GB1578637A - Line protection circuit breaker - Google Patents

Description

(54) LINE-PROTECTION CIRCUIT BREAKER (71) We, BROWN, BOVERI & CIE AKTIENGESELLSCHAFT, a German Company, of D 6800 Mannheim-KBfertal, Kalstadter Strasse 1, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a line-protection circuit breaker for interruption of electric currents exceeding a nominal or rated current range for a prolonged period of time (overload current trip) and for instantaneous interruption of the current flow upon the occurrence of a short-circuit current (short-circuit current trip), in which a first current path passes through a release magnet provided with a winding and in which a second current path connected in parallel with the first current path is formed by a temperature-dependent, currentsensitive element.

Line-protection circuit breakers of this and other types, for example miniature automatic circuit breakers and motorprotection circuit breakers have generally passed through numerous stages of development before reaching the precision and reliability necessary to meet modern requirements. The earlier stages of development had the object of increasing the accuracy and reliability of response, the object pursued at the present time being, inter alia, to reduce the dimensions of the appliances without forfeiting the desired properties and tolerances, to reduce the expenditure involved in the number of components, or to replace such components by less expensive ones, to dispense with cumbersome adjusting operations and, finally, to attain the desired aim by using materials or components which are cheaper and have a better storage stability. Attempts have also been made to impart to switching devices of this kind a greater energy reserve and thus to ensure a more reliable response and, upon the occurrence of a short-circuit to limit the flow of the short circuit current to a greater extent than hitherto and thus to improve the protection of the elements on the supply and load sides.

The solution of these development problems frequently requiring substantial inventive effort produces seemingly small yet useful progressive development results.

Considering, however, the number of parts involved in the manufacture of appliances of the aforementioned type, improvements which, at first glance, appear to be negligible, may often still have considerable economic significance.

The present invention is a case in point. It is based on the known results obtained in earlier stages of development, according to which, for example line-protection circuit breakers, are equiped with a directly or indirectly heated bimetallic element for controlling a series-connected isolating contact and with a release magnet, the winding of which is disposed in the same current path as the bimetallic element. The release magnet may also control the isolating contact through mechanical means independently of the bimetallic element. In this construction, the bimetallic element, which has a long response time has, upon the occurrence of a constant overload current, the function of interrupting the current flow with delay, the function of the release magnet being, however, to effect a practically instantaneous interruption of any occurring short-circuit current. Depending upon the voltages and magnitudes of current to be disconnected, it is advantageous, and may even be a necessity, to provide the isolating contacts with arc splitters in order to generate an arc voltage and thus to limit and quench the short-circuit current. The production and adjustment of the bimetallic element have a considerable share in the costs of a line-protection circuit breaker of this type. Moreover, the presence of a bimetallic element has the additional disadvantage that it may easily be affected by temporary or permanent increases in the ambient temperatures by which the response value may be undesirably affected.

Various attempts have been made to improve, to simplify, and to reduce the costs of, the aforementioned functional characteristics of line-protection circuit breakers of this type or similar types. Thus, for example, attempts have been made to obtain solutions which would permit the bimetallic element to be dispensed with. According to one such solution, which probably comes closest to the present invention, it is proposed to provide the inductive winding of a magnetic trip with a parallel-connected or series-connected resistor, the resistance value of which varies in dependence upon a monitored variable (German Offenlegungsschrift 1 563 837), the object being to produce a magnetic trip which in the overload current range operates in dependence upon the current time similarly to a thermal overcurrent trip and in the short-circuit current range operates exclusively as a function of the current like a current relay, that is to say both of the operating ranges are controlled by a single trip. It is proposed to use a semiconductor resistor the resistance value of which has a transient response at a determined temperature, that is to say, its positive temperature coefficient rises erratically within a determined temperature range.

The considerations on which this known proposal is based, are quite convincing and point in a direction which is theoretically practicable. However, semiconductor resistors available at an acceptable price level can be produced only for relatively high resistance values which generally can be subjected to only small current loads and, moreover, are subject to relatively substantial manufacturing tolerances. For the purpose referred to they are thus unsuitable for parallel connection with release magnets of the type referred to having a resistance value of the order of from about 1 to 5000 milliohm. Whether such a line-protection circuit breaker carries low currents or higher currents close to the limit of the rated current range is of no consequence. It will always be by far the greater partial current which will be connected through the winding of the release magnet, and the desired current-time dependence, if attained at all, is highly unreliable. As indicated above, there is the additional disadvantage that semiconductor resistors can be subjected to relatively low loads only and are thus incapable of producing reliable results in line-protection circuit breakers required to have an adequate short-circuit rupturing capacity.

It is an object of the invention to provide a line-protection circuit breaker of the type hereinbefore described which, at least in preferred embodiments of the invention, shall be suitable for series and mass production, in which a costly bimetallic element generally requiring adjusting operations to be carried out can be dispensed with and in which, following the considerations expressed in the above-mentioned German Offenlegungsschrift 1 563 837, the interruption of the current flow upon the occurrence of a slightly prolonged overload current as well as upon the occurrence of a short-circuit current can be controlled within the respectively required tolerance range by a release magnet of substantially conventional quality and dimensions.

In accordance with the invention, there is provided a line-protection circuit breaker for interrupting an electric current on overloads and for interrupting the electric current on short circuits, the circuit breaker comprising a release magnet having an armature and a winding, and a jumper wire, the jumper wire being formed of an ironnickel alloy, the resistance of the alloy increasing with its temperature, the circuit breaker providing a first current path passing through the winding and a second current path passing through the jumper wire, the first and second current paths being connected in parallel and the conductivity of the second current path being not less than the conductivity of the first current path when the circuit breaker is carrying a current within its rated current range. Ironnickel wires can be manufactured to diametral tolerances which show only minute deviations, they can be produced simply of precisely the exact length, their electrical resistance value thus differs only very slightly from a determined desired value and they can be connected by simple means in parallel with the winding. There is an additional advantage that nickel-iron wires can be so dimensioned as to ensure that, contrary to, for example bimetallic elements, their resistance value is affected only slightly by the ambient temperatures and the specific quality of their temperature characteristic, namely a steady, in some ranges almost linear, rising of the resistance value favourably assists the attainment of the desired functional results. It is an additional important advantage that the commutation of the current from the jumper wire to the winding upon the occurrence of a short circuit enables the release magnet to supply a higher energy of impact.

Preferably within the rated current range, the conductivity of the second current path is a multiple of the conductivity of the first current path. It is thus also possible to use a single release magnet with always the same inductive winding for several rated-current ranges. Thus, for example, where an inductive winding is designed for a continuous 1-ampere current, the winding may be used for a line-protection circuit breaker having a rated range of, for example 2-amperes (one 1-ampere current flows through the winding and another 1-ampere current flows through the jumper wire) as well as for a ratedcurrent range of, for example, 16-amperes, the jumper wire being then so dimensioned that, within the rated-current range, up to 1-ampere flows through the inductive winding and up to 15-amperes flow simultaneously through the iron-nickel wire.

The jumper wire is preferably made of an alloy comprising 25 to 35% by weight iron and 65 to 75% by weight nickel, e.g. about 30% iron and 70% nickel.

The jumper wire preferably has a positive temperature coefficient of resistance of 0.3 to 0.8% per "C.

In all protection circuit breakers, the response range and the reliability of response always require testing during the manufacturing process. The tests should advantageously be carried out prior to final assembly.

In accordance with the invention, preferably the ends of the iron-nickel jumper wire are therefore advantageously connected directly to the ends of the winding of the release magnet or to the connections in which the ends of the winding are received.

This affords the desired possibility of testing a pre-assembled sub-assembly comprising the winding and the iron-nickel jumper wire.

The invention is further described below by way of example with reference to the accompanying drawings, in which: Figure 1 shows a view of a line-protection circuit breaker according to the invention, the housing of the circuit breaker being shown in section; Figure 2 shows a simplified functional diagram of a line-protection circuit breaker according to the invention, the circuit breaker being shown in the condition in which current flows through it; and Figure 3 is similar to Figure 2 but shows the circuit breaker in the condition in which no current flows through it.

The line-protection circuit breaker shown in Figure 1 comprises a housing 1 (cut open) from which two terminals 2 and 3 and associated terminal screws 4 and 5 project.

An operating handle 6 pivotally movable between an "on" position and an "off" position projects from an upright front wall of the housing. The operating handle 6 is shown by full lines in its "off" position and by broken lines 6' in its "on" position. The housing 1 accommodates a principal electrical functional sub-assembly comprising an inductive winding 7 into which extends a plunger 8 held by a magnetic yoke 9. The plunger 8 and the magnetic yoke 9 constitute an armature. At its left end (as viewed in Figure 1), the plunger 8 is provided with a pin 10 which acts upon a tripping lever 11 when the plunger 8 is pulled into the inductive winding 7 as a result of a corresponding flow of current through the winding. The other end of the plunger 8 (the right end as viewed in Figure 1) is provided with a pin 12 which extends through a contact lever 13 and, at its end remote from the plunger 8, is secured to a flat head 14.

The housing further accommodates a substantial number of mechanically interacting parts, only some of which are shown in Figure 1. These parts are provided between the tripping lever 11 and the contact lever 13. The nature and operation of these parts will be apparent to the man skilled in the art and form no part of the subject matter of the present invention.

An iron-nickel jumper wire 15 is connected in parallel with the inductive winding 7.

The line-protection circuit breaker operates as described below.

The line-protection circuit breaker is connected to a phase of an electrical system by means of the terminals 2 and 3 and the terminal screws 4 and 5. The operating handle 6 is moved to its "on" position 6' shown in broken lines and is caused to engage by the aforementioned mechanically interacting parts enabling current to flow to a load system. When the operating lever 6 is moved to the "on" position 6' the contact lever 13 is moved to the position 13' indicated by broken lines. The current then flows from the terminal 3 through the contact lever 13 to a junctio (not shown in Figure 1) at which one end of the winding 7 and one end of the jumper wire 15 are conductively interconnected. This junction may be a direct electrical interconnection between the jumper wire 15 and the winding 7, or it may be an indirect electrical connection between the jumper wire and the winding formed by connecting means, such as soldering tags or clamps. From this junction, the current flow divides into two partial currents one of which flows through the winding 7 and the other of which flows through the jumper wire 15. The two partial currents re-unite at a junction at which the other end of the jumper wire 15 and the other end of the inductive winding 7 are directly or indirectly interconnected. The total current then flows to the load system (not shown in Figure 1).

Within a rated current range of the circuit breaker, the partial current flowing through the jumper wire 15 is equal to or greater than the partial current flowing through the winding 7.

It is known that iron-nickel wires have the property of changing their electrical resistance when their temperature changes the resistance increasing steadily with increasing temperature. At an amperage within the rated-current range of the line-protection circuit breaker, the temperature of the jumper wire 15 rises only slightly and its resistance also changes only slightly in consequence. This changes at a current load corresponding approximately to the response value of the appliance, since then the partial current flowing through the winding 7 begins to increase measurably, that is to say to an extent exceeding the partial current flowing through the jumper wire 15.

After a slightly prolonged period of constant overload current, the temperature of the jumper wire 15 has increased further with a correspondingly increased resistance value so that a correspondingly increased portion of the current is transferred to the winding 7 with the result that the release magnet responds after a restraint (not shown in Figure 1) of the plunger 8 has been overcome. The plunger 8 is pulled into the interior of the winding 7, the pin 10 acts upon the tripping lever 11, a release gear (not shown) is released and the contact lever 13 is moved from its 13' shown by broken lines to its position shown by full lines. This movement of the contact lever 13 is assisted and accelerated in that the head 14 of the pin 12 acts additionally upon the contact lever 13 thus pulling it off a contact surface between the contact lever 13 and the terminal 3. Fusing or welding of the point of contact is thereby reliably prevented and a high initial speed is imparted to the contact lever 13. The winding 7 may comprise a larger number of turns than can generally be provided in comparable appliances of this type. Thus the above-described process of breaking the circuit can thus be particularly effectively ensured. The housing 1 further accommodates a set or subassembly of arc splitters 16 for improved control of the arc generated during the switching or circuitbreaking process above-described and problems arising therefrom. It is known that such an arc-splitter subassembly is generally used for splitting the arc referred to, for distribution and removal of the heat generated and for effective limitation of the short-circuit current by the arc voltage thus generated.

Upon the occurrence of a short circuit, the resistance of the jumper wire 15 changes substantially instantaneously, that is to say, it is heated to a high temperature within one or two milliseconds with the result that a current surge acts upon the inductive winding 7. As a result, the lever system described above is released in a manner similar to that hereinbefore described and, in addition, the contact lever 13 is pulled off the point of contact with the terminal 13 by application of a substantially greater force so that, upon the occurrence of a short circuit, the increased risk of fusing or welding of the point of contact is avoided with adequate reliability.

The line-protection circuit breaker shown diagrammatically in Figure 2 is similar to that shown in Figure 1.

Referring to Figure 2, junction points 17 and 18 are connected to open ends of a phase of an electric current. A line 19 extends to a conductive bearing block or bracket 22 in which is pivotally held a contact arm 21 adjacent a contact 23. From the contact 23 a line 24 extends to a winding 25 which is connected to a line 26 extending to the junction point 17. An iron-nickel jumper wire 27 is connected in parallel with the winding 25 and directly electrically conductively interconnects the lines 24 and 26. A plunger 28, to the end of which a lever 29 is pivoted, extends into the winding 25.

The lever 29 is held in a fixed bearing 30 and is pivotally connected to a latch 31. At its end remote from the bearing 30 the lever 29 is provided with a plate made of a magnetizable material acted on by a permanent magnet 33 to hold the lever bar or linkage in the illustrated position. The device is shown in the position in which the contact arm 21 is held in the illustrated position of contact by the latch 31 against the resistance of a spring 34. In this position, the current flow corresponds substantially to the current flow in the line protection circuit breaker shown in Figure 1. The current fed to the lineprotection circuit breaker through the junction point 18 flows through line 19 to the conductive bearing block or bracket 22, through contact arm switch 21 to contact 23 and to the line 23 connected thereto. The current is then divided into two branches, one branch flowing through the winding 25, the other branch flowing through the ironnickel jumper wire 27. So long as the total current is within the rated range of the line-protection circuit breaker, the portion of the current flowing through the jumper wire 27 is at least equal to that flowing through the winding 25. The two partial currents are reunited in the line 26 extending to junction point 17 which is connected to a distribution network not shown in Figure 2.

The disconnecting or interrupting function of this line-protection circuit breaker is ensured as described below.

As the current increases in intensity, the portion of current flowing through the winding 25 increases without, however, changing the position of the plunger 28, since the lever 29 is initially restrained by the permanent magnet 32. When the rated current is slightly exceeded, the portion of current flowing through the winding 25 increases due to the rated current being exceeded and due to the rising temperature causing the resistance value of the jumper wire 27 to increase, the partial current flowing through the jumper wire 27 being increased less than the partial current flowing through the winding 25. With slightly prolonged overcurrent, the permanent magnet 13 is unable to continue to restrain the lever 29 which is thus pulled off the permanent magnet 33 with the result that the plunger 28 rapidly moves into the interior of the winding 25 thus entraining the lever 29 and the latch 31 secured thereto. The contact arm 21, thus deprived of support, is caused by the spring 34 to snap to an inclined position with the result that the flow of the current is interrupted.

Figure 3 shows the positions of the mechanical switching members relative to each other at the moment of disconnection.

Upon occurrence of a short circuit, the contact separation proceeds in a similar manner to that upon the occurrence of an overload current except that the plunger 28 responds within an extremely short time interval which is shortened particularly as a result of the fact that the resistance of the iron-nickel jumper wire 27 increases almost instantaneously and the portion of current flowing through the winding 25, simultaneously increases almost instantaneously.

The plunger 28 is thus pulled from its restrained position without any delay whatsoever and, moreover, with a force exceeding the force applied upon disconnection due to an overcurrent. In the circuit breaker of Figures 2 and 3, the increased force does not affect the force applied to pull the contact arm 21 off the contact 23. This is, however, the case in the circuit breaker of Figure 1. It may be added in this connection that the actual lever and transmission ratios in modern line-protection circuit breakers are considerably more complicated than is indicated in the diagram shown in Figures 2 and 3. However, the subject matter of the invention is not concerned with these mechanical functional constructions and thus there is no need to provide a realistic diagrammatic illustration of these functional constructions in this specification.

It will be appreciated from the foregoing description that simple, efficient and costsaving circuit breakers can be practically constructed in accordance with the invention and the advantages of such circuit breakers will be apparent from the foregoing description.

WHAT WE CLAIM IS: 1. A line-protection circuit breaker for interrupting an electric current on overloads and for interrupting the electric current on short circuits, the circuit breaker comprising a release magnet having an armature and a winding, and a jumper wire, the jumper wire being formed of an iron-nickel alloy, the resistance of the alloy increasing with its temperature, the circuit breaker providing a first current path passing through the winding and a second current path passing through the jumper wire, the first and second current paths being connected in parallel and the conductivity of the second current path being not less than the conductivity of the first current path when the circuit breaker is carrying a current within its rated current range.

2. A circuit breaker according to claim 1, wherein, within the rated current range, the conductivity of the second current path is a multiple of the conductivity of the first current path.

3. A circuit breaker according to either preceding claim, wherein the jumper wire is made of an alloy comprising 25 - 35% by weight iron and 65 - 75% by weight nickel.

4. A circuit breaker according to any preceding claim, wherein the jumper wire has a positive temperature coefficient of resistance of 0.3 to 0.8% per "C.

5. A circuit breaker according to any preceding claim, wherein the ends of the jumper wire are connected directly to the first current path.

6. A circuit breaker according to any preceding claim, wherein the jumper wire is provided with heat insulation.

7. A circuit breaker according to any preceding claim, further comprising a pair of contacts connected in series with the first and second current paths, the contact being arranged to open upon relative movement of the armature and the winding caused by an increase in current flowing through the winding.

8. A line-protection circuit breaker substantially as described herein with reference to and as illustrated in Figure 1 or Figures 2 and 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. changing the position of the plunger 28, since the lever 29 is initially restrained by the permanent magnet 32. When the rated current is slightly exceeded, the portion of current flowing through the winding 25 increases due to the rated current being exceeded and due to the rising temperature causing the resistance value of the jumper wire 27 to increase, the partial current flowing through the jumper wire 27 being increased less than the partial current flowing through the winding 25. With slightly prolonged overcurrent, the permanent magnet 13 is unable to continue to restrain the lever 29 which is thus pulled off the permanent magnet 33 with the result that the plunger 28 rapidly moves into the interior of the winding 25 thus entraining the lever 29 and the latch 31 secured thereto. The contact arm 21, thus deprived of support, is caused by the spring 34 to snap to an inclined position with the result that the flow of the current is interrupted. Figure 3 shows the positions of the mechanical switching members relative to each other at the moment of disconnection. Upon occurrence of a short circuit, the contact separation proceeds in a similar manner to that upon the occurrence of an overload current except that the plunger 28 responds within an extremely short time interval which is shortened particularly as a result of the fact that the resistance of the iron-nickel jumper wire 27 increases almost instantaneously and the portion of current flowing through the winding 25, simultaneously increases almost instantaneously. The plunger 28 is thus pulled from its restrained position without any delay whatsoever and, moreover, with a force exceeding the force applied upon disconnection due to an overcurrent. In the circuit breaker of Figures 2 and 3, the increased force does not affect the force applied to pull the contact arm 21 off the contact 23. This is, however, the case in the circuit breaker of Figure 1. It may be added in this connection that the actual lever and transmission ratios in modern line-protection circuit breakers are considerably more complicated than is indicated in the diagram shown in Figures 2 and 3. However, the subject matter of the invention is not concerned with these mechanical functional constructions and thus there is no need to provide a realistic diagrammatic illustration of these functional constructions in this specification. It will be appreciated from the foregoing description that simple, efficient and costsaving circuit breakers can be practically constructed in accordance with the invention and the advantages of such circuit breakers will be apparent from the foregoing description. WHAT WE CLAIM IS:

1. A line-protection circuit breaker for interrupting an electric current on overloads and for interrupting the electric current on short circuits, the circuit breaker comprising a release magnet having an armature and a winding, and a jumper wire, the jumper wire being formed of an iron-nickel alloy, the resistance of the alloy increasing with its temperature, the circuit breaker providing a first current path passing through the winding and a second current path passing through the jumper wire, the first and second current paths being connected in parallel and the conductivity of the second current path being not less than the conductivity of the first current path when the circuit breaker is carrying a current within its rated current range.

2. A circuit breaker according to claim 1, wherein, within the rated current range, the conductivity of the second current path is a multiple of the conductivity of the first current path.

3. A circuit breaker according to either preceding claim, wherein the jumper wire is made of an alloy comprising 25 - 35% by weight iron and 65 - 75% by weight nickel.

4. A circuit breaker according to any preceding claim, wherein the jumper wire has a positive temperature coefficient of resistance of 0.3 to 0.8% per "C.

5. A circuit breaker according to any preceding claim, wherein the ends of the jumper wire are connected directly to the first current path.

6. A circuit breaker according to any preceding claim, wherein the jumper wire is provided with heat insulation.

7. A circuit breaker according to any preceding claim, further comprising a pair of contacts connected in series with the first and second current paths, the contact being arranged to open upon relative movement of the armature and the winding caused by an increase in current flowing through the winding.

8. A line-protection circuit breaker substantially as described herein with reference to and as illustrated in Figure 1 or Figures 2 and 3 of the accompanying drawings.