FR2759490A1 - CIRCUIT BREAKER ASSEMBLY WITH CURRENT SUPPRESSION ELEMENT FOR THE PROTECTION OF INDUCTION MOTORS - Google Patents

Abstract

This current suppressing element circuit breaker assembly (19) protects an electric motor without tripping upon a current reversal in the motor. The electronic trip unit (15) provides protection against instantaneous, short-term and long-term overcurrents to prevent abnormal short-circuit currents in the protected circuit. The current suppression unit (20) quickly removes strong short circuit currents until the circuit breaker responds to isolate the protected installation.

Description

Circuit breaker assembly with current canceling element for

  protection of induction motors.

  When in the tooling industry electric motors are repeatedly switched between forward and reverse, strong inrush currents are temporarily produced for short periods of time. To prevent a break in the circuit each time the current changes direction, we generally use

  fuses in series with overcurrent relays, in order to protect

  manage the associated installation against abnormal overcurrent situations. Due to thermal aging of fuses subjected to

  repeated strong currents, these fuses must be replaced periodically

  wheat. The higher the inrush current, which phenomenon is associated with high efficiency motors, the greater the degree of thermal aging, so that fuses of the highest caliber are required to resist thermal aging when motors are used. i

  high yield. U.S. Patent No. 5,426,406.

  titled "Induction Motor Protective Circuit Breaker Unit", describes the choice of fuse and circuit breaker in order to reduce thermal damage to the fuse and to have effective coordination with the

  overcurrent relay. Because of its specialized application.

  the combination of these heavy-duty fuses and overcurrent relays has found limited applications outside the industry

of tools.

  U.S. Patent 5,539,370, entitled "Inductive Motor Protective Circuit Breaker Unit", describes a polymeric short-circuit protection element which limits the short-circuit current from low resistance to one high resistance. The resistance curve of the polymer is characterized by a positive temperature coefficient (PTC) and, for a particular temperature, exhibits an abrupt transition between a low resistance and a high resistance. Repeated current reversals due to tooling operations cause cyclic heating of the polymer, with little or no cooling periods. In order to prevent the polymer from inadvertently going from a low electrical resistance to a high electrical resistance when heated, it is necessary to have polymer elements with higher nominal steady state intensities. However, larger elements cannot provide optimal short circuit protection

  because of the greater energy required to cause the commu-

  tation. U.S. Patent No. 4,884,164, entitled "Molded Case Electronic Circuit Interrupter", describes an industrial-grade circuit breaker including an electronic trip unit that can be set over a wide range of overcurrent conditions

  short-term and long-term.

  U.S. Patent No. 4,967,304, entitled "Digital Circuit Interrupter With Electric Motor Trip Parameters",

  describes a digital circuit breaker with trip parameters

  of the electric motor which contains control algorithms

  suitable for motor protection applications.

  US Patent Application 08/514,076 filed August 11, 1995 titled "Current Limiting Device" describes an element

  current limiting polymer which does not depend on a characteristic

  resistance tick with positive temperature coefficient.

  It would be economically advantageous to produce a circuit breaker employing an electronic trip unit with a current canceling unit which is not sensitive to

  cyclic thermal aging which does not need to be periodically

  only replaced when used in tooling operations. An object of the invention is to propose a combined assembly comprising a circuit breaker and a current suppression unit, which does not interrupt the protected circuit during a motor reversal, which can be adjusted to ensure coordination with the relay thermal overcurrent, which provides optimal protection against

short circuit currents.

  The invention therefore provides a circuit breaker for protecting

  induction motors which includes an electro-

  and a current suppression unit containing a polymeric current limiting element which does not depend on a curve

  resistance with positive temperature coefficient. The trigger unit

  The electronic control is set for short and long term overcurrent protection. The current canceling unit is designed to limit the short-circuit current until the

  circuit breaker responds to isolate the protected circuit.

  Therefore, the present invention provides a set of disjonc-

  current suppressor element which includes - a circuit breaker box, - at least one pair of circuit breaker contacts inside the circuit breaker box to interrupt a circuit current, - an actuation mechanism placed in the box circuit breaker and used to separate the circuit breaker contacts, - a trip unit placed inside the circuit breaker box and used to rotate the actuating mechanism so

  to separate the circuit breaker contacts in the event of a situation

  overcurrent in a protected circuit,

  - at least one current limiting box located near

  from the circuit breaker box, and - at least one current limiting element, this current limiting element being electrically coupled to the circuit breaker contacts, so that a circuit current flows through

  ) the current limiting element and is limited to a predetermined value-

  mined in the event of an overcurrent situation.

  The circuit breaker box includes an electrically insulated base and cover. The trigger unit contains electronic means

  to monitor and respond to the overcurrent condition.

  The current limiting box is attached to the circuit breaker box. The current limiting element includes at least one

  polymer material, electrically conductive, which has a vapor temperature

  rization less than 1000 C. The electrical resistance of the conductive polymer material has

  not a positive temperature coefficient.

  The conductive polymeric material can use an electrically conductive charge. The circuit breaker assembly with current canceling element further comprises a pair of first and second electroconductive electrodes, the first electrode being placed on a first side of the conductive polymeric material and the second electrode being

  placed on the opposite side of the latter.

  The circuit breaker assembly with current canceling element includes means for applying a compressive force

to the conductive polymer material.

  This means for applying a compressive force may comprise first and second compression springs, the first compression spring being placed between a first side of the

  current limiting box and the first electrode, and the second

  compression spring being placed between a second side of the

  current limiting box and the second electrode.

  The circuit breaker housing contains an integrated means for

  receive a means integrated in the current limiting box.

  The means integrated in the circuit breaker box can comprise

dovetail slots.

  The circuit breaker assembly with current canceling element comprises at least one twinning strip which starts from the current limiting box and is coupled to at least one strip

  circuit breaker load connection from the circuit breaker housing.

  The circuit breaker assembly with current canceling element

  includes at least one load connection strip with limita-

  tion of current flowing from the current limiting box may

  connected to an electrical distribution circuit.

  The circuit breaker box and the current limiting box can be made of a single circuit breaker box with

removal of current.

  The invention will be better understood on reading the description

  following detail, made with reference to the accompanying drawings in which: Figure 1 is a perspective view from above of a circuit breaker assembly with current canceling element according to the invention, Figure 2 is a partial side view in section of the current suppression unit contained in the circuit breaker assembly with current suppression element of FIG. 1, and FIG. 3 is a graphic representation of the overcurrent protection offered by the circuit breaker assembly element

  deletion of the current of figure 1.

  FIG. 1 shows an assembly 19 of circuit breaker with current suppression element, which comprises an electronic circuit breaker, described in the already mentioned American patent n 4,884,164, and a unit 20 for suppression of current. The electronic circuit breaker comprises a circuit breaker base 11, a circuit breaker cover 12 and an accessories cover 13, described in US Patent No. 4,754,247 entitled "MCCB Accessory Enclosure", which is fixed on opposite sides

  of the actuating lever 14. The unit 15 for electro-

  The packaging contained in the cover is described in US Patent No. 4,649,455 entitled "Rating Plug for MCCB". Dovetail protrusions 21 formed integrally with the current suppression unit housing engage with slots 16 in

  dovetail formed in the cover of the circuit breaker. Screws 22.

  shown in Figure 2, are accessible by upper openings

  17 and serve to couple from an electrical point of view the current suppression unit 20 to the electronic circuit breaker 10. Charging terminals 23 provide the electrical connection with the protected circuit and are

  accessible through holes 24 for access to the terminals.

  The mechanical and electrical connection between the current suppression unit 2 () and the electronic circuit breaker 10 is shown in FIG. 2. Dovetail projections 21 integrated into the current suppression unit provide mechanical locking with of

  dovetail slots 16 formed in the cover 12 of the circuit breaker.

  Twinning bars 25 coming from the current suppressing unit are mechanically and electrically fixed to the load connection bars 18 leaving the electronic circuit breaker, by screws 22 which are accessed by upper openings 17. The suppressing unit current comprises a housing 32, a current limiting element 26 which operates in the manner described in the already mentioned American patent application no. 08/514 076. Des) electrode terminals 27a, 27b are electrically connected to the electrodes 29a, 29b of the current limiting element 26 and, respectively, to the twinning bars 25 and to the load connection bars 23. The current limiting element comprises a polymer conductor 28 electrically connected in series with the electrodes adjacent 29a, 29b. Springs 30a, 30b are placed between the electrodes and support surfaces 3a, 3b to exert a

  compression force between the electrodes and the polymer conductor.

  Lugs 33 which are accessed through the terminal access holes 24 are fixed to the charging terminals to ensure connection with the

  electrical energy distribution circuit.

  The inverse time / current operating characteristic of the unit 19 has, according to the invention, a combined protection profile, which will be better understood if reference is made jointly to FIGS. 1 and 3. The combined protection profile is the combination of the protection profile 41 of an electronic circuit breaker and the protection profile 42 of the current suppression unit. The absence of PTC effect in the current suppression unit 20 gives optimal coordination with the circuit breaker protection profile in the region of point A, which is conventionally called the saturation point of the short response profile. duration. Optimal coordination requires the current suppressor to operate to the right or above point A, otherwise a premature response from the suppressor 20

  current could interfere with the proper functioning of the circuit breaker

  associated electronic author. This can be done either by eliminating the PTC characteristic of the current limiting element or, as shown here, by using a current limiting element which does not

  not dependent on a PTC characteristic for current suppression.

  The previous protections, provided by a fuse or a limiter

  polymer current with positive temperature coefficient, are repre-

  sensed by the CTP protection curves 43a, 43b. The CTP 43a protection curve shows a roughly equivalent performance

  to the protection curve 42 of the current suppression unit for-

  instantaneous short-circuit currents much greater than X. However,

  in the region of point A, the CTP protection curve 43a does not correspond

  does not lay on the protection curve 41 of the electronic circuit breaker as demonstrated by the fact that the PTC curve is below and to the left of point A. To obtain the desired correspondence around point A, the PTC protection curve 43b must be determined precisely. But, for instantaneous short-circuit currents well

  greater than X, the CTP protection curve 43b shows a perfor-

  mance significantly lower than the protection curve 42 of the current suppression unit. The protection difference between the PTC protection curve 43b and the protection curve 42 of the current suppression unit is represented by the hatched region B.

  We will better understand the advantages brought by the function-

  the unity of the invention (CSCB unit) if we consider simultaneously

  Figures 1 to 3. When a nominal operating current crosses the protected circuit, the electronic circuit breaker 10 and the unit 20) for removing the current from the CSCB unit are at rest. In the event of a short or long lasting current

  at X ', the CSCB unit responds quickly to limit the intensity of the short-

  circuit, as described in the American patent application already

  mentioned n 08/514 076. The correspondence between the unit of suppress-

  current and the electronic trip unit in the circuit breaker guarantees that the electronic circuit breaker will receive and respond to a trip signal, as described in the aforementioned US Patent No. 4,884,164, to effectively isolate the

protected circuit.

  A circuit breaker assembly with current suppression element has therefore been described, which comprises a current suppression element connected in series with an electronic circuit breaker comprising an electronic tripping unit. This circuit breaker assembly with current canceling element provides short circuit and long term short circuit protection without having to be replaced periodically.

  It is understood that the foregoing description has not been

  given only by way of illustration and not limitation and that variations

  your or modifications can be made within the framework of the

present invention.

Claims (15)

  1. A circuit breaker assembly with current canceling element, characterized in that it comprises - a circuit breaker box, - at least one pair of circuit breaker contacts inside said circuit breaker box to interrupt a circuit current, - an actuation mechanism placed in said circuit breaker housing and used to separate said circuit breaker contacts, - a trip unit (15) placed inside said circuit breaker housing and used to pivot said actuation mechanism in order to separate said circuit breaker contacts in the event of an overcurrent situation in a protected circuit, - at least one current limitation box (32) located near said circuit breaker box, and - at least one element (26) of current limitation, said   current limiting element being electrically coupled   that to said circuit breaker contacts, so that a circuit current flows through said current limiting element and is limited to a   predetermined value in the event of an overcurrent situation.   2. A circuit breaker assembly with current cancellation element according to claim 1, characterized in that said housing   circuit breaker comprises a base (11) and a cover (12, 13), electrical   insulators. 3. A circuit breaker assembly with current cancellation element according to claim 1, characterized in that said trip unit contains electronic means for monitoring said   overcurrent condition and respond to it.   4. A circuit breaker assembly with current cancellation element according to claim 1, characterized in that said housing   current limitation is fixed to said circuit breaker box.   5. A circuit breaker assembly with current suppression element according to claim 1, characterized in that said current limiting element comprises at least one polymeric material (28), electrically conductive, which has a vaporization temperature lower than O10 1000 C.   6. A circuit breaker assembly with current cancellation element according to claim 5, characterized in that the electrical resistance of said conductive polymer material does not have a positive temperature coefficient. 7. A circuit breaker assembly with current cancellation element according to claim 5, characterized in that said material   conductive polymer contains an electrically conductive filler.   8. A circuit breaker assembly with current cancellation element according to claim 5, characterized in that it comprises   in addition to a pair of first and second electrodes (29a, 29b), electro-   conductive, said first electrode being placed on a first side of said conductive polymeric material and said second electrode being   placed on the opposite side of the latter.   9. A circuit breaker assembly with current cancellation element according to claim 8, characterized in that it comprises a   means for applying a compressive force to said poly- material driver mother.   10. A circuit breaker assembly with current suppression element according to claim 9, characterized in that said means for applying a compressive force comprises first and second compression springs (30a, 30b), said first spring of   compression being placed between a first side of said limiting box   tion of the current and said first electrode, and said second compression spring being placed between a second side of said housing   current limitation and said second electrode.   11. A circuit breaker assembly with current cancellation element according to claim 4, characterized in that said circuit breaker housing contains an integrated means intended to receive a means   integrated into said current limiting box.   12. A circuit breaker assembly with current cancellation element according to claim 4, characterized in that said means of the   circuit breaker housing includes dovetail slots (16).   13. A circuit breaker assembly with current cancellation element according to claim 1, characterized in that it comprises at least one twinning bar (25) which starts from said current limiting box and is coupled to at least one bar (18 ) connection of   load of the circuit breaker which leaves said circuit breaker box.   14. A circuit breaker assembly with current-canceling element according to claim 13, characterized in that it comprises at least one load connection strip with current limitation which leaves from said current limitation box to be connected to a   electrical distribution circuit.   - 15. A circuit breaker assembly with 1 () current canceling element according to claim 1, characterized in that said circuit breaker box and said current limiting box are made of a   single circuit breaker box with current canceling element.