Method for driving a tap changer, and drive system for a tap changer

Abstract

In a drive system (1) for a tap changer, a motor (2) is supplied with current from a voltage supply (4). In order to cover the required peak currents in the motor (2) during individual phases of a switching process of the tap changer, the motor (2) is supplied with current from an energy storage device (5), and outside of a switching process, the energy storage device (5) can be charged from the voltage supply (4).

Description

[0001] METHOD FOR DRIVING A TAP CHANGER AND DRIVE SYSTEM FOR A TAP CHANGER

[0002] The invention relates to a method for driving a tap changer and a corresponding drive system.

[0003] Tap changers are used to switch between different winding contacts of a transformer. This ensures that the voltage supplied by the transformer to a power grid remains within a defined fluctuation range around a setpoint, despite variable grid load. Tap changers as such are well known; they include, in particular, on-load tap changers, in which the switching process takes place between different winding contacts of the transformer while the transformer is supplying voltage to a power grid, and off-circuit tap changers, in which the transformer is disconnected from the power grid it supplies for the switching process. Switching between different winding contacts of the transformer is achieved by mechanical actuation of electrical contacts in the tap changer. This mechanical actuation can be driven by a motor.

[0004] During a single switching operation, the mechanical actuation of the electrical contacts in the tap changer requires different torques. The electric motor used to drive the tap changer must be supplied with power corresponding to these required torques. The power supply used to power the electric motor must also be able to cover the peak current demand that occurs during some phases of the switching operation, which can be several times greater than the current required during other phases. However, the use of a correspondingly powerful power supply is uneconomical and requires a lot of space.

[0005] The object of the invention is therefore to provide a method for driving a tap changer and a corresponding drive system to overcome these disadvantages. This object is achieved by a method according to claim 1 and by a drive system according to claim 4. The subclaims each relate to advantageous embodiments.

[0006] According to the method of the invention for driving a tap changer, current is supplied to a motor for the tap changer in order to perform a switching operation. The switching operation is monitored by a motor controller; the motor controller regulates the current supplied to the motor. According to the invention, the current is supplied to the motor from a voltage supply when the current required to drive the motor is below a predefined threshold. If the current required to drive the motor is above this predefined threshold, according to the invention, at least part of the current is supplied to the motor from an energy storage device that is different from the voltage supply.

[0007] This process therefore does not require a power supply capable of covering the maximum current peaks required, which correspond to the high torque requirements for the mechanical actuation of electrical contacts in the tap changer. The energy storage system is designed to cover this peak load.

[0008] The energy storage device can consist of one or more capacitors. These capacitors can operate at the same voltage level as the power supply. However, it is also possible to provide a voltage transformer between the capacitors and the motor; this allows greater freedom in the selection of capacitors and therefore makes it easier to meet any additional requirements, such as space requirements, service life, and thermal resistance.

[0009] The motor is an electric motor; the specific type of electric motor can be suitably selected by the person skilled in the art. It can be a DC motor, in particular a brushless DC motor, without limiting the invention to this. Since high torque is also provided by the motor's power supply during phases of the switching process in which this is required, mechanical energy storage devices, such as spring energy storage devices, can be dispensed with.

[0010] In one embodiment, the energy storage device is charged from the power supply. If no switching process is taking place, the power supply can be used to charge the energy storage device if necessary. For this purpose, the charge level of the energy storage device can be checked in advance by the motor control unit. Since a regular switching process requires power to be supplied from the energy storage device to the motor, the motor control unit ensures that no switching process is initiated until the energy storage device has at least a predefined minimum charge level sufficient to perform a switching process.

[0011] In one embodiment, monitoring the switching process by the motor control system involves the motor control system receiving signals from a rotary encoder that represent an angular position of a drive shaft of the tap changer. The drive shaft of the tap changer is a shaft in the tap changer whose rotation causes the electrical contacts in the tap changer to be mechanically actuated, and to which the motor for driving the tap changer is mechanically coupled, either directly or via a gear. The rotary encoder can directly detect the angular position of the drive shaft or the angular position of another shaft in the drive train of the tap changer, such as a shaft of the motor itself. It is important here that the angular position of the respective shaft can be used to determine which phase the switching process of the tap changer is in.It should also be noted that the properties of the mechanical coupling between the respective shaft, such as the shaft of the motor, and the drive shaft of the tap changer, for example from a transmission ratio of a gear between the respective shaft and the drive shaft of the tap changer, result in a relationship between the angular position of this shaft and the angular position of the drive shaft of the tap changer, so that, for example, signals from the rotary encoder which indicate the angular position of the shaft of the motor also represent the angular position of the drive shaft of the tap changer within the meaning of this application.

[0012] Generally, it should be noted that the claimed method serves to drive a tap changer to perform a switching operation of the tap changer. In practical use, the tap changer is connected to a transformer that feeds a power grid. Accordingly, the claimed method is integrated into more comprehensive methods for controlling the tap changer and regulating the power grid. These more comprehensive methods then result in, for example, the determination of the need for a switching operation and corresponding signals to the motor control system requesting such a switching operation.

[0013] The drive system according to the invention for a tap changer comprises a motor for driving the tap changer, a motor controller for the motor, a power supply, and an energy storage device. The drive system is configured to carry out the method according to the invention described above. This includes the motor controller being designed, in particular programmed, to receive and process information relevant to a switching operation and, depending on the results of this information processing, to control the current flow to the motor such that the switching operation is carried out according to the method steps.

[0014] In one embodiment, the motor controller comprises a management unit configured to regulate whether power is supplied to the motor from the voltage supply and / or from the energy storage device. If the current required for the respective phase of the switching process is below a predefined threshold, the current is supplied solely from the voltage supply. If the current required for the respective phase of the switching process is above the predefined threshold, the current is supplied from the voltage supply and the energy storage device or solely from the energy storage device. In a further development, the management unit is further configured to regulate charging of the energy storage device from the voltage supply.

[0015] In an even more specific embodiment, the motor controller further comprises a power output stage and a control unit. The current supplied to the motor is switched in the power output stage. The control unit controls a switching operation of the tap changer by evaluating signals from a rotary encoder, which represent an angular position of a drive shaft of the tap changer, and by correspondingly controlling the switching of the current in the power output stage. The management unit is designed to regulate whether the current to be switched in the power output stage is supplied to the power output stage from the voltage supply and / or from the energy storage device.

[0016] The invention and its advantages are explained in more detail below with reference to the attached drawings.

[0017] Figure 1 shows schematically an embodiment of a drive system according to the invention.

[0018] Figure 2 shows schematically the course of a current for the motor during a switching process.

[0019] The figures refer only to embodiments of the invention and are not to be construed as limiting the invention to the embodiments shown.

[0020] Fig. 1 schematically shows a drive system 1 according to the invention. Motor 2 is provided for driving a step changer. For this purpose, the motor 2 is controlled by a motor controller 3, which for this purpose receives signals from a rotary encoder 6, which in this example indicate an angular position of a shaft of the motor 2. The motor 2 can be supplied with power from a voltage supply 4 and / or from an energy storage device 5 via the motor controller 3. The motor controller 3 includes a management unit 31, a power output stage 32, and a control unit 33. The power output stage 32 switches the power to the motor 2. This power is provided to the power output stage 32 via the management unit 31, wherein the management unit 31 controls, depending on the phase of a respective switching process, whether the power is provided to the power output stage 32 from the voltage supply 4 or from the energy storage device 5.Depending on the detailed design of the drive system 1, the provision of power from the energy storage device 5 can be alternative or additional to the provision of power from the voltage supply 4.

[0021] The control unit 33 controls the switching process of the tap changer. The signals from the rotary encoder 6 provide information about the phase of the switching process; additional measurement data, such as current intensities and current phases in components of the tap changer, can also be used for this purpose. Depending on the information about the phase of the switching process, the control unit 33 controls the switching of the current in the power output stage 32. Information about the phase of the switching process can also be sent to the management unit 31 to enable it to decide whether the current to the power output stage 32 is supplied from the voltage supply 4 or (if necessary additionally) from the energy storage device 5.

[0022] Fig. 2 shows a diagram 100, with an abscissa 101 corresponding to the course of a switching operation of a tap changer, and an ordinate 102 on which a current intensity to the motor 2 of the drive system 1 (cf. Fig. 1) is shown, which drives the tap changer during this switching operation. The course of a switching operation can be specified, for example, via the respective angular position of a shaft, such as the drive shaft of the tap changer or a shaft of the motor 2. Without limiting the invention thereto, it may be the case that a full revolution of the drive shaft of the tap changer corresponds to a complete switching operation; in this case, the current intensity course shown in diagram 100 extends over a range of 360 degrees along the abscissa 101. In the same way, the course of the switching operation could also be described via an angular position of a shaft of the motor 2.

[0023] The switching process shown in diagram 100 is clearly divided into several phases 110 - 150.

[0024] The switching process begins in phase 110. First, stationary mechanical components (including the electrical contacts in the tap changer, as well as any gears and the rotor of the electric motor) must be set in motion, i.e., accelerated. The torque required for this must be supplied by motor 2, which requires high currents. These currents exceed the currents that can be provided by voltage supply 4. Therefore, in phase 110, additional current is supplied to motor 2 from energy storage device 5.

[0025] In phase 120, the previously accelerated mechanical components move. It is only necessary to maintain this movement. This requires torques and corresponding currents that are considerably lower than the maximum currents occurring in phase 110. The required current can be provided solely from power supply 4.

[0026] In phase 130, the contact required for the switching process occurs between various mechanical components of the tap changer. Continuing the movement, and thus the switching process, requires torques and currents that are significantly higher than in phase 120. These currents exceed the currents that can be provided by power supply 4. Therefore, in phase 130, additional power is supplied to motor 2 from energy storage 5.

[0027] In phase 140, the mechanical components continue to move toward their respective designated end positions after the switching process. It is only necessary to maintain this movement, similar to phase 120. The required current can be provided solely from power supply 4. In phase 150, the moving mechanical components must be decelerated so that they come to a standstill at their respective designated end positions. This deceleration process results in currents whose magnitude can certainly reach the values ​​occurring in phases 110 or 130, but with the opposite sign. The energy corresponding to these currents can be dissipated, for example, by conducting the currents through a suitable resistor.An alternative possibility would be to use these currents to at least partially charge the energy storage device 5; this can be achieved by appropriate configuration of the management unit 31 and the power output stage 32.

[0028] List of reference symbols:

[0029] 1 drive system

[0030] 2 engines

[0031] 3 Motor control 4 Power supply

[0032] 5 energy storage

[0033] 6 rotary encoders

[0034] 31 administrative unit

[0035] 32 Power amplifier 33 Control unit

[0036] 100 diagram

[0037] 101 Abscissa (switching process)

[0038] 102 Ordinate (current to motor)

[0039] 110 - 150 phases of a switching process

Claims

Claims 1. Method for driving a tap changer, the method comprising the steps: Providing power to a motor (2) for the step switch to carry out a switching operation; Monitoring the switching process by a motor controller (3), wherein the motor controller (3) regulates the current supplied to the motor (2); characterized in that the current is supplied to the motor (2) from a voltage supply (4) when the current required to drive the motor (2) is below a predefined threshold value; and in that at least part of the current is supplied to the motor (2) from an energy store (5) which is different from the voltage supply (4) when the current required to drive the motor (2) is above the predefined threshold value.

2. Method according to claim 1, wherein the energy storage device (5) is charged from the voltage supply (4).

3. Method according to one of claims 1 or 2, wherein the monitoring of the switching process by the motor control (3) comprises the motor control (3) receiving signals from a rotary encoder (6) which represent an angular position of a drive shaft of the tap changer.

4. Drive system (1) for a tap changer, the drive system (1) comprising: a motor (2) for driving the tap changer; a motor controller (3) for the motor (2); a voltage supply (4); an energy storage device (5); characterized in that the drive system (1) is configured to carry out the method according to one of claims 1-3.

5. Drive system (1) according to claim 4, wherein the motor control (3) comprises a management unit (31) which is designed to regulate whether current is provided to the motor (2) from the voltage supply (4) and / or from the energy storage device (5).

6. Drive system (1) according to claim 5, wherein the management unit (31) is further designed to regulate a charge of the energy storage device (5) from the voltage supply (4).

7. Drive system (1) according to one of claims 5 or 6, wherein the motor control (3) further comprises: a power output stage (32) designed to switch the current to be provided to the motor (2); a control unit (33) designed to control a switching operation of the tap changer by evaluating signals from a rotary encoder (6) representing an angular position of a drive shaft of the tap changer, and by appropriately controlling the switching of the current in the power output stage (32); wherein the management unit (31) is designed to regulate whether the current to be switched in the power output stage (32) is provided to the power output stage (32) from the voltage supply (4) and / or from the energy store (5).

Images