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How to diagnose and eliminate transformer core earth fault

by:Transmart     2021-01-18
How to diagnose and eliminate transformer core earth fault - 2019 05 - 07 09:39:07 transformer winding and iron core is a major part of the electromagnetic energy transmission, transformation. Ensure the reliable operation of them is people issues of concern. Statistics show that failure caused by the core problem, transformer's third place in the accident. Manufacturing of transformer core flaw has attracted attention, and a reliable grounding, iron core in the core monitoring, and ensure the one-point earthing ways through technical improvement. The test and operation department also found iron core fault mentioned is quite high. Transformer core fault still occurred frequently, however, the main reason is because of iron core multipoint earthing and core grounding caused by bad. Now for the two kinds of fault condition judgment and handling methods are introduced. 1, multipoint earthing faults exclusion ( 1) Transformer can't shut down the failure of temporary elimination method: (1) there are introduction grounding line, if the fault current is larger, can temporarily open the ground running. But must strengthen the surveillance, to prevent the failure point disappears suspension potential to appear core. (2) if the multipoint earthing fault belongs to the unstable type, can work on the ground in the string into a sliding resistance, made the current limit under 1 a. , the selection of sliding resistance is open the working grounding line measured voltage divided by the current on the ground. (3) to use monitoring point of failure rate of gas chromatographic analysis. (4) by measuring the find the exact point of failure, if cannot processing, then the normal work of the core ground lug can be moved to the point of failure in the same location, to greatly reduce the circulation. ( 2) An overhaul. After monitoring found multipoint earthing transformer fault, for the transformer can be shut down, should be timely shipments, after thoroughly eliminate the multipoint earthing fault. Ways to eliminate such failure, depending on the type of multipoint earthing and the reason, the corresponding repair measures should be taken. But there are some cases, a power outage can't find the point of failure after the core, in order to exactly find the ground, the scene can adopt the following methods. 1) dc method. Open the connection piece of core with clip, on the yoke on both sides of the silicon steel sheet into 6 v dc, and then use dc voltmeter measurement voltage between silicon steel sheet at all levels, in turn when the voltage is equal to zero or table indicating reverse, can think that there is a fault location. (2) communication method. The transformer low voltage winding is connected to the ac voltage of 220 ~ 380 v, there are magnetic flux in core at this time. If there is a multipoint earthing faults, there will be a current is measured with a milliammeter ( Iron core and a connection piece should be open) 。 With milliammeter along the iron yoke point measurement, at all levels in the table when ma current is zero, is the place for the point of failure. 2, multipoint earthing occurs when abnormal phenomena ( 1) Eddy current in iron core, iron losses increase, core local overheating. ( 2) Severe multipoint earthing, and untreated for a long time, continuous operation will lead to oil and winding transformer is overheating, make oil paper insulation aging gradually. Can cause iron core lamination two pieces of insulation aging and fall off, will cause a larger core overheating, iron core will be burned. ( 3) Longer multipoint earthing, degrade oil-immersed transformer oil and combustible gas, the gas relay action. ( 4) Make body with iron core overheating in the wooden block and clamp carbide. ( 5) Serious multipoint earthing can make the earth wire burn out, make the lost normal one-point earthing transformer, consequence is unimaginable. ( 6) Multipoint earthing can also cause discharge phenomenon. 3, when the iron core is normal need a bit of ground: when the normal operation of transformer, electric winding and tank between the electric field, and the core and other metal components in the electric field. Because of the capacitance distribution, different field, if the core is not reliable grounding, will produce charge and discharge phenomenon, damage of oil and solid insulation dielectric strength, so the core must be reliable grounding. Iron core is composed of silicon steel sheet, to reduce the eddy current, chip has certain insulation resistance ( Generally only a few ohms to dozens of ohm) , because the capacitance is great, in alternating electric field can be regarded as pathway, so only in the core of one-point earthing can fold the iron core lamination potential muffling at ground potential. When the core or the metal artifacts such as there are two or more than two ( Multipoint) Ground, the ground will cause between the closed loop, its key chain part of the magnetic flux, the induced electromotive force, and form a loop, produce local overheating, even burning iron core. Only one-point earthing transformer core, is the normal and reliable grounding. The core must be grounded, and must be a one-point earthing. Core failure is mainly caused by two aspects of reasons, one is construction technology of bad cause short circuit, the second is due to the attachment and external factors caused multipoint earthing.
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