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Factors affecting the electrical performance of transformer oil in oil-immersed transformers

Transformer oil is an important part of oil-immersed transformers, which directly affects the performance of the entire transformer, so the quality of transformer oil is our concern. Today we explain the five factors that affect the electrical performance of transformer oil:
      1. Water content of transformer oil
      Moisture exists in transformer oil in three forms: deposition, dissolution, and bonding. The smaller the water content in the oil, the higher the power frequency breakdown voltage.
      When the water content is greater than 200×10-6, the breakdown voltage does not change because the excess water sinks to the bottom of the oil and does not affect the breakdown voltage value during the oil test.
      Reducing the water content of the oil plays an important role in improving the operational safety of the oil-immersed power transformer and slowing down the oil aging. In order to reduce the water content of the oil, the oil may be subjected to a vacuum heating treatment, the oil temperature is heated to 60 to 70 ° C, and a high vacuum is applied to lower the water content in the oil.
       2. Impurities in transformer oil
       The breakdown strength of pure oil is very high. When impurities and moisture are present in the oil, the breakdown voltage of the oil is significantly reduced. There is a large amount of insulating material in the transformer, and the oil contains fibrous impurities, and the fibers containing moisture are more conductive.
      The effect of suspended particles in oil on the dielectric strength of power-frequency voltage is related to the number, size and nature of the particles.
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      3. Gas content of transformer oil
      Gas content is one of the main control indicators of transformer oil, and gas content directly affects the insulation performance of ultra-high voltage transformers. The gas content of the transformer oil during operation is preferably not more than 4%, and the gas content of the 500kv transformer oil is controlled within 0.5%. The transformer above 60kv requires static filling before vacuum oil injection and finished product test. The purpose is to eliminate air bubbles inside the transformer body and oil to prevent bubble discharge during product testing.
      4, the uniformity of the electric field
      Improving the uniformity of the electric field can significantly improve the power frequency breakdown voltage of high quality transformer oil. For the oil containing impurities under the impact voltage, the impurities can not form a "small bridge", and the uniformity of the electric field can improve the pressure resistance of the oil.
      5, the flow speed of the transformer oil
      When the transformer oil flows, it rubs against the insulating material to generate static electricity. The higher the flow rate, the higher the voltage. The phenomenon that oil flows in a transformer to generate electricity is called oil flow charging. The oil flow can cause distortion of the electric field of the transformer. The oil-charged voltage is superimposed on the test voltage. When the superimposed electric field strength exceeds the partial discharge field strength or the breakdown field strength of the insulating material, the safe operation of the transformer will be jeopardized. Therefore, the oil-immersed distribution transformer must control the oil flow speed, increase the cross section of the oil flow passage, reduce the electrification voltage of the oil flow, and prevent the partial discharge or insulation breakdown of the insulation caused by the oil flow.

ZTELEC produces high quality oil immersed transformers with low loss, energy saving and environmental protection.

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