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US 4,053,938 AGranted
Temperature sensing transformer primary switch
AssigneeRTE Corporation
InventorMichael J. Estes
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AssigneeRTE Corporation
InventorMichael J. Estes
Estimating the term…
A temperature sensing transformer primary switch for a distribution transformer, the switch being mounted within the distribution transformer below the level of the dielectric fluid and being manually operable externally of the transformer for opening the primary circuit and deenergizing the transformer, the switch including a temperature sensing device mounted on the internal end of the transformer below the level of the dielectric fluid to open the primary switch in response to overload temperatures produced on the transformer's secondary circuit. The temperature sensing device includes a compression spring and a wax motor for releasing the energy stored in the compression spring as the temperature of the dielectric fluid reaches a predetermined maximum temperature. The spring is preloaded sufficiently by a manual operation to actuate the switch at the maximum temperature. A pressure responsive switch assembly is provided for opening the primary switch.
A temperature sensing assembly for opening a distribution transformer snap action type primary switch when the temperature of the fluid in the transformer exceeds the maximum safe operating temperature of the transformer, said assembly comprising:
In a fluid insulated distribution transformer, a primary switch connected in series with the primary winding of the transformer and being immersed in the transformer dielectric fluid, said primary switch including a switch body, an overcenter snap switch blade mounted on said body and an operating rod for manually opening and closing said switch blade externally of said transformer, and a temperature sensing assembly responsive to the safe operating temperature of said transformer and immersed in said dielectric fluid, said temperature sensing assembly including a spring positioned to engage the operating rod and means responsive to the temperature of the dielectric fluid for compressing said spring until the spring bias force is sufficient to open said primary switch, whereby the primary winding is opened at the maximum safe operating temperature of the transformer.
A pressure responsive assembly for opening a distribution transformer primary switch at the maximum safe operating pressure of the transformer, said assembly comprising a bellows mounted on the primary switch and an operating rod connected to said primary switch and including an overcenter linkage assembly connected to said bellows, bias means acting on said linkage assembly to open said primary switch on collapse of said linkage, said bellows being connected to collapse said linkage at the safe operating pressure.
In a fluid insulated distribution transformer, a primary switch connected in series with the primary winding of the transformer and being immersed in the transformer dielectric fluid, said primary switch including a switch body, an overcenter snap switch blade mounted on said body for movement between open and closed positions with respect to the primary switch contacts, and an operating rod for manually opening and closing said switch blade externally of said transformer, said operating rod including first and second sections, and a pressure responsive assembly connected to said first and second sections of said operating rod for opening said primary switch at the maximum safe operating pressure of said transformer, said pressure responsive assembly being mounted on the primary switch and linkage means interconnecting said operating rod sections for transferring the motion of said pressure responsive assembly to said primary switch, and means for biasing said operating rod sections toward each other to open said primary switch when said linkage means collapses.
In a fluid insulated distribution transformer,
Dependencies are inferred from the claim text.
Drawings are temporarily unavailable. Open the PDF at USPTO
Details: means for producing snap action
Responsive to abnormal temperature: in oil-filled electric apparatus
Electric switches
Emergency protective circuit arrangements
Term ended 11 Oct 1994 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
In distribution transformers it has been the general practice to include a secondary circuit breaker or a load sensing fuse to deenergize the transformer secondary when the secondary winding is subject to overload conditions. The secondary breaker must be fairly large because of the currents encountered in the secondary circuit and as a result adds significantly to the cost of the transformer. Load sensing fuses are conventionally one shot devices which require replacement on fusing as well as producing a substantial increase in the temperature of the dielectric fluid.
The temperature sensing transformer primary switch of the present invention is connected in the primary circuit of the transformer and is immersed within the dielectric fluid within the transformer to open the primary circuit when the temperature of the dielectric fluid exceeds the maximum safe operating temperature of the distribution transformer. The primary switch is of the type described in U.S. application Ser. No. 415,937, filed on Nov. 15, 1973 and entitled "Self-Protected Distribution Transformer" now abandoned and refiled as application Ser. No. 598,988 and is connected in the primary circuit to allow for the manual opening of the primary circuit externally of the transformer. A temperature sensing assembly is mounted on the internal end of the primary switch and is immersed in the dielectric fluid to sense the temperature of the fluid and open the primary switch under fault or overload conditions. The temperature sensing device includes a wax motor which has an operating temperature band of 10.degree. F. or less. The wax motor provides a linear response at the preset temperature band. This linear response is of sufficient force to actuate the primary switch either directly or by preloading a spring at the predetermined maximum operating temperature of the transformer. The switch can also be connected to respond to a predetermined pressure in the transformer casing.
FIG. 1 is a schematic view of the temperature sensing transformer primary switch shown connected in the primary circuit of a distribution transformer;
FIG. 2 is a view partially in section showing the temperature sensing device on the primary switch with the switch in the closed position;
FIG. 2a is an enlarged view of a portion of FIG. 2;
The temperature sensing transformer primary switch 10 of the present invention, as shown in FIG. 1, is connected in the primary circuit 12 of a distribution transformer 14. The distribution transformer 14 is schematically shown positioned in a sealed casing 16 and immersed within a dielectric fluid 18 within the casing 16. The primary winding of the transformer 14 is connected through the switch 10 to a fused bushing 20 by means of the circuit 12 as is generally understood and as more fully described in copending application Ser. No. 415,937. The switch 10 can be used for manually opening the primary circuit 12 externally of the casing 16 or the switch 10 can be opened by means of a temperature sensing assembly 22 (FIGS. 2-7 and 11) mounted on the primary switch 10 or by means of a pressure responsive assembly 24 (FIGS. 8 and 9).
Generally, the primary switch 10 includes a body 26 which is retained in an opening 28 in the wall of the casing 16 by a nut 29 and sealed therein by a gasket 30. An overcenter snap switch blade 32 is mounted on the internal end of the body 26 and is movable into and out of contact with electrical contacts 34 to complete the primary circuit 12. The overcenter switch blade 32 is manually actuated by means of an operating rod 36 that extends outwardly through an opening 38 in the body 26 so that it is manually operable externally of the casing 16. The operating rod 36 is sealed within the opening 38 by O-ring seals 40 and is connected directly to the overcenter snap switch blade 32. An internally threaded opening 42 is provided on the internal end of the body 26.
The temperature sensing assembly 22, as shown in FIGS. 2-7, includes a temperature responsive actuator in the form of a wax motor 44 which is commercially available and generally operates at the melting temperature of a quantity of wax 46 sealed within a cylinder 48 in the wax motor. More particularly, the wax motor 44 can be designed to respond to a very narrow temperature band. This band can be predetermined by proper selection of the motivating wax 46 to correspond to the maximum safe operating temperature of the distribution transformer 14. At the required temperature the wax 46 will melt and expand producing a force that can be transferred to the primary switch 10 to open the primary circuit 12 when the temperature of the dielectric fluid 18 approaches the safe maximum operating temperature of the transformer.