Winding Duct Construction For Power Transformer

Abstract

The ducts between adjacent layers of windings are formed into a plurality of longitudinal passageways of generally square cross section. A flat strip of insulating material twisted about the central longitudinal axis thereof is provided in each of the passageways to augment the heat flow from the winding to the coolant flowing in the passageway.

Description

WINDING DUCT CONSTRUCTION FOR POWER TRANSFORMER

The present invention relates to forced convection cooling systems for power transformers, and in particular, to improvements in the structure of the cooling ducts in the windings of the transformer to augment the heat transfer from the windings to the liquid coolant circulated in the ducts.

A typical forced oil and forced air-cooled power transformer apparatus includes a tank filled with insulating oil coolant, a power transformer immersed in the fluid, and a cooler or radiator system having an inlet end coupled to one end of the tank adjacent one end of the windings and an outlet end connected to the tank adjacent the other end of the windings. The windings of the power transformer are provided with a plurality of ducts each generally rectangular shaped in cross section extending from one end of the windings to the other thereof and each situated between adjacent layers of the windings. A pump is provided to circulate the oil coolant through the ducts and the cooler. A fan is provided in the forced air-cooling circuit of the cooler to produce airflow over the cooler or radiator tubes thereof to remove the heat from the oil coolant. In such an arrangement as described, good heat transfer is highly desirable between the windings and the oil coolant circulating in the ducts as the oil coolant can be operated at a temperature closer to the temperature of the windings and hence the transformer can be operated at a higher power rating. Such mode of operation with higher oil temperature also means that the cooler can operate more efficiently in removing heat from the oil due to larger temperature gradients existing between the cooler tubes and the circulated air currents.

The present invention is directed to the reduction in the thermal resistance between the windings and the cooling ducts of a transformer to decrease the temperature drop necessary to drive a given amount of heat from the conductors of the winding to the coolant oil circulated in the ducts.

Accordingly, an object of the present invention is to provide a structure for winding ducts of a power transformer for improving the heat transfer between the windings and the oil flowing in the ducts.

Another object of the present invention is to provide simple structure of low cost requiring a minimum of modification of existing duct structures for decreasing the thermal resistance between the winding of a transformer and the coolant flowing in the ducts.

In accordance with an illustrative embodiment of the present invention as applied to a power transformer, there is provided a plurality of passageways in the ducts formed between adjacent layers of a winding of the transformer. In each of the passageways are provided a means for imparting a vortical motion to the coolant flowing therethrough. One form of such means is a flat insulating strip twisted about the central longitudinal axis thereof. The passageways are preferably generally square in cross section.

The novel features which are believed to be characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a plan view of a power transformer apparatus including a tank in which the transformer is included and a cooler or radiator connected thereto for cooling the liquid coolant in which the transformer is immersed;

FIG. 2 is a front view of the transformer apparatus of FIG. 1;

FIG. 3 is an enlarged sectional view of a winding of the transformer of FIG. 2 taken along section lines 3-3 showing an embodiment of the present invention;

FIG. 4 is an enlarged developed view of a section of FIG. 4 included in the indicated dotted enclosure thereof; and

FIG. 5 is a side view of the section shown in FIG. 4.

Referring now to FIGS. 1, 2 and 3, there is shown a tank 10 containing an insulating liquid coolant 11, such as oil, in which a power transformer 12 is immersed. Associated with the tank for the purpose of cooling the oil therein is a cooler 13. The inlet end 14 of the cooler is connected to an upper portion of the tank 10 adjacent one end of the transformer 12 for receiving coolant that has been heated by power dissipated in the transformer. The outlet end 15 of the cooler, is connected to the inlet end of a circulating pump 16, the outlet end of which is connected to a lower portion of the tank 10 adjacent the other end of the transformer. A ducting 17 is provided to channel the cooled coolant from the pump 16 into the ducts located in the windings and core of the transformer 12. The cooler 13 includes a plurality of radiator tubes through which the liquid coolant flows. A fan 20 is provided for forcing air or other suitable gaseous medium over the surface of the cooler tubes to remove the heat in the coolant flowing through the tubes. The power transformer 12 includes a core 21 and windings 22 and 23. The core 21 includes a plurality of ducts 24, only one of which is shown, extending from one end adjacent the lower portion of the tank to the upper portion of the tank. Each of the windings 22 and 23 includes a plurality of ducts 25, only one of which is shown in each winding between adjacent layers of the windings extending from one end to the other end thereof.

Reference is now made particularly to FIG. 3 which shows a sectional view of winding 22 of the transformer taken along section line 3-3. The winding includes a plurality of layers only two of which, layers 30 and 31, are shown. The layers 30 and 31 are maintained in spaced insulating relationship by a plurality of insulating spacers 32, for example, made of wood or other suitable insulating material to provide a generally rectangular shaped duct 25. Spacers 32 provide good mechanical support between adjacent windings. Another group of insulating spacers 33 provide a proper structural form to the duct 25, that is, they form a plurality of passageways 34, each of generally square cross section. The spacer 33 may be made of wood or of stacked paper insulation.

Referring now particularly to FIGS. 4 and 5 there are shown developed views of a portion of the duct included in the dotted box 35 of FIG. 3. FIG. 5 shows an elevation view of the section of FIG. 4. Each element of FIGS. 4 and 5 corresponding to elements of FIG. 3 has the same numerical designation. The duct 25 includes a plurality of the wide spacers 32 preferably made of some material such as wood or plastic to provide good support between adjacent layers 31 and 32 of the windings and also includes a plurality of narrow spacers 33 located between the wide spacers 32. The narrow spacers 33 may be made of wood or other suitable material such as paper. The narrow spacers are arranged to provide a plurality of generally square cross section passageways 34 in the duct 25. In each of such passageways is located a thin flat strip of insulating material 36 twisted about the central longitudinal axis 37 thereof and secured along the edge 38 or 39 thereof which is at points 40 tangent to an adjacent spacer. If desired, the strip 36 may be secured to the ends of the passageway 34. The width of the strip 36 is made substantially equal to the side of the square passageway 34. Accordingly, the cylindrical surface representing the locus of the longitudinal edges 38 and 39 of the strip 36 is tangent to the four sides of the square passageway 34 and encompasses a major portion of the volume of the passageway.

In the operation of the transformer system, power generated and dissipated in the windings 22 and 23 of the transformer is cooled by the oil flowing in the ducts 25. The oil is moved through the passageways 34 of the ducts by the action of the pump 16. The twisted flat strip 36 located in each of the passageways imparts a vortical motion to the oil flowing therein. Such vortical motion has two principal actions in improving the heat transfer from the windings 22 and 23 to the oil flowing in the passageways 34. The peripheral velocity of the vortical flow in the passageway is greater than the mean flow of oil from one end of the other of the passageway. Accordingly, as oil is flowing more rapidly over the heat transfer surface of the windings and the passageways, a greater amount of heat is transferred to the oil bringing the fluid up to a temperature closer to the temperature of the windings. The vortical motion also has the effect of forcing the heavier and cooler oil in the passageways to the walls of the passageways where it is most effective in removing heat from the windings adjacent thereto. The vortical motion also has the effect of removing the hot oil from the vicinity of the heated walls of the passageways. Accordingly, the net effect of the actions described is to raise the temperature of the oil flowing from the upper ends of the passageways and the ducts of which they are a part. In addition, the vortical motion produces turbulence in the fluid flow which facilitates and promotes heat transfer to the fluid from the windings. The hot oil flows into the inlet passageway of the cooler 13 where it is pumped through the tubes of the cooler by the pump 16. The fan 20 forces ambient air over the tubes of the cooler 13 to remove the heat therefrom. As the arrangement of the present invention increases the temperature of the oil applied to the inlet of the cooler 13 without raising the limit set for the winding temperature, improved power handling capability is obtained in the transformer system. In addition, as the cooler operates more efficiently when the differential between the oil temperature and the cooling air temperature is higher, the present arrangement achieves a more efficient cooling in the airflow system.

I intend by the appended claims to cover all modifications that fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

Claims

I claim:

1. A forced convection cooling system for a power transformer comprising:

a tank containing insulating liquid coolant,

a transformer immersed in said coolant, said transformer including a winding, said winding being in the form of a plurality of layers of wire having adjacent layers of said winding spaced to provide a plurality of ducts, each duct extending from one end of the winding to the other end thereof,

a radiator system for said coolant having an inlet end connected to said tank adjacent one end of said windings and having an outlet end connected to said tank adjacent the other end of said winding,

pumping means connected in the fluid flow circuit including said ducts and said radiator system, and

each of said ducts including a plurality of passageways, each passageway including means for producing a vortical motion in the fluid flowing through the passageway.

2. The combination of claim 1 in which said vortical motion producing means is a flat strip twisted about the central longitudinal axis thereof, the cylindrical surface representing the locus of the longitudinal edges of said strip encompassing a major portion of the volume of said passageway.

3. The combination of claim 2 in which each of said strips is essentially tangent to three sides of said passageway.

4. The combination of claim 2 in which each of said passageways is substantially square in cross section and the width of said stripes being substantially equal to a side of said square.

5. The combination of claim 2 in which a plurality of insulating spacers extend along the length of said winding in said duct to space one layer of said winding from an adjacent layer, said twisted tape being secured to one of said spacers at points of tangency therewith.

6. The combination of claim 5 in which said twisted tape is an insulator.

7. A liquid-cooled power transformer comprising:

a winding, said winding being in the form of a plurality of layers of wire having adjacent layers of said winding in spaced relationship to provide a plurality of ducts extending from one end of said winding to the other end thereof,

each of said ducts including a plurality of passageways, each passageway including means for producing a vortical motion to the fluid adapted to flow therethrough.

8. The combination of claim 8 in which said ducts are oval in shape and in which said passageways are substantially square in cross section.