Self-cooled Transformers Research Articles

Natural Circulating Flow and Winding Cooling Characteristics for A Self-Cooled Transformer Model Cooled by Perfluorocarbon Liquid.

To develop a new type of self-cooled transformer which uses perfluorocarbon liquid as the cooling and insulating medium, natural circulating flow characteristics of the coolant and cooling characteristics of the windings were investigated using a natural circulating loop composed of a two-dimensional winding model and a cooler. The winding model had three different configurations. Each model included model conductors in which thermocouples and thin heater pins were soldered and wrapped in insulating paper. Circulation flow rates, pressure drops and temperatures in the circulating loop and the windings were measured for different coil heat fluxes and different heights of the cooler center from the winding center. From the results, natural circulating flow characteristics of the coolant and its cooling characteristics in the windings were clarified. Furthermore, a computer program was developed to predict flow rates in the circulating loop and temperature rise of the windings. The program could also calculate pressure drops in the windings and cooler. Comparisons were made betweed experimental and calculated results, and the program gave valid predictions of flow rates in the natural circulating loop and temperature rises of coils in windings.

自然冷却変圧器の巻線間流量配分

自然冷却変圧器の巻線間流量配分

The Flow Rate in a Self-Cooled Transformer

This paper presents a method for calculating the flow rate of circulating oil in self-cooled transformers. The flow rate characteristics of such transformers, obtained in measurements with models are also presented

The Flow Rate in a Self-Cooled Transformer

The Flow Rate in a Self-Cooled Transformer

Measurement of Self Cooled Transformer Sound Levels in Relatively High Ambients

Measurement of the sound level of a self-cooled transformer can be made at high ambient levels provided the ambient contains little or no sound from other inductive apparatus at the transformer sound frequencies. By measuring the components of transformer noise through narrow pass-band filters that largely exclude broad-band ambient noise and making a true RMS summation of components mathematically, it is shown that useful measurements can be conducted in ambients as high as eight decibels above the transformer sound level. A beneficial by-product is the detailed description of the frequency composition of transformer noise made available to the designer and user.

Oil Temperature Rise of Oil-Immersed Self-Cooled Transformers

Oil Temperature Rise of Oil-Immersed Self-Cooled Transformers

Abridgment of loading transformers by temperature

It is pointed out that safe loading of transformers by temperature requires not only an accurate knowledge of the thermal laws but also a knowledge of what is a safe temperature limit to be maintained continuously which condition, with the present method of limiting the load to nameplate rating, seldom, if ever, happens. In view of our present knowledge and experience, the author questions the advisability of loading transformers continuously up to the present A. I. E. E. limit of 105 deg. cent, hot-spot and argues for the establishment of a differential of 10 deg. cent, between the limit to be maintained continuously by means of overloads and the limit to be reached occasionally with rated load. It is shown that by the use of the thermal laws and without increasing the maximum or hot-spot temperature, transformers can be overloaded 1 per cent for each deg. cent, by which the ambient is below 30 deg. cent, (air) for self-cooled transformers; 25 deg. (water) for water-cooled transformers. The results of laboratory aging tests conducted on class A insulations in air and in oil are given. These tests show that the rate of aging is, roughly, double for each 8 deg. cent, increase in temperature. By the use of these data and by integrating the hot-spot temperature rise curve resulting from different load factors, the permissible peak load which causes the same deterioration in the insulation as a steady load is obtained. By combining the two rules, increased kv-a. with lower ambients and increased kv-a. with lower load factors, there is obtained a series of loading curves giving the permissible kv-a. capacities for differentcooling mediums and load factors. On an average, these curves are conservative because they apply to transformers having quite a wide range of characteristics which affect the temperature rise.

Loading Transformers By Temperature

It is pointed out that safe loading of transformers by temperature requires not only an accurate knowledge of the thermal laws but also a knowledge of what is a safe temperature limit to be maintained continuously which condition seldom, if ever, happens with the present method of limiting the load to nameplate rating. In view of our present knowledge and experience the author questions the advisability of loading transformers continuously up to the present A. I. E. E. limit of 105 deg. cent. hot spot and argues for the establishment of a differential of 10 deg. cent. between the limit to be maintained continuously by means of overloads and the limit to be reached occasionally with rated load. In other words, for continuously maintained maximum temperatures the hot spot should not exceed 95 deg. cent. It is shown by the use of the thermal laws that without increasing the maximum or hot spot temperature, transformers can be overloaded 1 per cent for each degree centigrade by which the ambient is below 30 deg. cent. (air) for self-cooled transformers, 25 deg. (water) for water-cooled transformers. The results of laboratory aging tests conducted on class A insulations in air and in oil are given. These tests show that the rate of aging is roughly double for each 8 deg. cent. increase in temperature.

Effect of Color of Tank on the Temperature of Self-Cooled Transformers under Service Conditions

The effect of color on the temperature of oil-immersed self-cooled transformers under service conditions has been a mooted question for a great many years. Based upon the relative absorption powers of the various colors often used in painting transformer tanks the lighter colors should give appreciably lower temperatures in hot climate sections. The results of three series of field tests conducted on actual transformers are given in the paper. The results, however, do not show the advantages for the light colors that would be expected, based solely upon the absorption powers of the colors. A method of calculation is used to check the test results, taking into consideration the various factors which apply to a transformer and do not apply to, say, a piece of metal painted and exposed to the sun's rays, such as the ratio of the area of the surface exposed to the sun to the total surface dissipating heat, the difference in thermal capacities, and the condition where in one case the test piece is dissipating heat, as well as receiving heat from the sun, whereas in the other case it only receives heat from the sun. It is shown that when all the factors are taken into consideration the calculated results check very closely the observations.

Abridgment of effect of color of tank on the temperature of self-cooled transformers under service conditions

Abridgment of effect of color of tank on the temperature of self-cooled transformers under service conditions

Electrical Features of the Conowingo Generating Station and the Receiving Substations at Philadelphia

The paper outlines the principal electrical features of the Conowingo development. This includes a description of the main units and their connections, and an outline of the station auxiliary supply and the 220,000-volt substation which it was necessary to build on the roof of the power plant. A description is included of the 220,000-volt substation at Plymouth Meeting, the Philadelphia terminus of the Conowingo lines, as well as the lines of the Pennsylvania-New Jersey Interconnection. At this substation are located the 30,000-kv-a. synchronous condensers installed for stability purposes, as well as a 66-kv. installation. Three winding 220/69/13.3-kv. self-cooled transformer banks of 130,000-kv-a. rating, arranged for tap changing under load, are installed here. A description is also included of the Westmoreland Substation where the 66-kv. lines from Plymouth Meeting tie in with the 66-kv. ``backbone'' of the Philadelphia Electric System. At this substation, 30,000-kv-a. synchronous condensers for power-factor correction are located, as is also an extensive 13,200-volt installation for controlling transmission lines to various distribution substations.

Temperature rise of stationary electrical: Apparatus as influenced by radiation, convection and altitude

Part I of the paper takes up first the division of losses by radiation and convection from tall vertical planes. It is shown that the loss by convection from tall planes can be expressed by the formula <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$W_{c} = 0.0014\ A \theta^{5/4}$</tex> in which W <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> is the watts, A the square inches of surface and θ the temperature rise in degrees centigrade. It is then shown that the division of losses from a black plane is, for temperature rises up to 100 deg. cent., approximately 45 per cent convection and 55 per cent radiation. Based upon this division, a simple formula is given for determining the ratio of losses for an irregular surface where the greater part of the loss is by convection. The effect of various colors on the temperature rise of transformers having both plain and corrugated tanks is discussed. In Part II it is shown that altitude does not affect radiation. The general average of the results obtained by various investigators shows that convection varies as the square root of the air density. Based on this, it is shown that for a constant loss by convection the temperature rise increases about 4.6 per cent for each 1000 meters increase in altitude. For transformers where a part of the loss is by radiation (unaffected by air density) the effect is reduced by the ratio of the convection loss to the total loss. Also the effect on the winding rise over the ambient is further reduced by the fact that the winding rise over the oil is not affected by altitude. The effect of the copper loss, however, is to increase the effect of altitude because the resistance is increased by temperature. Based upon the above facts it is shown that the temperature rise and rating of the two main classes of oil-immersed self-cooled transformers are affected by altitude as follows: Per cent increase in Copper Rise per 1000 Meters Increase in Altitude Per cent decrease in Kv-a. per 1000 Meters Increase in Altitude Self-cooled transformers (a) with plain tanks 1.75 1.35 (b) with corrugated, tubular and radiator tanks 3.0 2.3

A 100,000-volt portable substation

Expanding needs of the Southern Power system, paralleled many miles by railroads, required a flexible-connection transformer relay of large capacity, easily portable, and self-contained on a single car. The equipment in operation is of 4000 kv-a. actual capacity, and provided with high- and low-tension switch gear, instruments, panel, wiring and cables, oil-insulated, self-cooled transformers with motor-driven blower for forced air draft, special means of establishing the high-tension delta with 100,000-volt clearances, after transformer terminals and high-tension switches have been raised by a portable derrick, from receptacles where all fragile parts are protected from malicious tampering. Besides meeting standard freight car requirements for transportation, substantial, specially braced trussed superstructure is provided for supporting cabs and switch gear, which latter, as well as transformer terminals, must be lowered, during transit, to meet railroad clearances. Unusual flexibility of voltage connections is secured, contributing largely to the successful operation. Current for lights, instruments and blower motor is obtained from auxiliary transformer windings incorporated with the main units. Low-tension arrangements allow operation at various voltages with minimum switching. The entire equipment is designed for simplicity and dispatch in disassembly for transit, and reassembly in new location.

A 100,000-Volt Portable Substation

Expanding needs of the Southern Power system, paralleled many miles by railroads, required a flexible-connection transformer relay of large capacity, easily portable, and self-contained on a single car. The equipment in operation is of 4000 kv-a. actual capacity, and provided with high-and low-tension switch gear, instruments, panel, wiring and cables, oil-insulated, self-cooled transformers with motor-driven blower for forced air draft, special means of establishing the high-tension delta with 100,000-volt clearances, after transformer terminals and high-tension switches have been raised by a portable derrick from receptacles where all fragile parts are protected from malicious tampering. Besides meeting standard freight car requirements for transportation, substantial, specially braced trussed super-structure is provided for supporting cabs and switch gear, which latter, as well as transformer terminals, must belowered, during transit, to meet railroad clearances. Unusual flexibility of voltage connections is secured, contributing largely to the successful operation. Current for lights, instruments and blower motor is obtained from auxiliary transformer windings incorporated with the main units. Low-tension arrangements allow operation at various voltages with minimum switching. The entire equipment is designed for simplicity and dispatch in disassembly for transit, and reassembly in new location.

Dissipation of heat from self-cooled, oil-filled transformer tanks

This paper is confined to a presentation of the relative merits of the most commonly used designs of tanks for self-cooled transformers. However, since any tank, in addition to dissipating the heat, must fulfill the following requirements, no consideration has been given to discussion of impractical constructions.

Dissipation of Heat from Self-Cooled, Oil-Filled Transformer Tanks

This paper is confined to a presentation of the relative merits of the most commonly used designs of tanks for self-cooled transformers. However, since any tank, in addition to dissipating the heat, must fulfill the following requirements, no consideration has been given to discussion of impractical constructions.