As a professional manufacturer of power transmission and distribution equipment, JINSHANMEN TECHNOLOGY CO., LTD has rich experience in the research, production and maintenance of transformers. The company mainly produces oil immersed power transformers, dry-type power transformers, oil immersed three-dimensional coiled power transformers, dry-type three-dimensional coiled power transformers, mining explosion-proof dry-type transformers, mining explosion-proof mobile substations, amorphous alloy power transformers, on load capacity regulating power transformers, locomotive dry-type transformers, as well as prefabricated substations, modular substations, wind energy box type substations, high and low voltage switchgear and other transmission and distribution equipment. Among them, the 500 kva 3 phase transformer and oil filled distribution transformers are widely used in industrial and commercial fields, and their stable operation is crucial to the safety of power supply. The iron core is the core component of the transformer, and its fault will directly affect the operation efficiency and service life of the transformer. This article will detail the common testing and treatment methods of transformer core faults, focusing on the application in 500 kva 3 phase transformer and oil filled distribution transformers.
I. Common Testing Methods for Transformer Core Faults
The core fault of the transformer is mostly manifested as multi-point grounding, which will cause local overheating of the core, increase energy consumption, and even damage the core insulation in severe cases, endangering the safe operation of the transformer. For 500 kva 3 phase transformer and oil filled distribution transformers, choosing the correct testing method can quickly locate the fault and avoid further expansion of the fault. The common testing methods are as follows:
1. Clamp-on Ammeter Method (Online Measurement)
For transformers with external core leads, especially oil filled distribution transformers and 500 kva 3 phase transformer, the clamp-on ammeter method can accurately test the core multi-point grounding fault without power failure. It is recommended to measure the current of the grounding lead regularly every year. Generally, the current should be below 100 milliamps. If it is greater than this value, close monitoring should be strengthened. After the transformer is put into operation, measure the resistance of the grounding wire several times continuously as the initial value. If the initial value itself is large, it indicates that it is caused by the large leakage magnetic flux of the transformer itself. If the measured values in the later period are not much different, it can be considered that there is no fault grounding point. If the current of the grounding wire is greater than 1 ampere and increases significantly compared with the initial value, it may be a low-resistance grounding or metal grounding fault, which should be handled in a timely manner to avoid affecting the normal operation of the 500 kva 3 phase transformer or oil filled distribution transformers.
2. Chromatographic Analysis Method (Live Oil Sampling)
This method is especially suitable for oil filled distribution transformers and 500 kva 3 phase transformer with oil immersed structure. Sampling is carried out for chromatographic analysis. If the total hydrocarbon increases significantly, and methane and ethylene in the gas are the main components, while carbon monoxide and carbon dioxide gas change little or basically remain unchanged compared with the past, it can be judged as bare metal overheating, which may be caused by core multi-point grounding or insulation damage between core silicon steel sheets, and further inspection is required. If acetylene appears in the above total hydrocarbons, it is likely to be an unstable core multi-point grounding that appears intermittently. This kind of fault is hidden and easy to be ignored, so regular oil chromatographic detection is very important for the daily maintenance of oil filled distribution transformers and 500 kva 3 phase transformer.
3. Insulation Resistance Method (Power Failure Test)
Use a 2500-volt megohmmeter to measure the resistance between the iron core and the shell. If the insulation resistance is 200 megohms or more, it indicates that the core insulation is good. If the megohmmeter indicates that the iron core is connected to the shell, an ohmmeter can be used to measure the resistance between the iron core and the shell. For 500 kva 3 phase transformer and oil filled distribution transformers, if the measured value is 200 ~ 400 ohms, it indicates that there is a high-resistance grounding point in the iron core, and the transformer core multi-point grounding fault needs to be handled.
If the measured value is more than 1000 ohms, the current flowing through the ground wire is small, and it is difficult to eliminate the fault. It can be left untreated and continue to operate, and regular online monitoring can be carried out, such as the clamp-on ammeter method (for those with external core leads) and oil chromatographic analysis method. If any abnormality is found, it can be handled in time. If the measured value is 1-2 ohms, it is judged that there is a metal grounding point in the iron core, and the transformer must be handled immediately to prevent the fault from expanding and causing greater losses, especially for 500 kva 3 phase transformer and oil filled distribution transformers that are in long-term heavy load operation.
II. Treatment Methods for Transformer Core Multi-point Grounding
When multi-point grounding occurs in the transformer core, effective treatment measures should be taken according to the cause of the fault and the actual operation of the transformer. For 500 kva 3 phase transformer and oil filled distribution transformers, the following common treatment methods can be adopted to ensure the rapid recovery of the transformer and reduce the impact on power supply:
1. Series Resistor in Grounding Circuit
For transformers with external core grounding wires, such as some 500 kva 3 phase transformer and oil filled distribution transformers, a resistor can be connected in series in the core grounding circuit to limit the core grounding current. It should be noted that this method can only be used as an emergency measure, and the root cause of the fault should be found and eliminated in time after the emergency treatment to ensure the long-term stable operation of the transformer.
2. Tank Lifting Inspection for Metal Foreign Bodies
If the core grounding fault is caused by metal foreign bodies, generally, the problem can be found by lifting the tank for inspection. This method is applicable to oil filled distribution transformers and 500 kva 3 phase transformer. During the inspection, the internal parts of the transformer should be carefully checked to remove the metal foreign bodies that cause the grounding, and the insulation of the core should be inspected at the same time to avoid secondary faults.
3. Treatment Methods for Grounding Faults Caused by Burrs and Metal Powder Accumulation
For the grounding faults caused by core burrs and metal powder accumulation, the following methods have obvious treatment effects, especially for 500 kva 3 phase transformer and oil filled distribution transformers, which can effectively eliminate the fault without damaging the core structure:
1) Capacitor Discharge Impact Method;
2) AC Arc Method;
3) High Current Impact Method, that is, using an electric welding machine.
III. Conclusion
The core is the key component to ensure the stable operation of the transformer. The timely testing and scientific treatment of core faults are of great significance to extend the service life of the transformer and ensure the safety of power supply. For 500 kva 3 phase transformer and oil filled distribution transformers, which are widely used in various fields, mastering the above testing and treatment methods can effectively reduce the failure rate and improve the operation efficiency. JINSHANMEN TECHNOLOGY CO., LTD has been committed to providing high-quality transformers and professional technical support. If you have any questions about the maintenance of 500 kva 3 phase transformer, oil filled distribution transformers and other transformers, you can contact us at any time.