1 Introduction

In the process of electric energy transmission and distribution, power transformers are the core of energy conversion and transmission. They are the only way for all walks of life in the national economy and thousands of households to source energy. They are the most important and critical equipment in the power grid. The safe operation of power equipment is the first defense system to avoid major accidents in the power grid, and power transformers are the most critical equipment in this defense system. A serious accident of the transformer will not only cause damage to itself, but also interrupt the power supply, causing huge economic losses to the society.

2 Common faults and diagnostic measures

2.1 Transformer oil leakage

Oil leakage from transformers will not only cause greater economic losses and environmental pollution to power companies, but will also affect the safe operation of transformers, possibly causing unnecessary outages and even damage to transformers, causing production losses to power customers. and inconvenience in life. Therefore, it is necessary to solve the problem of oil leakage from transformers.

Oil leakage from the fuel tank weld. For oil leakage at plane joints, welding can be performed directly. For oil leakage at corners and reinforcement joints, the leakage point is often not found accurately, or leakage occurs again due to internal stress after repair welding. For such leakage points, an iron plate can be added for repair welding. For the two-sided connection, the iron plate can be cut into a spindle shape for repair welding. For the three-sided connection, the iron plate can be cut into a triangle according to the actual position for repair welding. This method also Suitable for leakage welding of corner welds of bushing current transformer secondary lead boxes.

Oil leakage from the elevated seat of the high-voltage casing or the manhole flange. These parts are mainly due to improper installation of rubber gaskets, and the flanges can be sealed with glue during operation. Before sealing, use sealing glue to seal the gap between the flanges. After the sealing glue is completely solidified, remove a flange fastening screw, screw the nozzle of the glue gun into the screw hole, and then inject the sealant with high pressure. Flange clearance until glue is extruded from each flange screw cap.

Low pressure side casing leakage. The reason is that due to the stretching of the busbar and the short lead of the low-voltage side, the glue beads are pressed on the threads. When the busbar is stretched, the busbar can be connected with a telescopic joint according to regulations; if the lead is too short, the length of the lead can be readjusted; if it is difficult to adjust the lead, sealant can be added to each sealing surface where the rubber beads are installed; in order to increase the Large pressing force can replace the porcelain pressure cap with a copper pressure cap.

Explosion-proof pipe leaks oil. The explosion-proof pipe is a safety measure to prevent the transformer tank from rupturing due to excessive pressure inside the transformer due to internal faults. However, the glass membrane of the explosion-proof tube is easily broken due to vibration during the operation of the transformer, and the glass cannot be replaced in time. Moisture therefore enters the oil tank, causing the insulating oil to become damp and reducing the insulation level, endangering the safety of the equipment. For this purpose, just remove the explosion-proof pipe and modify the pressure relief valve.

2.2 Multi-point grounding of the core

The transformer core has and can only have one point of grounding. If there are two or more points of grounding, it is multi-point grounding. The multi-point grounding operation of the transformer core will cause the core to malfunction, endangering the safe operation of the transformer, and should be dealt with in time.

DC current impulse method. Remove the grounding wire of the transformer core and apply DC voltage between the transformer core and the oil tank for short-term large current impact. The impact is 3 to 5 times. This can often burn off the excess grounding points of the core and effectively eliminate the problem of multi-point grounding of the core. Effect.

  open box to check. If the positioning pins on the box cover are not turned over or removed after installation, resulting in multiple grounding points, the positioning pins should be turned over or removed.

If the insulating cardboard between the clamp feet and the iron yoke falls off or is damaged, new cardboard of a certain thickness should be replaced according to the insulation specifications.

Because the clamp limbs are too close to the iron core and the warped laminations collide with them, the clamp limbs and the warped laminations should be straightened so that the distance between them meets the insulation gap standard.

Remove metal foreign matter, metal particles and impurities in the oil, remove sludge from all parts of the oil tank, and vacuum dry the transformer oil to remove moisture if possible.

2.3 The joint is overheated

The current-carrying joint is an important part of the transformer itself and its connection to the power grid. If the joint is not connected properly, it will cause heating or even burnout, seriously affecting the normal operation of the transformer and the safe power supply of the power grid. Therefore, the problem of joint overheating must be solved in time.

Copper and aluminum connections. The terminals of the transformer are all made of copper. Do not connect aluminum conductors to copper terminals with bolts outdoors or in humid places. When water containing dissolved salts, i.e., electrolyte, penetrates into the contact surface between copper and aluminum, an electrolytic reaction will occur under the action of the electrical coupling, and the aluminum will be strongly electrically corroded. As a result, the contacts are quickly damaged to the point where they become hot and may even cause a major accident. In order to prevent this phenomenon, when the aluminum conductor and copper conductor need to be connected in the above device, a special transition contact with aluminum on one end and copper on the other end is used.

Normal connection. There are quite a lot of ordinary connections on the transformer. They are all key parts of overheating. For flat joints, process the butt surface into a flat surface. Remove impurities on the flat surface. It is best to evenly apply conductive paste to ensure a good connection.

The oil-immersed capacitor bushing is overheated. The solution can be to use a positioning sleeve to fix the heating sleeve. First, disassemble the general cap. If the general cap and lead connector threads are burned, use a dental tap to repair them to ensure that the threads fit well, and then connect the positioning sleeve and the general. Place a thin gasket between the caps with the same cross-section size and appropriate thickness as the positioning sleeve, and reinstall the general cap so that the general cap can be fixed on the top flange of the casing when tightened.

The tolerances of the lead connector and the general cap thread buckle should be good, otherwise they should be replaced to ensure that there is sufficient pressure between the thread buckles when tightened to reduce the contact resistance.

3 Transformer online monitoring technology

The purpose of online monitoring of transformers is to determine the status of the transformer through the collection and analysis of the transformer's characteristic signals, in order to detect the initial fault of the transformer and monitor the development trend of the fault state. At present, the online monitoring of power transformers is one of the most studied objects in the world, and many different methods have been proposed.

Dissolved gas analysis technology in oil. Since different faults inside the transformer will produce different gases, the purpose of transformer insulation diagnosis can be achieved by analyzing the composition, content, gas production rate and relative percentage of gases in the oil. Several typical dissolved gases in oil, such as H2, CO, CH4, C2H6, C2H4 and C2H2, are often used as characteristic gases for analysis. After detecting the components and contents of each gas, the internal fault of the transformer can be determined using methods such as the characteristic gas method or the ratio method.

Partial discharge online monitoring technology. When there is an internal fault in the transformer or the operating conditions are poor, partial discharge (PD) will occur due to excessive local field strength. Obvious changes in the PD level and its growth rate can indicate the changes taking place inside the transformer or reflect the voids, metal particles and bubbles of solid insulation produced due to certain defective states in the insulation.

Vibration analysis method. Vibration analysis is an effective method widely used to monitor such transformer faults. By monitoring and analyzing the vibration signal of the transformer, the purpose of monitoring the status of the transformer is achieved.

Infrared temperature measurement technology. Infrared thermal imaging technology uses infrared detectors to receive the infrared radiation signal of the measured target, amplifies it, converts it into a standard video signal, and then displays the infrared thermal image through a TV screen or monitor. When the transformer leads are in poor contact, overload operation, etc., local overheating of the conductive circuit will be caused. Multi-point grounding of the iron core will also cause overheating of the iron core.

Frequency response analysis method. Frequency response analysis is an effective method for determining whether a transformer winding or lead structure is deflected. The mechanical displacement of the winding will produce subtle changes in inductance or capacitance, and the frequency response method achieves the purpose of monitoring the status of the transformer winding by measuring such subtle changes.

Winding temperature indication. The winding temperature indicator is used to monitor the temperature of the transformer winding, give an over-limit alarm, and initiate protection tripping when necessary. A new technology for temperature monitoring of large transformer windings has been developed, which embeds an optical fiber into the transformer winding to directly measure the real-time temperature of the winding, thereby improving the predictive modeling technology of the transformer and achieving the purpose of real-time monitoring of the temperature status of the transformer winding. .

Other condition monitoring methods. Low Voltage Impulse Response (LVIR) is also an effective transformer condition monitoring method, and is already a recognized method for determining whether a transformer can pass a short circuit test. In addition, leakage inductance testing between windings, relative humidity testing of oil, insulation resistance testing, etc. are also common methods for transformer condition monitoring.

XZTY9000B High and Low Voltage Clamp Ammeter