SWITCH UNIT

Description

[0001] The invention relates to a switching unit with a load tap changer and a drive unit as well as a method for performing a switching operation by means of the switching unit.

[0002] Load-operated tap changers are known from the prior art and typically comprise a load switch and a selector. They are usually actuated by a motor drive in conjunction with a spring energy storage device. When a changeover occurs, the motor drive pre-tensions the springs of the energy storage device. This either compresses compression springs or extends tension springs. From a defined mechanical point, the energy stored in the springs is released abruptly, and the load-operated tap changer is actuated. This type of actuation offers no means of controlling the energy required for the changeover, at least from the moment the spring energy is released. WO-A-2020 / 229122 discloses a load-operated tap changer from the prior art.

[0003] The object of the invention is therefore to create a switching unit without spring energy storage that intelligently uses the energy required for switching and is simple and compact in design.

[0004] This problem is solved with a switching unit according to claim 1. The features of the dependent claims constitute advantageous further developments of the invention.

[0005] A further object of the invention is to create a method for carrying out a switching operation using the switching unit, which can be carried out safely and efficiently.

[0006] This problem is solved by a method according to claim 6. The features of the dependent claims constitute advantageous further developments of the invention.

[0007] According to a first aspect, the invention proposes a switch unit comprising: a load tap changer with an actuating shaft that actuates a switching device; a drive system with a motor; wherein the drive system is mechanically coupled to the load tap changer and actuates it; when actuating the load tap changer, the drive system uses the actuating shaft as a storage device for kinetic energy, such that the actuating shaft is accelerated and the switching device is actuated by means of kinetic energy from the actuating shaft and further energy supplied by the motor.

[0008] The switching unit according to the invention enables particularly efficient actuation of the switching elements and thus the switching of the load tap changer. The actuating shaft is initially accelerated and absorbs kinetic energy. During this phase, the actuating shaft is mechanically connected to the switching elements but does not yet actuate them. Only from a point defined by the design are the switching elements actuated. At this point, the kinetic energy of the actuating shaft and the energy from the motor of the drive system are used to actuate the switching elements and thus perform a switching of the load tap changer. The mass of the actuating shaft and the motor of the drive system are optimally matched to the switching elements. When the switching elements are actuated, this prevents the motor speed from dropping below a minimum value.This ensures that switching times are always met. Overcurrent resistors are not subjected to circulating current for extended periods. Furthermore, a precisely matched, non-oversized motor is used. This makes the switching unit cost-effective. The momentum of the actuating shaft is thus utilized to optimally perform load switching.

[0009] The switch unit can be designed in any way, whereby the actuating shaft and the switching device are mechanically coupled in such a way that the actuating shaft actuates the switching device according to a defined angle of rotation.

[0010] The actuating shaft can have cams on its outer surface that are partially distributed around its circumference. The switching unit can have several switching elements, including vacuum interrupters and / or selector contacts. The switching elements could include actuating levers that, by means of rollers, move along the outer surface of the actuating shaft. When the actuating shaft rotates, the switching elements are only actuated when the respective roller of an actuating lever engages a cam. The vacuum interrupters are opened and closed accordingly during actuation. The selector contacts make contact with fixed contacts that are connected to tapped sections of a control winding.

[0011] The switch unit can be designed in any way, whereby The actuating shaft is rotated at least once when the load step switch is actuated, and the motor shaft is rotated several times.

[0012] Depending on the design of the gearbox between the motor and the actuating shaft, the motor shaft rotates several times during a switchover. The actuating shaft rotates at least once and at most three times during a switchover, i.e., at least 360 degrees or at most 1080 degrees.

[0013] The switch unit can be designed in any way, whereby a moment to accelerate the actuating shaft is approximately or greater than a moment to actuate the switching device(s).

[0014] According to a second aspect, the invention proposes a method for performing a switching operation by means of a switch unit, wherein: In a first step, the actuating shaft is accelerated by the motor of the drive system, the actuating shaft absorbs kinetic energy and no switching device is actuated; in a second step, the switching device is actuated by means of the kinetic energy from the actuating shaft and energy from the drive system; in a third step, the actuating shaft is braked by the motor of the drive system.

[0015] When performing a switching operation using the switching unit, particularly when switching the load tap changer or actuating it, the switching process is divided into several steps. In the first step, the actuating shaft is accelerated by the motor of the drive system. During this process, the actuating shaft stores kinetic energy. In the second step, the switching mechanism is actuated. The energy required for this is drawn from the kinetic energy of the actuating shaft and additional energy from the motor of the drive system.

[0016] The invention and its advantages are described in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of the switch unit; Fig. 2 a driving profile of a motor of a drive system of the switch unit in two diagrams; Fig. 3a-3b three driving profiles of drive systems with different actuating shafts based on two diagrams each; Fig. 4 a flow diagram for a switching operation of a switch unit.

[0017] Figure 1Figure 1 shows a schematic representation of an exemplary embodiment of a switching unit 1 with a load tap changer 17 and a drive system 3, which is connected via a drive shaft 16 to the load tap changer 17 and its actuating shaft 20 and to the several switching elements 21. This drive system 3 is used to perform the switching of the load tap changer. The load tap changer 17 can include a load changeover switch, selector, double reversing switch, reversing switch, and / or preselector, or it can also be configured as a load selector. The switching elements 21 can be designed as vacuum switching tubes and / or simple contacts or selector contacts immersed in oil. The drive system 3 includes a motor 12, which can drive the drive shaft 16 via a motor shaft 14 and, optionally, via a gearbox 15. The drive shaft 16 is connected to the actuating shaft 20 in the load tap changer 17.A control device 2 of the drive system 3 comprises a power unit 11, which includes, for example, an inverter (not shown) for the controlled or regulated power supply of the motor 12, as well as a control unit 10 for controlling the power unit 11, for example via a bus 19. The drive system 3 has a feedback system 4, which is functionally assigned to the drive shaft 16. The feedback system 4 can be an encoder system 13. Likewise, the encoder system 13 can be part of the feedback system 4. The feedback system 4 or the encoder system 13 is connected to the power unit 11. Furthermore, the encoder system 13 is coupled directly or indirectly to the drive shaft 16.

[0018] The encoder system 13 is configured to detect an initial value for a position, such as an angular position, in particular an absolute angular position, of the drive shaft 16 and thus also of the actuating shaft 20. For this purpose, the encoder system 13 can, for example, include an absolute encoder, in particular a multi-turn absolute encoder or a single-turn rotary encoder, which is attached to the drive shaft 16, the motor shaft 14, or another shaft whose position is uniquely linked to the position of the drive shaft 16. For example, the position of the drive shaft 16 or actuating shaft 20 can be uniquely determined from the position of the motor shaft 14, such as via a gear ratio of the transmission 15. Furthermore, the encoder system 13 can include a virtual rotary encoder that determines the position of the motor shaft 14 and derives the position of the drive shaft 16 or the actuating shaft 20 from it.

[0019] The feedback system 4 is configured to detect a value for the position of the drive shaft 16 and thus also a position of the actuating shaft 20. With an encoder system 13, which is designed as a multi-turn absolute encoder or a single-turn rotary encoder, the value for the position of the drive shaft 16 is provided as a protocol.

[0020] When the encoder system 13 is implemented as a virtual rotary encoder, the value for the position of the drive shaft 16 is determined from the rotor position of the motor 12. For this purpose, inductive feedback from the movement of the rotor in the motor windings of the motor 12 can be used, for example. Since the strength of the feedback varies periodically, the rotor position can be determined approximately, particularly by means of signal analysis, such as FFT analysis. Because one full revolution of the drive shaft 16 corresponds to a multitude of revolutions of the rotor, the position of the drive shaft 16 and also of the actuating shaft 20 can be determined with much higher accuracy.

[0021] The encoder system 13 can also be configured as a combination of a virtual rotary encoder and an auxiliary contact that is directly or indirectly connected to the drive shaft 16. The value for the position of the drive shaft 16 is then derived from the signals of the virtual rotary encoder and the auxiliary contact.

[0022] The control device 2, in particular the control unit 10 and / or the power part 11, is designed to control or regulate the motor 12, depending on a feedback signal which the feedback system 4 generates based on the value.

[0023] The control device 2, for example the control unit 10, uses the value for the position of the drive shaft 16 or actuating shaft 20 to determine the position of the load tap changer 17. The control device 2, for example the control unit 10, controls and regulates the motor 12 so that it maintains a predetermined speed according to the specifications.

[0024] When performing a switching operation or when the load tap changer 17 is actuated, the system always attempts to accelerate the drive system 3, and in particular the motor 12, to a predetermined speed, maintain this speed during the switching operation, and reduce the motor speed to 0 at the end of the switching operation. During the switching operation or when the load tap changer 17 is actuated, the speed of the motor 12 must not fall below a predetermined minimum value.

[0025] The actuating shaft 20 and the switching means 21 are mechanically connected or coupled to each other. The actuating shaft 20 can have cams which, from a certain point in the rotation of the actuating shaft 20, open and close the switching means 21, in particular vacuum switching tubes, for example via toggle levers. It is assumed that the energy required to actuate the switching means 21 is always the same. In other words, a constant torque must always be applied to actuate the switching means 21.

[0026] Since this is not an ideal system, it can be assumed that the motor 12 provides the energy required to actuate the switching means 21 only with a delay, and thus the speed of the motor 12 initially drops. After a delay, the motor 12 then provides the energy, which also increases the speed.

[0027] Figure 2Figure 1 shows a possible driving profile of the motor 12 for switching or actuating the switch unit 1, and in particular the division of the switching into several steps in different diagrams 25 and 26. For better explanation, these diagrams are arranged one above the other. In the first diagram 25, the rotational speed n of the motor 12 is plotted against time. The actuating shaft 20 is accelerated by the motor 12 of the drive system 3. As can be seen here, the rotational speed of the motor 12 increases linearly in a first step 60 over a certain time until a certain value, i.e., a certain rotational speed, is reached. This is the first step 60 of the switching process or the switching operation. In the second diagram 26, which is shown below the first diagram 25, the course of the kinetic energy is shown.The kinetic energy is formed from the rotational speed and the inertia of the actuating shaft 20 and the inertia of the switching means 21.

[0028] Here too, the first step 60 of the switching process is shown in a delimited manner. While the motor 12 of the drive system 3 accelerates the actuating shaft 20, the kinetic energy increases in the entire mechanical system of the switch unit 1.

[0029] In the second step 70, the switching means 21 are actuated. Advantageously, in addition to the energy from the motor 12, the kinetic energy of the actuating shaft 20 is used to actuate the switching means 21. In other words, the momentum of the mass of the actuating shaft 20 assists the motor 12 in actuating the switching means 21. The actuating shaft 20 is used as a storage device for kinetic energy. In the second step 60, it can be seen that the speed of the motor 12 briefly drops when the switching means 21 are actuated and then rises again to the specified value.

[0030] By actuating the switching means 21, particularly when the Maltese gears of the switching means 21 are actuated, their inertia is suddenly coupled to the inertia of the actuating shaft 20 at a certain point. This results in a transfer of kinetic energy from the actuating shaft 20 to the switching means 21. Since the total energy remains constant, the rotational speed of the actuating shaft must necessarily decrease. Because the inertia of the actuating shaft 20 and that of the switching means 21 must now be accelerated so that the motor reaches the specified rotational speed, the kinetic energy also increases. When actuating the switching means 21, it is particularly important that the rotational speed does not fall below a certain minimum value 27. Falling below this minimum value could result in the switching means 21 being actuated too slowly.Switching times would then not be adhered to, meaning that arcs in the switching devices 21 could not be extinguished or switching resistors would be subjected to excessive load for too long.

[0031] In the Figures 3a to 3c The combinations of three different actuating shafts 20 as storage devices for kinetic energy and the motor 12 are described using three driving profiles. In the first upper diagram 30 in Figure 3a The torques occurring during the actuation of the load tap changer 17 within a given time interval are shown. The first area 32 shows the torque required to accelerate the actuating shaft 20. The second area 33 shows the torque required to actuate the switching means 21. The third area 34 shows the torque required to decelerate the actuating shaft 20. Diagram 31 below shows the speed profile of the motor 12 over time.

[0032] The moment of inertia of the actuating shaft 20 is small in this example. Therefore, only a small torque is required to accelerate the actuating shaft 20. Very little kinetic energy is stored in the actuating shaft 20. Since this energy is significantly less than the work required to actuate the switching elements 21, the speed of the motor 12 drops sharply because the non-ideal drive system 3 requires a certain amount of time to replenish the lost energy. In other words, the energy extracted from the system is very large in relation to the kinetic energy present before the actuation of the switching elements 21. This causes the minimum speed 34 to fall below the required value, which negatively affects the switching operation. For example, switching times in the load tap changer 17 cannot be maintained.

[0033] The second pair of diagrams 40, 41 in Figure 3bFigure 1 shows the operating profile of an embodiment of the switch unit 1 in which the moment of inertia of the actuating shaft 20 is very high. Therefore, a large torque 42 must be applied to accelerate the actuating shaft 20. A significant amount of kinetic energy is stored in the actuating shaft 20. Since this energy is considerably greater than the work required to actuate the switching means 21, the motor speed hardly drops once the torque of the switching means 21 is applied. In other words, the energy extracted from the system is very small in relation to the kinetic energy present before the actuation of the switching means 21. The minimum speed 44 is not undercut, which has a positive effect on the switching process. However, in this case, a very powerful motor 12 is required to bring the actuating shaft 20 up to the required speed n.High-performance motors make a drive system expensive and therefore uneconomical. The third area, 44, shows the torque required to brake the actuating shaft 20.

[0034] In the third pair of diagrams, 50, 51 in Figure 3c A driving profile of an optimal embodiment of the switch unit 1 is shown, in which the moment of inertia of the actuating shaft 20 and the motor 12 are matched to the torque 53 required when actuating the switching means 20. The mass of the actuating shaft 20 is precisely such that, when actuating the switching means 21, the rotational speed remains just above a minimum value and the torque 52 for accelerating the actuating shaft 20 does not become too high. A smaller, more suitable motor 12 can be selected.

[0035] In other words, the moment of inertia of the actuating shaft 20 is chosen to be so large that the absolute value of the torque 52 for accelerating and braking the actuating shaft 20 is greater than or equal to the torque required by the switching means 21 during switching or actuating the load tap changer 17.

[0036] Figure 4 Figure 60 shows a method for performing a switching operation using switch unit 1. In the first step, the actuating shaft 20 is accelerated by the motor 12 of the drive system 3. The actuating shaft 20 absorbs kinetic energy. The switching means 21 are not yet actuated. In a second step, the switching means 21 are actuated. Here, the kinetic energy of the actuating shaft 20 and the energy of the drive system 3 are used. In the third step, the actuating shaft 20 is decelerated by the drive system 3.

[0037] The term "switching" refers to the operation of the load tap changer. This involves switching from one winding tap of a tap-changer to an adjacent winding tap-changer of the same tap-changer.

Claims

1. A switch unit (1) comprising: - a on-load tap-changer (17) with an actuating shaft (20) which actuates a switching means (21), - a drive system (3) with a motor (12); wherein - the drive system (3) is mechanically coupled to the on-load tap-changer (17) and actuates the latter, characterized in that - the drive system (3) uses the actuating shaft (20) as a store for kinetic energy when the on-load tap-changer (17) is actuated, such that the actuating shaft (20) is accelerated and the switching means (21) is actuated by means of kinetic energy from the actuating shaft (20) and additional energy provided by the motor (12).

2. Switch unit (1) according to claim 1, wherein - the actuating shaft (20) and the switching means (21) are mechanically coupled in such a way that the actuating shaft (20) actuates the switching means (21) according to a fixed angle of rotation.

3. Switch unit (1) according to one of claims 1 or 2, wherein - the actuating shaft (21) is rotated at least once during an actuation of the on-load tap-changer (17) and the motor shaft (14) is rotated several times.

4. Switch unit (1) according to one of claims 1 to 3, wherein - a torque for accelerating the actuating shaft (20) is approximately or greater than a torque for actuating the switching means (21).

5. Switch unit (1) according to any one of claims 1 to 4, wherein - a plurality of switching means (21) are provided, which are designed as vacuum interrupters and / or selector contacts.

6. Method for carrying out a changeover by means of a switch unit (1) according to claims 1 to 5, wherein: - in a first step (60), the actuating shaft (20) is accelerated by the motor (12) of the drive system (3), the actuating shaft (20) absorbs kinetic energy and no switching means (21) is actuated; - in a second step (70), the switching means (21) is actuated by means of the kinetic energy from the actuating shaft (20) and an energy from the drive system (3).

7. Method for performing a changeover according to claim 6, wherein: - in a third step (80), the actuating shaft (20) is braked by the motor (12) of the drive system (3) until it comes to a standstill.