidity. If so, start the hot air to dry the surface to prevent insulation breakdown. For oxygen-cast dry-type transformers, this surface wetting does not affect the insulation inside the windings and, therefore, can be put into operation after processing. Once the transformer is put into operation, the heat generated by its loss will return the insulation resistance to normal.

  5) Carefully check the fasteners and connectors for looseness to ensure the mechanical strength of the dry-type transformer

  During the long-term operation of the transformer, due to external short-circuit and other reasons, the fasteners and connecting parts caused by the end force and vibration are inevitably loose. When the above phenomenon occurs, hot spots may occur. To this end, the indicator wax should be placed at the high and low pressure end and all places where overheating may occur. Regular observation, combined with cleaning, for preventive testing, and tightening the end and connecting parts.

  6) Actively carry out derusting work to prevent core corrosion

  The core of the dry-type transformer is exposed to the air and is highly rust-resistant. If a large area of iron core corrosion occurs, the loss of the transformer will increase, the efficiency will decrease, and even the life of the transformer will be directly affected. Therefore, it is necessary to regularly remove rust and rust to avoid corrosion of the core. Other reasons: transformer winding turn-to-turn short circuit, interlayer concept, phase-to-phase short circuit and ground short circuit. The above-mentioned faults are caused by major defects such as aging or damage of the main insulation of the winding; the insulating oil of the transformer is seriously affected by the excessive oil level; the insulation of the oil surface is insufficient to penetrate, and the windings fall into the debris; Wear windings. The transformer winding is deformed or broken, the insulation between the iron chips is damaged, and the iron core is grounded at multiple points or the grounding is poor. The causes are: poor manufacturing and assembly, uncompressed windings; electromagnetic force of short-circuit current; poor wire welding; wire breakage caused by lightning; manufacturing defects; insufficient strength. The insulation of the silicon steel sheet is aging, and the displacement or friction between the strong vibration sheets occurs, the iron core fasteners are loosened, and the iron core is grounded at two points, and the heat is burnt out between the sheets. The reason for multi-point grounding is mostly the insulation aging between the iron core and the feed screw. The core grounding piece is disconnected and the core grounding is also invalidated. This accident is not easy to find.

  In addition, there is flashing of the high-voltage bushing of the transformer, burnt of the tap, deterioration of the transformer oil, etc. The reason is that the surface of the casing is dirty, the casing is cracked, or the casing is broken, the casing is not tightly sealed, and the insulation is insulated. Damaged, debris falling between the casings. For transformers with voltage regulating switches, the insulation performance of the insulation board is deteriorated, the oil level of the transformer is lowered, the tap changer is exposed to the air, and the position of the tap changer is misaligned, which causes frequent failures. The internal fault of the transformer causes discharge, which causes the oil-immersed transformer to cool down and the insulating oil is decomposed. The transformer oil is thermally oxidized for a long time, which deteriorates the oil quality.