Control method and device for a switchgear actuator

IS 2 173 282 T3

DESCRIPTION

Control method and device for a switch actuator.

Field of the invention

The present invention relates to a method and a device for controlling electrical switches. More particularly, the invention relates to a method and device for controlling a switch that uses a loudspeaker voice coil actuator to quickly and reliably open and close a current switch. Description of Related Art

In a power distribution system, a switch may be incorporated into the system for a number of reasons, such as to provide automatic protection in response to abnormal load conditions, or to allow the opening and closing of sections of the system. Various types of switches include a switch for deliberately opening and closing a power distribution line, such as a line directed to a capacitor bank; a fault current switch, to automatically open the line when a short circuit current is detected, and a circuit resetter that, when a short circuit current is detected, opens and closes rapidly a predetermined number of times until it either disappears the short circuit, or the resetter locks in a position that leaves the circuit open.

Vacuum switches have been widely used in the art because they offer fast, low-energy arc interrupting, with long-life contacts, low mechanical fatigue, and a high degree of operational safety.

In a vacuum switch the contacts are hermetic in a vacuum chamber. One of the contacts is a mobile contact having an operating member that extends through a vacuum seal in the chamber.

Summary and objects

One of the objects of the present invention is to provide a switch actuator mechanism and thereby control that arcing and surge currents are minimized during opening and closing.

Another object of the present invention is to provide a switch actuator and regulator mechanism that therefore performs a correct monitoring of the system.

Another object of the present invention is to provide a switch actuator mechanism capable of a wide range of displacement profiles, thus eliminating the need for many types of mechanical systems.

Another object of the present invention is to provide a switch actuator mechanism capable of being controlled by any commercially available motor control circuitry or circuitry dedicated to travel control.

Yet another object of the present invention is to provide a switch actuator mechanism capable of providing speeds and forces incapable of being achieved by mechanical systems of the prior art.

Still another object of the present invention is to provide an improved synchronous operation switching mechanism, which leads to a significant reduction of the surge currents generated during switching operation.

Generally, in switches incorporating vacuum switches, various spring-actuated mechanisms have been used which are connected to an operating member to reliably open or close the switch contacts. One such device that is commonly used is the simple hinge connection. The primary function of these mechanisms is to minimize arcing by very rapidly driving their contacts to the open or close positions. Various applications may require the use of a number of spring loaded mechanisms with associated linkages and linkages.

An actuator is normally provided in order to prime these mechanical systems, either by compression or extension of the biasing spring. These actuators may include, but are not limited to: solenoids, motors, or hydraulic devices. Compared to the inherent switch speed requirements to effectively interrupt current, these actuators are relatively slow with poor response times. For this reason they are not normally used to directly actuate the switch contacts but are used to prime the rapid actuation spring mechanisms. The main disadvantage of this system is that the spring-actuated operation does not, in itself, lead to it being easily controllable and fine-tuning the operation of the mechanism requires considerable engineering effort.

In practice, this means that many different mechanisms must be designed to accommodate the different operating requirements of switches, short-circuit breakers, and circuit reclosers, and within each of these classes of switches, there are different mechanisms that are used. required depending on the application, including voltage and current specifications.

In addition, in view of the high voltages typically used in power distribution applications, rapid and precise movement of the switch contacts is desirable to minimize the creation of arcs between the contacts and the generation of surge currents. . Depending on the application, whether it is a connection to a capacitor bank or a short-circuit interruption, it can be determined, by those skilled in the art, when the most advantageous time for opening or closing of the device occurs. switch contact. This optimum moment is related to a precise point in the voltage or current wave for which interruption of the current or contact will cause the least creation of electric arcs and surge currents. Since conventional spring-actuated mechanisms do not by themselves lead to this degree of control

In precise terms, this invention offers a feasible means of achieving over-wave or synchronous switching. Such synchronous switch operation is beneficial, both in terms of reducing wear on the switch contacts, as well as the significant reduction in surge currents generally experienced by the power distribution system downstream of the switch unit.

An additional aspect of a controlled switching unit, which operates synchronously, is that the speed with which the contacts close can be controlled. In conventional systems, the contacts are actuated uncontrollably against each other at a very high speed and it is possible for the contacts to bounce a certain number of times before coming to rest. This bouncing phenomenon is undesirable because the creation of corresponding arcs can soften the contacts and create strong welds when the contacts finally mate.

Both DE-A-2601799, on which the preamble of claim 1 is based, and EP-A-0528357 describe current switches with mobile contacts actuated by an actuator controlled by a control system.

In accordance with the present invention, a current switch is provided comprising:

a current interrupting device having at least one movable contact; and an actuator coupled to the movable contact of the current switch; characterized by:

a feedback sensor to detect an actuator position during an actuation cycle;

a sensor for sensing the shape of a voltage wave on a line to be switched and supplying information regarding the voltage wave shape; and a control system coupled to the feedback sensor, in such a way that it receives information from the feedback sensor concerning the position of the actuator during the actuation cycle, and coupled to the sensor, so that it receives information from the sensor concerning the way of voltage wave; The control system that controls the movement of the actuator during the actuation cycle based on the feedback sensor information and the sensor information, so that the current of the line to be switched is interrupted or established, in the desired location on the voltage waveform.

A corresponding method is also provided.

The above features and advantages of the present invention will be clear from the following more detailed description of the invention. The accompanying drawings, listed below, are helpful in explaining the invention.

The text that follows explains the invention with reference to illustrative embodiments, in which:

Figure 1 shows a schematic diagram of a switch employing a loudspeaker coil actuator;

Figure 2 shows a cross section of

282 T3 4 a switch embodiment;

Figure 3 is a cross section of the vacuum module shown in Figure 2;

Figure 4 shows an enlarged view of the operating mechanism of the embodiment shown in Figure 2;

Figure 5 shows an exploded view of the primary components of the operating mechanism;

Figure 6 shows a graph illustrating system voltage versus time and switch dielectric dip;

Figure 7 is a schematic view of a circuit that can be used with the present invention;

Figure 8 is a graph illustrating a displacement profile that can be used with the present invention;

Figure 9 is an illustration of a speaker voice coil actuator that can be used with the present invention;

Figure 10 is a view of a latch mechanism that can be used in the present invention;

Figure 11 is a view of the pressure contact spring mechanism that can be used with the present invention;

Figure 12 is a graph illustrating the synchronous time of the opening operation of a capacitor switch.

Detailed description of the invention

For a better understanding of the invention, reference would be made to the following detailed description taken in conjunction with the accompanying drawings, in which examples of preferred embodiments of the present invention are illustrated and described. Each reference number remains consistent throughout the drawings.

In figure 1, an incoming power distribution line 2 is connected in series with a current switch 4, thus allowing switch 4 to open the line. Line 2 can be opened by a predetermined command, or in the case of a short circuit current breaker, if a short circuit current exceeds a predetermined threshold value. One of the contacts of the current switch 4 is connected to one end of an operating plug 6. The other end of the operating rod 6 is operatively connected to an actuator, such as a speaker voice coil actuator 8. The loudspeaker coil actuator 8 acted directly on the operating plug 6 in order to open or close the contacts of the current switch 4.

The speaker moving coil actuator 8 is a limited motion direct drive device that uses a magnetic field and winding 10 of turns to produce a force proportional to the current applied to the coil. The electromechanical conversion of the loudspeaker moving coil actuator 8 is governed by the Lorentz Force Principle, which states that if a current-carrying conductor was located within a magnetic field, a force would act on it. The magnitude of the force is determined by the equation:

IS 2 173 282 T3

F = kBLIN

Where F equals force, k is a constant, B is the magnetic flux density, L is the length of the conductor, I is the current intensity of the conductor, and N is the number of turns of the conductor.

The current through the speaker voice coil winding 10 is controlled by a control mechanism 12. Any commercially available control mechanism 12 may be employed. For example, suitable control mechanisms 12 include: simple electrical circuit controllers, programmable logic controllers, or distributed control systems. The control mechanisms 12 can be connected to a feedback device 14, which supplies an input signal in reference to the position of the operating stem 6.

The control mechanism 12 can also be connected to a latch device 16. When it receives the order from the control mechanism 12 to secure the operating rod 6, the latching mechanism 16 leaves the operating rod 6 fixed in the position in which it was found. In an alternative device, the latch mechanism 16 may be a permanent magnet or a mechanical latch that is not coupled to the control device 12.

In figure 2 a cross-sectional view of one of the embodiments of the invention is shown; A solidly insulated elongated one-piece encapsulation 18 encloses the operating stem 6 and the current switch 4. Encapsulation 18 may be made from ceramic, porcelain, any suitable epoxy, or any other suitable solid insulating material. A high voltage phase side electrical terminal 22 and a high voltage load side electrical terminal 20 protrude through the solidly sealed joint 18, and are connected to the current switch 4. The high voltage electrical terminals 20 and 22 are arranged diametrically 180 apart.^or, and are parallel to each other. Encapsulation 18 ensures both solid isolation between high voltage electrical terminals 20 and 22, as well as solid isolation between each of the high voltage electrical terminals and electrical ground (not shown).

The current switch 4 includes a vacuum or bottle module 24, shown in cross-section in Figure 3, with a pair of switch contacts 71 and 72, disposed within the vario module 24. The vario module 24 provides a housing and emptied environment for operation of the switch contact pair. Module 24 is usually constructed from an elongated, generally vacuum tubular, ceraomic coating 73, preferably formed from alumina. One of the switch contacts 71 is mobile and the other switch contact 72 is stationary or fixed.

A special adapter 76 attaches to the pin of the stationary contact 72, allowing the associated high voltage electrical terminal 22 to exit at a 90 angle.^or.

The moving switch contact 71 is attached to the upper longitudinal end of the operating stem 6. One method of securing is to use a headless threaded bolt 32 over an internal threaded connection 74 within the movable pin 75 of movable contact 71. When the switch contacts are in the closed position as shown, a low resistance electrical circuit, or short, is created between high voltage electrical terminals 20 and 22. The current switch 4 further includes a current exchange unit and an interface 26 between the vario module 24 and the current exchange unit. The current exchange unit contains a movable piston 28 and a fixed outer casing 30. In this embodiment, the operating stem 6 is made from an electrically insulated material.

The other end of the operating rod 6 is secured to a flange 34 on the voice coil actuator 8 by a rigid pin 36. The pin 36, which holds the aforementioned components fixed in position, may be secured by any appropriate means, such as a pair of retaining rings. A linear recirculating ball bearing 38 and split collars 40, which hold the ball bearing, provide smooth movement of the operating rod 6. The loudspeaker voice coil winding 10 was disposed between the outer body of the loudspeaker voice coil actuator 8 and the flange 34.

The side pins 42 are attached to the outer body of the speaker voice coil actuator 8 and connect with side brackets 44 to securely hold the speaker voice coil actuator 8 to a protective housing 46. Protective housing 46 is attached to a cover 50 for protective housing 46 by housing pins 48, and protective housing cover 50 is connected to solidly insulated chamber 18 by locking pins 52.

Like solidly insulated encapsulation 18, protective shell 46 is also made from ceramic, porcelain, any suitable epoxy, or any other suitable solidly insulating material.

In this embodiment, the feedback device 14 is a position sensor, such as a linear potentiometer 14. Linear potentiometer 14 can be made from a three terminal rheostat or an electrical resistor with one or more slide contacts, which function in this way as an adjustable voltage divider. The linear potentiometer 14 supplies information regarding the position of the operating stem 6 to the control mechanism 12 that controls the speaker voice coil actuator 8. Alternatively, the feedback device 14 may be an optical encoder.

The latching device 16 was intended to secure the operating stem 6. The latching device may be a controllable device, such as an electromagnet, or a simple mechanical latch or permanent magnet latch that includes: a latch magnet 54, a spacer 56 made of a non-ferrous material, a bolt 58 that secures magnet 54 hooking to cover 50 of

ES 2 173 282 T3 the protective casing, a latch plate 60 made of steel or iron, and a latch plate pin 62 which secures the latch plate 60 to the operating rod 6.

In order to gain a better understanding of the invention, reference may be made to Figures 4 and 5. Figure 4 shows an enlarged view of the operating mechanism of the preferred embodiment shown in Figure 2, and Figure 5 shows a view Exploded view of the primary components of the operating mechanism.

Now the details concerning the control mechanism of the present invention will be described.

Figure 6 illustrates a voltage signal 100 drawn on a graph comparing the voltage level v (t) with time t. In a 60 Hz application, each half cycle is ideally 8.33 ms. However, the actual cycles may vary due to harmonics or asymmetric conditions such that a given half cycle may be greater or less than 8.33 ms.

In order to minimize arcing and surge currents in a capacitor switch application, the switch contacts ideally close immediately at the null points where v (t) equals zero. See point A in the figure

6. However, since the contacts cannot be closed instantaneously, the timing of the initiation of the opening and closing sequences must be carefully controlled in order to minimize the formation of overvoltage currents and electric arcs.

A preferred embodiment of a control circuit 200 for use with the present invention is illustrated in FIG. 7. At the core of the control circuit 200 is a microprocessor 202 that is suitable for use within a wide temperature range.

The voltage waveform of the power distribution line that is controlled by switch 4 is analyzed by a voltage waveform analyzer 204, a phase lock circuit 206, and a V cross detection circuit 208._zero. Information concerning the voltage waveform of the line to be interrupted, which includes the timing of the null points A where the voltage v (t) is zero, is input to the microprocessor 202. Alternatively, it may A voltage waveform analyzer 204 is used that measures the voltage waveform directly from the line without the phase lock circuit 206.

The opening and closing commands are entered into the microprocessor 202 through inputs 210 and 212 respectively. The opening and closing commands can be created manually, they can be started at times programmed by a clock, they can be started by an external control or they can be triggered by the detection of a short circuit, depending on the particular application of switch 4.

A reset command 214 can be entered into microprocessor 202 to manually reset microprocessor 202 when necessary. For example, if switch 4 is manipulated manually, microprocessor 202 may not adjust to the current state of switch 4. In such a situation, microprocessor 202 must be reset.

Status indicators may be provided to indicate various conditions of circuit 200 or switch 4. Such indicators may include a maintenance light 216 to indicate when maintenance is needed, a power light 218, a switch open indicator 220, an indicator 222 switch closed, and a counter 224 that can be used to count the cycles or operations of the system.

A preferred embodiment of the present invention may include two control systems. A first control system is conventional, so it will not be explained here in detail, and determines when the line controlled by switch 4 should be opened or closed. The first control system may include a short-circuit detector or a timer for interruption. line once a short circuit has been detected, or at a predetermined time.

Alternatively, an open or close order can be entered directly into the system. The opening and closing orders, both originating from the first control system or manually, are entered into the microprocessor 202 through inputs 210 and 212 respectively.

The second control system 200, illustrated in Figure 7, analyzes the line voltage waveform and determines the optimal time to initiate the opening and closing of switch 4, in order to minimize surge currents and overvoltage. formation of electric arcs.

Each switch 4 has a dielectric resistance that defines the probability that an electric arc will jump from one contact to the other. The dielectric resistance depends on a number of factors including the internal environment of the switch 4 and the distance between the contacts 71,72. Figure 6 illustrates the variation or decrease in dielectric resistance between contacts 71 and 72 versus time as the distance between the contacts decreases. See line C in figure 6. Ideally, the dielectric resistance between the contacts should be infinite until the exact moment of closure of contacts 71, 72. See line B in figure 6. Actually, the slope of the resistance dielectric tends to drop, reducing rapidly as the contacts get closer to each other. If the slope of the dielectric drop is high enough, and the dielectric resistance remains greater than the waveform voltage, the generation of arcs and surge currents is eliminated or significantly reduced.

Another factor to be considered during switch operation is the relative speed between the contacts during opening and closing. If the contacts move slowly, the slope of the dielectric drop will be low, and arcing will be prone to occur. On the contrary, if the contacts move too fast, especially during closing, the contacts will tend to bounce off each other, causing arcing and shock.

ES 2 173 282 T3 Unnecessary surge currents. Accordingly, there can only be a single displacement scheme for each application of a switch. Figure 8 shows a displacement diagram, in which the abscissa represents the position of the moving contact 71 and the ordinate represents the speed at which the contact 71 moves. The point 0 on the abscissa represents the starting point or the position of maximum opening of the contact 71, and the point x represents the closing position, in which the contact 71 is touching the fixed contact 72. At the zero point, when the close command is initiated, the speed is zero. The speed is increased as quickly as possible to a maximum speed V_mox. The velocity remains equal to V_max as long as possible, but then shortened as you approach contact point x in order to minimize bounce.

During an opening sequence, the displacement profile is also important to prevent the reestablishment or re-ignition of electric arcs shortly after the start of the opening. If the contacts separate at too slow a speed, or at a time when the voltage is too high, excessive arcing can occur. Ideal travel profiles for opening and closing sequences can be determined by those skilled in the art and pre-programmed into circuit 200.

Turning attention to Figure 12, the timing of the opening operation in a capacitor switching application can be better understood. Figure 12 refers to the opening sequence of a system that includes a capacitor bank. Line 4 indicates the voltage level of the fully charged capacitors. The switch begins to open at point 2, and the electric arc is formed. However, at this point, the current decreases and the arc is extinguished when the current is zero, at point 3. The system voltage is now at its maximum value, but the voltage between the contacts is small due to to the charge of the capacitor bank, which approaches the maximum value of the system voltage. As the system voltage begins to drop, the voltage across the capacitor bank remains high, resulting in an increase in voltage between the contacts. The contacts must be separated with sufficient acceleration so that the dielectric increases more rapidly than the increasing voltage between the contacts, in order to avoid the reestablishment or re-ignition of arcs.

The displacement control function can be achieved by means of software loaded into the microprocessor / microcontroller or by the addition of dedicated displacement control chips that interfere with the microprocessor. A particular displacement profile is programmed into memory, which may be a separate EEPROM chip in an external control circuit 226, or into the memory of the microprocessor or microcontroller. The displacement control circuit 226 is connected to the feedback device 14 (encoder) and to a pulse width modulator (MAP) circuit 228. The MAP 228 controls the current that is applied to the speaker voice coil actuator 8. Since the driving force of the speaker moving coil operator 8 is proportional to the current applied to the speaker moving coil operator 8, the speed of the actuator 6 (and moving contact 71) is controlled by MAP 228. As a result, the loudspeaker voice coil actuator 8 is controlled by a closed loop feedback system that includes the position encoder 14 that outputs a position signal from the actuator 8 to the displacement control circuit 226. Travel control circuit 226 compares the actual position of actuator 8 with the ideal travel profile preprogrammed in travel control circuit 226. Based on the comparison of the actual position with the ideal displacement profile, the loudspeaker moving coil actuator 8 is controlled by the MAP so that its movement closely approximates the ideal displacement that was intended.

Actuator control is further modified by circuits 204, 206 and 208 which check the actual voltage waveform of the line to be interrupted. For example, for a particular application, it can be determined that contacts 71 and 72 should open or close at an instant 1 ms after the zero value point A (figure 6) of the voltage signal v (t). The ideal preprogrammed displacement profile in the displacement control circuit 226 includes the total reaction time and movement of the actuator 8, from the moment the start signal is sent, to the moment the contacts 71 close. and 72. If the ideal displacement profile indicates that the reaction and movement time for the contacts to close after the start signal is 7ms, the microprocessor analyzes the real voltage wave of the line to be interrupted and determines a specific time between null points at which the start signal should be sent. Circuits 204, 206, and 208 first set the actual cycle period and the length of the resulting time interval between the zero value points. The control circuit 200 then initiates the operation of the loudspeaker moving coil actuator 8 at the instant after the zero value point which is equal to the real time difference between the zero value points and the actuator movement and reaction time. 8. Therefore, if the actual voltage waveform indicates that there is 8.3 ms between the zero value points and that the actuator movement and reaction time is 7 ms, the opening sequence starts 1.3 seconds. after a point of zero value. In an alternative embodiment, the system can assume that the real time between zero value points is 8.33 ms, and the start is calculated based on that assumption.

In some embodiments of the present invention, a plurality of offset profiles can be programmed into circuit 200, and the appropriate offset profile can be selected by an operator input signal.

Once the sequence has started, the actual offset of operator 8 is controlled by me6

ES 2 173 282 T3 through encoder 14 and compared with the ideal displacement profile. The current applied to the actuator 8 is adjusted by MAP 228, based on the comparison of the actual movement of the actuator 8 with the ideal displacement profile.

Figure 9 illustrates another embodiment of a speaker voice coil actuator 308 that can be used with any of the embodiments of the present invention. Loudspeaker voice coil actuator 308 includes a ring magnet 310, which is preferably a 4 MGO ceramic magnet. The magnet 310 is housed between a lower pole piece 312 and an upper pole piece 314. These pole pieces are formed from ferromagnetic materials, such as iron or steel. Pole pieces 312 and 314 include a central opening 316 through which an operating stem 318 extends. The operating rod 318 is held on the pole pieces 312 and 314, by means of self-lubricating bearings 320 by polymers such as IGUS® bearings 320.

An aluminum plate 328 is attached to the stem 318. At the peripheral edge of the plate 328 a coil 330 extends from the plate 328 to a slot 332 for the passage of air formed between the lower pole piece 312 and the magnet 310. The Coil 330 may be formed from flattened wire so as to maximize the number of turns that will fit within slot 332 for air passage.

The actuator 308 may be powered by a 24 volt battery or by any other suitable power supply method, including an automatic range AC to DC converter.

In order to hold the device in a particular position, the operating stem 318 may include a slot 320 into which a ball 322 is inserted. See Figure 10. A spring 324 and a cap 326 push the ball 322 onto the slot 320. to keep stem 318 in a fixed position. The stem 318 can be released from the sphere 322 by the application of a force, the level of which depends on the resistance of the spring 324.

In order to ensure a good connection between contacts 71 and 72, a spring 340, or other force can be applied on stem 6, or 318, to push contact 71 against contact 72 with a predetermined force, such as 27 - 45 kg. The spring can be compressed by the action of an actuator. Turning attention to Figure 11, the operating stem 6, 318 may include a flange 342 that provides a surface on which the spring 340 is pressed. Another bearing surface 344 may be provided to grip the opposite edge of spring 340.

Spring 340 provides the added benefit of maintaining adequate force between the two contacts 71 and 72. For example, after repeated operations, arcing can cause the contacts to wear out. Thanks to the force of the spring, the two contacts are urged against each other even though they have worn out. Furthermore, the application of force causes a reduction in the electrical resistance between the contacts in the closed position, thus reducing heat losses.

If the contacts wear, the operating stem 6, 318 will move a greater distance in order to accommodate the wear. As the position sensor 14 detects the distance traveled by the rod 6, 318, the system can be programmed to turn on the maintenance signal 216 or some other indicator, to indicate that there has been excessive wear on the contacts 71 and 72 . The system can also modify its travel profile to allow for such an increase in thrust.

Although only the preferred embodiments have been specifically illustrated and described herein, it can be appreciated that many modifications and variations of the present invention are possible by virtue of the foregoing teachings as well as within the purview of the appended claims, without departing from the scope of the present invention. of the invention.