GB2082408A

GB2082408A - Earth leakage circuit-breaker

Info

Publication number: GB2082408A
Application number: GB8118653A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-08-21
Filing date: 1981-06-17
Publication date: 1982-03-03
Also published as: BE890026A; ATA426180A; ES503752A0; NL8102641A; CH655411B; SE8104979L; FR2489038B1; ES8204223A1; SE447684B; IT1143408B; GB2082408B; FR2489038A1; DE3129277A1; IT8149106A0; DE3129277C2

Abstract

A core-balance transformer 4 has a core 9 consisting of highly permeable magnetic material the residual induction of which is less than 40% of the saturation induction (measured statically) and the secondary winding of the transformer has a number of turns in excess of 100. The secondary is connected by way of a rectifier 6 to a capacitor 5 which discharges via a voltage-dependent semiconductor element 7, on reaching a predetermined charged voltage, into the coil of a permanent magnet tripping device 8. <IMAGE>

Description

SPECIFICATION Fault current circuit-breaker The invention relates to a fault current circuitbreaker consisting of contact apparatus, a tripfree switching mechanism and actuating member, a summation transformer, an electronic energy storage circuit and a fault current tripping device with a permanent magnet in a housing consisting of insulating material with connecting terminals for the installation leads. According to the invention, the summation transformer comprises a core consisting of a highly permeable material, whereof the residual induction is less than 40% of the saturation induction (measured statically) and a secondary winding which has a number of turns exceeding 100 and is connected to the fault current tripping device of the switching mechanism by way of an electronic energy storage circuit which is independent of the mains voltage.The energy storage circuit which is independent of the mains voltage consists of a capacitor, which is charged by way of suitable rectifier circuits by the summation transformer in a manner dependent on the fault current and which discharges by way of a voltage-dependent semiconductor element on reaching a certain charging voltage of the capacitor in pulses by way of the trip coil of the fault current tripping device. Consequently the fault current circuit-breaker is tripped. The fault current tripping device is preferably a polarized tripping device and has an air gap in the excitation circuit. The rectifier circuit is advantageously constructed as a voltage multiplication circuit.

The fault current circuit-breaker has been in use for several decades and it is therefore time to gather the facts together, examine them critically and find new technical solutions in case a necessity arises for this.

The three basic circuits possible for the construction of fault current circuit-breakers were disclosed more than twenty years ago (1,2). The fault current circuit-breakers recommended at that time with pulse or stored energy tripping, an invention which led the way (Austrian PS 1 97. 468) was built in Austria in large numbers and have proved reliable. They were also patented and used abroad (French PS 1 202 203, GB PS 841.181). At that time a glow lamp was used as the switching member in the energy storage circuit, which made this solution expensive (high number of secondary winding turns in the summation transformer) and required too much space.Although the circuit-breakers had advantages with regard to reliability and characteristic behaviour, because the tripping energy was substantially higher than in direct circuits without an electrical energy storage circuit, competition with a trend towards ever decreasing prices and dimensions of the fault current circuit-breakers led to pulse tripping being used solely for special circuit-breakers (for example neutralization circuit-breakers). In this economic battle, irrelevant arguments were used at that time, such as for example the requirement of extremely short tripping times, which naturally leads to difficulties in the case of storage circuits.Today, on the basis of the results of modern electropathology, it is known that for protecting against direct and in the case of indirect contact, as long as the tripping time of the circuit breaker is less than 0 2 secs, it has no special significance. Tripping times which are too short and unnecessarily high tripping sensitivities lead solely to incorrect tripping due to admissible discharge currents or when connecting cables and'upon the occurrence of atmospheric excess voltages. Economic damage has occurred (deep freezers) particularly in overhead-line systems.

The operational reliability of the circuitbreaker is much more important and in this case the above described development has eliminated unfavourable results. Increasingly more sensitive tripping devices were developed, in which case it was no longer possible to overcome manufacturing problems and environmental factors. Today examinations of the installations show that several percent of the fault current circuit-breakers installed are not operational. This is an intolerable situation which causes great anxiety.

One solution of this serious problem on the one hand provides the introduction of neutralization, which together with fault current circuit-breakers facilitates an extremely high grade and reliable protective measure in the form of the so-called neutralization protective circuit, on the other hand in systems where neutralization is not allowed, the series connection of two fault current circuit-breakers.

Naturally, in this case, the succeeding switch should switch selectively, that is to say that in the case of a fault only the installation protected by the latter is disconnected and the preceding circuit-breaker, which protects several parts of the installation in the distribution, remains connected. This requirement can be fulfilled in a simple manner by the energy storage circuit. This circuit also prevents the above-mentioned incorrect tripping in the case of atmospheric excess voltages, indeed it even facilitates the incorporation of excess voltage diverters after the fault current circuit-breakers. Upon the response of the excess voltage diverters, current flows from the mains to earth for a short time (below 10 m secs), through the fault current circuit-breaker with direct tripping without the electrical energy storage circuit being switched off.

Now it happened that before too long suitable semiconductor members were obtainable, which since they were inexpensive and had small dimensions were able to supercede the glow lamp as the switching member. With switching voltages of about 10 volts, they facilitate small numbers of secondary winding turns of the summation transformer and virtually any tripping characteristics of the circuitbreaker. In order to keep the capacitor small also, permanent magnet tripping devices are advantageously used as tripping devices, which can be adjusted in a less critical manner and can be allowed to operate with higher tripping forces than in the case of direct circuits without an electrical energy storage circuit.In the case of economical core dimensions of the summation transformer, in order to achieve a form of the tripping characteristic of the fault current circuit-breaker which is favourable for protection against contact, according to the invention the secondary winding is provided with a number of turns which is in excess of 100. The excitation winding of the permanent magnet tripping device must be provided with a number of turns which provides the most favourable form of tripping pulse for the fault current tripping device used, upon discharge of the capacitor. This is possible in the simplest manner with the socalled polarized permanent magnet tripping devices, the excitation circuits of which comprise an air gap. Consequently the excitation winding can be produced on winding machines and the manufacture is largely automated (3).

However, the modern concept of a fault current circuit-breaker must also control tripping in the case of pulsating direct currents.

Indeed it was always known that fault current circuit-breakers can only be effective with alternating current. If the fault current has d.c.

components, then the tripping sensitivity of the circuit-breakers, is influenced in an unfavourable manner. Since an increasing number of electronic components are used in household appliances, the d.c. problem must also be solved, in which case it has been found that in the case of the circuits used in practice in electrical household appliances, in the case of an earth fault, the flowing fault current can occur always solely in the form of a pulsating direct current.

Now in recent years, magnetic materials have been developed in which despite relatively high permeability, the difference between residual induction and saturation induction is high. This means that measured statically, residual induction amounts to less than 40% of saturation induction. However, with this material it is possible, admittedly with lower tripping sensitivity, to achieve operation of the fault current circuit-breakers with fault currents in the form of pulsating direct currents. Then, since the induced voltage in the secondary winding with the same effective value of the primary current is less than with sine-wave alternating current, the energy storage circuit may in this case provide a more favourable tripping behaviour.Above all, the energy content of the tripping pulses, which are provided by the switching voltage of the semiconductor member, are the same and so is the reliability of tripping.

Thus, according to the invention, the modern concept of a fault current circuit-breaker comprises a switch with a mains voltageindependent electronic energy storage circuit in the tripping device circuit, a summation transformer with a core consisting of a highly permeable magnetic material with a large difference between the residual and saturation induction and a permanent magnet tripping device, which is preferably constructed as a polarized tripping device.

Figure 1 shows one embodiment of the invention by way of example. The contact apparatus 1 of the fault current circuit-breaker is energized or de-energized by way of the switching mechanism 2 by means of the actuating member 3 or the fault current tripping device 8. The excitation winding of the fault current tripping device 8 is connected to the pulse capacitor 5 by way of the voltagedependent switching member 7, which is illustrated as a semiconductor member. The capacitor is charged by way of the rectifier circuit 6 by the secondary winding of the summation transformer 4 depending on the value of the flowing fault current. The core 9 of the summation transformer is made from a highly permeable magnetic material, the residual induction of which is less than 40% of the saturation induction.

As a further example of the invention Fig. 2 shows a tripping device circuit, in which the pulse capacitor 5 is charged by the secondary winding of the summation transformer 4 by way of a voltage doubler circuit. A polarized tripping device is used as the tripping device, which in the excitation circuit comprises an air gap between the pole shoes 10 and the armature 11, so that when the armature is lifted off, the winding 12 can be placed on the pole shoe in the finished wound state.

Claims

1. Fault current circuit-breaker consisting of a contact apparatus (1), a trip-free switching mechanism (2) and actuating member (3), a summation transformer (4), an electronic energy storage circuit and a fault current tripping device with permanent magnet (8) in a housing consisting of insulating material with connecting terminals, characterised by the fact that the summation transformer has a core consisting of highly permeable magnetic material, the residual induction of which is less than 40% of the saturation induction (measured statically) and the secondary winding of which having a number of turns in excess of 100 is connected by way of a mains voltage-independent electronic energy storage circuit to the fault current tripping device of the switching mechanism, in which case the mains voltage-independent electronic energy storage circuit consists of a capacitor (5) which is charged by way of suitable rectifier circuits (6) by the summation transformer (4) in a fault current dependent manner and which discharges by way of a voltage-dependent semiconductor element (7) on reaching a certain charging voltage of the capacitor in pulses by way of the tripping coil of the fault current tripping device (8) and thus trips the fault current circuit-breaker (Fig. 1).

2. Fault current circuit-breaker according to claim 1, characterized by the fact that the fault current tripping device (8) is constructed as a polarized tripping device and has an air gap in the excitation circuit (Fig. 2).

3. Fault current circuit-breaker according to claim 1 and/or 2, characterised by the fact that the rectifier circuit (6) consists of a voltage multiplication circuit.

4. Fault current circuit-breaker substantially as hereinbefore described with reference to the accompanying drawings.