US3164797A

US3164797A - Wire wound electrical resistor

Info

Publication number: US3164797A
Application number: US328328A
Authority: US
Inventors: Joseph M Ramrath
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1963-12-05
Filing date: 1963-12-05
Publication date: 1965-01-05
Anticipated expiration: 1982-01-05

Description

Jan. 5, 1965 J. M. RAMRATH 3,164,797

WIRE WOUND ELECTRICAL RESISTOR Filed D80. 5;1963

United States Patent Ofiice 3,164,797 Patented Jan. 5, 1965 3,164,797 WIRE WOUND ELECTRICAL RESISTOR Joseph M. Ramrath, Mattapan, Mass, assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis. Filed Dec. 5, 1963, Ser. No. 328,328 6 Claims. (Cl. 33862) This invention relates generally to wire wound electrical resistors adapted for immersion in a cooling medium such as oil.

In some electric circuit breakers, for example, the contacts are immersed in oil and a resistor also immersed in the oil is connected across each set of contacts so as to be in parallel with the are drawn when the contacts separate. This is done to equalize the recovery voltage across two or more arcs in series and to otherwise influence the interrupting performance of the circuit breaker, particularly during line or capacitor switching. Such resistors, especially those of relatively low ohmic value, comprise large amounts of resistance material (volume being directly proportional to the PR losses in the resistance material) and even though current flow therethrough is of very short duration, the resistance material must absorb considerable amounts of electrical energy and dissipate it in the form of heat to the surrounding oil. Because such resistors are large and handle relatively high voltages (as much as 230 kv. in some instances), it is necessary to insulate them to permit their installations in the limited space available within the circuit breaker. However, since the temperature rise in the resistance material must be kept low to preserve its life and since the insulation acts as a heat barrier, it requires an undue length of time for heat dissipation. Thus, if there is frequently repeated breaker operation, the resistor may become dangerously overheated.

One presently known type of relatively low ohmic value resistor unit comprises a multiplicity of coil segments stacked adjacent one another on a spindle and the entire unit is covered with insulation. Each coil segment comprises a ribbon of flat resistance wire coated with insulating material and wound upon itself. The coil segments are electrically connected in series and in such a manner so that the resistor unit is substantially noninductive when current flows therethrough. A resistor unit of this type is subject to the problem described above and is relatively costly to manufacture.

Accordingly, it is an object of the present invention to provide new and improved resistor units which are adapted for submersion in an arc extinguishing fluid such as oil.

Another object is to provide resistor units of the aforesaid character which employ a maximum of resistance material and a minimum of electrical insulating material and which are adapted to dissipate rapidly large amounts of heat to the surrounding oil.

Another object is to provide resistor units of the aforesaid character wherein oil flows around the exterior of and through the interior thereof and wherein all of the resistance material employed is in direct contact with the oil.

Another object is to provide resistors of the aforesaid character which are simpler in construction than known devices, which are relatively economical to fabricate and are reliable in use.

Another object is to provide a resistor unit of the aforesaid character which employs two oppositely wound coils and is substantially noninductive.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates several preferred embodiments of the present invention but it is to be understood that the embodiments illustrated are susceptible to modification with respect to details thereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is a side elevational view, partly in section, of a substantially noninductive electrical resistance unit incorporating the present invention;

FIG. 2 is an end view, partly in section, of the resistor unit shown in FIG. 1;

FIG. 3 is a side elevational view, partly in section, of another embodiment of an inductive electrical resistor unit incorporating the present invention; and

FIG. 4 is an end view partly in section, of the resistor unit shown in FIG. 3.

Referring to FIGS. 1 and 2, the numeral 14! designates a substantially noninductive resistor unit incorporating the present invention which is vertically mounted between suitable supporting members 12 in spaced relationship thereto. It is to be understood that when in use resistor unit 1% is intended to be entirely immersed in a cooling and insulating medium, such as oil, contained within an electrical device such as an oil type circuit breaker.

Resistor unit 10 comprises a pair of spaced apart end plates 14- and 16 fabricated of insulating material. Since the

end plates

14 and 16 are understood to be substantially identical to each other, only the former will be hereinafter described in detail. End plate 14 is circular in form and is provided with a plurality of radially disposed slots 18 for accommodating wire supporting members or strips hereinafter described. In the embodiment shown, eight slots 18 are provided and proved satisfactory but it is to be understood that some other number of slots could be employed. End plate 14 is further provided with a plurality of holes or perforations 20, eight being shown, for permitting oil flow through the interior of the resistor unit 16). End plate 14 is also provided with a plurality of tapped holes 22 around its periphery to accommodate screws 24 which secure an insulating and protective housing 26 of cylindrical shape in place. End plate 14 is provided with a central opening 28 for accommodating means, such as a spindle 38, which adapts it for mounting to the supporting member 12 in spaced relationship thereto.

The pair of

end plates

14 and 16 are axially aligned so that the slots 18 therein are in registry and each pair of such registering slots accommodates an inner mounting strip 32 and an outer mounting strip 34, each of which is made of insulating material. Each inner mounting strip 32 is in the form of an elongated member having a plurality of wire engaging notches 36 along the edge thereof which faces outwardly when it is disposed in its slots 18 in the

end plates

14 and 16. Each inner mounting strip 32 is also understood to be provided with a pair of indentations 38 on its inwardly facing edge for engagement with the bottom of the slots 18 in the

end plates

14 and 16, respectively, which serve for alignment purposes and to give added rigidity to resistor unit 10.

Means are provided to secure each inner mounting strip 32 to the

end plates

14 and 16. Thus, each inner 1nount-' ing strip 32 projects a short distance beyond the

end plates

14 and 16 and is provided with a small hole 4%) for accommodating a wire 42 which is threaded through each small hole in all the inner mounting strips and twisted or otherwise fastened together at its ends to hold the inner mounting strips in place.

Electrical terminals

44 and 46 are mounted at opposite ends of one of the inner mounting strips 32 adjacent the outer faces of the

end plates

14 and 16, respectively. The

terminals

44 and 46 are located so as not to interfere with the placement or removal of housing 26. During assembly and after the inner mounting strips 32 are in place, a first length 48 of coiled resistance wire is con- :3 nected at one of its ends to terminal 4-4, is wound on the inner mounting strips 32 to form a first or inner coil 50, and is connected at its other end to terminal 46. More particularly, for example, the first length 48 of resistance wire is wound in a left-hand direction and laid in the first row of notches as in the inner mounting strips 32 nearest end plate 14. After the first row of notches is occupied, the wire is laid in the second row and so on until all rows of notches have been utilized.

Each outer mounting strip 34 is in the form of an elongated member having a plurality of wire engaging notches 52 along the edge thereof which faces outwardly when it is disposed in its slots 13 in the

end plates

14 and 16. In the embodiment shown, outer mounting strip 34 is provided with the same number of notches as there are notches 36 in the underlying inner mounting strip 32.

Means are provided to secure each outer mounting strip 34 in place. Thus, each inner mounting strip 32 is provided with a tapped hole 54 near its opposite ends and each outer mounting strip 34 is provided with an untapped hole 56 near its opposite ends which register with the corresponding tapped hole 54 in the inner mounting strip. A screw or bolt 58 extends through an untapped hole 56 in outer mounting strip 34 and is threaded into a tapped hole 54 in inner mounting strip 32 to secure the former to the latter.

During assembly and after the outer mounting strips 34 are in place, a second length as of coiled resistance wire is connected at one of its ends to terminal 44, is wound on the outer mounting strips 34 to form a second or outer coil 62, and is connected at its other end to terminal 46. In order for resistor unit it to be substantially noninductive it is necessary that outer coil 62 be wound in a direct-ion opposite to that of inner coil 50. Thus, the second length 60 of resistance wire is wound in a right-hand direction and is laid in the first row of notches 52 in the outer mounting strips 34 nearest end plate 14. After the first row of notches is occupied, the wire is laid in the second row and so on until all rows of notches have been utilized. It is to be understood that outer coil 62 is electrically connected in parallel with inner coil 563 between the

terminals

44 and 46.

While for purposes of illustration inner coil 59 has been described as being wound in the left-hand direction and outer coil 62 in the right-hand direction, it is to be understood that their directions of winding could be reversed.

After outer coil 62 is in place, insulating housing 26 is slid over the assembly and secured in place by means of the screws 24 and resistor unit It? is ready for installation.

Referring to FIGS. 3 and 4, the numeral 7t designates another embodiment of an inductive resistor unit incorporating the present invention which diifers from resistor unit It principally in that it is provided with only one coil 72. Mounting strip '73 replaces the two

mounting strips

32 and 34, and has notches 74 similar to notches 52 in the outer mounting strip 34. In all other respects, however, resistor unit 7b is constructed of thesame components and in the same manner as resistor unit 10.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a resistor unit for immersion in an electrically nonconductive liquid medium, in combination, a pair of spaced apart perforated insulating end plates, each end plate being provided with a plurality of radially disposed slots, a plurality of insulating strips supported between said end plates, each strip being disposed in registering slots in said end plates, each strip having a plurality of notches in its outwardly facing edge, at least one coil of resistance wire wound on said strips so as to lie in the notches therealong, a pair of terminals at opposite ends of said resistor unit, each terminal being mounted adjacent the outer surface of a respective end plate and electrically connected to one end of said coil, means for securing said plurality of strips in the slots of said end plates, and an insulating housing enclosing said strips and said coil.

2. In a resistor unit for immersion in an electrically nonconductive liquid medium, in combination, a pair of spaced apart perforated insulating end plates, each end plate being provided with a plurality of radially disposed slots, a plurality of insulating strips supported between said end plates, each strip being disposed in registering slots in said end plates and the ends of each strip projecting beyond the outer surface of the end plates, each strip having a plurality of notches in its outwardly facing edge, at least one coil of resistance wire wound on said strips so as to lie in the notches therealong, a pair of terminals, one terminal being mounted on the outwardly projecting end of one of said strips near one end plate and electrically connected to one end of said coil, the other terminal being mounted on the outwardly projecting end of one of said strips near the other end plate and electrically connected to the other end of said coil, means for securing said plurality of strips to said end plates, said means comprising a wire for engaging the outwardly projecting ends of said strips near one end plate, and an insulating housing enclosing said strips and said coil.

3. In a resistor unit for immersion in an electrically nonconductive liquid medium, in combination, a pair of spaced apart perforated insulating end plates, a plurality of inner insulating strips supported between said end plates, an inner coil of resistance wire wound on said inner strips, a plurality of outer insulating strips supported between said end plates, an outer coil of resistance material wound on said outer strips, a pair of terminals at opposite ends of said resistor unit, each terminal being mounted adjacent the outer surface of one of said end plates and electrically connected to one end of said inner coil and one end of said outer coil, and an insulating housing enclosing said inner and outer strips and said inner and outer coils.

4. The combination according to claim 3 wherein said inner and outer coils are wound in opposite directions so that the resistor unit is substantially noninductive.

5. In a resistor unit for immersion in an electrically nonconductive liquid medium, in combination, a pair of spaced apart perforated insulating end plates, each end plate having a plurality of radially disposed slots, a plurality of inner and outer insulating strips supported between said end plates, each pair of registering slots in said end plates accommodating an inner strip and an outer strip, each inner strip and each outer strip having a plurality of notches in its outwardly facing edge, means for securing said inner and outer strips to said end plates, an inner coil of resistance wire wound on said inner strips so as to lie in the notches thereof, an outer coil of resistance Wire wound on said outer strips so as to lie in the notches thereof, a pair of terminals, one terminal being mounted on the outwardly projecting end of one of said strips near one end plate and electrically connected to one end of said inner coil and one end of said outer coil, the other terminal being mounted on the outwardly projecting end of one of said strips near the other end plate and electrically connected to the other end of said inner coil and the other end of said outer coil, and an insulating housing enclosing said inner and outer strips and said inner and outer coil.

6. The combination according to claim 5 wherein said inner and outer coils are wound in opposite direction so that the resistor unit is substantially noninductive.

References Cited in the file of this patent UNITED STATES PATENTS 1,840,168 Mucher Jan. 5, 1932 3,017,255 Norris Ian. 16, 1962 FOREIGN PATENTS 566,559 Great Britain Ian. 3, 1945

Claims

1. IN A RESISTOR UNIT FOR IMMERSION IN AN ELECTRICALLY NONCONDUCTIVE LIQUID MEDIUM, IN COMBINATION, A PAIR OF SPACED APART PERFORATED INSULATING END PLATES, EACH END PLATE BEING PROVIDED WITH A PLURALITY OF RADIALLY DISPOSED SLOTS, A PLURALITY OF INSULATING STRIPS SUPPORTED BETWEEN SAID END PLATES, EACH STRIP BEING DISPOSED IN REGISTERING SLOTS IN SAID END PLATES, EACH STRIP HAVING A PLURALITY OF NOTCHES IN ITS OUTWARDLY FACING EDGE, AT LEAST ONE COIL OF RESISTANCE WIRE WOUND ON SAID STRIPS SO AS TO LIE IN THE NOTCHES THEREALONG, A PAIR OF TERMINALS AT OPPOSITE ENDS OF SAID RESISTOR UNIT, EACH TERMINALS BEING MOUNTED ADJACENT THE OUTER SURFACE OF A RESPECTIVE END PLATE AND ELECTRICALLY CONNECTED TO ONE END OF SAID COIL, MEANS FOR SECURING SAID PLURALITY OF STRIPS IN THE SLOTS OF SAID END PLATES, AND AN INSULATING HOUSING ENCLOSING SAID STRIPS AND SAID COIL.