35kV Power Transformer Take Active Defensive Measures
Power 35kV Power Transformers are one of the main equipments in power plants and substations. The function of the 35kV Power Transformer is not only to increase the voltage to the power supply area, but also to reduce the voltage to all levels of the use of voltage to meet the needs of electricity. In short, both the step-up and the step-down must be done by the 35kV Power Transformer. In the process of transmitting electric energy in power system, it is necessary to produce two parts of the loss of voltage and power, and the voltage loss is inversely proportional to the voltage when conveying the same power, and the power loss is inversely proportional to the square of the voltage. Using 35kV Power Transformer to increase voltage, reduce transmission loss.
The water in the 35kV Power Transformer has two existing states, one is bound, the other is free. The water dissolved in oil can move with the flow of oil, called free water. Physical adsorption on the solid insulation and metal surface moisture, can be covered with dissolved into the oil to become free water, known as quasi free water. The quasi free water content in paper insulation is in%, and the free water in the oil is in ppm. The content of quasi free water is larger than that of free water. For example, the ratio of paper insulation to oil is 1:10, when the free water in the paper is 0.5%, the free water in the oil is 10mg/l, and the quasi free water is 50 times times more than the free water.
The content of free water in oil increases with the increase of temperature, and the content of quasi free water in paper decreases with the increase of temperature. The 35kV Power Transformer in the operation of paper insulation and oil in the water is constantly in exchange.
The 35kV Power Transformer in the operation of the oil in the non-stop cycle, the 35kV Power Transformer in the electric field and temperature field is uneven. It is easy to get water in high electric field and low temperature. Therefore, with the extension of the 35kV Power Transformer running time, the distribution of water in the insulation is more and more uneven, so that the local accumulation of water is formed.
It is generally seen that the water inside the intrusion 35kV Power Transformer is considered damp, which is a narrow concept of damp. From the point of view of generalized damp, the actual damp form of 35kV Power Transformer can be divided into two kinds:
① dominant dampness: Dominant damp is usually referred to as "35kV Power Transformer damp." That is to see the bottom of the tank or the body of water, and found the cause of moisture intrusion or way.
Dominant moisture into the 35kV Power Transformer is generally more water, if directly deposited at the bottom of the tank, temporarily to the insulation is not harmful; but when the water is soaked to the body, some insulation is immersed through, it will inevitably lead to insulation breakdown. In this case, the insulation breakdown mechanism belongs to the thermal breakdown, that is, in the local insulation flow through the conduction current, Giorges the paper insulation carbonization developed into a penetrating discharge. Thus not only the insulation is burnt out, but also the conductor can occur to melt. The typical case of this kind of accident is not uncommon, and it is easy to get a consensus when analyzing the 35kV Power Transformer insulation accident. It is a "low-level damp accident" and is now getting less and fewer.
② recessive damp: "recessive damp" refers to the accident did not occur before the water intrusion, but the original moisture quietly in the insulation on the local collection. When the water is accumulated enough to produce a partial discharge, a partial discharge is first started. The partial discharge produces the gas, causes the discharge to develop further. But the generation and diffusion of gases is a dynamic process. When the gas production is larger than the diffusion, the partial discharge continues and develops into a penetrating breakdown quickly. If the gas production is less than the diffusion volume, then the partial discharge is temporarily stopped, the water will be gathered again, or the partial discharge can be selected in another way. The intermittent time varies greatly depending on the position of the discharge, and some can even rest for several years. The dendritic discharge along the paperboard is typical of this discharge pattern. For the local discharge development space is limited, such as the turn between the insulation between the lower and the cushion block in the oil angle in the accumulation of water, once the partial discharge, quickly lead to turn insulation or between sections (cake) insulation breakdown, the formation of sudden insulation accident. The former uses the appropriate line detection technology, may detect and defend the sudden accident. But for the latter, we must take active defensive measures to prevent the local accumulation of free water.