Internal Overheating Fault of Power Transformer

As an important guarantee for economic development and normal life and learning per capita, the power system is very important to the realization of the overall economic construction goals. The role of transformers in power supply equipment cannot be ignored. Therefore, ensuring the safety of transformers is the most important thing for the power system at present, and it is also an important guarantee for the sustainable development of the power system.

1. The function of transformer

The so-called transformer mainly refers to a device that uses the principle of inductance to change the current voltage. It is mainly composed of a primary coil and an iron core. As shown in Figure 1.

In the power supply system, transformers are mainly used to transform voltage, transform current, transform impedance capability, isolation voltage, stabilize voltage, etc. to ensure the normal operation of power supply equipment.

During the operation of the power supply system, the transformer mainly plays the role of insulation and heat dissipation. During the normal operation of the power supply system, the transformer has a good function of dredging the heat generated during the operation of the equipment, ensuring that the power supply equipment will not cause malfunctions or damage to the equipment due to internal overheating. In addition, when the transformer changes the supply voltage, it will not have any impact on the power. Therefore, when the voltage changes, the current will also change, causing the resistance to change. Therefore, in the power supply system, Transformers mainly play the role of insulation.

In addition, in circuit oscillation, the transformer can not only perform resistance and capacitance, but also perform its own circuit coupling oscillation. Therefore, the transformer also has a frequency-selective loop resonance effect.

2 Causes of overheating inside the transformer

Transformers are the basis for ensuring the normal operation of power supply equipment and have a good evacuation function for the heat generated during the operation of the equipment. Therefore, once the transformer overheats inside, it will inevitably have a huge impact on the normal operation of the power supply equipment. At present, in the operation of many power supply systems, faults caused by internal overheating of transformers are very common. So, in order to solve this problem, we must first analyze the causes of overheating inside the transformer.

2.1 Internal overheating of the transformer caused by tap changer failure

The internal overheating fault of the transformer caused by the tap changer accounts for about 50% of the total faults. This situation mainly occurs in transformers with frequent voltage regulation and large current loads. Due to frequent voltage regulation, the joints between the contact switches are seriously worn, and the heat generated when the current passes through will reduce the elasticity of the transformer joint switch, resulting in a drop in the pressure between the two joints. This phenomenon often causes The resistance pressure between the two joints increases, which causes the heat generation between the contact resistors to increase, and the heat source increases the oxidation of the line surface between the two joints, thus forming a vicious cycle that causes the inside of the transformer to Damage occurs due to overheating.

For example: For a 20MVA on-load transformer in a power plant, because the factory personnel did not pay enough attention to the contact problem of the transformer tap changer, the resistance contact pressure continued to increase during the operation of the power supply equipment, causing the metal parts between the two joints to The temperature is overheated and burned, and when the operator adjusts the voltage of the transformer, arcing occurs in the middle of the transformer, causing a short circuit, or even causing the transformer to catch fire and explode, causing damage to the transformer and causing resistance to the normal operation of the enterprise.

2.2 Overheating inside the transformer caused by lead interface failure

Overheating inside the transformer caused by lead joint problems is also a very common factor. This type of problem mainly occurs where the low winding of the transformer is connected to the transformer bushing. Because this interface is a fixed interface, the main reason for the failure is that the equipment maintenance personnel did not check the stability of the screws at the interface after the maintenance, which caused the contact surface of the transformer to oxidize under strong current operation. , thus forming a larger resistance, and then the strong contact resistance gradually causes heating inside the transformer, resulting in serious damage to the transformer.

2.3 Internal heating of transformer caused by core failure

During the operation of the transformer, internal heating of the transformer caused by the iron core is also very common. Under normal circumstances, only one point of the iron core is allowed to be grounded. However, at present, when some transformers are running, multi-point grounding often occurs, forming a multi-point potential induction state, which causes a first-class operating mode inside the transformer, causing the inside of the transformer to continuously heat up, eventually causing the transformer to burn out.

3. Preventive measures against internal heating of transformer

The normal operation of the transformer is the prerequisite for ensuring the normal operation of the power supply system. Therefore, the power system and related departments have taken several preventive measures against the causes of internal heating of the transformer, as follows:

3.1 Preventive measures for tap changer failure

In view of the overheating fault inside the transformer caused by the tap changer, the oil spectrum analysis of the tap changer should be carried out after switching 4000 times and running for at least 3 months. Regular resistance DC testing of the transformer tap changer should be carried out every year. If If abnormal conditions are found, the tap changer must be removed and inspected in time to ensure the safety of the transformer. In addition, for non-excitation voltage-regulating transformers, the winding DC voltage must be tested before the equipment is put into operation, and it can only be put into operation after passing the test. At the same time, transformers that often experience large voltage adjustments and excessive voltage loads must be inspected and tested at any time. If necessary, oil chromatography analysis of the transformer should be performed to ensure the safety of the transformer during operation.

3.2 Preventive measures for lead interface failure

In view of the heating phenomenon of the transformer caused by the lead interface, firstly, after the installation and maintenance of large transformers, the DC resistance must be detected, and oil chromatography analysis should be performed on such transformers. In addition, when the transformer is in operation, infrared temperature measuring instruments are mainly used to detect the temperature of the transformer in operation. Once an abnormality is discovered, oil chromatography analysis of the transformer must be carried out in a timely manner, and the DC resistance must be detected if necessary. , handle power outage.

3.3 Preventive measures for iron core failure

In order to solve the internal heating problem of the transformer caused by core failure, the electric shock method must be used to discharge the transformer first, and at the same time, the low-voltage AC shock method should be used to evacuate the power of the transformer. In addition, a resistor can be added at the connection point between the outside of the iron core and the ground to reduce damage to the transformer caused by the core ground current. In addition, if the fault point cannot be dealt with in time, the fault point and the normal grounding point of the iron core should be moved to the same position to reduce the harm caused by current circulation to the transformer.

4 Conclusion

In summary, ensuring the safe operation of the transformer is a necessary condition for the normal operation of the power supply equipment. Therefore, during transformer maintenance, fixed-point maintenance must be carried out according to the fault location to ensure the operational safety of the transformer and the operational safety of the power system.

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