Introduction to Insulating Liquid in Electrical Equipment

Label:Insulating Liquid, Electrical Equipment

Mar 6, 20243060

Introduction to Insulating Liquid in Electrical Equipment

You can see insulating liquid in electrical appliances, such as transformers, switches, rectifiers, cables and capacitors. The liquid can work alone or together with solid insulating materials to serve as both an electrical insulation medium and a thermal conductive medium for electrical equipment. It mainly plays the role of cooling, insulation, and arc extinguishing. It's crucial for running of electrical equipment.


What can insulating liquid do?


Insulating liquid plays the roles of insulation, heat dissipation and cooling in transformers, reactors, and mutual inductors. If an arc occurs in the above equipment, it also plays the role of arc extinguishing. It plays the role of insulation in oil-filled bushings. In oil pressure switches, it plays the role of arc extinguishing and insulation.


1. Insulation


In electrical equipment, insulating liquid can isolate live parts with different potentials so that there is no short circuit. The dielectric constant of air is 1.0, and the dielectric constant of transformer oil is 2.25. In other words, the dielectric strength of oil is much greater than that of air.


If the transformer coil is exposed to the air, it will be broken down quickly when working. If the transformer coils are filled with transformer oil, the insulation strength is increased, and it will not be punctured. It's safer.


2. Heat dissipation and cooling


During the live operation of the transformer, there will be 'copper loss' and 'core loss'. Heat is inevitable. If the heat in the coil is not dissipated, it will inevitably accumulate more heat, and increase the internal temperature of the iron core, which will damage the solid insulation covering the outside of the coil, and even burn it out. So we need insulating liquid.


The heat generated inside the coil is first absorbed by the liquid, and then dissipated through the circulation of the liquid, thus ensuring the safe running of the equipment. There are natural circulation cooling, natural air cooling, forced oil circulation air cooling and forced oil circulation water cooling. Generally, most large-capacity transformers apply forced oil circulation cooling.


When the turbine is running at high speed, the oil continuously circulating in the tanker system can take away a large amount of heat generated by the friction in the bearings. The turbine oil is constantly circulating in the system, and the temperature will continue to rise. The reason is that the internal friction of the oil in the bearing generates heat.


The oil is in contact with the journal, it is heated by the turbine rotor. Therefore, when the oil circulates in the system, it will continuously take away the heat generated by the equipment and discharge the heat through the oil cooler. You can think of insulating liquid as the heat transfer medium. It plays the role in cooling and dissipating heat.


3. Arc extinguishing


Insulating liquid plays the role of arc extinguishing in switches. When the oil-immersed switch cuts off the electric load, there will be an arc between the fixed contact and sliding contact. The arc temperature at this time is very high. If the heat is not taken away to cool the contacts, then after the initial arc occurs, there will be continuous arcs, which will easily burn the equipment, and also cause overvoltage and damage the equipment.


When the oil-immersed switch is initially turned off and subjected to arc, the high temperature will cause the oil to undergo violent thermal decomposition, and produce about 70% of hydrogen.


At the same time, due to the large thermal conductivity of hydrogen (41), hydrogen can absorb a large amount of heat, and directly cool the contacts, thereby achieving the purpose of arc extinguishing.


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