GB1570138A

GB1570138A - Tripping device with thermal deleay

Info

Publication number: GB1570138A
Application number: GB53036/77A
Authority: GB
Original assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Priority date: 1976-12-22
Filing date: 1977-12-20
Publication date: 1980-06-25
Also published as: AR214656A1; ZA777220B; FR2375712A1; IT1088788B; CH604365A5; EG12966A; JPS5379244A; DE2700989A1; ES464472A1; BR7708475A

Description

(54) TRIPPING DEVICE WITH THERMAL DELAY (71) We, BBC BROWN, BOVERI & COMPANY LIMITED, a Swiss Company of CH-5401, Baden, Switzerland, 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 tripping device with thermal delay for a circuit-breaker for mains and/or motor protection, particularly in low-voltage mains, including a magnetic trip coil.

Tripping devices with thermal delay, which serve to control protective circuitbreakers in electric power supplies, are known in numerous variants. As a rule, the circuit-breaker tripping device is required to imitate, thermally the heating characteristic of the apparatus or motor to be protected. After reaching a certain heating (limiting temperature), the device acts on a mechanism, either mechanical or electro-magnetic, in a direct (switch) or in an indirect (relay) manner, as a result of which the circuit is interrupted. In addition, a direct device, generally acting electromagnetically, is provided to switch off high excess currents (short-circuit) without delay. In practice, various trip characteristics are required for the circuitbreaker, depending on the application. In general, the permissible excess current of an electric load and of the associated power supply depends on time.

According to the present prior art, an attempt is made to imitate such excesscurrent/time characteristics with bimetallic strips. Such devices are known from numerous publications (for example, F. W.

Kussy: "Elektrische Niderspannungsgerate und Antriebe", Berlin 1969, pages 879894; furthermore Theodor Schmelcher: "Ueberstromschutz Niderspannungsanlagen", Siemens AG, 1974, pages 45-77).

In order to produce a complete excess current characteristic in a circuit-breaker in a conventional manner, two tripping mechanisms are necessary, which generally have to be made independent of one another and with considerable expense: first a thermal trip, generally on the basis of bimetals, secondly an electromagnetic trip, mechanically or electrically delayed, for the higher excess-current range (short-circuit).

Thermally delayed tripping devices on the basis of hot-wire, fusible-solder and today primarily bimetallic elements necessitate additional precision trip mechanisms which suffer from their own inertia. At the same time, a precise adjustment of the bimetallic strip is difficult and allowance must always be made for considerable diversity. For a high selectivity with the dependent co operation of various circuit-breakers, expensive cascade connections of a plurality of trip mechanisms (bimetallic strips with different characteristics) are often necessary. The thermal delay by means of bimetallic members is only possible down approximately into the seconds range, which corresponds to about 10 times the rated current. If a delay is to be effected in the range of shorter times or higher excess currents, additional expensive mechanical or electrical means are necessary (see the document cited above by Theodor Schmelcher, pages 70--72, Figures 55, 56, 57 and 58; Figure 62b on page 76). Beyond about 15 times the rated current, a shortcircuit protection serving to protect the bimetallic strip itself from destruction is additionally necessary, quite apart from whether and how the load or part of the power supply associated with the circuitbreaker is or is not to be protected from high excess currents (see the document cited above by Theodor Schmelcher, page 62). An alteration in the trip characteristic of a circuit-breaker generally makes the alteration of nearly all the leading components necessary, particularly the bimetallic strips acting thermally. As a result, a large number of forms of embodiment are necessary for various strengths of current and characteristics.

This invention provides a tripping device with thermal delay for a circuit-breaker for the protection of a power supply and/or a motor, said tripping device comprising an electrical circuit having parallel first and second electrical paths, either with a pair of control resistors arranged in series in each said path and a magnetic trip coil connected between the junctions of the respective pairs of resistors to form a bridge with one of these four control resistors being dependent on temperature, or with a first magnetic trip coil included in one of said paths having a common magnetic circuit with a second magnetic trip coil included in said electrical circuit and with said first magnetic trip coil having an electrical resistance dependent on temperature or with a temperature dependent control resistor being included in a said path, the electrical circuit being arranged for heating of the temperature dependent control resistor or coil with temperature dependent resistance, due solely to electrical current passing through that control resistor or coil, to cause electrical current through the circuit to be commutated, wholly or in part, from the first path to the second whereby to operate an armature of the trip coil or trip coils to break the electrical circuit. Embodiments of the invention to be described herein realize thermal trip characteristics for electric circuit-breakers which is capable of imitating all the states which occur in practical operation in the whole excess-current range up to a shortcircuit, with the simplest possible construction and without the aid of complicated mechanisms. Furthermore, these tripping devices cover a large number of characteristics and current ranges while retaining the same control element as far as possible, so that the number of types can be kept small for a given field of application.

Finally, the devices are distinguished by high accuracy, satisfactory selectivity in relation to adjacent tripping devices and by high reproducibility.

The main principle on which the invention is based consists in providing systems wherein the excess current is commutated automatically more or less quickly and to a greater or lesser extent to the coil circuit to be tripped by the disequilibrium produced by itself, as a result of a suitable combination of temperaturedependent and ohmic resistors with one or two magnetic trip coils. Fundamentally, this can be effected by bridge circuits with four control resistors or by circuits with two parallel trip coils with a common magnetic circuit, the magnetic fluxes of which are added or subtracted or cancelled out with the operating current. In general, it will be seen that, in each embodiment to be described herein, a strike armature of the trip coil is operated to break the circuit in response to current being commutated, wholly or in part, from one path to another in response to a resistance change of the temperature dependent control resistor.

Further details of the invention are apparent from the following circuit diagrams and examples of embodiment explained in more detail below with reference to Figures.

Figure 1 shows a bridge circuit with a PTC resistor; Figure 2 shows a bridge circuit with an NTC resistor; Figure 3 shows a bridge circuit with two PTC resistors offset diagonally; Figure 4 shows a bridge circuit with two NTC resistors offset diagonally; Figure 5 shows a bridge circuit with one PTC resistor in one path and one NTC resistor in the other path; Figure 6 shows a bridge circuit with one PTC resistor and an NTC resistor in series therewith, in the same path; Figure 7 shows a bridge circuit with a PTC resistor and an NTC resistor in series therewith in one path and an NTC resistor in the other path; Figure 8 shows a bridge circuit with an NTC resistor and a PTC resistor in series therewith in one path and a PTC resistor in the other path; Figure 9 shows a bridge circuit with two PTC resistors and two NTC resistors; Figure 10 shows a circuit with a lowresistance trip coil and a PTC resistor in one path and a high-resistance trip coil acting in the same sense in the other path; Figure 11 shows a circuit with a lowresistance trip coil and a PTc resistor in one path and a high-resistance trip coil acting in the same sense and a PTC resistor in the other path; Figure 12 shows a circuit with a PTC resistor in one path, a high-resistance trip coil in the other path and a low-resistance trip coil acting in the same sense in the whole circuit; Figure 13 shows a circuit with two parallel trip coils acting in opposite senses and a PTC resistor; Figure 14 shows a circuit with two parallel trip coils acting in opposite senses and an NTC resistor Figure 15 shows a circuit with two parallel trip coils acting in opposite senses and two PTC resistors; Figure 16 shows a circuit with two parallel trip coils acting in opposite senses, two PTC resistors and an ohmic protective resistor; Figure 17 shows a circuit with a highresistance trip coil and a PTC resistor in one path and a low-resistance trip coil acting in the opposite sense in the other path; Figure 18 shows a circuit with a highresistance trip coil and an NTC resistor in one path and a low-resistance trip coil acting in the opposite sense in the other path; Figure 19 shows a circuit with a lowresistance trip coil and a PTC resistor in one path and a high-resistance trip coil acting in the opposite sense in the other path: Figure 20 shows a diagram with trip characteristics for a circuit as shown in Figure 16; Figure 21 shows a diagrammatic section through one form of embodiment of the tripping device in a circuit-breaker: Figure 1 shows a bridge circuit with two parallel current paths each of two seriesconnected resistors, the magnetic trip coil 1 of the protective circuit-breaker (see also coil 25/26 of the basic sketch, Figure 21) forming the bridge. 2 is a temperaturedependent PTC resistor which is in series with the ohmic resistor 4 and forms the first current path. The second path is formed by the ohmic resistors 3 and 5 connected in series. Under normal operating conditions (rated current) the bridge is balanced as regards voltage and no current flows in the trip coil 1 forming the diagonal. On excess current, the PTC element 2 becomes heated and, beyond a certain temperature, its resistance increases by several orders of magnitude. This rise takes place the more quickly, the higher the excess current is.

Thus there is a precisely definable resistance/time or current/time function. As a result of the resistance rise of 2, the bridge is brought out of equilibrium and a current now flows across the trip coil 1 which causes the circuit-breaker to respond. In the extreme case-on the assumption that the resistance of the PTC resistor 2 is theoretically "infinite" and the resistance of the coil 1 is ignored-the whole current of the first path is commutated to the coil 1. By suitable selection of the values for the resistors 2, 3, 4 and 5 and the coil resistance of 1, practically all the trip characteristics required in operation can be realized.

In this embodiment, a CLDT element (current limiter dependent on temperature) in accordance with the applicant's laid-open German patent application 25 10 322 was used as a temperature- dependent PTC resistor 2 and had the following characteristics: Shape: cylindrical Cross-sectional area: 0.275 cm2 Length in direction of current 1.22 cm Weight: 1.6 g Resistance at 25 C: 6 mQ Resistance at 160"C: min.60 mQ Wsec Thermal capacity: 1.3 Degree This element was installed in the circuitbreaker in such a manner that it had a heat dissipation of 6.6 m W/degree. The trip coil 1 had the following data: Resistance at 250C: 3 mQ Trip current: 3.9 A By appropriate selection and correlation of the resistors 3, 4 and 5, the trip characteristics "H", "L" etc. standardized by VDE 0641 and CEE publication 19 can be achieved (see also Figure 17). The characterisitc V, corresponds to a thermally delayed tripping over the whole excess current range as far as complete short-circuit current. In the case of this example of embodiment, the values of the ohmic resistors 3, 4 and 5 associated with the various characteristics were as follows: Resistor 3 4 5 H-characteristic 8.4 9.2 33 mQ L-characteristic 8.9 10.0 25 mQ G-characteristic 39.6 10.9 130 mQ K-characteristic 77.9 11.0 345 mQ V,-characteristic 79.5 11.5 152 mQ Figure 2: This bridge circuit corresponds to that of Figure 1 with the difference that the PTC resistor 2 is replaced by the NTC resistor 6.

On an excess current, the resistance of the latter is reduced considerably as a result of which the bridge comes out of equilibrium and the trip coil conducts a corresponding current which causes the device to respond.

The effect-on the assumption that theoretically the resistance value of 6 disappears-is the same as in the circuit of Figure 1. Preference would be given to the circuit of Figure 1 or Figure 2 according to practical requirements, and materials already present such as coils, resistors etc.

Figure 3: By extending the circuit of Figure 1 by another PTC resistor 7 in the second path offset seen in the direction of current, the circuit of Figure 3 results. Here the effects of 2 and 7 reinforce one another in the event of excess current in such a manner that now the coil 1 alone conducts practically the whole current. This circuit is therefore distinguished by increased response sensitivity in comparison with the previous ones. It may be used to advantage where a single PTC resistor is not sufficient or trip coils which are already available but which do not in themselves have sufficient sensitivity for the circuit of Figure 1 are to be used.

Figure 4: Here what was said under Figure 3 applies. The PTC resistors 2 and 7 are replaced by NTC resistors 6 and 8. The whole excess current flows practically only via 6, 8 and trip coil 1. The remarks under Figure 2 apply similarly here.

Figure 5: This Figure represents a bridge circuit with a PTC resistor 2 in the first path and an NTC resistor 6 in the second path, which reinforce one another in the manner stated under Figure 3 in the event of an excess current. The latter flows practically only via 4, 1 and 6.

Figure 6: This circuit is a modification of Figure 5, wherein the NTC resistor 6 has been transferred to the diagonally opposite point in the developing excess-current path and is provided with the reference numeral 8. The effect remains the same as under Figure 5.

Figure 7: This circuit results from extending Figure 5 or Figure 6 by another temperaturedependent resistor. The NTC resistor 6 introduced additionally in comparison with Figure 6 increases the sensitivity of the trip coil 1 by a further amount.

Figure 8: This Figure shows another circuit possibility with 3 ' temperature-dependent resistors, the NTC resistor 6 and the PTC resistor 7 being in the first path and the PTC resistor 2 and the ohmic resistor 5 being in the second path. The excess current is forced onto the line 5, 1, 6. Circuits as shown in Figure 7 and Figure 8 have an increased excess-current sensitivity in comparison with the preceding circuits Figure 9: In the complete construction, the tripping device on a bridge-circuit basis is equipped with a total of four temperature-dependent resistors, including 2 PTC resistors 2 and 7 and 2 NTC resistors 6 and 8. The arrangement is completely symmetrical and is superior to all the preceding ones in sensitivity. Under certain practical conditions, such as very high requirements regarding the selectivity of a train of circuit breakers, the increased technological expense of this circuit would be justified.

Figure 10: Figure 10 shows a circuit with two parallel current paths, the first path being formed by a low-resistance trip coil 9 and a PTC resistor 12 connected in series therewith, but the second being formed by a highresistance trip coil 10 and an ohmic resistor 13. Together with the strike armature of the circuit-breaker, the coils 9 and 10 form a common magnetic circuit 11, the direction of winding being such that the coil fluxes are added. This is indicated by arrows below the coil symbols parallel to their longitudinal direction in the Figure. The arrows therefore represent the direction of the magnetic flux not the direction of the current. The components in the lowresistance path and those in the highresistance path are so dimensioned that the resulting flux of the coils 9 and 10 is not sufficient to cause the strike armature to respond at the rated current. The PTC resistor 12, which is constructed in the form of a current-limiting element dependent on temperature (CLDT element) is so designed that it is just below the temperature threshold of the effective resistance range at the rated current. With small excess currents, the CLDT element 12 is heated and its resistance increases abruptly and the greater part of the current is transferred to the high-resistance path 10, 13. As a result of the greatly increased flux in the coil 10, the strike armature responds. In the event of high excess currents (short-circuit), the element 12 has no time to heat up and the circuit-breaker responds immediately, without delay, as a result of the abrupt increase in the flux in the circuit 11. Below a limit once laid down for the short-circuit case for the electromagnetic rapid tripping, all the characteristics for lower excess currents can be realized in a simple manner.

This circuit has the advantage that the transfer from rapid tripping to thermally delayed tripping is displaced simply by altering the number of turns in the trip coil 9 and so various tripping characteristics can be achieved without the additional adaption of further components. While retaining the PTC resistor 12 and its heat dissipation conditions, the current path 10, 13 can be designed with as high a resistance as possible, as a result of which an effective current limitation is achieved during the process of switching off the circuit-breaker.

After response (spontaneous increase in resistance) of the PTC resistor 12, every excess current is limited in its rise in time and its height, so that the arc-quenching device of the circuit-breaker is reinforced appreciably in its effect. In order to protect the element 12 from excess temperature, the dimensioning of the leading components must be precisely adapted to the arcquenching device.

In the present example a circuit-breaker of 16A rated current was equipped with a CLDT element 12 having the following characteristics: Shape: cylindrical Cross-sectional area: 0.44 cm2 Length in direction of current: 1.95 cm Weight: 4.08 g Resistance at 250C: 6 mQ Resistance at 1200C: min. 600 mQ Wsec Thermal capacity: 3.39 degree The element was installed in the circuitbreaker in such a manner that it had a heat dissipation of 19 mW/degree.

The resistance of the low-resistance coil 9 was 2.6 mu. The high-resistance current path 10, 13 had a coil 10 with eight turns and a total resistance of 300 mQ. The strike armature was adjusted in such a manner that tripping was effected with a total magnetic flux of 150 AT.

The switching characteristic was adjusted as follows: Low-resistance trip coil 9: number of turns H-characteristic: 3.5 L-characteristic: 2 In addition, however, the CLDT element 12 also has a current-limiting action with heavy short-circuit currents, when, after the electromagnetic tripping, the arc-current causes a response of the element and so a current commutation is effected to the highresistance current path 10, 13.

Figure 11: This circuit only differs from the preceding one in that the ohmic resistor 13 in the high-resistance path is replaced by another PTC resistor 14. The latter may be any PTC resistor or preferably a CLDT element. It is a condition that, by dimensioning of all the leading components, care is taken to ensure that, in the event of excess current, the PTC resistor 12 in the low-resistance path responds before that in the high-resistance path. The two elements 12 and 14 must therefore differ in their characteristics. This can be brought about in various ways. The difference may consist in the absolute value of their resistance, in their thermal capacity, in their temperature/resistance characteristic or their response Joule integral which represents a measure for the energy converted into heat during the heating-up phase until response. Several of these characteristics may differ simultaneously in the two elements. The element 14 reinforces the current limitation so to speak "with a time lag" during the disconnection and quenching process.

Figure 12: In this circuit, a low-resistance coil 9 is connected in series with two current paths connected in parallel. The first current path is formed by a PTC resistor 12 (preferably a CLDT element), the second is formed by a high-resistance trip coil 10 and an ohmic resistor 13. Here the whole operating current always flows through the coil 9, as a result of which its contribution to the total magnetic flux is correspondingly greater.

Apart from this, the behaviour of the circuit is similar to that of Figure 10, and the dimensioning is also effected in accordance with similar criteria. The adjustment of the tripping characteristic is here effected by adaption of the number of turns of the coil 9. In this circuit, too, the ohmic resistor 13 can naturally be replaced by a PTC element 14 as in Figure 11.

Figure 13: The tripping device is formed by two parallel current paths, each path having a trip coil 15 or 16, which, together with the strike armature, form a common magnetic circuit 11. The trip coils 15, 16 are so wound or current flows through them in such a manner that their fluxes are substracted one from the other. Thus the oppositely directed arrows shown below the coils in the Figures symbolize the direction of the magnetic flux not the direction of current. Under normal operating conditions (rated current) the fluxes of the two coils cancel one another out partially or completely so that, in the latter case, no magnetomotive force acts on the strike armature. By anology with Figure 1, this corresponds substantially to the balanced bridge. The PTC resistor 17 is in the first current path while an ordinary ohmic resistor 18 is provided in the second path. The excess current causes a rapid increase in the resistance of 17, is automatically commutated to 16, 18 and produces a powerful resulting flux in the circuit 11, which forces the strike armature to respond. Various characteristics are achieved, inter alia, by the fact that with rated current the flux of the coil 9 only partially cancels out that of the coil 10.

Figure 14: In this circuit, as in Figure 2, an NTC resistor 19 is used to produce a magnetic unbalance in the circuit 11 in the event of excess current. As a result of the decrease in resistance of 19, the greater part of the excess current is commutated to the trip coil 15, as a result of which the strike armature of the circuit-breaker responds. The effect is identical to that of Figure 13 and additional dimensioning possibilities, differing from the latter, result for resistor 18 and trip coils 15 and 16. What was said under Figure 13 applies with regard to the adjustment of the characteristics.

Figure 15: Figure 15 shows a circuit with two parallel current paths, each being formed by a trip coil 15 or 16 and a PTC resistor 17 or 20 connected in series therewith. At the rated current, the magnetic fluxes of the coils 15 and 16 cancel one another out partially or wholly so that little or no effect is exerted on the strike armature belonging to the common magnetic circuit. The two paths of this circuit can be made completely symmetrical electrically, in that even the PTC resistors 17 and 20 have the same characteristics, that is to say have the same resistance range for the same increase in temperature. CLDT elements (see above page 8) are preferable for the PTC resistors 17 and 20, and alter their resistance spontaneously by phase transition at a specific temperature. This change in resistance must take place in a very short interval in relation to the total trip time of the circuit-breaker. The PTC elements 17 and 20 only differ from one another by a small amount in their response Joule integral:

This integral is determined by the time/temperature function of the CLDT element which in turn depends on the course of the current. The excess current starts at the moment t=0 and heats the element up to the moment t=T. Then T is the duration of the excess current which is necessary for the abrupt increase in the resistance of the CLDT element. The duration T depends both on the thermal capacity (thermal time constant) and on the cooling conditions (heat dissipation) of the element. The response Joule integral, which represents the amount of energy totally converted into heat during the heating-up phase of the element to the limiting temperature of the change in resistance effected, can therefore be different for two elements with the material characteristics otherwise remaining the same. The element having the smaller Joule integral, for example 17, responds first, as a result of which the excess current is commutated to the second path formed by the element 20 and the coil 16, as a result of which the circuit-breaker is tripped magnetically.

Immediately after the beginning of the commutation of the excess current, the element 20 is likewise heated with acceleration thereby, which leads to an abrupt increase in its resistance. As a result, the excess current is in turn limited in its rise and its height, as a result of which the arcquenching device of the circuit-breaker is appreciably reinforced in its action. The dimensioning of the leading components when using the circuit of Figure 15 must be precisely adapted to the arc-quenching device. It is presupposed that the circuitbreaking capacity of the circuit-breaker is sufficient to protect the PTC resistors 17 and 20 from excess temperature.

In the present practical example, which illustrates a special case, CLDT elements from the same batch were used as PTC resistors 17 and 20 and differed only in their dimensions and consequently their thermal capacities: PTC resistor: 17 20 (CLDT element) Shape - cylindrical cylindrical Volume: 74 100% Cross-sectional area 0.237 0.275 cm2 Length in direction of current 1.05 1.22 cm Weight: 1.18 1.6 g Resistance at 250C: 6 6 mQ Resistance at 1600C: 60 min. 60 mQ Wsec Thermal capacity: 0.96 1.3 degree The resistance of each of the trip coils 15 and 16 amounted to 3 mQ. The dimensions given related in the present case to a circuitbreaker for a rated current of 16A and a thermally delayed tripping was achieved over the whole excess-current range up to a complete short-circuit current in accordance with characteristic V, of Figure 20. Attention is here expressly drawn to the fact that the possible forms of the circuit of Figure 15 are not restricted to this narrow example of an embodiment. In particular, other characteristics differing from V, can be achieved by introducing slight asymmetries into the two current paths.

This can be done either by altering the resistors 17 and 20 or the number of turns of the coils 15 and 16 or by both together.

Figure 16: This circuit differs from that of Figure 15 in that an ohmic resistor 21 is connected in parallel with the two parallel current paths 15, 17 and 16, 20, and protects the PTC resistors 17 and 20 from too high an incident power (high voltage and simultaneous excess current) and hence from an inadmissible excess temperature.

Figure 17: Figure 17 shows a circuit with two parallel current paths, the first path being formed by a high-resistance trip coil 10 and a PTC resistor 14 connected in series therewith, whereas the second is formed by a lowresistance trip coil 9. In accordance with Figure 13, the coils 10 and 9 form a common magnetic circuit 11 with the strike armature, and with the rated current their fluxes partially or completely cancel with one another out. The PTC resistor 14 only has to carry a small portion of the rated current so that it can be kept small in dimensions. In the event of an excess current, its resistance value increases greatly so that substantially no more current flows through the coil 1U and only the greatly increased flux in the coil 9 acts on the strike armature and causes this to respond.

The present example of an embodiment was based on a circuit-breaker with a rated current of 63A. The strike armature was adjusted so that the response took place with a resulting flux (coil 9 and coil 10 together) of 135 AT. The dat Weight: 1.6 g Resistance at 250 C: 6 mQ Resistance at 1600C: min. 60 mQ Wsec Thermal capacity: 1.3 degree The element was installed in the circuit breaker in such a manner that it had a thermal dissipation of 6.6 m W/degree.

The high-resistance trip coil 10 forming the parallel path was adapted to the above components in such a manner that the following data resulted: Resis- Number High-resistance tance of trip coil (mQ) turns H-characteristic: 28 11 L-characteristic: 28 8.5 G-characteristic: 119 46.3 K-characteristic: 232 48.3 V,-characteristic: 232 40 Figure 20: The characteristics of the example of an embodiment corresponding to the circuit of Figure 19 are illustrated graphically in this diagram. The ratio of excess current: rated current (VIZ) is entered in abscissae, while the ordinate represents the tripping time in seconds. Abscissa and ordinate are on the logarithmic scale. The characteristics "H", "L", "G" and "K" come within the tolerance range which is laid down by the corresponding standards (VDE 0641 and CEE publication 19). The curve designated by "V," corresponds to the thermal delay up to full short-circuit current. The lower, more or less horizontal branch of the curve (below about 0.01 sec) is determined by the mechanics of the circuit-breaker (mechanical time element) and is largely dependent of the thermal delay. Since the double-coil tripping of the circuits shown in Figures 13 to 19 permits a considerably more sensitive adjustment of the strike armature, however, improvements in the direction of shorter times are possible in this range also. Qualitatively, the curves also apply to all the other circuits and examples of embodiment.

Figure 21: In this Figure, a form of embodiment of the tripping device is illustrated diagrammatically in section and corresponds, in principle, to one of the circuits as shown in Figure 17, Figure 18 or Figure 19. The conductor branches behind the input terminal 23 and two paths are available to the current. The first path is formed by the resistor 24, dependent on temperature, which may consist of a PTC or NTC resistor, and the trip coil 25, whereas the second is formed by the trip coil 26 acting in the opposite sense. With the strike armature 27, the coils 25 and 26 form a common magnetic circuit. After the combination of the paths, the current flows through the contact lever 28, the movable contact 29 and the fixed contact 30 to the output terminal 31. Under normal conditions (operating current), the movable contact -29 is pressed against the fixed contact 30 via the contact lever 28 by means of a latch mechanism, not illustrated, the spring 32 being tensioned. In the event of an excess current, the strike armature 27 responds, impinges on the trip-releasing catch 33 which in turn releases the latch mechanism, whereupon the spring 32 separates the movable contact 29 from the fixed contact 30 via the contact lever 28.

The arc developing during the opening of the contacts is blown into the spark arrester 34 where it is extinguished. The hand lever 35 is provided to tension the spring 32 and for the mechanical opening and closing of the circuit-breaker.

The tripping device is not restricted to the forms of embodiment illustrated in Figures 1 to 21. In particular, the circuits may be supplemented by further combinations of PTC and NTC resistors, which reinforce one another in their effect. Such extensions can be easily derived from the basic circuit diagrams given. In all the circuits, additional ohmic resistors may be introduced into the current paths, and conversely the trip coil may consist partially or wholly of the ohmic resistance of the path in question.

Furthermore, in Figures 10, 11 and 13 to 19, the PTC resistor, for example may consist of a material which is suitable for the production of the coil, as a result of which temperature-dependent resistor and trip coil form an electrical-geometrical unit.

This the case, for example, when Fe/Ni wire or strip is used as a PTC resistor.

Furthermore, the use of the tripping device is not restricted to the constructional embodiment shown in Figure 21. In particular, relays or other electrical devices acting indirectly may be equipped therewith for the interruption of the current.

Here it must once again be expressly emphasised that the possible tripping characteristics are in no way limited to the curves illustrated in Figure 20. In principle, any conceivable characteristic can be achieved by comparatively simple means.

As a result of the tripping devices according to the invention, devices were provided which rendered possible the realization of any desired thermal tripping characteristic over the whole excesscurrent range of the circuit-breaker up to the maximum short-circuit current. In addition, the circuits according to the invention permit of a very wide range of variation in the characteristic with a single resistance element dependent on temperature, merely by adapting the magnetic trip coil. A far-reaching matching of the circuit-breaker characteristic to that of a fuse is possible. The device avoids consequent multi-stage tripping mechanisms with complicated mechanical drives. Even in the range of high excess currents (shortcircuit), a trip delay dependent on current is achieved without expensive auxiliary devices such as auxiliary masses on the strike armature, mechanical retard mechanisms or electrical capacitors. A particular advantage results from the invention that no alteration in the basic construction of conventional electric circuit-breakers is necessary and the electro-magnetic tripping device can be taken over. In addition, a plurality of ratedcurrent ranges can be covered by one and the same control resistance element dependent on temperature. Each PTC resistor may comprise a V203 and/or BaTiO3 and/or Fe/Ni base. Each NTC resistor may comprise a VO2 base.

WHAT WE CLAIM IS: 1. A tripping device with thermal delay for a circuit-breaker for the protection of a power supply and/or a motor, said tripping device comprising an electrical circuit having parallel first and second electrical paths, either with a pair of control resistors arranged in series in each said path and a magnetic trip coil connected between the junctions of the respective pairs of resistors to form a bridge with one of these four control resistors being dependent on temperature, or with a first magnetic trip coil included in one of said paths having a common magnetic circuit with a second magnetic trip coil included in said electrical circuit and with said first magnetic trip coil having an electrical resistence dependent on temperature or with a temperature dependent control resistor being included in a said path, the electrical circuit being arranged for heating of the temperature dependent control resistor or coil with temperature dependent resistance, due solely to electrical current passing through that control resistor or coil, to cause electrical current through the circuit to be commutated, wholly or in part, from the first path to the second whereby to operate an armature of the trip coil or trip coils to break the electrical circuit.

2. A tripping device as claimed in claim 1, in which the temperature dependent control resistor or temperature dependent trip coil exhibits an abrupt change in resistance with rising temperature.

3. A tripping device as claimed in claim 1 or 2, in which a PTC resistor or an NTC resistor and an ohmic resistor are connected in series in one path of the bridge and two ohmic resistors are connected in series in the other path.

4. A tripping device as claimed in claim 1 or 2, in which a PTC resistor or an NTC resistor and an ohmic resistor are connected in series in each of the two paths of the bridge in such a manner that the resistors dependent on temperature and the ohmic resistors in the two paths are staggered in relation to one another.

5. A tripping device as claimed in claim 1 or 2, in which a PTC resistor and an ohmic resistor are connected in series in one path of the bridge and an NTC resistor and an ohmic resistor are connected in series in the other path.

6. A tripping device as claimed in claim or 2, in which a PTC resistor and an NTC resistor are connected in series in one path of the bridge, and two ohmic resistors are connected in series in the other path.

7. A tripping device as claimed in claim 1 or 2, in which a PTC resistor and an NTC resistor are connected in series in one path of the bridge and an NTC resistor or a PTC resistor and an ohmic resistor are connected in series in the other path.

8. A tripping device as claimed in claim I or 2, in which a PTC resistor and an NTC resistor are connected in series in each of the two paths of the bridge in such a manner that the PTC resistors and the NTC resistors are in staggered relationship in the two paths.

9. A tripping device as claimed in claim 1 or 2, comprising a said control resistor and said first trip coil connected in series in said second of the two parallel paths and a said control resistor and the second trip rail connected in series in said first path, in such a manner that the trip coils form a common magnetic circuit with a strike armature thereof and are wound in the same sense, so that their fluxes are added, and that the control resistor in series with the second trip coil is a PTC resistor.

10. A tripping device as claimed in claim 9, in which the first and second parallel paths are respectively a low-resistance path and a high-resistance path, with said PTC resistor, which is in the form of a current limiting element dependent on temperature (CLDT element) and said second trip coil which has a small number of turns are in the low-resistance path and said first trip coil which has a large number of turns and an ohmic control resistor are in the highresistance path.

11. A tripping device as claimed in claim 10, in which the ohmic control resistor has zero resistance value.

12. A tripping device as claimed in claim

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. invention permit of a very wide range of variation in the characteristic with a single resistance element dependent on temperature, merely by adapting the magnetic trip coil. A far-reaching matching of the circuit-breaker characteristic to that of a fuse is possible. The device avoids consequent multi-stage tripping mechanisms with complicated mechanical drives. Even in the range of high excess currents (shortcircuit), a trip delay dependent on current is achieved without expensive auxiliary devices such as auxiliary masses on the strike armature, mechanical retard mechanisms or electrical capacitors. A particular advantage results from the invention that no alteration in the basic construction of conventional electric circuit-breakers is necessary and the electro-magnetic tripping device can be taken over. In addition, a plurality of ratedcurrent ranges can be covered by one and the same control resistance element dependent on temperature. Each PTC resistor may comprise a V203 and/or BaTiO3 and/or Fe/Ni base. Each NTC resistor may comprise a VO2 base. WHAT WE CLAIM IS:

1. A tripping device with thermal delay for a circuit-breaker for the protection of a power supply and/or a motor, said tripping device comprising an electrical circuit having parallel first and second electrical paths, either with a pair of control resistors arranged in series in each said path and a magnetic trip coil connected between the junctions of the respective pairs of resistors to form a bridge with one of these four control resistors being dependent on temperature, or with a first magnetic trip coil included in one of said paths having a common magnetic circuit with a second magnetic trip coil included in said electrical circuit and with said first magnetic trip coil having an electrical resistence dependent on temperature or with a temperature dependent control resistor being included in a said path, the electrical circuit being arranged for heating of the temperature dependent control resistor or coil with temperature dependent resistance, due solely to electrical current passing through that control resistor or coil, to cause electrical current through the circuit to be commutated, wholly or in part, from the first path to the second whereby to operate an armature of the trip coil or trip coils to break the electrical circuit.

12. A tripping device as claimed in claim

9, in which the first and second parallel paths are respectively low-resistance and high-resistance paths, with a said PTC resistor, which is in the form of a currentlimiting element dependent on temperature (CLDT element) and said second trip coil, which has a small number of turns in the low-resistance path and said first trip coil, which has a large number of turns and a PTC resistor in the high-resistance path, in such a manner that the PTC resistors differ in their resistance and/or in their thermal capacity and/or in their temperatureresistance behaviour and/or in their response Joule integral

in which T signifies the duration of the excess current which is necessary for the effective raising of the resistance of the PTC resistor.

13. A tripping device as claimed in claim 1 or 2, in which said second trip coil has a small number of turns and is connected in series with the two parallel current paths, the first path being formed by a PTC resistor in the form of a current-limiting element dependent on temperature (CLDT element) and the second path being formed by said first trip coil, which has a large number of turns, and an ohmic control resistor.

14. A tripping device as claimed in claim 1 or 2, in which each of the two parallel paths comprises a said control resistor and a said trip coil connected in series therewith, in such a manner that the trip coils form a common magnetic circuit with the strike armature thereof and are oppositely wound so that, during normal operation of the circuit-breaker, their fluxes partially or completely cancel one another out, and that at least one of the series resistors is a PTC resistor or an NTC resistor.

15. A tripping device as claimed in claim 14, in which a PTC resistor or an NTC resistor is provided in one path and an ohmic resistor is provided in the other path.

16. A tripping device as claimed in claim 14, in which the resistors in the two parallel paths are PTC resistors having different characteristics.

17. A tripping device as claimed in claim 16, in which the two trip coils have substantially the same characteristics and that a current-limiting element dependent on temperature (CLDT element) is provided in each path in such a manner that the characteristic of the CLDT element in the one path differs by a small amount in its response Joule integral

from that of the CLDT element in the other path, T signifying the duration of the excess current which is necessary for the abrupt raising of the resistance of the CLDT element.

18. A tripping device as claimed in claim 16, further comprising an ohmic protective resistor connected in parallel with the two parallel paths.

19. A tripping device as claimed in claim 14, in which the two parallel paths are respectively a high-resistance path and a low-resistance path, with a PTC resistor or an NTC resistor and a trip coil with a large number of turns in the high-resistance path and a trip coil with a small number of turns and a control resistor of zero resistance value in the low-resistance path.

20. A tripping device as claimed in claim 14, in which the two parallel paths are respectively a high-resistance path and a low-resistance path, with a PTC resistor in the form of a current-limiting element dependent on temperature (CLDT element) and a trip coil with a small number of turns in the low-resistance path and a trip coil with a large number of turns and a control resistor with zero resistance value in the high-resistance path.

21. A tripping device as claimed in one of the preceding claims, in each PTC resistor comprises a V203 and/or BaTiO3 and/or Fe/Ni base and each NTC resistor comprises a VO2 base.

22 A tripping device substantially as herein described with reference to any one of Figures 1 to 19 and 21.