EP2842151B1 - Driver circuit for a circuit breaker - Google Patents

Description

TECHNICAL AREA

The present invention relates to an actuating device for controlling an electrical disconnection device, such as a medium voltage or high voltage circuit breaker.

STATE OF THE PRIOR ART

A circuit breaker, for example in a gas-insulated electrical substation called GIS according to the English "Gas Insulated Substation", is equipped with a control. This control provides the energy and torque needed to move the circuit breaker contacts.

The controls can be hydraulic, pneumatic or spring type. The present invention is more particularly described for a spring drive, but also applies to other types of controls.

Under the effect of an actuating mechanism, a spring-loaded control mechanically acts to open or close the contacts of a circuit breaker. A conventional actuation mechanism includes a coil that drives a plunger when current flows through the coil. The plunger is connected to a movable pawl, so that the spool controls the mechanical operation of the spring drive by moving the plunger and hence the pawl.

A coil capable of being traversed by a current capable of displacing the plunger and the pawl typically comprises 1103 turns wound around a magnetic core. This means that the inductance of the coil is high, as is its time constant since it is proportional to the inductance. Thus, the action time with known solutions currently reaches 5.5 ms.

This value contributes significantly to the break time of a circuit breaker. Since high-voltage circuit breakers in 60 Hz electrical networks often have to clear a fault in two cycles, their cut-off time is limited to 33.3 ms. To achieve this value, the action time of the actuating mechanism must be as limited as possible.

The document US 5,889,645 relates to a control mechanism of a gas valve in an oven. This mechanism has two coils for actuating the gas valve. The coils are driven by a single input signal emitted by a microprocessor and amplified by a transistor.

This implies that a failure of the microprocessor or transistor would prevent the control mechanism from operating. Thus, even by transposing the teaching of this document to the control of an electrical disconnection apparatus, such as a circuit breaker, a control device having a satisfactory level of reliability would not be obtained.

Indeed, a medium voltage circuit breaker or high voltage is in use for a period that can typically be 25 to 40 years. This time is very long for an actuator circuit and in particular for components such as transistors that can have a shorter life. A solution in which a component may thus fail the circuit breaker is not satisfactory.

The document US 5,159,522 relates to an electric clutch control also comprising two coils. One of them operates the clutch and the other maintains it in its actuated state.

According to one embodiment, a first input terminal and a first transistor feed a first coil, while a second input terminal and a second transistor feeds the two coils.

By transposing the teaching of this document to the control of an electrical disconnection device, such as a circuit breaker, this time we would not have the disadvantage related to the risk of failure of a transistor. However, this solution is more complex and requires in particular two separate power supplies.

The document JP 2009302358 discloses a circuit in which a coil is fed via a transistor and a capacitor in a first phase. In a second phase, the transistor is blocked and the current flowing through the coil is limited by a resistive element in series with the coil.

This type of circuit can not be transposed to the control of a circuit breaker. Indeed, for a circuit-breaker, the current to be interrupted in the activation circuit must be less than 4 A (continuous) according to IEC 622271-1, § 5.4.4.5.4. This implies a minimum value of resistance for a given voltage. For example, for 110 V and 4 A, the sum of the resistances of the coil and the resistive element is at least 27.5 Ohm.

Furthermore, the dead time of the mechanism must be low, typically less than 300 ms to comply with the cycle of operation detailed in IEC 62271.100, § 4.104.

This implies that the intrinsic resistance of the coil must be low, typically 4 Ohm. Thus the resistance of the resistive element is at least 23.5 Ohm.

These values have two consequences: the energy dissipated by the resistive element would be six times greater than that dissipated by the coil, which is not desirable. In addition, the coil would have a very small number of turns to have a low intrinsic resistance. A current of 4 A through this coil would not create sufficient magnetic flux to drive the moving parts into their actuated position.

The document US 4 222 123 A relates to a control circuit of a high speed solenoid comprising a stop coil and two parallel branches connected to the solenoid.

DISCLOSURE OF THE INVENTION

• La première branche comporte uniquement une première bobine,
• La seconde branche comporte une seconde bobine d'impédance plus faible que la première, en série avec un commutateur commandé par un circuit de commutation.

The invention aims to solve the problems of the prior art by providing an actuator circuit of a control of a circuit breaker, characterized in that it comprises two branches in parallel between two terminals and in that

• The first branch comprises only a first coil,
• The second branch has a second impedance coil lower than the first, in series with a switch controlled by a switching circuit.

Thanks to the invention, the action time of the actuator circuit is reduced and remains compatible with the speed requirements of a circuit breaker.

In addition, the first branch has a redundancy function. If the second branch becomes inoperative, for example because of the failure of a component, then the first branch provides the function of actuating the command. Thus, a failure of a component does not prevent the operation of the device. Since the first coil has a higher impedance than the first one, the current flowing through the first coil remains relatively small compared to the current in the second coil and can be interrupted by an auxiliary switch.

According to a preferred characteristic, the switching circuit is adapted to limit the intensity of the current flowing through the second coil and to open the second branch after a predetermined time, after a potential difference is applied between the two terminals.

Thus, the current to be interrupted remains at a value of less than 4 A (continuous), and complies with the requirements of IEC 622271-1.

According to a preferred characteristic, the switch comprises a component chosen from a a field effect transistor, an NPN junction transistor, a thyristor or a mechanical relay.

These components contribute to obtaining a reduced action time for the actuator circuit.

According to a preferred characteristic, the first and second coils are wound around the same core. Thus, induced currents are created, including a current in the first coil when the current is interrupted in the second coil, which ensures full displacement of the plunger.

The invention also relates to a control of a circuit breaker comprising an actuator circuit as previously presented. It may be a spring loaded control.

The invention also relates to a circuit breaker comprising a control provided with an actuator circuit as previously presented.

The control and the circuit breaker have advantages similar to those previously exposed.

BRIEF DESCRIPTION OF THE DRAWINGS

• La figure 1 représente de manière schématique un disjoncteur équipé d'une commande à ressort munie d'un circuit actionneur selon l'invention,
• La figure 2 représente le circuit actionneur selon l'invention.

Other features and advantages will appear on reading a preferred embodiment given by way of non-limiting example, described with reference to the figures in which:

• The figure 1 schematically represents a circuit breaker equipped with a spring-type control provided with an actuator circuit according to the invention,
• The figure 2 represents the actuator circuit according to the invention.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

With reference to the figure 1 , a medium or high voltage circuit breaker 20 comprises a spring control 21 which provides the energy and torque necessary for the movement of the contacts of the circuit breaker.

The circuit breaker 20 and the control 21 are conventional except for an actuator circuit 22 which controls the control 11. The circuit breaker and the control are not described in detail here. The actuator circuit is detailed below.

With reference to the figure 2 , the actuator circuit according to the invention comprises two parallel branches between two terminals 5 and 6 to which a potential difference can be applied to operate the actuator circuit.

The first branch comprises only a coil 1. For example, the coil 1 comprises 1000 turns and has an impedance of 35 Ohm. This branch has a redundancy function. If the second branch becomes inoperative, for example because of the failure of a component, then the first branch provides the actuating function of the spring control. It is then a so-called degraded mode of operation.

The second branch has a coil 2 and other components that will be detailed later. For example, the coil 2 has 363 turns and has an impedance of 3.55 Ohm. Of course, other impedance values of the coils 1 and 2 can be chosen, provided that the impedance of the coil 1 is greater than that of the coil 2. The second branch provides the so-called normal operating mode.

Because of the difference in impedances, the operation in degraded mode (first branch) will then be a little slower than in normal mode (second branch). For example, measured values on a prototype are 3.2 ms in normal mode and 5.5 ms in degraded mode.

According to one embodiment, the coils 1 and 2 are formed by winding around the same core.

The second branch is now described. From terminal 5, the coil 2 is connected in series with a switch which can open the second branch. The switch is connected to the terminal 6. In a preferred embodiment, the switch mainly comprises a transistor 3. The transistor 3 is a field effect transistor, for example of the MOSFET type. The drain of the transistor 3 is connected to the coil 2 and the source of the transistor 3 is connected to the terminal 6. Other types of components can be used as a switch, in particular an NPN junction transistor, a thyristor or a mechanical relay. .

The transistor 3 limits the intensity of the current flowing through the coil 2 to a value that makes it possible to interrupt the current by an auxiliary switch. As already mentioned, the breaking capacity of an auxiliary switch is limited to a current of maximum intensity of 4 A. With a coil 2 of impedance 3.55 Ohm, and in the absence of current limitation by the transistor 3, if a voltage is applied to the terminals 5 and 6 respectively located at the ends of the two branches, this would lead to a current of 31 A in the coil 2. This value being much greater than the maximum allowable value of 4 A, the transistor 3 limits the current going through the reel 2.

A diode 4 is connected in parallel with the coil 2. The anode of the diode 4 is connected to the drain of the transistor 3 and the cathode of the diode 4 is connected to the terminal 5. The diode 4 limits the effects of the overvoltage appearing at the opening of the second branch by the transistor 3.

The transistor 3 is controlled by a control circuit, or switching, which comprises a bipolar transistor 8 whose collector is connected to the gate of the transistor 3.

The collector of the transistor 8 is also connected to a terminal of a resistor 12 whose other terminal is connected to the terminal 5. The emitter of the transistor 8 is connected to the terminal 6. The resistor 12 is for example 56 kOhms.

The base of the transistor 8 is connected to the anode of a Zener diode 9 whose cathode is connected on the one hand to a capacitor 10 and a resistor 11 in parallel. The capacitor 10 and the resistor 11 are connected to the terminal 6. The capacitor 10 has for example a capacity of 0.1 μF and the resistor 11 is 56 kOhms.

The cathode of the Zener diode 9 is on the other hand connected to a resistor 13, itself connected to the terminal 5. The resistor 13 is for example 200 kOhms.

The operation of the switching circuit is as follows.

As soon as a potential difference is applied at the terminals 5 and 6, a current flows through the second branch and therefore the coil 2 and the capacitor 10 is charged via the resistor 13. When the voltage across the capacitor reaches a certain value, example 10.7 V with the previously given numerical values, a current flows through the transistor 8, from its transmitter to its base.

Because of the resistance 12, the electrical potential of the collector of the transistor 8 and the gate of the transistor 3 then drops.

The transistor 3 then opens the second branch, so that the current flowing through the coil 2 is interrupted, after about 2 ms.

It should be noted that because of the impedance of the coil 1 which is higher than that of the coil 2, the current flowing through the coil 1 remains low enough to be interrupted by an auxiliary switch.

As already mentioned, the coils 1 and 2 are preferably wound on the same core. This creates induced currents. When the transistor 3 interrupts the passage of the current in the coil 2, it induces a current in the coil 1. This induced current can be used to maintain the magnetic field necessary to move the plunger of the mechanism. Indeed, the current in the coil 2 is interrupted after for example 2 ms. This time may be too short for the diver to reach his final position actuated. The current induced in the coil 1 then allows the diver to finish his race.

In a variant, the control circuit of transistor 3 is an RC circuit. In this case, a capacitor is connected between the terminal 5 and the gate of the transistor 3, and a resistor is connected between the terminal 6 and the gate of the transistor 3. The resistance and capacitance values are chosen so that the time constant RC is equal to a determined value, for example 2 ms.

It should be noted that the invention finds not only application in a gas-insulated electrical substation called GIS according to the English "Gas Insulated Substation", but also in other types of connection apparatus, for example aeronolated, circuit breakers in oil bath, both indoors and outdoors.

Claims (6)

1. An actuator circuit for actuating a circuit breaker controller, the circuit comprising two branches in parallel between two terminals (5, 6),

   • the first branch includes only a first coil (1); and

   • the second branch includes a second coil (2) having impedance that is lower than the first, in series with a switch (3) controlled by a switch circuit.
2. An actuator circuit according to claim 1, characterized in that the switch circuit is adapted to limit the strength of the current flowing in the second coil (2) and to open the second branch after a predetermined time period, after a potential difference has been applied between the two terminals (5, 6).
3. An actuator circuit according to claim 1 or claim 2, characterized in that the switch (3) includes a component selected from a field-effect transistor, an NPN junction transistor, a thyristor, and a mechanical relay.
4. An actuator circuit according to any one of claims 1 to 3, characterized in that the first and the second coils (1, 2) are wound around a single core.
5. A circuit breaker controller (21) comprising an actuator circuit according to any one of claims 1 to 4.
6. A circuit breaker (20) comprising a controller provided with an actuator circuit according to claim 5.

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