In the operation process of the power system, the transformer, as the core equipment for power transmission and conversion, its operating temperature is directly related to the safety, stability and service life of the equipment. Under normal circumstances, the transformer winding, as the main component generating heat, should have a higher temperature than the upper oil temperature. However, in actual operation, some equipment will have the abnormal phenomenon that the upper oil temperature is higher than the winding temperature. This problem also occasionally occurs in 1000 kva oil filled transformer and 35kv distribution transformer. This article will detailedly analyze the causes of this abnormal phenomenon, and introduce the relevant product advantages of JINSHANMEN TECHNOLOGY CO., LTD, providing professional reference for industry practitioners.
First of all, we need to clarify the basic principle of transformer temperature measurement: the temperature bulb of the transformer winding thermometer is inserted into the oil hole at the top of the transformer oil tank. When the transformer load is zero, the reading of the winding thermometer is the temperature of the transformer oil; when the transformer is loaded, the current proportional to the load is taken out through the transformer current transformer, adjusted by the converter, and then flows through the electric heating element embedded in the bellows. The heat generated by the electric heating element will increase the displacement of the elastic element. Therefore, under the loaded state, the displacement of the elastic element is jointly determined by the top oil temperature of the transformer and the load current. The temperature indicated by the winding thermometer is the sum of the top oil temperature and the temperature rise of the coil relative to the oil, reflecting the temperature of the hottest part of the coil.
During normal operation, the winding temperature should be higher than the upper oil temperature. If the opposite situation occurs, it does not mean that the equipment must have a serious fault, but the cause needs to be checked in time to avoid the expansion of hidden dangers. Combined with the actual operation experience of 1000 kva oil filled transformer and 35kv distribution transformer, the specific causes are mainly divided into two categories: measurement error and abnormal transformer operation status.
I. Measurement Error: "Illusion" Caused by Inaccurate Data
1. Failure of Temperature Measurement Device
Both 1000 kva oil filled transformer and 35kv distribution transformer rely on special devices for temperature measurement: the oil temperature is measured by a temperature bulb inserted into the oil hole at the top of the oil tank, and the winding temperature is indirectly measured through the cooperation of current transformer, converter and electric heating element. If the measurement device fails, it will directly lead to data distortion and the illusion that the oil temperature is higher than the winding temperature. Common faults include: damage of PT100 sensor for oil temperature measurement, poor line contact, failure of temperature transmitter, etc. For example, if the corresponding relationship between the resistance value of the PT100 sensor and the temperature deviates, the measured oil temperature value will be too high, which will lead to abnormal comparison with the winding temperature; line aging or loosening will also affect signal transmission, resulting in measurement errors.
2. Deviation Caused by Difference in Measurement Positions
The oil temperature is measured at the top of the oil tank, while the winding temperature is calculated by indirect means. The measurement positions of the two cannot fully reflect the real average temperature of the winding and the oil. For medium-voltage equipment such as 35kv distribution transformer, its oil tank volume is large, and the top oil temperature is more affected by the ambient temperature. If the ambient temperature is abnormally high during measurement, the measured oil temperature value will be high; the heat transfer inside the winding is uneven, and the selection of different measurement points will also affect the calculation result of the winding temperature. The superposition of the two may lead to the situation that the oil temperature is higher than the winding temperature. This deviation is more prominent when the 1000 kva oil filled transformer is running at full load.
II. Abnormal Transformer Operation Status: "Hidden Dangers" of the Equipment Itself
1. Excessive Core Loss
The iron core is one of the core components of the transformer. Its loss (hysteresis loss, eddy current loss) will generate a lot of heat, which is transmitted to the surrounding insulating oil. If the iron core has problems such as short circuit and aging of silicon steel sheet insulation, it will lead to a significant increase in iron core loss. The speed of heat generation exceeds that of the winding, which in turn makes the oil temperature rise rapidly, even exceeding the winding temperature. This situation is more common in 1000 kva oil filled transformer with a long service life. If not handled in time, it will accelerate the aging of insulating oil and affect the service life of the equipment.
2. Additional Heating Caused by Leakage Flux
Leakage flux will be generated during the operation of the transformer. If the leakage flux is too large, it will cause heating of the equipment structural parts or tank wall. After this heat is transmitted to the insulating oil, the oil temperature will rise. For 35kv distribution transformer, factors such as unreasonable winding arrangement and loose iron core joints may lead to increased leakage flux, and then the abnormal phenomenon that the oil temperature is higher than the winding temperature. The heating caused by leakage flux will not only affect the temperature balance, but also damage the equipment structural parts, which needs to be focused on.
3. Abnormal Cooling System
The cooling system is the key to transformer heat dissipation. Whether it is 1000 kva oil filled transformer or 35kv distribution transformer, the normal operation of its cooling system directly determines the temperature control effect. If the cooling system fails, such as submersible pump shutdown, fan damage, fouling of heat dissipation pipes, unopened radiator valves, etc., the heat dissipation efficiency will be greatly reduced. At this time, the heat of the insulating oil cannot be dissipated in time, and the increase range of the oil temperature will exceed that of the winding temperature, eventually resulting in the phenomenon that the oil temperature is higher than the winding temperature. Especially in the high-temperature environment in summer or when the equipment is running at full load, the impact of abnormal cooling system will be more serious.
III. Professional Solutions and Product Guarantee - JINSHANMEN TECHNOLOGY CO., LTD
In view of the abnormal transformer temperature problem, in addition to checking faults in time, choosing high-quality transformer products is also the key to avoiding hidden dangers from the source. As a professional manufacturer of power transmission and distribution equipment, JINSHANMEN TECHNOLOGY CO., LTD has advanced production technology and a complete quality inspection system, which can provide high-quality transformer products for the market and effectively reduce operational hidden dangers such as abnormal temperature.
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 1000 kva oil filled transformer and 35kv distribution transformer produced by the company adopt high-quality iron core and winding materials, optimize the winding arrangement and cooling system design, effectively reduce iron core loss and leakage flux, ensure reasonable temperature distribution during equipment operation, reduce the occurrence of abnormal phenomena such as oil temperature higher than winding temperature, and provide reliable guarantee for the safe and stable operation of the power system.
In summary, it is not a normal phenomenon that the upper oil temperature of the transformer is higher than the winding temperature. Its causes mainly include measurement errors and abnormal equipment operation. It is necessary to conduct targeted investigation according to the equipment model (such as 1000 kva oil filled transformer, 35kv distribution transformer). Choosing high-quality products produced by professional manufacturers and doing a good job in regular equipment maintenance can effectively avoid such problems and extend the service life of the transformer.