US1675370A - Thermal relay - Google Patents

Description

July 3, 1928. 1,675,370

F. H. MILLER THERMAL RELAY Original Filed June 9. 1920 77 JV 'ATTORNEY torque may be developed therein.

Patented July 3, 1928.

UNITED STATES PATENT OFFICE.

FREDERICK H. MILLER, QF VTILKINSBURG, PENNSYLVANIA, ASSIGNOR T0 v\VILQCPIBTG- HOUSE ELECTRIC & MANUFACTURING GOMRANY, A CORPORATION, OF PENNSYI VANIA.

THERMAL RELAY.

Continuation or application Serial No. 387,571, filed, Janet), 1920. lhis application filed March 12, 1925.

, Serial No. 14,963.

My invention relates to electrical proteca tive devices and particularly to thermal relays. i

athermal relay that shall have sufiicient time interval in the operation thereof to efiect protection of electrical apparatus from overloads.

Another" object "or my invention is to provide a relay, of the above-indicated character,.that shall employ abimetalhc element of such shape that a .relativelylarge quantity of heat, and, consequently, a'relatively large Another object of my invention is to pro vide a relay of the above-indicated character, that shall be simple and economical in construction'and'reliable in operation.

Heretofore, considerable diiiiculty 'has been encountered in developing suflicient heat in a small bimetallic element to obtain. a torque of the required value'be'cause the resistance of the element was too small to cause a heat loss therein of suflicient value to develop the required torque.

In view of this difliculty of developing sui'ficient heat in a bimetallic element, I provide an element that corresponds in size to that previously employed but so slotted as to embody a current-conducting path greatly exceeding in length the original currentconducting path of the element. of the slotting of the element, not only is the length of the current-conductingpat-h greatly increased but the cross-sectional area of the conducting path is so decreased that the efiective resistance of the element is greatly multiplied. The heat losses and, consequently, the torque developed, are correspondingly increased.

Figure 1 of the accompanying drawings is a diagrammatic view of an electric circuit embodying my invention.

Fig. 2 is a perspective view of the bimetallic element employed in the device shown in Fi 1.

liig. 3 is an end view, partially in elevation and partially in section, of the bimetallic element shown in Fig. 2.

An electrical apparatus 1 is adapted to receive energy from a circuit 2 through a circuit interrupter 3 and is provided with a thermal relay 4 to permit the interrupter 3 By reason to open when the temperature of the apparatus 1 attains or exceeds a predetermined v v I j dangerous value. The interrupter 3 is pro- One object of my invention is to provide vided with a. holding electromagnet 5 and a restraining spring 6 that is adapted to open the interrupter '3 when the holding magnet 5'becomes de-energized.

The relay 4 comprises a cylindrical casing 7 that has two ferrules 8 and 9 mounted on the respective ends thereof. A supporting member 10 is supported, at one end, by a screw 11 that extends through the ferrule 8, and at the other end, by a supporting member 12 that is mounted on an insulating block 13 by means of a screw 14. The insulated block 13 is disposed within the ferrule 9 adjacent to the-end thereof, and thescrew '14 is so accessible as to readily permit the connection of an external conductor thereto. A contact member 15 is also mounted on the supporting member 12 and is adapted to be engaged by a movable contact member 16 that is supported by a bimetallic element 17. The bimetallic element 17 is composed of two metals having unequal coefficients of expansion. One end of the bimetallic element 17 is so mounted on the supporting member 10 as to be in electrical engagement therewith, and the other end of the element is electrically connected to the ferrule 9 by means of a flexible conductor 18. A supporting member 19, of flexible insulating material, is disposed along one side of the bimetallic element 17 and is secured thereto by a plurality of rivets 20, or some similar means, and serves to maintain the bimetallic element substantially rigid. The movable contact member 16 is secured to the movable end of the bimetallic member 17 and is in electrical engagement therewith.

As current traverses the circuit to energize, or to actuate, the apparatus 1, the bimetallic element 17 of the relay 4 serves as a conductor between the ferrule 8 and the ferrule 9, in connection with the flexible conductor 18, and is, therefore, heated in accordance with the heating of the apparatus 1 by the current passing therethrough. As.

' the contact member 16 to be disengaged from the contact member 15.

By so constructing the bimetallic element 17 that the resistance thereof is of the correct value to generate a predetermined amount of heat therein in accordance with the temperature rise of an electric translating device to f be protected and that the combined heatstorage capacity vof said element and of the cylindrical casing 7 is of the correct value, the relay 4: may be caused to function in accordance with the'thermal characteristics of thejele'ctric translating devicewith which'it may be in circuit. 7

The circuit'of the electromagnet 5, which is normally completed through the contact members '15 and 16, is opened upon] the disengagementof the contact members. The

electromagnet 5 is thereupon de-energized',

and the circuitinterrupter 3 is, consequently, opened by the restraining spring 6;

"lVhen current ceases to traverse the element 17 the temperature thereof decreases, andiengagement between the contact members 15 and'16 is re-established.

It will be understood that the main teature of my invention is to increase the inherent heating capacity of a bimetallic element to permit the use of a relatively stifi element to obtain protection when the element is traversed by relatively low values of current without the use of external heating means.

Although I have shown one form of relay embodying a slotted bimetallic element, I do not limit therelement to the particular mode of slotting that is illustrated, or to a relay embodying an element having the particulararrangement that is illustrated, as various modifications may be made therein within the spirit and scope of the invention as set forth in 'the appended claims. I claim as my invention:

1, A thermal element comprising a 'bimetallic strip having a'plurality of laterally extending slots, said slots being alternately open at opposite edges thereof to increase the length of the current-conducting path,

therethrough, and means for controlling the relative movement between the different portions so constituted.

' 2'. A thermal element comprising a. bi-

metallic strip having a'plurality ofzlateralv tions relatively movable with respect to each 7 other, and means whereby said portions are caused to cooperate to eflect a predetermined operation of the bimetallic element as a whole. 7 V I In testimony whereof, I have hereunto subscribed myname this 11th day of March,

1925. i V t V FREDERICK H. MILLER.

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