RU67772U1 - ELECTROMAGNETIC DRIVE OF CIRCUIT BREAKERS - Google Patents

Abstract

The utility model relates to electrical engineering, in particular, to vacuum circuit breakers with an electromagnetic drive and their control circuits in automatic recirculation cycles.

The essence of the solution: switching electromagnets on and off IGBT transistors with the formation of a rectangular control pulse of the switching electromagnet using a threshold-key element and a timing RC circuit; the limit switch has closing and opening contacts, switchable from the latch and shunting the RC resistor, and disconnecting the two-stage voltage divider, supplying the trip transistor circuit and connected to the threshold-key element through the resistor and diode, the common point of which is connected through the capacitor to the common minus of the power source and a capacitor control supply circuit, plus which is connected via an isolation diode to this source; the collector-emitter junction of the switching transistor is shunted by an energy absorber; the threshold-key element can be made in the form of a thyristor and a zener diode or in the form of trigger circuits with logic elements.

Description

The utility model relates to electrical engineering, in particular, to vacuum circuit breakers with an electromagnetic drive and their control circuits in cycles with automatic restart (AR). The drive turns on the circuit breaker, cocks the trip spring and presses the contact spring of the vacuum arc chambers (VDK) with a latch. The circuit breaker is tripped by the indicated springs after the latch is knocked down by the tripping electromagnet or by releases.

Recently, there has been a tendency to simplify complex mechanisms for tripping drives during emergency trips due to the use of high-speed electronic control circuits for turning on and off solenoids, while eliminating the main drawback of electromagnetic drives - the inertia of current and magnetic flux decay, and, consequently, of forces that can continue fractions of a second, with the times required for AR, one or two orders of magnitude less. A switching device is known (USSR AS No. 1252834, class N01H 47/32 1986), in which the remote switch is controlled by two coils of electromagnets using two bipolar transistors npn and pnp types. In this case, exponentially falling control signals supplied from one switching contact are supplied to the transistor bases through RC chains.

The big disadvantages of the device are: the need to use very powerful transistors operating in the amplifier rather than in saturated modes, and the inability to use recloser cycles due to a single control contact.

That is, such a device is unsuitable for high-speed medium voltage circuit breakers with switching electromagnet currents of tens of amperes and with times of 30 ... 40 milliseconds operating in automatic reclosure cycles.

Known electromagnetic drive circuit breakers (RF patent No. 2074438, class N01N 33/42; 33/66: 33/59, 1994), containing the main elements of the drive and vacuum circuit breaker: VDK, preloaded springs, insulating rods, common to three phases a shaft with levers, a disconnection spring, an inclusion electromagnet (EV), a shaft turning through a lever when turned on, an overhang is connected to the EV armature that controls the block contacts at the end of inclusion and an emphasis fixed at the end of inclusion by a spring-loaded latch,

which is controlled by a shutdown electromagnet (EO). The power supply of the EV coil is carried out from a constant or rectified voltage source through an electronic switch. The output of electromagnetic energy from the EV coil after the current is cut off by an electronic key is carried out through a diode-resistor circuit shunting the coil.

Significant disadvantages of the drive: the structure of the electronic key is not disclosed; the energy output from the coil is ineffective - it is maximum at the initial moment at the maximum current, and decreases with decreasing current, which increases the disconnection time and decreases the initial separation speed of the VDK contacts, the voltage on the electronic key is determined by the sum of the supply voltage and the voltage drop across the resistor, which is maximum in first moment; the installation of the protruding block-contact ledge on the armature, which usually has a stroke of 20 ... 40 mm, is unreliable due to the need to install a large margin along the armature with a rapid drop in current in the coil to ensure a secure fit on the latch at the end of switching, as due to large fluctuations in the supply voltage, as well as due to changing environmental conditions and electrical wear of the VDK contacts; it is not known from the design how the control circuits of the EV and EO interact with automatic reclosure, how is blocking from unauthorized repeated switching on when the signals of turning on and off O acting simultaneously.

Known electromagnetic drive switching device (RF patent No. 2074430, class. Н01Р 7/08, ННН 47/32, 1994), selected for the prototype, containing a coil of the switching electromagnet, shunted by a diode; a transistor switch, based on a composite bipolar transistor, the collector-emitter junction of which is shunted by a protective element against overvoltages that may occur due to the delay in opening the shunt diode; a RC timing chain and a threshold-key element in the form of a dynistor, to the anode of which are connected: the common point of the timing chain directly, and the base of the transistor through a diode; one of the resistors of the RC timing chain is bridged by the closing contact of the limit switch controlled by the armature of the switching electromagnet at the end of switching on; the control capacitor is connected to a constant or rectified voltage power supply through a diode and a resistor.

In the prototype, in fact, the structure of the electronic control key of the electromagnet switching on the second analogue is disclosed. But he has all the disadvantages of this analogue.

The proposed electromagnetic drive allows you to eliminate all the noted disadvantages of analogues and prototype and to create a simple and reliable design of the drive and the switch with high speed and service life, minimal energy consumption; to replace complex slow-acting mechanical systems with high-tech compact high-speed electronic elements, the connections of which make it easy to solve interlocking and monitoring issues that satisfy all the requirements for circuit breakers with automatic reclosure.

The proposed drive is characterized in that bipolar transistors with an insulated gate are used as transistors, the collector-emitter junction of the switching transistor is shunted by an energy absorber designed for the total energy of the switching coil, and the gate of this transistor is connected to the first voltage divider consisting of the first zener diode and the second resistor connected by the free end of the zener diode to the common minus, and by the free end of the second resistor to the switching contact connected to the plus of the conden power saturation; between the capacitor and the resistor of the time-delaying RC circuit, a first additional diode is connected, at the anode of which a point common with the resistor of this chain is connected via a second additional diode to the threshold-key element; the gate of the disconnecting transistor is connected to the first stage of the second voltage divider in the form of a second zener diode and a third resistor, forming with the fourth resistor the second stage of this voltage divider, the free ends of which are connected from the second zener diode to the common minus, and from the fourth resistor through the disconnection contact to plus a power capacitor, wherein one or both steps of the second voltage divider are bridged by the opening contact of the end switch controlled by the latch; the common point of the second stage of the second voltage divider through the fifth resistor and the third additional diode is connected to the cathodes of the second and second additional diodes and the threshold key element, and the common point of the fifth resistor and the third additional diode through the additional capacitor is connected to a common minus.

The threshold-key element can be made in the form of a thyristor, to the control electrode of which a zener diode and a resistor are connected, the other ends of which are connected to the minus of the supply capacitor and the anode of the thyristor; the threshold-key element can also be performed on trigger circuits, for example, in the form of a one-shot or logic with three AND elements and one NOT; In addition, the scheme

The control makes it easy to integrate the voltage sensor of the power supply, the NC contact of which is connected in series with the ON contact, and the NO contact of this sensor shunts the second voltage divider and the trip contact. The essence of the proposed solution allows us to obtain the following positive results: eliminate the main drawback of the electromagnetic drive - its inertia, due to the rapid interruption of the current in the switching on electromagnet with high-tech electronic elements and a pulsed energy-intensive energy absorber, this eliminates complex, less reliable mechanical systems of free trip, which significantly increases the term drive and entire circuit breaker services; drive control circuitry allows to ensure minimum short-circuit current flow time, fully close the circuit breaker with latching for automatic reclosure due to the use of a microswitch controlled by a latch, which ensures separation and maximum initial speed of disconnection of welded VDK contacts; the drive has high reliability even in case of failure of the end microswitch; the drive easily provides all the required interlocks during automatic reclosure, including from repeated switching on with the simultaneous action of on and off signals; the drive control circuit has great functionality, makes it easy to integrate alarm and blocking elements, and can partially take over the relay protection system; the drive allows for quick multiple reclosure cycles.

The design of the drive with circuit breaker elements is shown in the drawings: Fig. 1a shows a structure with control circuit elements in the disconnected position of the drive and circuit breaker; on figb - the same in the on position; figure 2 is a circuit diagram of a control unit; figure 3 - diagrams of the current decline in the coil of the electromagnet enable after turning off the switching transistor: (1) for the prototype and the second analogue. (2) - for the proposed solution, (3) - the same with a lower inductance of the coil, (4) - line current retention; figure 4 - embodiments of a threshold-key element with an external RC timing chain for them: a) a single-shot, b) trigger digital logic with three AND elements and one NOT.

The electromagnetic drive of the circuit breakers (FIG. 1) contains an on-circuit electromagnet (EV) 1 with a coil 2 and an armature 3 kinematically connected to one of the levers 4 mounted on the shaft 5, insulating rods 6 of the three phases of the switch are kinematically connected to the other ends of the levers, the other ends which are connected to the preloaded nodes 7, containing preload springs 8, pressing contacts of the airborne transport system 9 in the

position. The lever 4 is spring-loaded with a trip spring 10. An anchor 11 has a stop 11 that interacts with the end face 12 of the latch 13 at the end of the switch. The emphasis 11 can be fixed not on the anchor, but on one of the levers 4 or on the shaft. The spring-loaded latch 14 is limited in rotation: clockwise - by the stop 11. and counterclockwise - by the rod 15 of the shut-off solenoid (EO) 16 with the coil 17. The latch 13 in the disconnected position of the actuator presses on the spring-loaded element 18 of the limit switch 19 with the closing contact 20 and disconnecting contact 21. The ends of these contacts and coils of EV and EO are connected to the control unit 22, powered by a constant or rectified voltage source.

The control unit includes (Figure 2): including 23 and disconnecting 24 bipolar transistors with an isolated gate (SE); contacts in the control circuits of transistors: 25 - on and 26 - off; a power capacitor 27 of the control circuits connected positively to the power source through the first resistor 28 and the first diode 29 and having a common minus with the power source; the gate of the turning transistor 23 is powered by a first voltage divider consisting of a second resistor 30 and a first zener diode 31; the gate of the shutdown transistor 24 is powered by a second two-stage voltage divider, the first stage of which is formed by the second zener diode 32 and the third resistor 33, forming with the fourth resistor 34 the second stage of this divider; the gate of the transistor 23 through a second diode 35 is connected to a threshold-key element consisting of a threshold element - the third zener diode 36 and a key element - thyristor 37, the control electrode of which is connected to a common point of this zener diode and the sixth resistor 38, the RC timing circuit consists of resistors 39 and 40 and the capacitor 41 and the first additional diode 42 connected between them, the common point of the anode of which and the resistor 40 is connected through the second additional diode 43 to the threshold-key element and the cathode of the second diode 35 at point “a”; the collector-emitter junction of the transistor 23 is shunted by an energy absorber 44; the common point "b" of the second stage of the second voltage divider through the fifth resistor 45 and the third additional diode 46 is connected to the threshold key element and the cathodes of the diodes 35 and 43 at point "a", and the common point of the resistor 45 and diode 46 is connected through an additional capacitor 47 to a common minus, the coil 17 is shunted by a chain of resistor 48 and diode 49; resistor 50 shunts capacitor 41; resistors for removing charge from transistor gates and protective diode-capacitor circuits, shunting

collectors after current interruption, not shown; the voltage sensor 51 of the power source has a disconnect 52 and a make 53 contacts.

When used as a threshold-key element of an integrated circuit in the form of a single vibrator 54 (Fig. 4a) there are additional resistor 55 and a capacitor 57 giving a delay for installing a single vibrator, and a matching resistor 56; on Fig shows a trigger logic chip 58 with three elements AND and one element NOT.

The drive operates as follows. When a command is given for switching on - closing the switching contact 25 (Fig. 2), the switching transistor 23 is turned on, current starts flowing through the coil 2 of the switching electromagnet 1 (Fig. 1a), the armature 3 moves to retract (down in the drawing), shaft 5 s levers of 4 phases rotates clockwise against the disconnection spring 10, but with additional help from atmospheric pressure on the VDK bellows 9, the rods 6 and the preloaded 7 unit move up to close the VDK contacts, after which, with the further movement, the preloaded 8 springs begin to compress, creating an additional Gentle pressing on the end contacts of the VDK, ensuring their normal operation in long-term on mode or the necessary shutdown speed in case of short circuit. At the end of switching on, when the armature 3 approaches the end of the body of the EV magnetic circuit, the protrusion 11 comes out of contact with the latch 13 and forms a small gap with its end 12 (the necessary margin for installing the drive on the latch). Under the action of the spring 14, the latch rotates clockwise and the end 12 is above the protrusion 11 (Fig.1b), while the spring-loaded element 18 switches the make contact 20 and the make contact 21 of the end switch 19. From the moment of closing of the contact 25 (Fig.2) starts the capacitor 41 is charged through the resistors 39 and 40 of the timing RC circuit. After the contact 20 is closed, the capacitor 41 is accelerated to recharge through one resistance 39 to the stabilization voltage of the zener diode 36 and a voltage appears on the control electrode of the thyristor 37, which opens the thyristor, while the gate of the transistor 23 is shunted, which closes, breaking off the current of the switching coil 2, the accumulated electromagnetic energy of which is quickly it is quenched by the energy absorber 44. Synchronously with the current decrease in the coil 2, the magnetic flux in the magnetic circuit (charged) of the electromagnet 1 and the force acting on its armature fall. The stop 11 abuts against the end face 12 of the latch 13, fixing the drive and the switch in the on position (Fig.1b). Re-starting the drive after it has been disconnected, for example, from overcurrent releases in the event of a short circuit

it is possible only after turning off the on-contact contact 25, closing the thyristor and discharging the capacitor 41 to the resistor 50, which is important in reclosure cycles

The drive is disconnected when the trip contact 26 is closed (Figure 2) (contact 21 is open). There are two processes involved: the transistor 24 opens and the current starts flowing through the EO coil 17, which requires 15 ... 20 milliseconds, and at the same time, the capacitor 47 starts charging up to the thyristor 37 opening voltage for several milliseconds, blocking the opening of the transistor 23 in the presence of a switch-on signal (with closed contact 25). The voltage at the second stage of the second voltage divider (at point “b”) is higher than the opening voltage of the thyristor 37 (at point “a”), which is higher than the gate voltage when the transistor 23 is saturated with some margin. Typically, for IGBT transistors, the gate voltage is taken at 15 ... 20 V, which ensures the operation of the transistor in key saturated mode. After the actuation of the shutdown electromagnet 16, the latch 13 (Fig. 1b) rotates counterclockwise, releasing the stop 11, while the shaft 5 and levers 4, rods 6 and preload nodes 7 are rotated counterclockwise. Mentioned movable parts are accelerated by the action of the preload springs 8 and the breaking spring 10 and beat by the preload unit on the movable contacts of the airborne landing gear, disconnecting them. After opening the contacts, the further movement of the moving parts is idea due to kinetic energy and under the action of a trip spring; the effect of atmospheric pressure on the VDK bellows inhibits the movement of the moving parts of the drive and switch. At the end of the trip, braking and fixing of the drive and switch are usually carried out with a damper (not shown in the drawings). The drive and the switch are held in the off position by the spring of disconnection 10. After being knocked down by the electromagnet 16, the latch 13 through the element 18 opens the contact 20 and closes the contact 21 (Fig. 1a), while the gate of the transistor 24 (Fig. 2) is shunted, which turns off the power of the coil 17 ; the electromagnetic energy accumulated by this coil is discharged on the resistance of the coil and resistor 48. Here, it is not necessary to interrupt the current hard and fast. It is enough that the anchor of this electromagnet returns to the off state during a currentless pause of the circuit breaker, equal to 0.3 seconds for circuit breakers with automatic reclosure.

The decay rate of the current and the traction force in the coil of the electromagnet switch on depend, first of all, on the allowable voltage on the collector of the transistor and on the energy absorber, the magnitude of the current in the coil at the time of breakage, the inductance of the coil, which depends on the degree of saturation of the iron in the magnetic circuit and if it is charged or

cast, which greatly affects the eddy currents that delay the decay of the force. These processes are best optimized by the insulated gate bipolar transistors offered here, passing currents of tens of amperes with a recovery voltage across the collector of more than 1000 V.

Figure 3 shows a diagram of the current drop in the switching solenoid, where the initial data are taken: a cut-off current of 30A and an energy absorber in the form of a nonlinear resistor based on zinc dioxide with a limiting voltage of 625 V. Curve 1 corresponds to the analogue and prototype circuit with inductance 0, 3 H; curve 2 corresponds to the proposed solution with the same inductance; curve 3 corresponds to an inductance of 0.1 G (with current interruption) and a coil resistance of 7 Ohms (tested 10 kV circuit breaker, rated current 1000 A, rated tripping current 20 kA).

The horizontal line corresponds to the holding current, that is, the current creating the force of the electromagnet, equal to the efforts of the springs preloaded and breaking the spring. Important is the fact that the actuator lands on the latch at the time of current interruption, which determines the initial opening speed of the VDK contacts and their separation due to possible welding. As can be seen from curve 3, it is enough to have a delay time of the stop on the latch of just a few milliseconds, which ensures high speed circuit breaker. The proposed drive solves this problem through the use of powerful IGBT transistors, energy-intensive nonlinear resistors designed to absorb all the energy of the coil, and by controlling the end switch from the latch.

The current drop in the prototype and analogue is determined by the expression (1):

(one) ;

where u is the supply voltage, the time constant τ = L / R, r is the resistance of the coil, L is the inductance of the coil, R is the total resistance of the coil and the additional resistance shunting the coil.

In the proposed solution, the current decreases according to the expression (2):

(2) ,

where i _o is the interrupted current, which will be practically less (u / r) due to the interruption of the current by the limit switch controlled by the latch, and u _n is the voltage across the nonlinear resistor.

The second term in (2) shows the efficiency of increasing the voltage across the collector of the transistor and non-linear resistor.

The desire to reduce the current consumed by the electromagnet while maintaining the magnetizing force, which is important when using an energy storage device, requires an increase in the number of turns of the coil, which leads to a significant increase in inductance. In this case, the application of the proposed solution is even more effective in comparison with the analogue and prototype.

Using instead of a non-linear resistor (with a voltage that varies little on it depending on the current) a chain of resistor and capacitor will require the use of a large pulse capacitor.

In case of failure to switch the contact 20 of the limit switch, the current in the transistor will still be cut off, but with some delay when charging the capacitor 41 through both resistors 39 and 40 to the opening voltage of the thyristor 37, as described above. A diode 35 separates the gate of the transistor 23 from the RC circuit, providing an increase in voltage across the capacitor 41; diode 43 provides a steep edge of the enable signal. Variable resistor 39 allows you to adjust the RC timing chain to the minimum charge time of the capacitor 41 after switching the latch. The use of a thyristor and a zener diode in the proposed solution instead of a dinistor is advisable because of the large variation in voltage of the opening of the dinistors.

Due to the small currents of transistor control and small displacements of the latch, it is advisable to use a microswitch with a stroke of 3 ... 5 mm as an end switch.

Blocking from repeated switching on of the drive and the switch with the simultaneous action of signals B and O is carried out after the drive and the switch are completely turned on and then turning them off: blocking the signal of repeated switching on,

it is fed by the opened thyristor 37 through the switching contact 25, the resistor 30 and the diode 35 and through the resistors 39 and 40 and the diode 43. The drive and the circuit breaker are also switched off when turned on for a short circuit. If there is a requirement not to pass the signal to turn on when the signal to turn off, it is enough to disconnect the first stage of the second voltage divider with a normally open contact 21, that is, bypass the gate of the transistor 24.

The proposed electric drive control circuit makes it easy to control the voltage supplying the drive, that is, to integrate the release

minimum voltage. To do this, it is enough to have a voltage sensor in the form of a low-power relay 51 with an NC contact 52 connected in series with the ON contact and a NO contact 53 shunting both stages of the second voltage divider — resistors 33 and 34 and the trip contact 26. In the event of a voltage failure on the power source and therefore, on the relay coil, it will disconnect and close contact 53 and turn on the transistor 24, which will pass current through the coil 17 from the power capacitor 27, separated from the power source by the diode 29, and turn off the drive. Open contact 52 will not allow switching on at low supply voltage. The circuit will return to operating state when the relay 51 is turned on, that is, when the voltage at the power source rises to the desired value.

If contact 21 fails when it is turned on (it will remain closed), the drive can be switched off remotely by providing a make contact parallel to contact 53.

The circuit allows you to integrate the overcurrent release, if you provide a make contact in this release and set it parallel to the trip contact 26.

As the tests of the mentioned circuit breaker showed, the closed time of the circuit breaker in the BO cycle is only 15 ... 20 milliseconds, which allows you to quickly protect the object of energy consumption during a short circuit.

Claims (4)

1. An electromagnetic drive of the switches, comprising turning on and off the electromagnets, the coil of the first of which is connected directly to the plus of the DC or DC power supply, and the coil of the second of them is connected to the plus of the supply capacitor and through the first resistor and the first on-board diode is also connected to plus the power supply, which has a common minus with the supply capacitor, the second ends of the coils are connected to the collectors of the turning on and off transistors, the emitters some are attached to the common minus; on and off contacts; a limit switch with a make contact shunting one of the resistors of the timing RC circuit at the end of the circuit breaker; a threshold-key element to which a control electrode of a switching transistor is connected through a second diode, the free end of this element is connected to a common minus, disconnecting springs and preloaded; a latch locking the actuator and switch in the on position; diode-resistor circuit shunting the coil, characterized in that the transistors used are bipolar transistors with an insulated gate, the collector-emitter junction of the switching transistor is shunted by an energy absorber designed for the full energy of the switching coil, and the gate of this transistor is connected to the first voltage divider, consisting of from the first zener diode and the second resistor connected by the free end of the zener diode to the common minus, and by the free end of the second resistor to the switching contact, connected to the plus of the power capacitor; between the capacitor and the resistor of the timing RC circuit, a first additional diode is connected, at the anode of which a point is connected to the threshold-key element through a second additional diode to the threshold-key element, the gate of the disconnecting transistor is connected to the first stage of the second voltage divider in the form of a second zener diode and a third resistor, forming the second stage of this voltage divider with the fourth resistor, the free ends of which are connected from the side of the second zener diode to a common minus, and from the side the fourth resistor through the trip contact to the plus of the power capacitor, moreover, one or both stages of the second voltage divider are bridged by the opening contact of the limit switch controlled by the latch; the common point of the second stage of the second voltage divider through the fifth resistor and the third additional diode is connected to the cathodes of the second and second additional diodes and the threshold key element, and the common point of the fifth resistor and the third additional diode through the additional capacitor is connected to a common minus. 2. The drive according to claim 1, characterized in that the threshold-kuchevy element is made of a third zener diode and a thyristor, to the control electrode of which this zener diode and a sixth resistor are connected, the other ends of which are connected to the common minus and anode of the thyristor. 3. The drive according to claim 1, characterized in that the threshold-key element is made in the form of a trigger chip in the form of a single vibrator or logic with three AND elements and one NOT. 4. The drive according to claim 1, characterized in that the NC contact of the voltage sensor of the power source is connected in series with the ON contact, and the NO contact of this sensor bypasses the second voltage divider and the trip contact.