As the core device and central equipment, the inner composition of the transformer, the iron core is an important function and structure part of the magnetic circuit, energy conversion, and power safety. The transformer iron core failure can not be ignored from the power equipment and electrical safety. From the description of the working state of the transformer core, the principle of a little grounding of the transformer core is expounded, the reasons for the fault of the transformer core grounding are analyzed, and the method of fault handling and detection is provided.
1 Description of the working state of iron core in power transformer
The iron core of the power transformer is the central part of the structure. The flux and energy conversion of the power transformer require the iron core to provide functional support. In the normal operation of the power transformer core, the iron core produces a strong alternating magnetic field due to Gaodianya and large current. In turn, there will be a higher potential difference to the ground, which will produce a discharge phenomenon between the core of the power transformer and the fuel tank. Strong discharge may directly cause damage to the core, winding and shell of the Transformer. This leads to accidents and operational hazards of power Transformers.
2 The principle of a point grounding of the iron core of a power transformer
A point of grounding of the iron core of the power transformer is to tighten the Silicon steel sheet of the iron core to form a unified potential surface, which is connected to the clamping iron plate on the inside of the fuel tank through clamping or bolt fastening. The interior of the power transformer core, Unity of potential between iron core and fuel tank of power transformer. If the iron core of the power transformer is uneven, warped, and curved, it is easy to form a superelectric grounding of the iron core Silicon steel sheet of the power transformer. Since the power transformer iron core will generate an alternating current in the alternating electromagnetic field, it will form a local loop. As a result of the rapid release of local short-term heat in the iron core of the power transformer, the actual problems such as high internal temperature of the power transformer, large amount of harmful gas release, gas protection opening, power transformer shutdown, etc., affect the power transformer's function in the power system and network. Play.
3 Main Causes of Ground Fault of Iron Core in Electric Transformer
(1) Intrinsic foreign matter in power Transformers
From the perspective of the dimension of time, the existence of foreign matter has the following stages,
First, in the process of power transformer manufacturing, the iron core part was made too extensive, and the interior and iron core parts of the area were not thoroughly cleaned, resulting in the retention of debris, which in turn affected the grounding effect of the iron core of the power transformer.
Second, during the installation process of power Transformers, mechanical external forces have appeared, resulting in the deformation of the iron core of the power transformer, the distortion of the transformer box body, and the occurrence of falling materials, resulting in multiple points of grounding of the iron core, and then short-circuit, loop and overheating.
Third, in the process of oil injection in power Transformers, there are quality problems in oil quality, entering metal impurities, adsorption near the iron core of power Transformers, affecting the location control, forming multi-point grounding.
Fourth, in the course of power Transformers 'maintenance and operation, over time, granular metal debris and powdery debris that wear, corrode, shake and thread through the interior of power Transformers have been produced, affecting the normal operation of the iron core of power Transformers. Caused power transformer operation failure and hidden danger.
(2) Insufficient relevant spacing of iron cores in power Transformers
The distance between the iron core fixture of the power transformer and the center pile of the iron core is too close. When the power transformer is grounded, the distance is too short or poor, and the position moves during operation, causing the discharge phenomenon. The iron core cushion foot of the power transformer appeared loose, resulting in a collision between the iron core and the box body, causing a short circuit.
(3) Inflow of water into the power transformer
In the installation and maintenance of power Transformers, in the event of precipitation weather, no waterproof and isolation treatment of power Transformers was carried out, resulting in damage to the iron core insulation layer of power Transformers, and the cardboard was soaked by precipitation. If Gaodianya is added, it is easy to appear power Transformers. The core ground short circuit, Power transformer discharge failure.
4 Fundamental causes of overheating of iron cores in power Transformers
(1) The power transformer manufacturing level is not high. The more modern and automated power Transformers are, the more they need superb manufacturing processes, and some power transformer production units do not have the new structure, new materials, and new requirements for production, and there are practical problems such as insufficient precision, incomplete cleaning up, and non-standardized technology. Causes the power transformer core to overheat, affecting the overall stability.
(2) The installation technology of power Transformers is not high. In the process of installing the power transformer, it failed to adhere to the principle of a little grounding in the grounding of the iron core. Insufficient screw fastening, insufficient length of the ground line, deviation of the ground position, and the formation of the iron core collision, eventually forming the power transformer. Core grounding failure, The practical problems of overheating during the operation of the iron core of the power transformer are caused.
Treatment of power transformer core earth fault
The treatment methods of power transformer core grounding failure mainly include intermittent multi-point grounding failure, treatment of iron core multi-point grounding failure with insulation resistance value, and treatment of iron core multi-point grounding(also known as dead grounding) without insulation resistance value. Three main methods. In this paper, we take the example of intermittent multi-point grounding for example.
6 Detection of power transformer core grounding fault
(1) Normative inspection. The power transformer must remember to flip or remove the positioning pins at the time of installation, carefully check whether each component is properly sized, whether the length is suitable, and whether the connecting piece is only one piece. Also pay attention to whether the screw nut is screwed solid, check whether the Silicon steel sheet production process meets the best requirements. The possibility of multi-point grounding is fundamentally eliminated.
(2) Do a good job of cleaning up. After the power transformer is manufactured, installed, and modified, the internal parts are thoroughly cleaned up to avoid any extra wire or even a very small metal powder left inside the transformer, leaving the Silicon steel sheet in the future. Ground preparation.
(3) Clean up the fuel tank. In the operation of the transformer, the coolers and oil pumps are routinely inspected to prevent local overheating of the transformer core and loss of life. The powder particles generated by the friction between metals are prevented from entering the fuel tank with the oil, and there are too many powders in the fuel tank after the accumulation of time. If so, In the end, multi-point grounding will inevitably occur.
(4) Strengthen the monitoring of operations. To realize the discovery of the power transformer core earth failure can take timely remedial measures, or find suspicious factors when the existence of testing to power transformer core earth failure to prevent before.