HK123793A - Static tripping device for a circuit breaker in a cast case - Google Patents

Description

The invention relates to a static trigger of a moulded box circuit breaker having a pair of contacts per pole, elastically applied to the contact in the closed position of the circuit breaker and capable of being separated by an automatic failure control mechanism, comprising sensors that generate fault signals, a function of the currents passing through the protected conductors of the circuit breaker, and a processing unit to which the fault signals are applied to develop a fault trigger order for the circuit breaker, when a predetermined threshold is exceeded, the order being based on the value of the fault signals.

The contacts of an electrical circuit breaker must open open open to avoid any intermediate position of contact repulsion, the latter being nevertheless insufficiently separated for the arc drawn between the contacts to be extinguished. The persistence of the arc between the partially open contacts causes heating and destruction of the circuit breaker.

To ensure that a circuit breaker does not remain in an intermediate contact repulsion position, the default trigger threshold is usually set to a value below the repulsion threshold.It is difficult and expensive to make circuit breakers with well-defined repulsion and trigger thresholds and to compensate for these inaccuracies, it is common to choose a trigger threshold 20 to 50% below the repulsion threshold, resulting in a significant loss of selectivity.

The purpose of the present invention is to allow the manufacture of a trigger whose trigger threshold and repulsion threshold are confused.

Another purpose of the invention is a trigger that provides instantaneous activation when a circuit breaker is closed in case of a fault.

The trigger according to the invention is characterised by an arc detector being associated with each pair of contacts to detect the light emitted by the arc drawn during a separation of contacts, the arc signals emitted by the said arc detectors being applied to the processing assembly to cause an instantaneous trigger when simultaneously the fault signals exceed the said predetermined threshold.

Any separation of contacts, particularly by electrodynamic repulsive forces, causes the formation of a spark or arc emitting light easily detectable by optical sensors such as photoelectric components which are preferably placed away from the arc zone and connected to it by light conductors such as optical fibres. By arranging the arc sensors or detectors within the moulded housing, the disturbances due to external light can be avoided in a particularly simple way.It is easy to understand that the detection of the presence of an arc and the detection of a fault current do not require particular precision, since the light emitted by the arc is very abundant and the difference between a current that can cause the contacts to be repelled and the nominal current of the circuit breaker is very large. Depending on the current configuration or characteristics of the pole, electrodynamic repulsion can occur on a single pair of contacts of the circuit breaker and it is important to detect this repulsion by associating it with each pair of contacts of the circuit breaker,In the case of an optical fiber, it is possible to collect light emitted by any of the poles of the circuit breaker by passing this fiber through the various arc compartments near the contact pairs, but it is conceivable to have a detector in a location in the moulded case allowing to see through holes in the internal partitions of the moulded case, the light emitted by any of the contact pairs. To each pair of contacts, an optical fiber can be associated to transmit light to the processing unit.

The use of light to detect contact repulsion ensures that no triggering occurs before the contacts are separated by electrodynamic repulsion and, conversely, that the circuit breaker is instantly triggered when any pair of contacts is repulsed.

The static trigger according to the invention has analogue and/or digital processing circuits, the instantaneous trigger circuit being advantageously analogue in order to have a very short response time. The subordination of instantaneous triggering to the simultaneous presence of an arc signal and a fault signal can be achieved by an appropriate means, in particular by an ET circuit, which receives both arc and fault signals on its inputs.

The static trigger according to the invention also provides instantaneous protection when the circuit breaker is closed by default. In this case it is important to cause the circuit breaker to be opened immediately, regardless of the short-delay and long-delay trigger circuits which provide a timing which is computable with the trigger selectivity. A default shutdown automatically causes an arc on the contacts which is detected by the arc detectors as well as an overcurrent signalled by a fault signal, causing the circuit breaker to be opened. The device according to the invention advantageously replaces the timed contacts which inhibit the instantaneous trigger after a certain time.

Other advantages and characteristics will be more clearly seen in the following description of a method of manufacture given as a non-limiting example and shown in the attached drawing in which the single figure represents the synoptic diagram of a trigger according to the invention.

In the figure, a 3-conductor R, S, T power supply network (not shown) has a circuit breaker 10 capable of interrupting the circuit in the opening position. The mechanism 12 of the circuit breaker 10 is operated by a polarized relay 14 to trigger the circuit breaker in the event of overload or short circuit. An auxiliary contact 16, associated with the main contacts 17R, 17S, 17T of the circuit breaker 10, indicates the position of these main contacts 17R, 17S, 17T. To each conductor R, S, T is attached an 18 junction transformer that delivers a signal proportional to the current flowing through the associated conductor,The output of the three rectifier bridges 20 is connected in series in a circuit comprising a resistor 22, a zener diode 24 and a diode 26 to give at the terminals of the resistor 22 a voltage signal proportional to the maximum current flowing through the conductors R, S, T and at the terminals of the diode 24 a voltage supplying the electronic circuits. The voltage signal is applied to the input of the amplifier 28, the output of which is connected to an analogue-to-digital converter 30. The output of the analogue-to-digital converter 30 is connected to an input 1 of a microprocessor 32.The microprocessor 32 also has an output 2 connected to the polarized relay 14, an input 3 receiving the signals of a clock 34, an input 4 connected to a 36 key 44 keyboard, an input 6 connected to a ROM 38 memory, an input/output 5 connected to a non-volatile NOVRAM 40 memory, an output 7 connected to a display device 42 and an input 8 connected to the auxiliary contact 16.

The trigger in Figure 1 performs the protective function, in particular the long delay and/or short delay trigger respectively in the event of an overload and a fault in the circuit of the conductors R, S, T. The digital signal representing the maximum current value in the conductors R, S, T is applied to input 1 of the microprocessor 32 and compared with threshold values stored in memory to detect any exceeding of these thresholds and generate a temporary or instantaneous trigger order, which is transmitted to floor 14 to cause the opening of the circuit.

The invention can be used in any static trigger and is in no way limited to the trigger of the type described above. As an example, but not limited, the means of detecting current may include current sensors providing analogue signals representative of the derivative of the di/dt current and whose output is connected to integrated circuits, the output signals of the integrated circuits being transmitted to the microprocessor via an analogue-to-digital converter. The static trigger may also be analogue.

According to the present invention, the circuit breaker 10 has a casing of the type of a moulded case within which the main contacts 17R, 17S, 17T of the three poles of the circuit breaker are arranged. The three poles R, S, T are separated by walls defining the internal compartments of the moulded case and to each pole is attached an arc detector 46R, 46S, 46T arranged near the main contacts 17R, 17S, 17T. The light collected by the 46R, 46S, 46T arc detectors is transmitted by a fiber optic 48 to a photoelectric component 50 which emits an electrical signal proportional to the light captured,The output of the ET 52 is connected by a diode 56 to the polarized relay 14 and a diode 58 is inserted into the link between the output 2 of the microprocessor 32 and the polarized relay 14 to prevent interference between the trigger signals applied to the polar relay 14 by the microprocessor 32 and the arc-repellent instantaneous trigger circuit, respectively.

The static trigger according to the invention shall operate as follows:

In the event of overload or failure, the microprocessor 32 causes the circuit breaker 10 to fire in the usual manner, possibly temporarily. The separation of the contacts 17R, 17S, 17T causes the light to be emitted, detected by the arc detectors 46R, 46S, 46T, and transmitted by fiber optics 48 to the photoelectric component 50 which applies a signal to the 52 circuit. This circuit 52 ET which receives a fault signal at its other input to the polar relay 14 sends an overloaded trigger order, the latter order having already caused the triggering of the 10 circuit.

In the case of a high-intensity short-circuit current above the repulsion threshold of contacts 17R, 17S, 17T, or any of these contacts, they separate with arc formation detected by the 46R, 46S, 46T sensors. The arc signal applied to the ET 52 circuit, which simultaneously receives the fault signal from amplifier 28 and the threshold circuit 54, generates a trigger order transmitted to the polar relay 14. This trigger immediately occurs and causes the contacts of the circuit breaker 10 to be opened immediately, avoiding any intermediate position of the contacts which could cause a heating and destruction of the circuit breaker.The detectors 46R, 46S, 46T, which are placed inside the moulded housing, are protected from outside light and are not likely to cause untimely triggers. They detect, however, sparks or arcs appearing on the main contacts 17R, 17S, 17T when the circuit breaker 10 is normally closed or opened, particularly by manual operation, but the arc signal is blocked by the ET 52 port, which does not receive a fault signal on its other input.17S, 17T. The short-delay and long-delay trigger thresholds may be chosen near the contact threshold, any false manoeuvre being excluded by the arc detection device of the invention.

The inhibition of the instantaneous arc signal can of course be achieved by different means, including by overload detectors independent of the sensors driving the short-delay and long-delay firing. The light conductor can be a plastic optical fiber whose adjacent end of the main contacts 17R, 17S, 17T is stripped over a short length to capture the light from the arc, the stripped end of the fiber constituting the arc detector. Three independent fibers can of course be used, each associated with one of the three pairs of contacts, these fibers controlling the electronic 50 light-sensitive prejunction which may be a photodiode or a photistor. The optical fiber extinguisher 48 is stripped for example by means of this mechanism or a suitable mechanism which is subjected to a net discharge due to the presence of a sharp or sensitive light.

The instantaneous arc detection trigger of the invention can of course be used in different types of static trigger, in particular analogue type.

The trigger according to the invention also provides instantaneous protection during a failure lock by:

When circuit breaker 10 is closed by default, an arc appears on the main contacts 17R, 17S, 17T and this arc is detected by the detectors 46R, 46S, 46T which emit an arc signal applied to the gate 52. AND the default closure is operated, the fault current is detected by the circuit 54 which sends a fault signal to the gate AND causing the instantaneous triggering of the circuit breaker 10. In normal operation, the detectors 46R, 46S, 46T emit no signal and only the long- and short-delay triggers provide protection.

The invention is of course by no means limited to the particular implementation described.

Claims (6)

1. A solid-state trip device of a molded case electrical circuit breaker having per pole a pair of contacts (17R, 17S, 17T) elastically urged into contact in the closed position of the circuit breaker and capable of separating by the action of an automatic operating mechanism (12) on a fault, comprising sensors (18), which generate fault signals which are a function of the currents flowing in the conductors (R, S, T) protected by the circuit breaker, and a processing unit (20-32, 50-54) to which said fault signals are applied to generate a circuit breaker tripping order, when preset thresholds are exceeded, said order being time-delayed according to the value of the fault signals, characterized in that an arc detector (46R, 46S, 46T) is associated with each pair of contacts (17R, 17S, 17T) to detect the light emitted by the arc drawn when the contacts separate, the arcing signals emitted by said arc detectors (46R, 46S, 46T) being applied to said processing unit (20-32, 50-54) to bring about instantaneous tripping when at the same time the fault signals exceed said preset threshold.

2. The solid-state trip device according to claim 1, characterized in that said processing unit (20-32) performs, in addition to said instantaneous trip, a long delay and short delay tripping function.

3. The solid-state trip device according to claim 1 or 2, characterized in that said processing unit (50-54) comprises an AND circuit (52) to whose inputs the fault tripping order and the arc tripping order are respectively applied.

4. The solid-state trip device according to any one of the above claims, characterized in that said arc detectors (46R, 46S, 46T) are formed by a bared end of an optic fiber (48) transmitting light from the arcing zone of the circuit breaker to said processing unit.

5. The solid-state trip device according to any one of the above claims, characterized in that said processing unit comprises a light-sensitive electronic component (50), connected to the arcing zone of the circuit breaker by one or more light conductors (48).

6. The solid-state trip device according to any one of the above claims, characterized in that the instantaneous trip processing unit (50-54) is an analog circuit.