US2798919A - Electric circuit breaker - Google Patents

Description

July 9 1957 R. c. INGWERSEN C .2,798,919

ELECTRIC CIRCUIT BREAKER Filed Feb. 7. 1955 INVENTOR Rim-m R0 /wswesflv ATTORNEY ELECTRIC CIRCUIT BREAKER Richard C. Ingwersen, Jackson, Mich., assignor to Mechanical Products, Inc., llacksou, Mich., a corporation of Michigan Application February 7, 1955, Serial No. 486,378

4 Claims. (Cl. 200-116) This invention relates to electric circuit breakers which have overload protection provided by a bi-metal latch part connected in circuit with a movable Contact assembly and adapted for automatic release from a relatively xed abutment, upon the occurrence of a predetermined current overload, so as to permit the movable contact assembly to move immediately to open position with respect to a companion xed contact assembly. Circuit breakers constructed to operate as thus indicated are disclosed in several prior patents in my name, including Patent No. 2,485,736, dated October 25, 1949, and Patents 2,514,545, dated July 1l, 1950.

An advantage of these circuit breakers is that the bimetal latch parts are capable of being iinely calibrated so that they will possess a quick break action on overload, but the sensitivity of the latch parts becomes increasingly less as the currents ratings are increased so that the break action becomes slower, or sluggish, in the case of the high rated circuit breakers.

It becomes an object of the present invention, therefore, to improve the construction and operation of the known circuit breakers to the extent that a quick break action is possible with all current ratings. In this connection, it is an object of the invention to provide a circuit breaker in which the ow of the conducted current will take place along separate paths, one of which includes the bi-metal latch -part and the other of which involves an electrical shunt having contacts which will open at the instant current overload occurs and thereby leave the bi-metal part at the mercy of the current for quick break action.

In connection with these electric circuit breakers, employing a bi-metal latch part, it should be taken into accountV that bi-metal strip possesses the inherent characteristic that at a certain given temperature (in the order of 70 .F.) the bi-metal strip will be in a neutral flat state but, upon heating, the strip will bend to the arc of a. circle, with the high expansion side of the bi-metal strip assuming a convex shape. If the bi-metal strip is cooled below the given temperature it will bend in the opposite direction so that the high expansion side will assume a concave shape. All this assumes that there is nothing to restrain such bending motion.

In the use of the known circuit breakers under conditions where the ambient temperature undergoes extreme changes it becomes necessary to compensate for these extreme changes in the ambient temperature if the circuit breakers are to function properly. In aircraft, for instance, tted with these circuit breakers, it may happen that the aircraft may take-oit from zero, or sub-zero, ground temperature and in flight at high speed develop an interior elevated temperature as high as 260 F. due to the occurrence of body skin friction. While use has been made of refrigerated compartments for the personnel to compensate for such high temperature it is not convenient to refrigerate the entire aircraft interior and these circuit breakers have to be installed in non-refrigerated portions of the aircraft where, it should be noted, the

States Patent() ICC electrical cables are capable of functioning properly due to present design and insulation thereof. The situation arises, therefore, that since the electrical cables and other components have been designed to operate under these extreme changes in ambient temperature, if the circuit breakers of the general known construction are to be employed under such conditions they must also be made to operate properly throughout the entire temperature range.

f It is a further object of the invention, therefore, to improve the construction and operation of the prior art circuit breakers so that they are compensated for the eX- treme ambient temperature changes and will operate properly throughout a complete temperature range.

Further objects and advantages of the invention, residing in the construction, arrangement and combination of parts will become clear from consideration of the following description with reference to the accompanying drawings and from the appended claims:

In the drawings:

Fig. l is an elevational view of the interior of a prior art circuit breaker modified in accordance with the present invention, and

Fig. 2 is a similar view to Fig. l but of another form of the invention.

In Fig. l the circuit breaker is shown as comprising a casing 10 upon which there is mounted the re-set actuator plunger 12 for a U-shaped bi-metal latch part 14 carrying the movable contacts 16, 16' and held engaged against the fixed abutment ledge 18 by the action of the tensioned coil springs 20. The companion fixed contacts are indicated at 22, 22 and the improvement provided by the present invention involves connecting an electrical shunt between one of the xed contact terminals and the movable contact and bi-metal latch assembly. This shunt is formed by a bi-metal strip 24 connected at one end to one of the fixed contact terminals 26 and carrying at its opposite end a contact 28 shown in contact with a contact 30 on the conductor arm 32 of the said movable contact and bi-metal latch assembly.

The bi-metal strip 24 is of relatively low resistance and has its low expansion side 34 disposed remote from the Contact 30.

With the circuit breaker included in an electrical circuit in the contact closed position as shown the electrical flow will take place in part through the contacts 22', bi-metal strip 24, contacts 28, 30, conductor arm 32 and contacts 16, 22, and in part through contact 16', bi-metal latch 14 and contacts 16, 22, with the greatest ilow taking place via the bi-metal shunt strip 24 due to the low resistance of this strip.

Since the low expansion side of the strip 24 is remote from the contact 30, heating of the strip 24 by the conducted current will cause |the strip to bend away from the contact 30 and open the circuit at the contacts 28 and 30. At the instant the circuit is opened at these contacts the entire current ow will take place through the bi-metal latch part 14. In this connection it should be noted that it takes only a fraction of movement of the contact 28 to open the circuit at 28, 30 whereas there is a time interval before the latch part 14 is released from the abutment 18 to permit the circuit to be automatically opened at the contacts 16', 22', and 16, 22, such time interval corresponding to the lateral movement of the latch edge with respect to the abutment. However, since it is no longer necessary for the bi-metal latch 14 to carry the full current load it is possible to make this latch consistently sensitive throughout the different current ratings for which the circuit breakers are made to operate, whereby a finely calibrated condition of the bi-metal latch part is possible for the high current ratings as well as for the low current ratings.

The pressure of the contact 28 against the contact 30 is capable of adjustment by actuation of the grub screw 35.

In Fig. 2, the circuit breaker casing 36 has the re-set actuator plunger 38 mounted thereon for setting the brimetal U-shaped latch part 40 against the fixed abutment ledge 42 so that the movable contacts 44, 44 are held closed with respect to their companion lixed contacts 46, 46' and the coil springs 48 are ytensioned. All this is known from my said prior patents. The present improvement involves rendering this circuit breaker so as to be operable properly under conditions of extreme ambient temperature variation by connecting the movable contacts 44, 44' in a separate and shunt circuit formed by the electrical leads 50, 50' and a bi-metal strip and contact assembly indicated by the general reference 52. This assembly comprises two bi-metal strips l54, 54 connected at one end to anchor blocks S6, 56 and carrying contacts S, 58' at their opposite and free ends. These bi-metal strips are arranged with their high expansion sides facing an adjustment screw 60 which can be positioned immediately opposite the contact 58', as shown in full lines in Fig. 2, or at a remote position, as shown in the dotted position of this screw. When in the full line position the screw serves to restrain movement of the bi-metal strip 54 outwards with respect to contact 58 upon exposure to reduced temperature, it being noted that strip 54' is not included in the electrical conductive part of the circuit. The screw 60, in said full line position also serves to maintain the desired contact pressure between contacts 58, 58' by adjustment of the screw. When located in the dotted position, remote from the contact 58 the screw 60 loses its ability to restrain outward movement of the bi-metal strip 54 at its contact end and functions to maintain a desired contact pressure.

With the parts in the position shown and the circuit breakers connected in a circuit, the current flow will take place along two separate paths, one path being contacts 46, 44 (or 46', 44') bi-metal latch 40 and contacts 46', 44 (or 46, 44) and the other path being contacts 46, 44 (or 46', 44') conductor lead 50 (or 50'), contacts 58, 58 and contacts 46, 44 (or 46', 44'). Assuming 'the ambient temperature remained constant at the temperature corresponding to the given temperature at which bi-metal strip remains in a neutral ilat state there will be no ambient temperature compensation and the one bimetal strip 54 will remain unchanged. Since, however, the other bi-metal strip 54 is subject to the heat of the conducted current it will become heated and since its high expansion side faces the contact 58' this strip 54 will move away from this contact. At the instant it does so, contact 58 will disengage 58' and the current flow is then confined to the one path which includes the bi-metal latch 40. It will be appreciated that a mere fractional movement of contact 58 away from contact S8 will open the circuit at these contacts.

Now assume that the bi-metal strips are exposed to an ambient temperature above or below the given temperature at which `the bi-metal strips assume their neutral flat state, the strips 54 and 54' will bend together in the same direction and thereby maintain the contacts 58, 58' closed until the one bi-metal strip 54, due to it being heated to a higher temperature by the conducted current will move ahead of the other strip 54 and thereby produce relative movement between contacts 58, 58 and cause the circuit to be opened at these contacts. When this occurs the current flow will take place along the one path only, which includes the bi-metal latch part 40.

As above stated, the adjustment screw 60 may be situated, as shown in the full line position, to impose a restraint against movement of the bi-metal strips 54, 54 in the direction corresponding to ambient temperatures on the downgrade, including zero and sub-zero temperatures. This restraint causes the pressure at the contacts 58, 58 to be correspondingly increased, with the result that with current flowing, and the one strip 54 subjected to the heat thereof, there will be a time lag before the circuit will be opened at the contacts 58, 58', this time lag corresponding tothe increased contact pressure resulting from the presence of the restraining screw 60. The occurence of such time lag may be advantageous under conditions of zero and sub-zero ambient temperatures in the case where motors, actuators and other equiment with which the circuit breakers are connected have become frozen, or stiff, and require time in which to attain running speed.

It will be appreciated that, in practice, provision will be made whereby the conductors 50, and bi-metal structure 52 is accommodated within the circuit breaker casing. Y i

Having thus described my invention what I consider to be new and wish to cover by Letters Patent is as follows:

l. An electric circuit breaker having overload current protection including a bi-metal latch assembly operatively associated wth fixed and movable contacts, an electrical shunt connecting said contacts for conduction of current along two separate paths, only one of which includes said bi-metal latch, said shunt including bi-metal strips carrying separate contacts, one said strip being connected as a conductor in said shunt and the other strip being non-conductive and subject to actuation only by ambient temperature conditions, said bi-metal strips having their different expansion sides facing in the direction in which the circuit will be opened at said separate contacts due to increased heating of the conductive strip relatively to the non-conductive strip.

2. An electric circuit breaker as claimed in claim 1 including means for restraining the opening of the circuit at said separate contacts under conditions of low ambient temperature.

3. An electric circuit breaker having overload current protection, including iixed contact means and companion Contact means movable into and out of engagement with said xed contact means, latch means operatively and electrically connected with said movable contact means and actuatable upon the occurrence of a predetermined current overloadl to permit said movable contact means to move out of engagement with said fixed contact means,

. carrying engageable contact elements, one of said thermostat elements being disposed in the conductive path of said shunt means and the other of said thermostat elements being out of said conductive path and being subject to actuation only by ambient temperature conditions, whereby upon variations in ambient temperature said shuntcontact elements will remain in engagement with each other and whereby upon predetermined current overload said one thermostat element will be actuated so that said shunt contact elements will move out of engagement with each other.

4. An electric circuit breaker as claimed in claim 3 including means for restraining the disengagement of said shunt contact elements under conditions of low ambient temperature.

References Cited in the tile of this patent UNITED STATES PATENTS

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