FR2721433A1 - Excess current protection circuit - Google Patents

Abstract

The overcurrent protection circuit has current limiting fuses (6A-6C) for three phases. A disconnection switch (50 is connected to these fuses. The circuit also includes a delay unit (8) to excite a trigger coil (9) and to open the disconnection switch (5). After this, fuse signals are input into the remaining fuses and operate relays for the other phases when a fuse signal for at least one phase is input into a fuse. In one arrangement, the circuit has a movable contact (22) for each phase. One side of the contact (22) is electrically connected to a voltage supply terminal (6E). The other side is connected to and disconnected from a voltage source by a mechanical actuator (20). A current limiting fuse (6A) for one phase is connected between the supply terminal (6E) and a load side terminal (6F). A striker (6D) for one phase is provided at the load side terminal (6F) and springs away from it when at least the fuse corresponding to this phase melts. A relay (7) is actuated by the striker (6D). On operation of the relay (7), a delay unit (8) starts to operate after all fuses have sprung. The delay (8) excites a trigger coil (9) to operate the mechanical actuator (20). This causes the movable contact to be disconnected. The circuit may also include a damping member (32). This is operated on actuation of the relay (7) to prevent operation of the mechanical actuator (20) until the striker of the last fuse to melt has sprung.

Description

CIRCUIT FOR PROTECTION AGAINST OVERCURRENTS AND DEVICE
USING SUCH CIRCUIT

 The present invention relates to an overcurrent protection circuit constituted by the combination of current limiting fuses and a load-breaking disconnector for protecting an electrical circuit.

 Economical equipment is formed by the combination of current limiting fuses and a load break switch to interrupt a short circuit current and to protect an electrical circuit, since a short circuit current does not occur. can not be interrupted only by the load-breaking disconnector. A current limiting fuse has a deterioration range determined by the overcurrent circulation time and the number of repetitions of overcurrent occurrences. In this range, the occurrence of an unplanned merger or an unexpected phase interruption is likely. In addition, in the fundamental use of a current limiting fuse, since a variation or modification of the melting time for modifying an overcurrent is greater in a region of lower melting current in the melting characteristics of a current limiting fuse, such a current limiting fuse is used only to provide a protection against to a short circuit. Another device, such as a three-phase disconnect switch under load, serves to fundamentally provide protection against overload.

The previously mentioned characteristics of a current limiting fuse are described in the standard relating to a current limiting fuse, for example at lines 4 and 9 from the bottom of page 4 of the JIS Japanese Industrial Standard.
C4606-1988 and a variation of i20% of the characteristic of a current limiting fuse is allowed.

 The switching characteristics of a load-breaking disconnector used in conjunction with a current limiting fuse, in particular a switching characteristic indicating a switching capability, are represented by the limit value of a current which can be interrupted under the conditions prescribed in the standard. For example, on page 17 of Japanese JIS C4605-1987, it is stated that the power factor of a load during a load current switching test should be 0.65 - 0.75. and a switching operation is provided in the power factor range.

The switching characteristics for other power factors of the aforementioned range, for example about 0.1 of the power factor of the excitation current, are shown in the following table.
TABLE (unit A)

<tb> Current <SEP> nominal <SEP> 100 <SEP> 200 <SEP> 300 <SEP> 400 <SEP> 600
<tb> 1) <SEP> Ability <SEP> of <SEP> switching <SEP> of a
<tb> current <SEP> of <SEP> job <SEP> nominal <SEP> 100 <SEP> 200 <SEP> 300 <SEP> 400 <SEP> 600
<tb> 2) <SEP> Ability <SEP> of <SEP> switching <SEP> of a
<tb> current <SEP> of excitation <SEP> nominal <SEP> 5 <SEP> 10 <SEP> 15 <SEP> 20 <SEP> 30
<tb> 3) <SEP> Capacity <SEP> of <SEP> switching <SEP> of <SEP>
<tb> current <SEP> of <SEP> load <SEP> nominal <SEP> 10
<tb> the power factor is 0.65 - 0.75 in case 1) and the power factor in case 2) is lower than that in case 1), as described in line 1, page 17 of the Japanese standard
JIS C4605-1987.

In the table, it can be seen that the nominal excitation current switching capacity is greatly reduced in the ratio 11'20 of the switching capacity of the working current. Wiring in the PF.S form and a component connection of a circuit using current limiting fuses and a load-breaking disconnector are shown in Figure 4, page 16 of Japanese JIS 4620
1992, and on page 30 of this same standard, it is indicated that the breaking current range can be increased and that the protection of a phase interruption due to the fusing of the current limiting fuses can be obtained. by means of a mechanical and automatic tripping of the on-load disconnector with connection parts of the current limiting fuses, referred to as the actuating device, which performs the predetermined mechanical operations at the time of the melting of the fuse.

If there is a short-circuit between phases, for example between the part located on the secondary side of a transformer and a circuit breaker MCCB (English Mold Case
Circuit breaker, ie a circuit breaker placed in a molded case), a short-circuit current flows in the part located on the secondary side of the transformer and an overcurrent also circulates in the part located on the primary side. Then, the three-phase disconnect switch is open for 0.05 - 0.2 s after the current limiting fuse has blown.

 However, since the overcurrent of the primary side has a value in the range of a low melt flow, with a significant variation of 0.3 - 1.5 s for the melting time, in the case of of the short-circuit in the secondary side part of the transformer, the three-phase disconnector under load is opened by the actuator of the current limiting fuse, which has melted, even if only one of the fuses for the three melted phases. In addition, in the disconnecting switch under load, the switches of other phases, whose fuses have not melted, are able to interrupt overcurrent.

 Although the power factor of the overcurrent in the primary side portion varies depending on the transformer conditions, in the case of the occurrence of a short circuit on the secondary side portion of a transformer, its value is usually equal to about 0.1. For the 0.1 value of the power factor, the overcurrent can not be interrupted since the power factor is the value which is greater than the performance of the load disconnector.

 On the basis of tests, it has been established that a serious accident, such as a short-circuit between phases, may occur with a low probability, since the load-breaking disconnector does not allow the overcurrent to be interrupted. situation mentioned above.

 The present invention has been developed in view of the problems described above and is intended to provide a reliable overcurrent protection circuit to prevent the occurrence of an arc short circuit in a three-phase load-break disconnector. .

 The present invention relates to an overcurrent protection circuit comprising current limiting fuses for three phases and a load-breaking disconnector, which is connected to these fuses, characterized in that it comprises delay means for energizing a trip coil and opening said load-breaking disconnect after fusion signals have been sent to the other current limiting fuses, and relays working for other phases as well, when a fusion signal is sent to a current limiting fuse for at least one other phase.

 The present invention also relates to an overcurrent protection circuit, characterized in that it comprises: a movable contact for each phase, one side of which is electrically connected to a terminal located on the supply source side, another side of said movable contact being connected to and disconnected from said power source by a portion of an actuating mechanism, a current limiting fuse for a phase, inserted between said power source side terminal and a side terminal; charge, an actuator for a phase, provided on said load-side terminal and which expands sharply when at least one fuse, which corresponds to said phase, among current-limiting fuses for three phases, melts, a relay for a phase, actuated by said actuating device, delay means triggering the operation by means of the actuation of said relay, after the sudden deployment of all actuators, said delay means exciting the trigger coil to operate said actuating mechanism portion, and said movable contact being electrically disconnected from a fixed contact provided on one side of the energizing source; supply, by said operation of said actuating mechanism portion.

 The present invention also relates to an overcurrent protection device, characterized in that it comprises: a movable contact for each phase, one side of which is electrically connected to a terminal situated on the power source side, a other side of said movable contact being connected to and disconnected from said power source by an actuating mechanism portion, each of the current limiting fuses inserted between said power source side terminal and a load side terminal, a an actuating device for a phase, provided on said load-side terminal and which expands rapidly when at least one fuse, which corresponds to said phase, among current-limiting fuses for three phases, melts, a relay actuated by said actuating device, a damper, actuated when actuating said relay, to prevent operation of said part m actuation until a device for actuating a last current limiting fuse, which melts, unfolds sharply.

 The overcurrent protection circuit according to the present invention extends the period of time between the fusing of a current limiting fuse and a start of operation of a disconnect switch in charge of the maximum value of the dispersed times. melting current limiting fuses.

 This is why, thanks to the present invention, since the three-phase disconnecting disconnector is open after all three-phase current limiting fuses have melted, the muting impossibility and the short-circuit between phases are prevented, which improves the safety of the overcurrent protection circuit.

Other features of the invention will become apparent on reading the following description with reference to the accompanying drawings, in which:
Fig. 1 is a diagram showing an overcurrent protection circuit corresponding to an embodiment of the present invention;
Fig. 2 is a diagram showing an overcurrent protection circuit corresponding to another embodiment of the present invention;
Fig. 3 is a graph showing characteristics of the current limiting fuse shown in Fig. 1;
FIG. 4 is a vertical cross-sectional view of the current limiting fuse shown in FIG. 1; and
FIG. 5 is a vertical cross-sectional view of the current limiting fuse shown in FIG.

 The following facts were confirmed from arc-to-phase shortcircuit tests in a load-breaking disconnector for an overcurrent protection circuit.

 (1) In the case where a power factor reducing circuit, such as a transformer, motor, etc., is connected to the load side of the load-breaking disconnector and current limiting fuses, a short circuit shall be circuit between phases sometimes occurs by accident.

 (2) In the case where the melting time of a current limiting fuse for each phase has a variation as shown in FIG. 3, a short circuit between phases occurs.

 For example, in the case where current-limiting fuses for three phases first melt in the event of an accidental short-circuit, a three-phase load-breaking disconnector opens as a result. However, since the other two current limiting fuses are melting and, in addition, a transformer having a low power factor is connected on the secondary side, the power factor of the overcurrent protection circuit is less than that of a usual circuit.

 In general, the performance of a load break switch is set to perform the break operation in a power factor range of 0.65 - 0.75. When the power factor is below this range of power factors, the breaking current decreases dramatically as the phase of the voltage differs from that of the current. In the case where the power factor decreases and the current limiting fuses do not melt, under such conditions, it has been established that the short-circuit between phases at the switches present in the disconnector in charge, connected to the current limiting fuses during the melting process, appears as the arc can not be completely interrupted by the load disconnector.

 Embodiments for preventing phase-to-phase short-circuiting in accordance with the present invention will be explained with reference to FIGS. 1 to 3.

FIGS. 1 and 2 show overcurrent protection circuits, in accordance with the present invention, and FIG. 3 represents a graph of fusion characteristics, on which the abscissa indicates the melting instant t and the axis. ordinates the melt flow i, and dashed lines indicate the allowable limits of the merging characteristics. The structure of the load-breaking disconnector comprising the current limiting fuses located in the various overcurrent protection circuits are shown respectively in FIGS. 4 and 5.

 The part 1A located on the secondary side of the transformer 1 is connected to several loads, for example motors 3, by means of cables provided for loads 2. Circuits having a low power factor, such as capacitors, motors 3 and a transformer 1, each of which has an autoinductance, are connected to the load side.

 The three-phase disconnect switch 5 and the current limiting fuses 6A, 6B and 6C are connected between the part 1B located on the primary side of the transformer 1 and a power supply system 4. The melting time of the fuse current limitation 6, for example 6A, is dispersed in the range t1-t2-t3 for the melt flow Il as shown in FIG. 3. When the tripping device 2D of the current limiting fuse 6A is acting, the relay 7 producing a first delay is actuated, and a current flows in a delay circuit 8, and a trip coil 9 is energized, and the load-breaking disconnector 5 opens. In addition, the reference numeral 10 designates a source of direct current.

 The delay circuit 8 is a timer for the circulation of a current at a time t4 slightly delayed with respect to the time t3, which is the latest time of the merging instants of the current limiting fuses. When the trip devices 6D of the current limiting fuses 6A, 6B and 6C are triggered simultaneously at time t5, the second relay 7X transfers a current to the trip coil 9 and opens the load-breaking disconnector 5.

 In addition, the delay circuit 8 is of the AND circuit type, since it allows a current to flow through the coil 9 and opens the load-breaking disconnector 5 when all the fusing signals of the current limiting fuses 6A, 6B and 6C are sent.

 In the case where an accidental short circuit occurs at the locations 0 in the cables connected to the loads 2, a short-circuit current flows. Then the current limiting fuse 6A melts and the actuator 6D of the fuse 6A expands sharply in the direction represented by an arrow. However, since a current flows in the delay circuit 8 at the instant t4 after the melting times t2 and t3 of the current limiting fuses 6B and 6C and excites the trigger coil 9 and opens the switch disconnector in load 5, the circuit safety is improved.

In addition, since the second relays 7X for all phases operate and excite the trip coil 9 and open the load-breaking disconnector 5 as soon as the current limiting fuses 6A, 6B and 6C melt simultaneously at the same time. t5 fusion for melt streams il, i2 and i3,
The amplification of the load-side crash can be prevented, which also improves the safety of a circuit.

 The concrete structure of the load-breaking three-phase disconnector 5 shown in FIG. 2 will be explained with reference to FIG. 4. Since the structures for the three phases are identical, the structure of the overcurrent protection system will be explained. consisting of the current limiting fuse 6A and the load-breaking disconnector connected thereto (or the load-breaking disconnector having a delay function).

 The current limiting fuse 6A is removably connected between the load side terminal 6F and the power source side terminal 6E, both terminals being supported by an insulator 6G. When the current limiting fuse 6A melts and the actuating device 6D suddenly expands in the direction shown by an arrow, an actuating mechanism portion 20 of the load-breaking disconnector 5 acts and suppresses the engagement with a stop device 21. In addition, a movable contact 22, which is in contact with a fixed contact, not shown in the figure, pivots in the opposite direction of the clockwise and the connection between the terminal 6E and the control system. supply 4 is interrupted.

 Thus, when the actuating device 6D unfolds sharply in the direction represented by an arrow, a lever 25 moves in the direction represented by a dashed line, and an insulating actuating rod 27 is moved to the left under the effect of the rotation of a rod 26 in the opposite direction of the clockwise.

A relay lever 28 continues to push the relay 7 producing the first delay, rotating about a 28X axis of the relay. Then, after the instant t4, a current enters the delay circuit 8 and excites the trigger coil 9 which then pushes the stop device 21 in the direction of clockwise. Then the axis 28X of the relay, which is shown in the figure, is attached to a frame 40.

 The stop device 21 rotates on a pivot of the axis 2 IX of the stop device, in the clockwise direction and releases the engagement between a hook-shaped portion 21B of the stop device and an axis 29A of a holding lever. Then, when a holding lever 29 pivots on a holding pin 29X, a holding rod 29B and the insulating operating rod 29C turn counterclockwise and interrupt the connection between the terminal 6E and the feeding system 4 by rotating the movable contacts 22, which are in contact with the fixed contact in an arc suppression chamber 30, in a counterclockwise direction. The power supply system 4 is connected to the terminal 6E on the power source side, via an electrical connection portion 22A connected to the movable contact 22.

 Since the components must be actuated only in the opposite direction of the direction previously indicated as represented by the arrow in the case where the movable contact 22 is in contact with the fixed contact, no explanation will be given for the reverse operation.

 With regard to the structure of a load breaking disconnector 5A shown in FIG. 5, the same components as those of the load-breaking disconnector shown in FIG. 4 will not be explained, and only the components that are different from those in Figure 4.

 Thus a lever 28 of the relay rotates a pivoting lever 31 on an axis 31X and pushes a damper 32, during the rotation about a 28X axis of the relay.

The damper 32 acts on the pivoting lever 3 1 after the instant t4, as a delay circuit 8, and the rotation of the lever 31 moves the stop device 21, and the connection between the terminal 6E and the control system. 4 is interrupted under the effect of the rotation of the movable contact 22 which is in contact with the fixed contacts in the opposite direction of the clockwise, as operations mentioned above for FIG. 4.

 Since the components must be actuated only in the opposite direction of the aforementioned direction, as represented by the arrow in the case where the movable contact 22 comes into contact with the fixed contact, no explanation of the opposite operation will be given.

 The composition of the actuating mechanism part 20 is a simple structure, easily manufactured, which improves the efficiency during the assembly work of the part 20, since the latter can be constituted by mounting the damper 32 in place. as part of part 20.

 Since the three-phase on-load disconnector opens after all current limiting fuses for the three phases have melted, the present invention makes it possible to prevent the impossibility of interrupting an electrical or electrical connection. short circuit between phases, which improves the safety of a circuit.

Claims (10)

 An overcurrent protection circuit comprising current limiting fuses (6A-6C) for three phases and a load-breaking disconnector (5), which is connected to these fuses, characterized in that it comprises means delay circuit (8) for exciting a trip coil (9) and opening said on-load disconnect switch (5) after fusion signals have been sent to the other current limiting fuses, and relays are operating to other phases also, when a fusion signal is sent to a current limiting fuse for at least one other phase.  2. Overcurrent protection circuit according to claim 1, characterized in that it further comprises disconnector opening means for exciting a tripping coil (9) and opening said disconnected disconnector (5) when the moments of fusion of said current limiting fuses are almost all identical.  Overcurrent protection circuit according to Claim 1, characterized in that the said delay means (8) excite the said trip coil (8) and open the said load-breaking disconnector (5) once all the other fuses have been activated. current limiting means for other phases are melting and devices for actuating said current limiting fuses for other phases also expand rapidly, when at least one of said current limiting fuses (6A-6C ) for three phases melts and that an actuating device (6D) for said at least one of said current limiting fuses (6A-6C) unfolds sharply.  Overcurrent protection circuit according to claim 1, characterized in that a three-phase load-breaking disconnector is used as a load-breaking disconnector.  5. Overcurrent protection circuit according to any one of claims 1 to 3, characterized in that the delay determined by the moments of fusion of a current limiting fuse, which melts first, and a fuse current limiting circuit, which melts last among said current limiting fuses for three phases and by the operating times of the actuating devices (6D) is set in said delay means 18).  Overcurrent protection circuit according to any one of claims 1 to 3, characterized in that a circuit having a low power factor is connected to the second side of said load-breaking disconnector and said current limiting fuses. (6A-6C).  7. Protection circuit against sunntensites, characterized in that it comprises:  a movable contact t 22) for each phase, one side of which is electrically connected to a power source terminal (6E), another side of said movable contact (22) being connected to and disconnected from said power source; a portion (20) of an actuating mechanism.  a current limiting fuse (6A) for one phase, inserted between said power source side terminal (6E) and a load side terminal (6F).  said delay means (8) exciting the trip coil (9) to operate said actuating mechanism portion (90), and said movable contact (22) being electrically disconnected from a fixed contact provided on one side of the power source, by said operation of said actuating mechanism portion (20).  delay means (8) triggering the operation by means of the actuation of said relay (7), after the sudden deployment of all the actuating devices,  a relay (7) for a phase, actuated by said actuating device (6D),  an actuating device (6D) for a phase, pre-blank on said load-side terminal (6F) and which expands sharply when at least one fuse, which corresponds to said phase, fails from the current limiting fuses t6A-6E) for three phases, background,  8. Protection device against overcurrent, characterized in that it comprises  a movable contact (99) for each phase, one side of which is electrically connected to a terminal (6E) located on the side of the power source, another side of said movable contact (22) being connected to and disconnected from said source of power; supply by an actuating mechanism part,  each of the current limiting fuses (6A-6C) inserted between said power source side terminal (6E) and a load side terminal (6F),  an actuator (6D) for a phase, provided on said load-side terminal (6F) and which expands sharply when at least one fuse, which corrects for said phase, among current limiting fuses (6A-6C ) for three phases, background,  a relay (7) actuated by said actuating device (6D),  a damper (32), actuated upon actuation of said relay (7), to prevent operation of said actuating mechanical part (20) until a device for actuating a last limiting fuse current, which melts. unfolds sharply.  9. Overcurrent protection circuit according to one of claims 7 or 8, characterized in that a load-breaking disconnecting disconnector is used as a load-breaking disconnector.  10. Sun protection circuit according to one of claims 7 or 8, characterized in that a circuit having a low power factor is connected to the second side of said disconnect switch and said current limiting fuses ( 6.a-6C