Four major fault handling and preventive measures for transformers in China
Four major fault handling and preventive measures for transformers in China
Common four transformer failures
1. Transformer leakage oil
The leakage oil of the transformer is one of the common faults of the power transformer. The occurrence of this fault will often affect the normal operation of the transformer. The oil leaking out will pollute the environment and cause large economic losses. There may even be a situation in which the power system is out of service. Therefore, once the transformer has such a fault, it needs to be disposed of in time to avoid further harm.
This type of fault can be divided into different reasons depending on the location of its oil leakage. Transformer oil leakage generally occurs in the oil tank weld seam leakage, low pressure side casing oil leakage and explosion-proof tube oil leakage. The reason for this failure may be due to the operation of the fuel tank during welding, which causes the oil tank to leak oil too early; the position of the high-pressure casing is raised by the rubber pad, causing cracks in the flange connection and causing oil leakage; The low pressure side causes oil leakage due to the pressure of the beads and the short lead.
2. Connector overheating
The current-carrying joint is a bridge connecting the transformer and other components. The operation of the current-carrying joint directly affects the operating efficiency of the transformer. In actual use, the current-carrying joint is prone to overheating, which is generally due to a break of the transformer and the connection of the connection. There is a potential difference in the segment, which generates heat and causes a major safety accident. In addition, there may be impurities in the joint of the transformer, or the conductive paste film in the joint may become thinner with the use of time, and may occur. In the case of heat; the conductive sealing head of the oil-immersed transformer may also generate heat due to looseness or adhesion of the current-carrying joint due to incomplete sealing.
3. Multi-point grounding of the iron core
When the transformer is used, it can adopt one-point grounding and multi-point grounding. In actual use, the multi-point grounding of the transformer will generate a current loop, which will cause the core to malfunction, and cause local heating, transformer oil decomposition and deformation of the iron core silicon steel sheet. This makes it difficult for the transformer to operate normally and safely.
4. Transformer damp
The moisture in the transformer may be due to moisture leakage in the internal parts of the transformer, and the external moisture extends into the mailbox or the insulating oil in the insulating oil. The moisture in the transformer will affect its insulation and affect the safe operation of the transformer.
Countermeasures for common faults of transformers
1. Treatment of transformer leakage oil
Due to the numerous reasons for transformer leakage, it is necessary to perform different types of welding treatment for leakage oil caused by different reasons. For the cracks on the plane, it can be treated by direct welding. For the cracks on different planes, the iron plate needs to be cut into a spindle shape for repair welding to prevent the possibility of oil leakage afterwards. For different oil spill areas, different treatment methods are needed. The oil leakage at the fuel tank requires direct welding of the flat area. The crack at the corner needs to find the location of the leak first for special welding.
Welding at the corners requires consideration of the parameters of the internal stress in the corners to avoid re-leakage due to exceeding the internal stress limit. Leakage of the oil at the low-pressure side casing requires first troubleshooting, eliminating the short lead wire and over-stretching of the busbar. After adjusting the lead length and the busbar expansion joint, the fault problem can usually be solved. For oil leakage at the explosion-proof pipe, if the internal pressure of the transformer is too large, the fuel tank will be broken. It is necessary to remove the explosion-proof pipe and install a pressure type valve and other devices.
2. Multi-point grounding treatment of iron core
The multi-point grounding treatment method of the iron core of the transformer can be divided into two ways. One is to open the box and check the grounding point on the outer cover of the transformer in this simple and direct way, and check the use of the insulating paperboard. Discover and replace in time for conditions affecting normal use. Another method is to use the method of direct current surge to burn off the grounding point of the iron core by the thermal effect of the direct current. Generally, four to five times of direct current impact can solve the redundant grounding point.
3. Transformer moisture treatment
After the transformer is damp, it can adopt both offline processing and online processing. Off-line processing is limited by the use conditions compared to online processing. There are many difficulties in the implementation process. The maintenance process requires a long-term power outage, and may also cause accelerated aging of the transformer insulation. Off-line processing requires consideration of the characteristics of different voltage devices and structures, and the implementation of moisture and heat treatment. The online processing mainly removes the moisture in the transformer oil by means of online oil filtering, and injects water into the vacuum eye, so that the gas and water in the vacuum container are transferred to the environment.
After the transformer oil is degassed and dehydrated in a certain process, it is reinjected into the transformer. Compared with offline processing, online processing has the characteristics of short power outage time and difficulty in causing equipment damage.
Common transformer faults include leakage oil leakage of the transformer, overheating of the joint, moisture in the transformer, etc. The faults caused by different parts and different reasons need to be handled in a targeted manner, and the processing method must be flexible and changeable. The transformer maintenance personnel need to continuously summarize the experience, analyze the characteristics of the fault, and constantly improve the level of handling faults in practice.
2 major failures and causes of distribution transformers
The failure of the distribution transformer has gradually become the main failure of the distribution network. The damaged distribution transformer not only increases the pressure of management costs, but also affects the normal use of electricity for industrial and agricultural production and residents' lives, and becomes the most practical problem that plagues the power management of the grassroots management units. It is necessary to carefully summarize and analyze the types and causes of distribution transformer failures, and take corrective measures to provide reference and reference for the operation and management of distribution transformers.
1. Common fault types of distribution transformers
Winding fault, core fault, casing fault, secondary side short circuit, overvoltage induced fault, improper melt selection fault, tap changer fault, other insulation faults due to fault or improper operation of the distribution transformer itself.
2. Analysis of common failure causes of distribution transformers
Winding fault. The transformer current surges. Because some low-voltage lines are not in place, short-circuit often occurs. When the short-circuit occurs, the current of the transformer exceeds the rated current several times or even several times. The coil temperature rises rapidly, leading to insulation aging, and the winding is subjected to large electromagnetic torque. When displacement or deformation occurs, the insulating material forms a fragmentation and falls off, causing the wire body to be exposed and causing a short circuit between turns.
The core is faulty. The transportation is not correct, the production process is poor, and the iron core is grounded at multiple points due to the failure to remove the debris in time during installation or overhaul. The fastening bolts of the core bolts, the splint and the iron yoke of the iron core are loosened, and the casing is damaged and then contacted with the iron core to form a multi-point grounding, causing local overheating of the iron core to damage the coil insulation; metal foreign matter between the iron core and the splint Or metal powder, under the action of electromagnetic force to form a "metal bridge", causing multiple points of grounding. The core silicon steel sheet is short-circuited. Although the silicon steel sheet is coated with insulating varnish, its insulation resistance is small, and it can only block the eddy current. When the insulating varnish on the surface of the silicon steel sheet is operated for a long time, the eddy current loss or the damage will cause a large eddy current loss, iron. The core is locally heated, causing the transformer winding insulation breakdown to be short-circuited and burned, and the casing is faulty. Casing flashover discharge. The rubber beads aging and oil leakage, the conductive dust in the air is adsorbed on the surface of the casing to form scale, causing pollution flash in the case of heavy fog or light rain, so that the high-voltage side of the transformer is single-phase grounded or short-circuited; the transformer box cover is upside down, causing foreign matter Casing discharge or phase-to-phase short circuit; damage to the transformer bushing due to external impact or mechanical stress or thermal stress is also a factor causing flashover.
Short circuit on the secondary side. When the transformer has a secondary side short circuit or grounding fault, the secondary side will generate a short circuit current 20 to 30 times higher than the rated current. The primary side must generate a large current to offset the degaussing effect of the secondary side short circuit current. The large current generates a large mechanical stress inside the coil, causing the coil to compress, the insulating gasket and the backing plate are loose, the iron cleat screw is loose, and the high voltage coil is distorted or cracked, causing the transformer to malfunction.
A fault caused by overvoltage. Lightning strikes over voltage, most of the high and low voltage lines of distribution transformers use overhead lines, and the probability of being struck by lightning in the open area of the suburb is high. When the line is struck by lightning, a surge voltage of more than tens of times higher than the rated voltage is generated on the transformer winding. If the lightning arrester installed in the high and low voltage outlet of the distribution transformer cannot provide effective protection or some hidden dangers, such as the lightning arrester is not put into operation at the same time, the grounding of the arrester is poor or the grounding resistance is exceeded, the distribution transformer will be damaged by lightning damage. avoid.
The melt is not properly selected. The distribution transformer is usually protected by a fuse. If the fuse current selection is too small, it will be easily blown under normal operating conditions. If the fuse current is too large, it will not be protected. The selection criteria of the fuse are: fuses with a rated current of 1.5 to 2.0 times the rated current of the transformer with a capacity of 100 kVA or more; fuses with a rated current of 2.0 to 3.0 for the primary side of the transformer with a capacity of 100 kVA or less; low-voltage side fuses It should be selected at 1.1 times the rated current.
The tap changer is faulty. The tap changer is poorly crimped, its quality is poor, the structure is unreasonable, the spring pressure is not enough, the dynamic and static contacts are not completely in contact, the insulation distance between the displaced dynamic and static contacts becomes small, and a discharge or short circuit occurs between the two taps. Burning the transformer tap coil or the whole winding; for human reasons, the principle of the unloaded voltage regulation by the individual electrician is unclear. After the voltage regulation, the contact of the static and dynamic contacts is partially contacted, the dirt of the static contact is caused by the contact, and the discharge causes the transformer to burn out.
Other failures. In the daily operation and maintenance management of distribution transformers, problems often arise: First, during the repair or installation process, when the conductive rod nut of the transformer is tightened or loosened, the conductive rod may rotate with the conductive rod, which may lead to the soft copper piece drawn from the secondary side. Collision, causing phase-to-phase short-circuit or primary-side coil lead break; second, accidentally dropping the object, tool smashing the casing, lightly causing flashover grounding, and causing short-circuit; thirdly, installing anti-theft on the low-voltage side of the transformer The metering box, due to space problems, poor process crimping, and some directly wrapped with wires, resulting in excessive contact resistance on the low-voltage side, heat and sparking during large load operation, causing the conductive rod to burn out.
Preventive measures against damage to distribution transformers
1, do a good job before the inspection test
On-site inspection must be performed before the distribution transformer is put into operation. 1 The oil level gauge on the oil pillow should be in good condition, the oil level is clear and on the oil level line that matches the environment. If the oil level is too high, the transformer will be put into operation and the load will increase. The oil temperature will rise. The oil expansion will cause the oil to overflow from the respirator connection pipe at the top of the oil pillow. If it is too low, it may be stopped during light load or short time in winter. The oil level is lowered until the oil level gauge does not see the oil level. 2 Whether the casing, oil level gauge, oil drain valve, etc. are well sealed and there is no oil leakage. 3 Whether the explosion-proof tube (breathing airway) is unobstructed, and whether the moisture absorber of the respirator is invalid. The grounding of the transformer's outer casing is robust and reliable because it provides direct protection to the transformer. 4 Transformer first and second outlet bushings and their connection with the wire is good, and the color is correct. 5 The nameplate on the transformer should match the size of the transformer to be selected. 6 Use 1000 ~ 2500V megger to measure the insulation resistance of the primary and secondary windings of the transformer (not grounded by the measured winding), and the insulation resistance between the primary and secondary windings, and record the ambient temperature during the measurement. The allowable value of the insulation resistance should be compared with the historical situation or the original data, not less than 70% of the factory value (when the temperature is different, it should be converted to the same temperature and then compared). The mutual difference of the DC resistance of each phase of the transformer should be less than 4% of the average value, and the mutual difference between the DC resistances of the wires should be less than 2% of the average value.
If all the inspections are qualified, insert an alcohol thermometer above 100 °C into the temperature measuring hole of the transformer to monitor the operating temperature of the transformer at any time, then empty the transformer (without load), check the electromagnetic sound for abnormality, and measure the secondary side voltage. Whether the balance, such as balance, indicates that the transformer is normal, no short circuit between the turns, and the transformer can run normally with load.
2. Precautions during operation
1 In the process of using the distribution transformer, it is necessary to regularly check whether the three-phase voltage is balanced. If the voltage is seriously unbalanced, it should be adjusted in time. At the same time check the oil level, temperature, oil color of the transformer is normal, whether there is leakage, whether the color of the desiccant in the respirator has changed, if it has failed, it should be replaced in time, and the defect is found to be eliminated in time. 2 Regularly clean the dirt on the distribution transformer, install the anti-fouling cap of the casing, check whether the casing has flashover discharge, whether the grounding is good, whether there is disconnection and disconnection, and periodically ground the resistance. 3 In the disassembly and assembly of the electric transformer, the screw has a rotation condition, which must be strictly handled, and can be put into operation after confirmation. Reasonably choose the wiring method of the secondary side wire. Apply conductive paste to the contact surface to increase contact area and conductivity, and reduce oxidation and heat generation. 4 Install a lightning arrester on the primary and secondary sides of the distribution transformer, and ground the arrester grounding down conductor, the outer casing of the transformer, and the neutral point of the secondary side at 3 o'clock. 5 Avoid unbalanced operation of three-phase load. If the three-phase maximum unbalanced current or neutral current measured during the maximum load exceeds 25% of the rated current, the load should be redistributed between the three phases. 6 Distribution transformer secondary short circuit is the most direct cause of transformer damage, reasonable choice of distribution transformers. 7 Under normal circumstances, the high-voltage side (drop insurance) fuse of the distribution transformer is selected within 1.2~1.5 times of the rated current of the high-voltage side, and the low-voltage side is selected according to the rated current. In this case, even if a low-voltage short-circuit fault occurs, the fuse can It has the proper protection for the transformer.
I am Dongguan Juke Industrial Development Co., Ltd., our company is a transformer automation production equipment supplier, we are China transformer manufacturer, if you need to buy or customize transformer automatic production equipment, please contact our company, contact our business staff, below It is the introduction of our company and some machines produced by our company. If you need to buy or customize, you can contact our business staff for purchase or customization, thank you.
Dongguan Juke Industrial Development Co., Ltd. is a professional automation workshop production line solution provider for high frequency transformer peripheral equipment.
Juke Industry is dominated by Taiwanese technology, and all raw materials are selected and processed in strict accordance with Taiwan Standard Huai, and with the excellent technology and professional services to create maximum value for customers, and determined to become the world's high-frequency transformer automation equipment program The leading brand.
Juke Industry adheres to European standards. The product series include: transformer automatic inserter, transformer EI inserter, transformer core inserter, transformer automatic casing machine, transformer core assembly machine, automatic core encapsulation machine. , (automatic core assembly + package tape + test + wobble plate), transformer winding machine, CNC coil winding machine, CNC winding machine, single-axis winding machine, double-axis winding machine, multi-axis winding machine , 12-axis automatic winding machine, automatic winding + tape machine, (USB charger automatic film machine), automatic rubberizing machine, semi-automatic tape machine, vacuum impregnation machine, (different single and double cylinders) , transformer automatic flip type soldering machine, automatic soldering machine and semi-automatic soldering machine (also called flip soldering machine), magnetic ring inductance automatic foot machine, infrared tunnel furnace, ultraviolet curing oven, baking line and other high-frequency transformer peripheral automation Equipment, products are widely used in high and low frequency transformers, ballasts and motor manufacturers. In order to meet the needs of the market, in 2008, in Yixiu District, Anqing City, Anhui Province, a group of professional and technical personnel to provide quality services to customers.
If you need to customize or purchase the above products, you need to buy or customize the transformer automatic production equipment, you can contact our business staff to purchase or customize, the following is the contact information of our business staff.
Contact information of Dongguan Juke Industrial's business personnel:
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Address: Room 406, 4th Floor, Jupiter Industrial Park, Jufeng, No. 53 Shangnan Road, Shangjiao Community, Chang'an Town, Dongguan City