Maintenance of mine transformers

KS11 mining transformer has many advantages such as flame retardant, self-extinguishing, moisture resistance, high mechanical strength, small size, light weight and strong short-circuit ability, and has been widely used. However, mining transformers also have some disadvantages. For example, in the case of poor ventilation, their heat dissipation performance is not as good as that of oil-immersed mining transformers. According to our company’s many years of practical experience in using mine transformers, we summarize some experiences on the operation and maintenance of mine transformers for reference.

1. Do a good job of cleaning regularly
If excessive dust accumulation is found, it must be removed immediately to ensure air circulation. In places with large dust accumulation, mine transformers should be cleaned at least once every six months. For dust in ventilation ducts. Cleaning should be done with a vacuum cleaner or compressed air. If it is not removed in time, it will affect the heat dissipation of the mining transformer, and it will also cause the insulation of the mining transformer to decrease or even cause insulation breakdown. For example, our company’s 220kV Weizhuang substation 35kV substation was used in a power outage test. Using a 2500V optical ohmmeter to measure the insulation resistance of the iron core of the mining transformer, the insulation resistance of the iron core is reduced to 3MΩ, which is much lower than the last test data of 100MΩ. The main reason is that the dust in the ventilation duct of the mining transformer has not been cleaned. The resistance rises to 100MΩ.

2. Strengthen the operation and maintenance of ventilation equipment to ensure smooth ventilation of mining transformers
To ensure that the ventilation equipment is normal, mainly to ensure the normal operation of the fan. If the load is small, and it is proved that the mining transformer does not have any special hot spots (this can be detected by the infrared thermometer and the self-provided thermostat), the number of fans in operation can be reduced, but the normal operation of the fans must be ensured, because Once the mine transformer is thermally damaged, the internal winding will be seriously damaged, and the consequences will be unimaginable. Generally, the heat loss of 1kW is dissipated, and the ventilation volume should be 4 m3/min. For mine transformers without casings, isolation barriers should be installed around them. The doors and ventilation holes of the mine transformer room must have measures to prevent rain, snow and small animals such as birds and snakes from entering.

3. Strengthen temperature monitoring
Usually, it is necessary to strengthen the observation of the thermostat to see whether the three-phase temperature displayed is balanced, and whether there is a sudden change in the temperature display value of a certain phase. At present, the connector between the thermostat and the thermistor (temperature measurement) inside the mining transformer is a pin plug. Once the contact is poor, the thermostat will misjudge. However, if the monitoring is strengthened, the abnormal working state of the thermostat will be found, and measures should be taken in advance to avoid the occurrence of failures. For large-capacity mining transformers and mining transformers in important places, the mining transformer manufacturer can be required to install one more thermistor per phase when ordering, so as to realize the dual configuration of the thermostat, so that the avoid such failures.

4. Actively carry out dehumidification and dehumidification work to ensure its dryness
In some humid places (such as a lot of rain, dark places), if the out-of-service mining transformer is activated, it is necessary to check whether there is abnormal humidity. If so, start hot air to dry the surface to prevent insulation breakdown. For oxygen cast mine transformers, this surface moisture does not affect the insulation inside the winding, so it can be put into operation after treatment. Once the mining transformer is put into operation, the heat generated by its loss will make the insulation resistance return to normal.

5. Carefully check whether the fasteners and connecting parts are loose to ensure the mechanical strength of the mining transformer
During the long-term operation of mining transformers, due to external knowledge of the road and other reasons, the phenomenon of loosening of fasteners and connectors caused by end force and vibration will inevitably occur. When the above phenomenon occurs, it is possible to generate hot spots. For this reason, temperature-indicating wax sheets should be installed at the high and low pressure terminals and all places where overheating may occur, and regular observations should be made, and the terminals and connectors should be tightened in combination with cleaning and preventive tests.

6. Actively carry out rust removal work to prevent the core from rusting

The iron cores of mining transformers are exposed to the air and are easily corroded. If a large area of iron core is corroded, it will increase the loss of the mining transformer, reduce the efficiency, and even directly affect the life of the mining transformer. Therefore, it is necessary to remove rust and prevent rust regularly to avoid rusting of the iron core.

In addition, the current production of mining transformers has a lower withstand voltage level than oil-immersed mining transformers, so it is necessary to strengthen the configuration and maintenance testing of arresters. It is better to choose zinc oxide arrester as the arrester. The high-voltage side should be fed by cables, and should not be directly connected to overhead lines.