US2255638A

US2255638A - Overload relay

Info

Publication number: US2255638A
Application number: US315386A
Authority: US
Inventors: George C Armstrong
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1940-01-24
Filing date: 1940-01-24
Publication date: 1941-09-09
Anticipated expiration: 1958-09-09
Also published as: GB544464A

Description

p G, c. ARMSTRONG 2,255,638

OVERLOAD RELAY Filed Jan. 24, 1940 WITNESSES: INVENTOR www U ATTORNEY Patented Sept. 9, 1941 OVER-LOAD RELAY George G. Armstrong,

to Westinghouse E Company, of Pennlyl Wilklnsburg, Pa., assignor lectric 8: Mann! East Pittsburgh, Pa., Vania acturing a corporation Application January 24, 1940, Serial No. 315,386

12 Claims.

My invention relates to an overload relay, and more specifically to one that is responsive to heat generated in response to an overload current.

An object of my invention is to provide an overload relay for use on alternating current circuits, which may be immersed in air or oil and which will give outstanding performance on extremely high overload currents.

Another object of my invention is to provide an overload relay which is adjustable in rating.

Other objects and advantages will become more apparent from a study of the following specification when considered in conJunction with the accompanying drawing, in which:

Figure 1 is a side view partly in cross section of an overload relay involving the principles of my invention;

Fig. 2 is a modified showing of the movable contact arm; and

Fig. 3 is a sectional view taken along line III-III of Fig. 1.

A coil or winding l carrying the current of the circuit which is to be protected, and an insulating spool 2 are mounted upon an insulating base 3 which is arranged to hold the relay upon a panel by means of suitable mounting bolts (not shown). The insulated casing forms a hermetic seal making it possible to operate ,the relay in an oil bath. The coil is arranged to surround a copper tube 4 in which is placed a stationary pole 5 to which is attached on its upper face, a ring 01' an alloy steel material It (for example, Invar") having a curie point preferably above 100" C. A nickel-steel alloy having a curie point of about 125 C. is a very suitable example. A movable plunger 6 rests on the magnetic alloy ring it and is guided by a brass tube 1.

When the pole piece It is magnetized, the magnetomotive force of the coil l holds the plunger 6 down tightly against its upper surface. When the current in the coil l, due to an overload, exceeds a particular value, eddy currents built up in the copper tube 4 cause the temperature of the alloy pole piece element I8 to exceed the curie point, and there is thus a resultant loss in magnetic attraction between the alloy pole piece It and the plunger 6. This results in the plunger being attracted to the upper stationary pole ll driving the operating rod 8 upwards and causing the separation of the contact members I and Ill. The movable contact member 8 is normally urged downwardly by a phosphor bronze or steel spring l3 backed up by a guard I 4.

In contact with the lower pole piece 5 is an the center stud v netic flux which I which when turned about I! may be caused to vary the air gap l2 (see Fig. 3), thereby changing the magcirculates through the center oi the coil, and consequently varying the eddy currents set up in the copper tube 4 and the resultant heating. The circumferential edge of the lower ring 20 of the spool may be suitably calibrated and cooperate with the arrow 2| or other index on disc II. An insulating cap ll of "Moldarta or other suitable insulating material has a tapped insert II the eccentric disc ii in position.

The relay as shown rests automatically whenever the coil is deenergized. Hand reset may be provided by arranging a latch (not shown) to catch the movable contact carrying member I! in its open position, holding it there until manually released. The proportions of the magnetic circuit may be so arranged as to provide instantaneous trip at high currents as a result of saturation in the parts of the lower pole.

Fig. 2 is a partial cross sectional view taken at right angles to the view in Fig. 1 and showing a bimetallic element 22 which is adjustable by screw 23 and which bimetallic element compensates for changes in ambient temperature. The bimetal moves in the direction oi the arrow when the ambient increases. The temperature required for tripping may be varied by adjusting screw 23. The relay may be inverted to keep the coil heat from heating the bimetal.

This adjustable relay may be used either for air operation or for oil immersion. For oil immersion, slotting (not shown) in the plunger should be provided to by-pass any oil which may leak into the interior of the relay.

eccentric steel disc I The temperature at which the relay operatesmay be difierent from C. depending on the materials used, the construction of the coil, the application (1. e., whether or not it is to be sensitive to the ambient, etc.).

Although the reversibly magnetic element has been described as being of a nickel-iron alloy or 01' Invar, it will be apparent that any other magnetic material which loses or substantially loses its magnetic property as a result of heat, may be substituted therefor. For example, a nickel copper alloy, often referred to as Monel metal may be substituted. Likewise, an alloy of iron and nickel, with minor percentages of silicon or chromium, and which become non-magnetic when heated to a temperature dependent upon the percentages, may likewise be substituted.

particularly I am, of course, aware that others,

for adiustably clamping tion, an electromagnetic device 'move under the influence of property of substantially aiter having had the benefit of the teachings of my invention, may devise other devices embodyingmy invention, and I, therefore, do not wish to be limited to the specific showings made in the drawing and the descriptive disclosure hereinbefore made, but wish to be limited only by the scope of the appended claims and such prior art that may be pertinent.

I claim as my invention: i

1. An overload relay comprising, in combination, an electromagnetic device having a coil and a pair of magnetic pole pieces coaxially disposed with respect to said coil, a slidable, plunger type armature movable within and along the axis of said coil and which is selectively attracted to either of said pole pieces, a reversibly magnetic element disposed in the vicinity of one of said pole pieces and which loses its magnetism to an appreciable extent as the result of excessive current flow through said coil thereby allowing the armature to move under the influence of the other magnetic pole piece, and an electrical switch which is operable by said armature.

2. An overload relay comprising, in combinahaving a coil and a pair of magnetic pole pieces coaxially disposed with respect to said coil, a slidable, plunger type' armature movable within and along the axis of said coil and which is selectivelyattracted to either of said pole pieces, heating means responsive to current flow through said coil, a reversibly magnetic element disposed in the vicinity of one of said pole pieces and which loses its magnetism to an appreciable extent as the result of a predetermined value of heat developed by said heating means thereby allowing the armature to the other magnetic pole piece, and an electrical switch which is operable by said armature.

3. An overload relay comprising, in combination, an electromagnetic device having a coil and a pair of magnetic pole pieces coaxially disposed with respect to said coil, a slidable, plunger type armature movable within and along the axis of said coil and which is selectively attracted to either of said pole pieces, a metallic member having the property of developing a relatively high temperature as the result of eddy currents induced therein by current flow through said coil, a reversibly magnetic element disposed in the vicinity of one of said pole pieces and which loses its magnetism to an appreciable extent as the result of a predetermined value of heat developed by said metallic member and transferred to said reversibly magnetic element, thereby allowing the armature to move under the influence of the other magnetic pole piece, and an electrical switch which is operable by said armature.

4. An overload relay comprising, in combination, an electromagneticdevice having a coil and a pair of pole pieces coaxially disposed with respect to said coil, a reciprocable, plunger type armature movable within and along the axis of said coil and which is selectively attracted to either of said poles, lar element disposed in the vicinity of one of said poles, a thin tubular element which is coaxially disposed with respect to said magnetic tubular element and to said coil axis and which is heated as the result of eddy currents induced therein by current flow through said coil, said reversibly magnetic, tubular element having the losing its magnetic property upon being heated a predetermined 'amount thereby allowing said armature to bea reversibly magnetic tubu-.

aasaess come attracted by the other of said poles, and

an electrical switch which is operated by said tion, an electromagnetic device reciprocable armature.

5. An overload relay comprising, in combination, an electromagnetic device having a coil and a pair of pole pieces coaxially disposed with respect to said coil, a reciprocable, plunger type armature movable within and along the axis of said coil and which is selectivelyattracted to either of said poles, a reversibly magnetic tubular element disposed in the vicinity of one of said poles, a thin tubular copper element which is .coaxially disposed with respect to said magnetic tubular element and to said cell axis and which is heated as the result of eddy currents induced therein by current flow through said coil, said reversibly magnetic, tubular element having the property of substantially losing its magnetic property upon being heated above 100 C. thereby allowing said armature to become attracted by the other of said poles, and an electrical switch which is operated by said reciprocable armature.

6. An overload relay comprising, in combination, an electromagnetic device having a coil and a pair of pole pieces coaxially disposed with respect to said coil, a reciprocable, plunger type armature movable within and along the axis of said coil and which is selectively attracted to either of said poles, a reversibly magnetic tubular element disposed in the vicinity of one of said poles, a thin tubular element which is coaxially disposed with respect to said magnetic tubular element and to said coil axis and which is heated as the result of eddy currents induced therein by current flow through said coil, said reversibly magnetic, tubular element having the property of substantially losing its magnetic property upon being heated to approximately 125 (3., thereby allowing said armature to become attracted by the other of said poles, and an electrical switch which is operated by said reciprocable armature.

7. An overload relay comprising, in combinahaving' a'coil and a pair of magnetic pole pieces coaxially disposed with respect to said coil, a slidable, plunger type armature movable within and along the axis of said coil and which is selectively attracted to either of said pole pieces, a reversibly magnetic element in the vicinity of one of said pole pieces,

' a thin metallic cylindrical member coaxially disposed with respect to said coil and adjacent to said magnetic element and which is heated by eddy currents induced as the result of current flow through said coil, said reversibly magnetic element having a curie point of about C. or above thereby allowing the armature to move under the influence of the other pole piece upon the attainment of such temperatures by said reversibly magnetic element, and an electrical switch which is operable by said armature.

8. An overload relay comprising, in combination, an electromagnetic device having a coil and a pair of magnetic pole pieces coaxially disposed with respect to said coil, a slidable, plunger type armature movable within and along the axis of said coil and which is selectively attracted to either of said pole pieces, a reversibly magnetic element of Invar in the vicinity of one of said pole pieces, a thin metallic member adjacent to said magnetic element and which is heated by eddy currents induced as the result of current flow through said coil, said reversibly magnetic element having a curie point of about aasaees 125' (3., thereby allowing the armature to move under the influence of the other pole piece upon the attainment of such temperatures by said reversibly magnetic element, and an electrical switch which is operable by said armature.

9. An overload relay comprising, in combination, an electromagnetic device having a coil and a pair of magnetic pole pieces coaxially disposed with respect to said coil, 3, slidable, plunger type armature movable within and along the axis of said coil and which is selectively attracted to either of said pole pieces, a reversibly magnetic element disposed in the vicinity of one of said pole pieces and which loses its magnetism to an appreciable extent as the result of excessive current flow through said coil, thereby allowing the armature to move under the influence of the other magnetic pole piece, and an electrical switch which is operable by said armature, said electromagnetic device having a core which has an air gap independent of said armature, means for selectively adjusting the width of said air gap.

10. An overload relay comprising, in combination, an electromagnetic device having a coil and a pair of magnetic pole pieces coaxially disposed'with respect to said coil, a slidable, plunger type armature movable within and along the axis of said coil and which is selectively attracted to either of said pole pieces, a reversibly magnetic element disposed in the vicinity of one of said pole pieces and appreciable extent as the result of excessive current flow through said coil thereby allowing the armature to move under the influence of the other magnetic pole piece, and an electrical switch which is operable by said armature, said electromagnetic device having a core which has an air gap independent of said armature, an eccentrically mounted magnetic member which is adjustable to provide various widths 01' said air which loses its magnetism to an 11. An overload relay comprising, in combination, an electromagnetic device having a coil and a pair of magnetic pole pieces coaxially disposed with respect to said coil, a slidable, plunger type armature movable within and along the axis of said coil and which is selectively attracted to either of said pole pieces, a reversibly magnetic element disposed in the vicinity of one of said pole pieces and which loses its magnetism to an appreciable extent as the result of excessive current flow through said coil thereby allowing the armature to move under the influence of the other magnetic pole piece, and an electrical switch which is operable by said armature, said magnetic pole pieces and reversibly magnetic elements being hermetically sealed by a casing thereby adapting the device for immersion in a liquid insulating medium.

12. An overload relay comprising, in combination, an electromagnetic device having a coil and a pair of magnetic pole pieces coaxially disposed with respect to said coil, a slidable, plunger type armature movable within and along the axis of said coil and which is selectively attracted to either of said pole pieces, a reversibly magnetic element in the vicinity of one of said pole pieces, a thin metallic member adjacent to said magnetic element and which is heated by eddy currents induced as the result of current flow through said coil, said reversibly magnetic element having a curie point of about C. or above thereby allowing the armature to move under the influence of the other pole piece upon the attainment of such temperatures by said reversibly magnetic element, and an electrical switch which is operable by said armature, said poles, reversibly magnetic elements and thin metallic elements all being hermetically sealed by a. casing, thereby adapting the device for immersion in a liquid insulating medium.

GEORGE C. ARMSTRONG.