AU2003214138B2

AU2003214138B2 - Circuit breaker having fault-current cutoff

Info

Publication number: AU2003214138B2
Application number: AU2003214138A
Authority: AU
Inventors: Mitja Koprivsek
Original assignee: ETI Elektroelement dd
Current assignee: ETI Elektroelement dd
Priority date: 2002-03-18
Filing date: 2003-03-18
Publication date: 2006-03-09
Anticipated expiration: 2023-03-18
Also published as: WO2003079388A1; ATE424036T1; AU2003214138A1; CN101427338B; EP1495477A1; DE10211902A1; DE50311213D1; EP1495477B1; CN101427338A

Abstract

The invention relates to a circuit breaker for automatically interrupting an electrical flow of current (I), comprising a trip element (4), which has a tappet (26) for actuating a switching mechanism (3) and a coil (10) for generating an electromagnetic tripping force that moves the tappet (26) out of a first position and into a tripping position. The invention is characterized in that a second coil (12) is arranged coaxial to the first coil (10), whereby the second coil (12) is flown through by a current (i) that is controlled according to a signal output by a summation current transformer (42) as a response to the detection of fault-currents.

Description

WO 03/079388 Al The invention concerns an automatic circuit breaker for the automatic interruption of an electrical flow of current, in particular an automatic circuit breaker with fault current circuit breaking, with a tripping device which has a plunger for actuating a switching mechanism and a coil for generating an electromagnetic tripping force which moves the plunger out of a first position into a tripping position.

Automatic circuit breakers of this kind are adequately known, DE 199 42 694 Al showing as an example a tripping device used in automatic circuit breakers of this kind.

In wiring systems, the circuits are protected by automatic circuit breakers against thermal overload and against short circuiting. The usual automatic circuit breakers are, however, not capable of protecting people and property if small fault currents occur, such as arise for example when touching live parts or in case of insulation faults. In order to exclude this risk as well, so-called fault current circuit breakers have long been used in the wiring in addition to the automatic circuit breakers.

Owing to the associated high space requirements, combined safety switching devices have already been developed, having in addition to the properties of an automatic circuit breaker the properties of a fault current circuit breaker. An example of such combined safety switching devices can be found in DE 28 34 327 C2. The combined safety switching device known from this has a common switch latch as well as a contact system with explosion chamber, a sum current transducer for detecting the fault currents, an electronic analyser and a tripping device, namely, a bimetal for protection against thermal overload, a magnetic tripping device for short-circuit protection, and a sensitive holding magnet relay for circuit breaking when fault currents occur. For this combined safety switching device too, considerable space requirements are necessary.

It is the object of the present invention to provide a generic automatic circuit breaker which, while retaining a compact design, integrates a fault current circuit breaker.

This object is achieved according to patent claim 1 by the fact that a second coil is arranged coaxially with the first coil, wherein through the second coil flows a current which is controlled as a function of a signal which is emitted by a fault current detector as a response to the detection of fault currents.

Due to the arrangement of the second coil coaxially with the first coil, even in case of detection of a fault current by the fault current detector which is preferably designed as a sum current transducer, there is electromagnetic actuation of the plunger and hence tripping of the switching mechanism. This integration of the second coil in the tripping device and the resulting double use of the tripping device leads to an extremely compact design of the automatic circuit breaker integrating the function of a fault current circuit breaker, without needing as in the state of the art a separate tripping device for the fault current.

It is particularly advantageous if the automatic circuit breaker according to the invention is designed as a series-installed device. This results in the possibility of replacing traditional automatic circuit breakers which are present in already existing wiring systems, with the automatic circuit breaker integrating the fault current circuit breaker according to the invention.

The invention is described in more detail below with the aid of an example with reference to the drawings. The latter show: Figure 1 an automatic circuit breaker partly in section, Figure 2 a tripping device for an automatic circuit breaker according to the invention, and Figure 3 a circuit diagram of the automatic circuit breaker according to the invention.

Figure 1 shows, partly in section, an automatic circuit breaker 1 with an operating handle 2, a switching mechanism 3 which can be actuated by the operating handle 2, and a tripping device 4 which also acts on the switching mechanism 3.

The tripping device 4 has a first coil 10 which is electrically connected by one end to a first terminal 5 of the automatic circuit breaker 1. The other end of the first coil 10 is connected to a further terminal (not shown) of the automatic circuit breaker 1 by a switch which can be actuated by the switching mechanism 3.

Below, the structure of the tripping device 4 is described in more detail with the aid of Figure 2.

As already explained, the tripping device comprises the first coil 10 through which flows a current I to be monitored. Radially within the first coil 10, a second coil 12 is wound on a tube 14. Operation of the second coil 12 is described below. In order to improve heat transfer from the first coil 10 to a thermal tripping device, it is also conceivable that the second coil 12 is arranged radially outside the first coil 10. With the first coil on the outside, a heat-conducting bush (not shown) can also be held on the latter.

In the interior of the tube 14 is provided a core 16 which is fixed relative to the tube 14. Furthermore, in the tube 14 is provided an armature 18 which is slidable relative to the tube 14 in the axial direction of the tube 14. The armature 18 is guided in sliding relationship in the tube. A magnet yoke 20 which serves to close the magnetic field in the exterior space of the coil 10 has a first mounting opening 22 in which the core 16 is held, and a second mounting opening 24 in which is arranged the end of the tube 14 facing away from the core 16. The magnet yoke 20 can also form a mounting housing for mounting the tripping device 4 in a housing body 6 of the automatic circuit breaker 1.

The core 16 has a guide bore 17 in which a plunger 26 is guided in sliding relationship for actuating the switching mechanism 3. The plunger 26 is supported by its radially expanded end section 26' situated in the interior of the tripping device 4, on the bottom of a blind bore of the armature 18. A helical compression spring 28 which is supported by one end on the core 16 and by the other end on the radially expanded end section 26' of the plunger 26 keeps the plunger in contact with the axially slidable armature 18, so that the plunger 26 moves with the armature 18.

At its end passing through the first mounting opening 22 to the outside, the core 16 is engaged with a flange element 30, the flange element 30 being supported against the magnet yoke 20. On the. free face of the flange element which faces away from the magnet yoke 20 and which forms a preferably convexly curved surface, are arranged a bimetal plate 32 and on top of this an actuating plate 34.

The bimetal plate 32 in the cold state and the actuating plate 34 here have a shape corresponding to the convex face of the flange element In Figure 3 is shown the circuit diagram of a two-pole automatic circuit breaker with the characteristics of the present invention. This automatic circuit breaker 1 fulfils three protective functions, namely, protection against short circuiting, protection against overcurrent and protection against fault current.

The current I leading to the load to be monitored (not shown) flows through the line 38 and the switch 36 of the switching mechanism 3, which is normally closed but shown open in Figure 3, to the first coil 10 and through the latter to the load. The line 40 leading back from the load to the current source is passed via a pole of the switch 36 through the automatic circuit breaker 1.

A sum current transducer 42 serving as a fault current detector surrounds the lines 38 and 40 and is capable of detecting a fault current. The signal detected by the sum current transducer is delivered to an electronic analyser 44. This electronic analyser 4 amplifies the signal of the sum current transducer 42, and this amplified signal is delivered as current i to the second coil 12 in the tripping device 4, which is connected by its other end via the switch 36 to the return line Furthermore there is provided a testing device 46 which has a test button 48 with a test contact 50, a test resistor 52 and an auxiliary contact 54 in the switch 36.

The auxiliary contact 54 contacts the test resistor 7 only in the switched-on state of the switch 36 and so ensures that the electronic analyser 44 is live only in the switched-on state. Moreover, by the auxiliary contact 54 it is ensured that the direction of connection of the automatic circuit breaker is random. A testing device of this kind is prescribed by relevant regulations, and with it the operation of the automatic circuit breaker can be tested.

To protect the electronic analyser 44 from surge voltages from the network, the second coil 12 designed with high resistance simultaneously forms a protective resistor for the voltage supply of the electronic analyser 44. Also a varistor 56 which is provided in addition between the poles of the voltage supply for the electronic analyser 44, is provided for short-circuiting and so protecting the voltage supply of the electronic analyser 44 when an overvoltage occurs.

Below, the manner of operation of the automatic circuit breaker 1 is described.

When a short circuit occurs in the region of the lines on the load side or of the load, not shown, connected thereto, the current I increases in pulsed fashion, with the result that this increased current flowing through the first coil 10 of the tripping device 4 generates a magnetic force which acts on the armature 18 and which moves the armature 18 and with it the plunger 26 to the right into the position shown in Figure 2, with the result that the plunger 26 acts on the switching mechanism 3 to open the switch 36 and so interrupt the current flow.

When a minor overcurrent arises, leading to thermal loading of the tripping device 4, the bimetal plate 32 which serves as a thermal tripping device is heated until it reaches its snap temperature, at which it snaps out of the position concave to the left, into a convex position.

Due to this snapping of the bimetal plate 32, the actuating plate 34 which does not change its shape is pushed to the right in Figure 2 and in the process entrains the plunger 26, which at its free end protruding from the tripping device 4 is provided with a thicker portion 27, to the right against the spring force of the spring 28, with the result that the plunger 26 also acts on the switching mechanism 3 to make the switch 36 open and interrupt the flow of current.

When a fault current occurs, this fault current is detected by the sum current transducer 42, and the detection signal is passed to the electronic analyser 44 which in turn amplifies this signal and passes it on as current i to the second coil 12 in the tripping device 4.

Due to this amplified signal a magnetic field builds up in the second coil 12, which likewise moves the armature 18 and the plunger 26 connected thereto in an axial movement directed to the right in Figure 2, with the result that the plunger 26 acts on the switching mechanism 3 to make the switch 36 open and so likewise interrupt the flow of current.

The automatic circuit breaker according to the invention thus integrates three protective mechanisms in a simple and extremely space-saving manner, namely, thermal protection, short-circuit protection and fault current protection. This integration also reduces the number of components needed compared with the traditional state of the art, resulting in considerable economic advantages in mass production. The power loss resulting from additional integration of the fault current circuit breaker in the automatic circuit breaker is not greater than the power loss of a conventional automatic circuit breaker, so that 8 the automatic circuit breaker according to the invention has advantages in energy management, compared with a combination of a conventional automatic circuit breaker and a conventional fault current circuit breaker.

Claims

1. An automatic circuit breaker adapted to provide automatic interruption to O flow of an electric current, the circuit breaker comprising: a tripping device having a plunger adapted to actuate a switching mechanism, 00 oo Mc the plunger extending out from the tripping device and being provided with a _thicker portion at a free end remote from the tripping device; Sa first coil for generating an electromagnetic tripping force which moves the Splunger out of a first position into a tripping position; a second coil arranged coaxially with the first coil; a fault current detector adapted to a emit a signal as a current to the second coil as a response to the detection of a fault current a bimetal plate serving as a thermal tripping element, the bimetal plate being provided on a curved surface of a flange element of the tripping device; and an actuating plate disposed on said bimetal plate wherein the plunger passes through said bimetal plate and said actuating plate, wherein by means of the thicker portion, the actuating plate acts on the plunger in the tripping direction upon a thermally caused snapping of the bimetal plate.

2. An automatic circuit breaker according to claim 1, wherein the fault current detector is a sum current transducer.

3. An automatic circuit breaker according to either claim 1 or claim 2, wherein the automatic circuit breaker is designed as a series-installed device.

4. An automatic circuit breaker substantially as herein before described. An automatic circuit breaker substantially as herein before described with reference to the accompanying drawings.