High voltage power transformer winding temperature control system

Abstract

A winding temperature heater well for detecting the temperature of the oil about the coils in large transformers. The heater well comprising a temperature detecting device enveloped by a grid-patterned resistor element, the current through which varies directly with the current through the transformer, and a sleeve which protects the resistor and temperature detecting device from the oil. The heater well is embedded in a resin plate in such a manner as to allow calibration of the resistor from outside the plate.

I claim: 
     
       1. An electrically conducting plate, which can .[.e.]. .Iadd.be .Iaddend.cylindrically formed and which in such cylindrical form can be used as a resistor in a winding temperature heater well, comprising a section thereof which has formed therein a plurality of apertures increasing the electrical resistance of the plate uniformly therealong, wherein the apertures in the apertured section are sized and shaped as equivalent rectangles aligned in vertical and horizontal rows, vertical being the direction of current flow through the plate, each horizontal row displaced 180° with respect to vertically adjacent rows, defining horizontal and vertical paths about the apertures such that the vertical paths are twice the width of the horizontal paths. 
     
     
       2. A winding temperature heater well for use in measuring oil temperature fluctuations in power transformers due to increased electrical current flow through the transformers comprising: (a) a temperature detecting device with a temperature sensing bulb,   (b) a resistor element having a section thereof of highest resistivity with a plurality of apertures therein, wherein the apertured section is adapted to envelop the temperature sensing bulb but electrically insulated therefrom,   (c) an outer sleeve adapted to enclose the resistor element, to prevent contact of the oil therewith, and thermally insulated by an air pocket therefrom .[.but electrically connected therewith.]., and   (d) means for supplying to the resistor element an electrical current directly proportional to the power transformer current sufficiently low as to not damage the resistor element but sufficiently high as to heat the apertured section of the resistor element.   
     
     
       3. The heater well as claimed in claim 2 wherein the temperature sensing bulb and the resistor element are cylindrically shaped and electrically insulated from each other by a thin layer of material which is a poor thermal insulator but a good electrical insulator. 
     
     
       4. The heating well as claimed in claim 3 where the material is mylar tape. 
     
     
       5. The heater well as claimed in claim 3 wherein the apertures in the apertured section are sized and shaped so that the resistance of the resistor element is a constant throughout the apertured section .[., which section is the same size as and is adjacent to the temperature sensing bulb.].. 
     
     
       6. The heater well as claimed in claim 5 wherein the apertures are equivalent rectangles aligned in vertical and horizontal rows, each horizontal row displaced 180° with respect to vertically adjacent rows, defining horizontal and vertical paths thereabout .[.where the vertical paths are twice the width of the horizontal paths.]., vertical being the direction of current flow through the resistor element. 
     
     
       7. The heater well as claimed in claim 6 wherein the thermal insulation between the outer sleeve and the resistor element is provided by an air pocket. 
     
     
       8. A winding temperature thermal plate assembly for use with oil cooled power transformers to measure the cooling oil temperature comprising a liquid temperature well and at least one winding temperature heater well, each connected to respective temperature gauges, and each embedded at one end in a thermal plate which electrically and thermally insulates the two wells from the transformer walls, each winding temperature heater well including: (a) a temperature detecting device with a temperature sensing bulb which is connected to the temperature gauge associated with said winding temperature heater well,   (b) a resistor element having an apertured section of highest and uniform resistivity in thermal contact with, but electrically insulated from, the temperature sensing portion, the resistor element being electrically connected with a shunt calibrating resistor through a resistor stud which is embedded in and extends through the plate, with which the resistor element can be calibrated by an externally applied current;   (c) means for supplying to the resistor element an electrical current directly proportional to the power transformer current sufficiently low as to not damage the resistor element but sufficiently high as to heat the apertured section of the resistor element; and   (d) an outer sleeve thermally insulated by an air pocket from the resistor element and enclosing same to prevent contact of the oil therewith, .[.but electrically connected to the resistor element,.]. the sleeve and resistor element embedded at one end in the plate, the assembly further including a grounding stud for grounding electrostatic charges, the grounding stud in electrical contact with the liquid temperature well, the shunt calibrating resistor and the outer sleeve, said grounding stud embedded in and extending through the plate, the electrical connections in the assembly being all embedded in the plate except for those to the shunt calibrating resistor, the temperature detecting device insertable into the resistor element through an opening in the plate.   
     
     
       9. A winding temperature thermal plate assembly for use with power transformers to measure oil and winding temperatures comprising: (a) a plate which has both thermal and electrical low conductivity;   (b) a temperature detecting device, with a temperature sensing bulb connected to a temperature gauge, electrically insulated from the rest of the assembly;   (c) a resistor element having a section thereof of highest resistivity with a plurality of apertures therein, wherein the apertured section surrounds the temperature sensing bulb and is electrically insulated therefrom;   (d) an outer sleeve adapted to enclose the resistor element to prevent contact with and thermally insulate by a pocket of air the resistor element from the oil in the transformer;   (e) means for supplying to the resistor element an electrical current directly proportional to the power transformer current sufficiently low as to not damage the resistor element but sufficiently high as to heat the apertures section of the resistor element;   (f) a resistor stud;   (g) a grounding stud; and   (h) a ground connection; wherein   (i) the resistor element and outer sleeve are completely embedded at a first end in the thermal plate and are electrically connected at the second and other end,   (j) the resistor element is electrically connected near the first end to near a first end of the resistor stud,   (k) the outer sleeve is electrically connected to the grounding stud near the first end,   (l) the resistor stud is electrically connected at the first end to the electrical current supply means and near the other end to the grounding stud;   (m) the ground connection electrically intermittantly connectable to the ground stud for grounding for electrical discharges only;   (n) all of the electrical connections, except that from the resistor stud to the electrical current supply means and from the resistor stud to the grounding stud are embedded in the plate; and   (o) the resistor stud and grounding stud extend in both directions through the plate.   
     
     
       10. The thermal plate assembly as claimed in claim 9 further comprising a shunt calibrating resistor electrically connected in series between the resistor stud and grounding stud. 
     
     
       11. The thermal plate assembly as claimed in claim 10 further comprising additionally at least one of each of the temperature detecting device, temperature gauge, resistor element, outer sleeve, means for supply electrical current to the resistor element, resistor stud and shunt calibrating resistor, there being equal numbers of each in the plate assembly, wherein all the shunt calibrating resistors are electrically connected to the single grounding stud. 
     
     
       12. The thermal plate assembly as claimed in claim 11 further comprising at least one liquid temperature well embedded, at one end, in the plate. 
     
     
       13. The thermal plate assembly as claimed in claim 12 wherein in the apertured section of the resistor element the apertures are sized and shaped as equivalent rectangles aligned in vertical and horizontal rows, vertical being the direction of current flow through the plate, each horizontal row displaced 180° with respect to vertically adjacent rows, defining horizontal and vertical paths about the apertures such that the vertical paths are twice the width of the horizontal paths. 
     
     
       14. The thermal plate assembly as claimed in claim 13 wherein the plate is made from a thermosetting resin material which can be cast molded about the electrical connections. 
     
     
       15. The thermal plate assembly as claimed in claim 14 wherein an opening is provided through the plate to inside the resistor element and each of the liquid temperature wells to permit removable insertion of the temperature detecting devices after construction of the plate assembly. 
     
     
       16. The thermal plate assembly as claimed in claim 15 wherein there is provided a detachable housing to enclose the exposed outer portions of the resistor and ground studs. .Iadd. 17. The heater well as claimed in claim 2 wherein the outer sleeve is electrically connected to the resistor element. .Iaddend..Iadd. 18. The heater well as claimed in claim 5 wherein the apertured section is the same size as and is adjacent to the temperature sensing bulb. .Iaddend..Iadd. 19. The heater well as claimed in claim 6 wherein the vertical paths are twice the width of the horizontal paths. .Iaddend..Iadd. 20. The plate assembly as claimed in claim 8 wherein said outer sleeve is electrically connected to the resistor element. .Iaddend.