Actuator circuit for control of circuit breaker

Abstract

The invention relates to an actuator circuit for actuating a circuit breaker controller, the circuit being characterized in that it comprises two branches in parallel between two terminals and in that the first branch includes only a first coil; the second branch includes a second coil having impedance that is lower than the first, in series with a switch controlled by a switch circuit.

Claims

1. An actuator circuit for actuating a circuit breaker controller, the circuit comprising: two branches in parallel between two terminals, wherein: the first branch includes only a first coil; and the second branch includes a second coil having impedance that is lower than the first coil, in series with a switch controlled by a switch circuit and a diode connected in parallel to the second coil, wherein the switch circuit comprises a bipolar transistor, wherein a collector of the bipolar transistor is connected to one terminal of a first resistor, another terminal of the first resistor is connected to a first terminal of the two terminals, an emitter of the bipolar transistor is connected to a second terminal of the two terminals, and a base of the bipolar transistor is connected to an anode of a Zener diode, wherein a cathode of the Zener diode is connected to a capacitor and a second resistor connected in parallel to each other and to the second terminal, and wherein the cathode of the Zener diode is connected to a third resistor connected to the first terminal.

2. An actuator circuit according to claim 1, wherein: the switch circuit is adapted to limit the strength of the current flowing in the second coil-and to open the second branch after a predetermined time period, after a potential difference has been applied between the two terminals.

3. An actuator circuit according to claim 1 wherein: the switch 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 claim 3, wherein: the switch is a field-effect transistor, wherein the collector of the bipolar transistor is connected to a gate of the field-effect transistor.

5. An actuator circuit according to claim 1 wherein: the first and the second coils are wound around a single core.

6. An actuator circuit according to claim 1, wherein an anode of the diode is connected to the switch and a cathode of the diode is connected to one of the terminals.

7. A circuit breaker controller comprising an actuator circuit having two branches in parallel between two terminals wherein: the first branch includes only a first coil; and the second branch includes a second coil having impedance that is lower than the first coil, in series with a switch controlled by a switch circuit and a diode connected in parallel to the second coil, wherein an anode of the diode is connected to the switch and a cathode of the diode is connected to one of the terminals, wherein the switch circuit comprises a bipolar transistor, wherein a collector of the bipolar transistor is connected to one terminal of a first resistor, another terminal of the first resistor is connected to a first terminal of the two terminals, an emitter of the bipolar transistor is connected to a second terminal of the two terminals, and a base of the bipolar transistor is connected to an anode of a Zener diode, wherein a cathode of the Zener diode is connected to a capacitor and a second resistor connected in parallel to each other and to the second terminal, and wherein the cathode of the Zener diode is connected to a third resistor connected to the first terminal.

8. A circuit breaker comprising a controller provided with an actuator circuit having two branches in parallel between two terminals wherein: the first branch includes only a first coil; and the second branch includes a second coil having impedance that is lower than the first coil, in series with a switch controlled by a switch circuit and a diode connected in parallel to the second coil, wherein an anode of the diode is connected to the switch and a cathode of the diode is connected to one of the terminals, wherein the switch circuit comprises a bipolar transistor, wherein a collector of the bipolar transistor is connected to one terminal of a first resistor, another terminal of the first resistor is connected to a first terminal of the two terminals, an emitter of the bipolar transistor is connected to a second terminal of the two terminals, and a base of the bipolar transistor is connected to an anode of a Zener diode, wherein a cathode of the Zener diode is connected to a capacitor and a second resistor connected in parallel to each other and to the second terminal, and wherein the cathode of the Zener diode is connected to a third resistor connected to the first terminal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages appear on reading about a preferred embodiment described by way of non-limiting example, and with reference to the figures in which:

(2) FIG. 1 is a diagram showing a circuit breaker fitted with a spring controller provided with an actuator circuit of the invention; and

(3) FIG. 2 shows the actuator circuit of the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(4) With reference to FIG. 1, a medium- or high-voltage circuit breaker 20 includes a spring controller 21 that supplies the energy and torque necessary for moving the contacts of the circuit breaker.

(5) The circuit breaker 20 and the controller 21 are conventional except concerning an actuator circuit 22 that drives the controller 11. The circuit breaker and the controller are not described in detail here. The actuator circuit is described in detail below.

(6) With reference to FIG. 2, the actuator circuit of the invention comprises two branches in parallel between two terminals 5 and 6 to which a potential difference may be applied in order to make the actuator circuit operate.

(7) The first branch includes only one coil 1. By way of example, the coil 1 comprises 1000 turns and presents impedance of 35. This branch has a function of providing redundancy. If the second branch becomes inoperative, e.g. because of the failure of a component, then the first branch ensures the actuation function of the spring controller. It is then in a mode of operation known as degraded operation mode.

(8) The second branch comprises a coil 2 and other components that are described below. By way of example, the coil 2 comprises 363 turns and presents an impedance of 3.55. Naturally, other impedance values may be selected for the coils 1 and 2, provided that the impedance of the coil 1 is greater than that of the coil 2. The second branch provides the normal mode of operation.

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

(10) In an embodiment, the coils 1 and 2 are both formed by winding around a single core.

(11) The second branch is described below. From the terminal 5, the coil 2 is connected in series with a switch that is capable of opening 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, e.g. of the metal-oxide-semiconductor field-effect transistor (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 may be used as a switch, in particular an NPN junction transistor, a thyristor, or a mechanical relay.

(12) The transistor 3 makes it possible to limit the strength of the current flowing in the coil 2 to a value that makes it possible to break the current using an auxiliary switch. As mentioned above, the breaking capacity of an auxiliary switch is limited to a maximum current of 4A. With a coil 2 having impedance of 3.55, and in the absence of the transistor 3 limiting the current, if a voltage is applied to terminals 5 and 6, situated at the respective ends of the two branches, that would lead to a current of 31A in the coil 2. Since this value is much greater than the maximum permissible limit of 4A, it is the transistor 3 that limits the current flowing in the coil 2.

(13) A diode 4 is connected parallel to 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 that appears when the second branch is opened by the transistor 3.

(14) The transistor 3 is controlled by a control circuit, or switch circuit, that comprises a bipolar transistor 8, having its collector connected to the gate of the transistor 3.

(15) The collector of the transistor 8 is also connected to one terminal of a resistor 12 having its other terminal connected to the terminal 5. The emitter of the transistor 8 is connected to the terminal 6. By way of example, the resistor 12 has a resistance of 56 kilohms (k).

(16) The base of the transistor 8 is connected to the anode of a Zener diode 9 having its cathode connected firstly to a parallel-connected capacitor 10 and resistor 11. The capacitor 10 and the resistor 11 are connected to the terminal 6. By way of example, the capacitor 10 has a capacitance of 0.1 microfarads (F) and the resistor 11 has a resistance of 56 k.

(17) The cathode of the Zener diode 9 is connected secondly to a resistor 13, itself connected to the terminal 5. By way of example, the resistor 13 has a resistance of 200 k.

(18) The switch circuit operates as follows.

(19) As soon as a potential difference is applied to the terminals 5 and 6, a current flows in the second branch and therefore in the coil 2, and the capacitor 10 is charged via the resistor 13. When the voltage at the terminals of the capacitor reach a certain value, e.g. 10.7 V with the previously-given numerical values, a current flows in the transistor 8, from its emitter to its base.

(20) Because of the resistor 12, the electric potential of the collector of the transistor 8 and of the gate of the transistor 3 then falls.

(21) The transistor 3 then opens the second branch, to such an extent that the current flowing in the coil 2 is broken, after about 2 ms.

(22) It should be observed that because the impedance of the coil 1 is higher than that of the coil 2, the current that flows in the coil 1 always remains low enough to be able to be broken by an auxiliary switch.

(23) As mentioned above, the coils 1 and 2 are preferably wound on the same core. That creates induced currents. When the transistor 3 breaks the flow of current in the coil 2, said coil induces a current in the coil 1. This induced current may serve to maintain the magnetic field necessary for moving the plunger of the mechanism. The current in the coil 2 is broken, for example, after 2 ms. This time period may be too short for the plunger to reach its actuated final position. The current induced in the coil 1 thus makes it possible for the plunger to finish its stroke.

(24) In a variant, the control circuit of the transistor 3 is a resistance-capacitance (RC) circuit. In this event, 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. Their resistance and capacitance are selected so that the RC time-constant is equal to a determined value, e.g. 2 ms.

(25) It should be observed that the invention not only finds application in a gas-insulated substation (GIS), but also in other types of connection equipment, e.g. air-insulated switchgear, or dead-tank oil circuit-breakers, for use indoors or outdoors.