RO119744B1 - Heat pipe cooler for power transformers - Google Patents

Abstract

The invention relates to a heat pipe cooler for cooling the oil in the average or high power transformers. According to the invention, the cooler is made up of some heat pipes (4) whose active ends form an evaporator (5) which takes over the heat from the oil contained in an oil box (3) transferring it to some non-active ends, which form a condenser (6), from which the heat is dissipated by means of a fan (7) into the environment.

Description

The invention relates to a chiller with thermal tubes, for power transformers, intended for cooling the oil from medium and high power transformers.

An oil cooling system from transformers is used, which uses cooling batteries, provided with brass pipes and fins in the form of aluminum discs, or in honeycomb, aluminum or aluminum alloy construction. The oil takes on the heat that appears in the windings and core, during the operation of the transformer and gives it, with the help of cooling batteries and fans, to the environment.

The disadvantages that appear in the transformers equipped with these cooling batteries are mainly due to the high oil consumption caused by losses and deterioration in the cooling circuit, the large weight and size of the cooling batteries, as well as the fact that the oil is not cooled. at the optimum temperatures necessary for a good functioning.

Also known is an oil cooler (US 5345998) in which the oil is introduced into a chamber, through an orifice. Also in this enclosure is a thermal tube with fins. The heat is taken from the oil heated by this tube, which, with the help of a motor which rotates at the top of the heat tube, condenses the vapors and returns through a capillary tube at the bottom.

The disadvantages of this device consist in a faster wear of the thermal tube and the supports on it, due to the rotation, but also the risk of stopping the operation due to the engine stopping.

The thermal tube cooler for power transformers removes the disadvantages of the above, in that for cooling the oil in the transformer, it uses a thermal tube cooling battery, which has a very high heat transfer capacity from the oil to the outside. , a battery consisting of tubes closed between an oil box and an enclosure and which have a working fluid inside.

The proposed solution has the following advantages:

- increasing the heat transfer capacity from the transformer outside;

- reduction of the weight and size of the cooling batteries;

- the reduction of the electrical power, auxiliary, consumed in the cooling circuit of the oil;

- increasing the reliability and maintainability of the cooling batteries and, implicitly, the power transformers.

The following is an example of embodiment of the invention in connection with the figure which represents the construction of the thermal tube cooler.

The heat pipe cooler for power transformers according to the invention begins to work when a transformer 1 is switched on and the electric current begins to flow through the transformer windings. At this point, the oil in transformer 1 begins to heat up, due to losses in the transformer winding. When heated, the oil rises to the top of transformer 1, where it is taken from an oil box 3.

In box 3 of oil, there are inserted some 4 thermal tubes. Thermal tubes 4 have evaporator parts 5 which are inserted into an oil box 3 and mounted, tightly, in its lid, forming evaporator 2 of the cooler with thermal tubes 4.

The heat energy in the hot oil, from the box 3, is taken from the lower ends 5 evaporator of the thermal tubes 4 and transported to the upper ends 6 capacitor, through a continuous cycle of mass transfer and phase change, of the working fluid.

The upper parts 6 of the capacitor are located inside a metal enclosure 10, on which is mounted a fan 7 which cools the capacitor ends 6 of the thermal tubes 4. In this way, the oil temperature decreases and by means of a pump 8, the cooled oil is pumped into a buffer tank 9 and then reintroduced into transformer 1. The metal enclosure 10 rests on the oil box 3, by means of heat insulating spacers 11.

RO 119744 Β1

The thermal tube 4 is a device that achieves an efficient heat transfer, by 1 joining in a closed cycle, the phenomena of vaporization, vapor transport, condensation and condensation return of a working fluid. 3

The main components of the thermal tube, as presented above, are the closed pipe at both ends, the capillary structure and the working fluid. By heating one of the ends 5 of the heat tube 4, the working fluid vaporization, contained in the capillary structure, is produced, the formed vapors heading towards the colder end, where, by condensation, the heat of the external environment 7 is transferred.

The condensate returns to the vaporization area through the capillary structure, with the operating cycle resuming for as long as a temperature difference is maintained which can activate the process. 11 In the resting state, along the entire length of the thermal tube, the liquid and vapor phases of the working fluid are in permanent contact with each other. 13

The thermal tube 4 enters the operating mode, when a heat flow is applied to the vaporization zone, which is then discharged into the condensation zone. The temperature 15 and, consequently, the vapor pressure, rise to the evaporator side and decrease to the condenser side. This gives rise to a pressure difference in the vapor space, which has as a consequence 17 the movement of the vapor from the evaporator to the condenser.

The difference in the pressure pressure in the vapor is smaller than the difference in the vaporization pressures of the liquid, because, in order to maintain continuous evaporation, the vapor pressure of the liquid at the evaporator must be higher than the adjacent vapors. 21

Similarly, in order to maintain the continuity of condensation, the pressure in the condensing vapors must be greater than the vaporization pressure of the adjacent liquid. 2. 3

As a result of evaporation, the liquid-vapor interface is slightly withdrawn into the capillary structure and thus, in the evaporation zone, the radius of curvature of the meniscus decreases similarly, the condensation of the vapors 25 leading to the increase of the radius of curvature of the meniscus in the condensation zone. The pressure difference at the interface maintains the pressure balance between the vapor and the liquid at any point along the heat pipe. Thus, at the evaporator, due to the fact that the interface is concave relative to the vapors, the pressure in the liquid will be lower than the pressure in the vapors. 29

As we approach the capacitor, the concavity decreases (increasing the radius of curvature of the interface), the liquid pressure tending towards the vapor pressure, so that at the end 31 the capacitors of the two pressures become equal. The role of the capillary structure in the thermal tube 4 is precisely to provide an environment for the appearance of curved interfaces between liquid and vapor, which generates the pressure difference. It should be noted that the difference db pressure at the interface is dependent only on meniscus growth. These sizes determine the upper limit of the interface pressure difference, commonly referred to as capillary pressure.

Claims (1)

Cooling with thermal tubes for cooling the power transformers, characterized in that, for cooling the oil circulating through a power transformer (1), it uses 41 thermal tubes (4) whose lower end (5) evaporator takes the heat from the oil in the oil box (3) and carries it to the top ends (6) of the condenser, from where it is transferred to the environment 43, using a fan (7) mounted on a metal enclosure (10).