DEVICE AND METHOD FOR MONITORING A LOAD STAGE SWITCH

Description

[0001] The invention relates to a device for monitoring a load tap changer and a method for monitoring a load tap changer.

[0002] On-load tap changers are known from the prior art and typically comprise a load changeover switch and a selector. The tap changers are usually actuated by a motor drive in conjunction with a spring energy storage device. When performing a changeover, the motor drive pre-tensions the springs of the spring energy storage device. This either compresses compression springs or extends tension springs. At a defined mechanical point, the energy stored in the springs is released abruptly, and the on-load tap changer is actuated. The motor drive is mounted laterally on the transformer tank. A drive shaft leads from the motor drive to the on-load tap changer. Known methods are used to determine the torque at a first point when monitoring the on-load tap changer. This first point is located in the housing of the motor drive.For complete and accurate monitoring, the unknown torque at a second point in the load tap changer would be relevant. Furthermore, there is no constant mathematical relationship between the torque measured in the motor drive and the actual torque at the load tap changer. Rather, the torques occurring at the load tap changer, in relation to the calculated torques, change due to temperature influences, aging and wear of the load tap changer's mechanics, the bearings of the drive shaft and the drive gearbox, as well as other factors, throughout the entire operating life of the load tap changer, which typically extends over many years. Therefore, there is no stable, i.e., constant, torque transmission behavior between the motor of the drive and the load tap changer it drives over the entire operating period.

[0003] JP H07 106165 A discloses a device for monitoring a load tap changer according to the preamble of claim 1.

[0004] The object of the invention is therefore to create a device for monitoring a load tap changer that determines an accurate torque profile in the load tap changer and is simple and compact in design.

[0005] This problem is solved by a device according to claim 1. The features of the dependent claims constitute advantageous further developments of the invention.

[0006] A further object of the invention is to create a method for monitoring a load tap changer which determines the torque curve in the load tap changer safely and precisely.

[0007] This problem is solved by a method according to claim 5. The features of the dependent claims constitute advantageous further developments of the invention.

[0008] According to a first aspect, the invention proposes a device for monitoring a load tap changer, comprising a motor drive; a monitoring unit; a sensor for detecting an acoustic signal; where The monitoring unit determines a torque curve in the load tap changer based on a torque curve at the motor drive and the acoustic signal from the sensor.

[0009] The device enables the determination of the torque curve in the load changeover switch based on an acoustic signal and the torque curve at the motor. The acoustic signal is used to determine the precise moment at which the load changeover step occurred in the load tap changer. Based on this information, the motor's torque can be converted into the torque at the load tap changer with exceptional accuracy. The use of a sensor to detect an acoustic signal also allows for the retrofitting of older systems with this new device. The torque at the motor drive can be determined, for example, directly via a torque sensor or indirectly using measured data from the motor.

[0010] According to a second aspect, the invention proposes a method for monitoring a load tap changer, wherein a time range is determined based on an acoustic signal, in which a load switch step that occurs during a switching operation is determined; the time range is transferred into a torque curve of a motor drive; a time moment for the load switch step is determined in the time range of the torque curve; reference points are set in the torque curve of the motor drive based on the time moment for the load switch step; the torque curve of the motor drive is converted into a torque curve of the load tap changer.

[0011] By recording an acoustic signal and comparing it to a reference signal, the load switch step can be detected with exceptional accuracy. First, the time range within the acoustic signal at which the load switch step should occur is determined. This precise range is then transferred to the time-dependent torque curve of the motor drive and analyzed. Within this time range, the exact moment at which the load switch step, specifically the release of the spring energy storage device, occurred is determined. Starting from this point, the torque curve of the motor drive is referenced and converted into the torque curve of the load tap changer. Determining the precise time at which the load switch step occurs, and the subsequent referencing and conversion, make the method particularly accurate, safe, and reliable.

[0012] The determination of the load switch step, in particular the time domain in the acoustic signal, is initially carried out in such a way that An envelope is generated from the raw data of the acoustic signal measured during the switching process; the envelope of the acoustic signal is compared with a reference envelope; the reference envelope represents the load switch step; by comparing the envelope of the acoustic signal and the reference envelope, the time range in which the load switch step takes place is determined or limited.

[0013] The reference envelope is, for example, already stored in the monitoring unit's memory, or it is stored in the monitoring unit after a learning process. The reference envelope can be generated from several previously recorded and synchronized signals from multiple switching events. Furthermore, the reference envelope could be calculated as the mean, median, or weighted mean with added weighting factors from the raw data of several previously recorded and synchronized signals.

[0014] The reference envelope can have the same length as the envelope of the entire signal. Alternatively, the length of the reference envelope can correspond only to a defined region or predetermined section of the envelope. The comparison of the sensor envelope and the reference envelope is preferably performed using a correlation method, such as convolution or cross-correlation. The reference envelope contains the information describing the load switch step. This information is then sought in the envelope of the measured signal.

[0015] The torque curve of the motor drive can be determined via a torque sensor or by calculation based on motor-specific data and measured values. The length of the torque curve corresponds to the length of the envelope of the acoustic signal. The torque sensor is preferably mounted on the drive shaft of the

[0016] Motors and located at least at the beginning of the drive shaft.

[0017] During the load switching step or at the beginning of the load switching step, the spring energy storage device is usually unlatched.

[0018] After narrowing down the torque curve to the time domain defined by the envelope of the acoustic signal, the point in time or time moment at which the load switch step occurred can be determined within the corresponding time domain. This involves identifying the largest negative slope or the highest negative gradient within the narrowed-down time domain of the torque curve. This time moment represents the load switch step and, more precisely, the release of the spring energy storage device.

[0019] Furthermore, the torque curve of the motor drive is converted into a torque curve of the load tap changer using a linear function. This function is predefined and also stored in the monitoring unit.

[0020] The invention and its advantages are described in more detail below with reference to the accompanying drawing. It shows: Fig. 1 a schematic view of the device according to the invention for monitoring a load tap changer.

[0021] Figure 1Figure 1 shows a device 1 according to the invention for monitoring a load tap changer 2. The load tap changer 2 is installed in a transformer tank 3. The load tap changer 2 has a load changeover switch 21 with a spring energy storage device 22 and a selector 23. A motor drive 4 is arranged laterally on the transformer tank 3. The motor drive 4 has a housing 41 in which a motor 42 is arranged, which is connected to the load tap changer 2 via a drive shaft 43. The drive shaft 43 typically consists of several drive shafts and deflection couplings. To perform a switching operation, the motor 42 drives the load tap changer 2 via the drive shaft 43. During the switching operation, the selector 23 is first actuated, whereby a winding tap to be connected is preselected by a corresponding selector arm. In parallel, the spring energy storage device 22 is wound up.At a defined point in time, the spring energy storage device 22 is released and abruptly releases the energy previously stored during winding. This energy is used to actuate the load switch 21. Due to the non-ideal drive shaft tension 43, the torque at position 50 on the motor 42 or motor drive 4 does not correspond to the torque at position 51 on or in the load tap changer 2. In other words, the torque at the motor 4 is much higher due to the drive shaft tension 43 than the torque at or in the load tap changer 2.

[0022] The device 1 according to the invention has means and is capable of determining or recording the torque directly at the motor 42 during a switching operation, i.e., over time. A torque sensor can be used for this purpose, which is arranged directly on the output shaft of the motor 42 or directly at the beginning of the drive shaft assembly 43. "At the beginning of the drive shaft assembly 43" means that the torque sensor is arranged on a shaft that extends from or into the housing 41 of the motor drive 4. The sensor would transmit the measured torque curve to a monitoring unit 11. It is irrelevant whether the sensor is located inside or outside the housing 41. The torque can also be determined using the measured data from the motor 42 in conjunction with a suitable motor model.For this purpose, a central monitoring unit 11 measures or records the current, voltage, and phase angle of the motor 42 during the switching process. Subsequently, the data is converted into torque values ​​in a motor model within the monitoring unit 11, thus generating a torque curve. Further data that can be included in the calculation are the temperature of the motor 42 or the temperature in its vicinity. The monitoring unit 11 is designed such that it can both directly measure a torque curve and indirectly calculate it from the provided data.

[0023] Furthermore, the device 1 includes a sensor 6 for receiving acoustic signals. This sensor 6 is preferably located near the load tap changer 2, preferably near the load changeover switch 21, and particularly near the spring energy storage device 22, preferably on the housing of the transformer 3 or on the cover or head of the load tap changer 2. The sensor 6 can be designed as an acceleration sensor (e.g., a piezoelectric sensor or a MEMS sensor). The central monitoring unit 11 is designed for evaluating and / or acquiring the acoustic signals. It is connected by cable or wirelessly to the motor drive 4, in particular the motor or a torque sensor, and to the sensor 6. Furthermore, the monitoring unit 11 is used to carry out the method according to the invention, or the device carries out the method. The monitoring unit 11 can acquire and evaluate the raw data from the motor drive 4 and the sensor 6.Alternatively, the monitoring unit 11 only carries out the method according to the invention. Here, the motor drive 4 and the sensor 6 are equipped with appropriate means that acquire and process the respective raw data of the signals. Alternatively, several acoustic sensors 6 can be provided.

[0024] The in Figure 1The device shown performs the inventive method for monitoring a load tap changer 2. During a switching operation, i.e., during the actuation of the load tap changer 2, a torque profile of the motor drive 4 is first determined. Switching of the load tap changer 2 means that the load tap changer 2 switches a load current from one winding tap of a step-down transformer to an adjacent winding tap. The determination of the torque profile is carried out either with a torque sensor, by calculation based on motor-specific data and measured values, or by any other desired method. Simultaneously, an acoustic signal is detected during the switching operation using the sensor 6. Alternatively, several signals from several sensors 6 can be used, in which case the signals are combined into a single signal.This is done in monitoring unit 11 or in a separate unit as part of a preprocessing procedure.

[0025] In the next step, the raw data from sensor 6's signal is converted into an envelope. The envelope represents the energy of the oscillations within a frequency range. The next step involves determining the time interval within this envelope during which the load switching transition occurred. For this purpose, the envelope of the entire measured signal is compared with a reference envelope. To accelerate the process, a predefined area or segment of the envelope—not the entire envelope—can be compared with a reference envelope to narrow down the most probable time of the load switching transition. The reference envelope is generated from several envelopes of individual signals. Specifically, it is created from the raw data of several previously recorded and synchronized signals from a load switching operation.The reference envelope could be calculated as the mean, median, or weighted mean with added weighting factors from the raw data of several previously recorded and synchronized signals. The reference envelope contains the information that characterizes a load switching step.

[0026] The length of the reference envelope corresponds either to the total length of the envelope of the recorded signal or to the length of the specified range or predetermined section.

[0027] The envelope of sensor 6 and the reference envelope are compared using a correlation method, such as convolution or cross-correlation. Other methods for comparing the envelopes are also possible. The reference envelope, or a defined region or predefined section of the reference envelope, represents the load switching step. Either the entire envelope can be compared with the reference signal, or only a predefined region or predefined section of the envelope in which the load switching step occurred. This region or section can be predefined or alternatively determined through a learning process.

[0028] After comparison using correlation methods, a maximum match between the reference envelope and the envelope of the measured signal is determined. The time interval in the envelope of the measured signal with the greatest match to the reference envelope is marked as the load switching step.

[0029] After the time interval in which the load switch step occurred has been determined in the envelope, this time interval is transferred to the time-dependent torque curve. Within this now determined time interval of the torque curve, a specific point in time / moment is identified at which the release of the spring energy storage device, which is part of the load switch step, occurred.

[0030] Here, a time moment with the steepest negative slope, or the highest negative gradient, is determined within the corresponding time interval of the torque curve. Reference points are then established along the entire torque curve, starting from this time moment. In other words, the torque curve is aligned with this point (time moment). These reference points describe specific events during the switching operation of the load tap changer 2. Using these reference points, it can be determined which part of the load tap changer 2 was actuated and when. Finally, the torque curve of the motor 42 is converted into the torque curve of the load tap changer 2 using a linear function. The conversion of the torque curve of the motor drive 4 into that of the load tap changer 2 can also be performed in any other arbitrary manner.

[0031] The monitoring unit 11 can comprise a memory, a processing unit, and a communication unit. The monitoring unit 11 is designed such that it can execute the method according to the invention.

Claims

1. Device (1) for monitoring a on-load tap-changer (2), comprising - a motor drive (4); - a monitoring unit (11); - a sensor (6) for detecting an acoustic signal that is generated when the load changeover switch jumps during a changeover; - characterized in that the monitoring unit (11) determines a torque curve in the on-load tap-changer (2) on the basis of a torque curve on the motor drive (4) and the acoustic signal of the sensor (6).

2. Device (1) according to claim 1, wherein - the motor drive (4) has a torque sensor for determining the torque.

3. Device (1) according to claim 1 - 2, wherein - the torque on the motor drive (4) is determined by the monitoring unit (11) on the basis of measured data on the motor (42).

4. Device (1) according to claim 1 - 3, wherein - the sensor (6) is located near the on-load tap-changer (2) on the tap-changer head or on the transformer housing.

5. Method for monitoring an on-load tap-changer (2) with a device (1) according to one of claims 1 to 4, wherein - An acoustic signal is used to determine a time range at which a changeover switch jump occurs during a changeover; - the time domain is transferred to a torque curve of a motor drive (4); - a time torque for the diverter switch jump is determined in the time range of the torque curve; - reference points are set in the torque curve of the motor-drive unit (4) using the time torque for the diverter switch jump; - the torque curve of the motor-drive unit (4) is converted into a torque curve of the on-load tap-changer (2).

6. Method for monitoring a on-load tap-changer (2) according to claim 5, wherein - an envelope curve is generated from the acoustic signal; - the envelope of the acoustic signal is compared with a reference envelope; - the reference envelope maps the load switch jump; - the time range in which the load switch jump takes place is determined by comparing the envelope of the acoustic signal and the reference envelope.

7. Method for monitoring a on-load tap-changer (2) according to claim 5 to 6, wherein - the torque curve of the motor drive (4) is determined via a torque sensor or by calculation based on motor-specific data and measured values of a motor (42).

8. Method for monitoring a on-load tap-changer (2) according to claims 5 to 7, wherein - the spring energy accumulator (22) is unlatched during the diverter switch jump.

9. Method for monitoring a on-load tap-changer (2) according to claims 5 to 8, wherein - the time torque for the diverter switch step is determined, which is represented by the largest negative slope or the highest negative gradient in the time range of the torque curve.

10. Method for monitoring a on-load tap-changer (2) according to claims 5 to 9, wherein - the torque curve of the motor-drive unit (4) is converted into a torque curve of the on-load tap-changer (2) by means of a linear function.

11. Method for monitoring a on-load tap-changer (2) according to claims 5 to 10, wherein - the reference envelope is generated from several previously recorded and synchronized signals of several switchings.