What Is the Function of Oil in Power Transformer

1) Insulation performance: increase the insulation strength of various components in the transformer. The oil insulation strength of the transformer is good and has fluidity. It can fill all parts and any space of the transformer and discharge the air, so as to avoid moisture contact between the parts and the air and affect the insulation strength, so as to maintain good insulation between windings, between windings and iron core, and between windings and oil tank shell.2) Heat dissipation performance: the transformer oil cools the iron core and winding of the transformer. During the operation of the transformer, the temperature of the oil near the winding and iron core increases after heating, the volume expands, the specific gravity decreases and rises, and then enters the bottom of the transformer oil tank after cooling by the cooling device, so as to form oil circulation. During the cycle, heat is radiated to the cooling device, so that the iron core and winding are cooled.3) Anti corrosion performance: transformer oil can keep the original chemical and physical properties of insulating materials (such as wood) and make metals (such as steel) play an anti-corrosion role

General principles for power transformer when supplementary oil is requireda) Transformer oils with different oil bases shall not be used together;b) Oils of different grades (freezing point) of the same oil base shall not be used together;

c) The quality of mixed oil shall comply with the provisions of gb7595;d) When new oil or transformer oil of the same oil base and different grades equivalent to the quality of new oil is mixed, its availability shall be determined according to the measured freezing point of the mixed oil. It cannot be mixed only according to the qualified chemical and electrical properties:e) When the in-process oil is mixed with new oil of the same brand, the oxidation stability test of the mixed oil sample shall be carried out in advance, and the mixed oil can be used only when there is no sediment.

f) When imported oil or oil of unknown source is mixed with operating oil of different brands, the aging test of various oils and mixed oil samples shall be carried out in advance. The mixed oil can be used only when the quality of the mixed oil is not lower than that of the original operating oil; If the mixed oil is new oil, the quality of the mixed oil shall not be lower than the worst new oil.What are the protective functions of power transformerRole of gas protection

The main protection measure in the transformer is gas protection. The reduction of transformer oil level and the faults in transformer oil tank are reflected by gas. When the transformer has a slight fault, the oil level will drop, and the light gas will send a signal. When the gas has a serious fault, a large amount of gas will be generated, and the heavy gas will also trip.When there is a fault in the transformer, there will be heating in the fault part. In this way, the oil expansion will occur in the nearby transformer, the air will be discharged and the bubbles will gradually rise, while other materials and oil will produce gas under the action of discharge, so as to reduce the oil level.When the fault is very serious, after the gas gas is generated, the pressure inside the transformer is increased, so that the oil flows to the conservator. The baffle will overcome the resistance of the spring when the oil flow impacts, so as to move the magnet towards the dry spring and connect the contact of the dry spring. In this way, tripping will occur.

Function of differential protectionDifferential protection is the main protection of the transformer, which mainly reflects the faults of the outgoing line and winding of the transformer. It can trip the circuit breakers on each side of the transformer. According to different devices, differential protection can be divided into the following types: transverse differential protection is often used in shunt capacitor and short-circuit protection. When the equipment adopts double bus and double winding, transverse differential protection will be adopted; Longitudinal differential protection mainly reflects short circuit and inter turn short circuit, and the protection scope mainly includes outgoing line and bushing.Backup protection

The main transformer has the characteristics of large impedance during operation. Therefore, the fault of the main transformer on the low-voltage side will not affect the operation of the high-voltage side. The stability of high voltage side can effectively realize the protection function of voltage locking. However, when the main transformer fault is abnormal during operation, it can not respond in time. Therefore, during the operation of the main transformer, backup protection measures shall be taken. The parallel opening mode of high-voltage side and low-voltage side can be adopted to make the opening of locking circuit flexible.Function of voltage and current protection of transformerWhen a fault occurs outside the transformer, overcurrent will be generated; When there is an internal fault in the transformer, the backup of differential protection and gas protection will be generated. In the transformer, current protection devices should be installed. Different protection methods are selected according to different transformer capacity and system short-circuit current.

The requirements for current transformer for relay protection are: reliable insulation; A sufficiently large accuracy limit factor; Sufficient thermal and dynamic stability. The transformer for protection can meet the requirements of accuracy level under rated load. The maximum primary current is called rated accuracy limit primary current. The accuracy limit factor is the ratio of the rated accuracy limit primary current to the rated primary current. When the primary current is large enough, the iron core will be saturated and can not reflect the primary current. The accurate limit coefficient represents this characteristic. The accuracy grade of transformer for protection is 5p and 10p, indicating the allowable error of 5% and 10% at the rated accuracy limit primary current.