Fault detection in spring-loaded storage systems of medium-voltage circuit breakers

Abstract

A method for operating a spring-loaded storage actuator (30) of a medium-voltage switchgear (10) comprising the steps: - Measuring the time course of a drive current of an electric auxiliary drive (31) for tensioning a drive spring (34) of the spring storage drive (30) of the medium voltage system (10); - Tensioning the drive spring (34) with the electric auxiliary drive (31); - Creating an evaluation data set depending on the measured time course of the drive current, whereby an integral of the time course of the drive current is determined and wherein a first part of the integral is determined, which indicates a clamping work performed by the auxiliary drive; - Comparing the evaluation data set with an expectation; and - Outputting a maintenance signal depending on the result of a comparison.

Description

Technical area

[0001] The invention relates to a method for operating a spring-loaded drive of a medium-voltage switchgear, a spring-loaded drive which is designed to carry out the operating method according to the invention, and a medium-voltage switchgear with such a spring-loaded drive. Technical background

[0002] Switching operations in medium-voltage switchgear, such as opening a switch by removing a moving contact of a switch in the medium-voltage switchgear from its mating contact, must typically be carried out within a period of a few milliseconds after receipt of a corresponding control signal in order to minimize any risk to personnel and material. Therefore, spring-loaded actuators are used, which store the energy required for the switching operation of a switch in order to be able to respond to a corresponding control signal with the shortest possible delay. These spring-loaded actuators have one or more springs that are tensioned by an auxiliary electrical drive. The tensioning of the spring(s) usually occurs without increased requirements regarding the tensioning speed. The auxiliary electrical drive is usually connected to the spring via a gear or contains one.

[0003] Faults can occur in these spring-loaded operating mechanisms that impair the operation of the switch. These faults must be reliably and early detected as part of the safe operation of the medium-voltage switchgear to prevent faulty switching. These faults can be caused by the spring-loaded operating mechanism, its electrical auxiliary drive, or the combination of spring-loaded operating mechanism and electrical auxiliary drive.

[0004] Possible errors are: - Spring fatigue (the energy stored in the spring decreases over time) - Spring reinforcement (the energy stored in the spring increases over time) - (increasing) mechanical stiffness in the auxiliary drive including gearbox - Deterioration of the electrical characteristics of the auxiliary drive with reduction of the delivered mechanical power - Overload and resulting destruction of the auxiliary drive including the gearbox

[0005] Currently, there are no adequate methods available for reliably detecting faults and assigning them to individual components of a spring-loaded mechanism during operation of a medium-voltage switchgear. The systems used to date can only detect serious deviations, such as a malfunction of the overall assembly, and only during an individual test. This requires disconnecting the switch from the medium-voltage supply and connecting a special test device.

[0006] US 2017 / 0047181 A1 shows the recording and evaluation of the envelope curves of the motor current of an auxiliary motor of a circuit breaker.

[0007] Against this background, there is a need for a method for operating a spring-loaded actuator of a medium-voltage switchgear that allows fault detection during the intended operation of the medium-voltage switchgear. Summary of the invention

[0008] The method according to the invention for operating a spring-loaded drive of a medium-voltage switchgear comprises at least the following steps: - Measuring a drive current of an auxiliary electrical drive for tensioning a drive spring of the stored energy spring drive of the medium-voltage system; - Tensioning the drive spring with the electric auxiliary drive; - Creating an evaluation data set depending on the measured drive current; - comparing the evaluation data set with an expectation; and - Outputting a maintenance signal depending on a result of the comparison.

[0009] In the step of measuring the drive current, a temporal profile of the drive current is measured. The evaluation data set is created based on the measured temporal profile of the drive current. Furthermore, in the step of creating the evaluation data set, an integral of the temporal profile of the drive current is determined, with a first component of the integral being determined, which indicates the clamping work performed by the auxiliary drive.

[0010] The method offers the advantage that the condition of the stored-energy spring mechanism and its components, such as the spring and auxiliary drive, including the gear unit, can be recorded and assessed during a normal switching operation during the intended operation of the medium-voltage switchgear. The output of the maintenance signal allows maintenance measures to be planned in good time before failure or an unacceptable probability of malfunction of the stored-energy spring mechanism occurs and to be carried out at a time that minimizes the impact on the operation supplied or controlled by the medium-voltage switchgear, thus reducing downtimes as much as possible.

[0011] The invention is based on and incorporates the insight that the condition of the spring-loaded drive can be determined from the drive current of the electric auxiliary drive used to tension the spring. For example, the drive current increases when the auxiliary drive must apply greater torque due to increasing mechanical stiffness of the gearbox or the motor bearings of the auxiliary drive. However, the current can also decrease if the tensioning force of the spring decreases due to material fatigue over a large number of switching operations. If such a case is detected, the maintenance signal can indicate this, allowing appropriate maintenance measures to be initiated.

[0012] Medium voltage is defined as an electrical voltage in the range from 1000 volts to approximately 52 kilovolts.

[0013] By measuring the temporal profile of the drive current, several parameters can be determined and, for example, opposing effects that cancel each other out in a single measurement, each of which indicates a deterioration of the spring-loaded actuator, can be differentiated and identified. Thus, measuring the temporal profile of the drive current increases the probability that deterioration of the spring-loaded actuator can be detected in a timely manner and that the affected component of the spring-loaded actuator can be identified before the maintenance action is initiated, thus enabling a better assessment of the urgency of performing the maintenance action.

[0014] For example, the temporal profile can be measured based on a periodic measurement of the instantaneous current of the electric auxiliary drive. It is also possible to take individual measurements at specific times, covering points of the actual profile that are of particular interest when creating the evaluation dataset. This results in less measurement data to be processed overall, which simplifies evaluation and storage. Since these points, or at least some of them, may shift in time due to the observed deterioration, it is also possible to perform a series of individual measurements around these points and not measure the drive current, or measure it less frequently, between these series.

[0015] The integral of the drive current indicates how much electrical energy was used for the complete tensioning process. An increase in this value is a good indicator of deterioration of the spring-loaded drive.

[0016] The first part of the integral can, in particular, refer to the temporal portion of the measured time profile that extends from a local minimum after the activation of the auxiliary drive until its deactivation. The first part of the integral provides information about whether and how the elasticity of the spring has changed over time, which can, for example, result in an undesirably reduced movement speed of the switch's moving contact during the switching operation when the spring slackens.

[0017] In addition, a second component of the integral can be determined, which indicates drive losses of the auxiliary drive. This second component of the integral can, in particular, refer to a temporal segment of the measured time profile extending from the time of activation of the auxiliary drive up to the aforementioned local minimum, as well as to a base region of the time profile, which is limited upwards by the current intensity at this local minimum. The second component of the integral provides information as to whether motor mounts, gears, and other conversion and transmission of the auxiliary drive's motor power down to the spring have become stiffer or have otherwise deteriorated or changed.

[0018] In a combination of the last two embodiments of the method according to the invention, the first and second parts of the integral can be related to each other. This allows multiple error variants to be read off from a single ratio value, which can simplify the step of comparing with the expected value.

[0019] Preferably, at least one characteristic time is determined when creating the evaluation data set. In the step of comparing the evaluation data set, the at least one characteristic time and / or a drive current measured at the at least one characteristic time is compared with an expected value associated with the at least one characteristic time. The characteristic times are determined, for example, relative to a starting time of the activation of the auxiliary motor and denote times at which a known behavior expected for a given type of spring-loaded drive can be detected. For example, the at least one characteristic time can be a time selected from: - the beginning of a current flow through the auxiliary drive, - the start of tensioning the drive spring, - the occurrence of a local or global maximum of the drive current, - the switch-off time of the auxiliary drive and - the end of a current flow through the auxiliary drive.

[0020] The expectation with which the evaluation data set is compared can, in particular, be a historical data set or a predefined data set specific to a type of spring-loaded actuator. A historical data set can, for example, contain a data set of the same spring-loaded actuator recorded during the production of the spring-loaded actuator during a test tensioning of the spring in accordance with the relevant method steps of the method according to the invention, or an evaluation data set recorded during an earlier implementation of the method according to the invention. A specific data set predefined for the type of spring-loaded actuator can describe a generalized behavior of the spring-loaded actuator across production variations, whereby the described measurements during the production of the spring-loaded actuator can be omitted, saving time and money.

[0021] A second aspect of the invention relates to a spring-loaded actuator for a medium-voltage switchgear assembly, comprising an electrical auxiliary drive configured to tension a drive spring of the spring-loaded actuator, and a measuring unit configured to measure a drive current of the auxiliary drive. The measuring unit is also configured to transmit a measurement result to a control unit for implementing the method of the first aspect of the invention. The control unit can be implemented as a joint unit with the measuring unit or as a separate unit outside the spring-loaded actuator, for example, in a digital protection device of the medium-voltage switchgear assembly or a remote control center.

[0022] A further aspect of the invention introduces a medium-voltage switchgear assembly with a switch having a moving contact and a spring-loaded drive according to the preceding aspect of the invention, which is designed to move the moving contact of the switch in response to a control signal.

[0023] Finally, the invention relates to a data storage device with a computer program which, executed by a control unit, for example a control unit of a spring-loaded drive, a medium-voltage switchgear, a digital protection device or a remote control center, carries out the method according to the invention. Brief description of the figures

[0024] The invention is explained in more detail below with reference to exemplary embodiments. They show: Fig. 1 an embodiment of a medium-voltage switchgear with a spring-loaded drive according to the invention; Fig. 2 shows an example of a time profile of a drive current of an electric auxiliary drive of the spring-loaded drive according to the invention; and Fig. 3 an embodiment of a method according to the invention for operating the spring-loaded drive. Detailed character description

[0025] Fig. 1 shows an embodiment of a medium-voltage switchgear 10 with a spring-loaded actuator 30 according to the invention. The spring-loaded actuator 30 is connected to a moving contact 21 of a switch 20 of the medium-voltage switchgear 10 and is designed to move the moving contact 21 quickly and with the shortest possible delay in order to carry out a switching operation (in particular, to move it away from a counter contact 22 during the opening of the switch 20).

[0026] For this purpose, the spring-loaded actuator 30 has a drive spring 34, which, when tensioned, stores the energy required for the desired rapid movement of the moving contact 21 as spring energy, in order to quickly release it when triggered by a trigger 35. In the illustrated embodiment, the drive spring 34 is indirectly connected to the moving contact 21 via a transmission 36, which may, for example, comprise a lever arm mounted on a shaft or the like. However, embodiments in which the drive spring 34 is directly connected to the moving contact 21 are also conceivable.

[0027] The spring-loaded drive 30 can contain additional drive springs for opening or closing, possibly in parallel for several switching operations in a time period that is shorter than the duration of a renewed tensioning of a respective triggered drive spring.

[0028] The spring-loaded actuator 30 also has an auxiliary electric drive 31, which is designed to re-tension the drive spring 34 after it has been released. In the embodiment shown here, the auxiliary electric drive 31 comprises an electric motor 32, which is connected or connectable to the drive spring 34 via a gear 33.

[0029] The connection between the drive spring 34 and the electric auxiliary drive 31 can be implemented in a variety of ways, as is known in the technical field. For example, the gear 33 can be connected to a lever that is pivoted by the gear and has a spring eye into which the drive spring is suspended. By pivoting the lever, the drive spring is tensioned (or compressed, which is summarized in the context of the invention under the term "tensioning") and thus subjected to spring energy.

[0030] The spring-loaded drive of the embodiment of Fig. 1 further comprises a measuring and / or control unit 37, which is designed to control the trigger 35 to trigger the drive spring 34 and subsequently activate the electric auxiliary drive 31 or the electric motor 32 to retension the drive spring 34. The trigger 35 can, for example, comprise a mechanical blockage of the gear 33, which is released by the trigger, so that a freewheel of the gear is activated and the drive spring is released.

[0031] The measuring and / or control unit 37 is in Fig. 1 is shown as a single unit that is part of the spring-loaded actuator 30, but can also be implemented as a distributed arrangement comprising, for example, a measuring unit and a control unit arranged remotely from it. In such a case, the measuring unit can be arranged in the spring-loaded actuator and the control unit in a digital protection device in the medium-voltage switchgear or at a remote location such as a control center. The functions of the control unit shown can also be distributed across multiple units. For example, the trigger 35 can be controlled by a unit arranged in the spring-loaded actuator 30, but the evaluation of the measured values ​​described below can be carried out in another, particularly remote, unit.

[0032] The measuring and / or control unit 37 is designed to measure a drive current of the electric auxiliary drive 31 during tensioning of the drive spring 34 and, based on the measured drive current, to determine the condition of the spring-loaded drive 30 and / or certain components of the spring-loaded drive 30. The result of this evaluation can be output as a maintenance signal to a signal receiver 38, which can be, for example, a display of the medium-voltage switchgear 10 or a remote control center, in order to indicate the degree of necessity for a maintenance measure and, if applicable, the component of the spring-loaded drive 30 requiring maintenance.

[0033] Fig. 2 shows an example of a time profile of a drive current I of an electrical auxiliary drive 31 of the spring-loaded drive 30, as it is used, for example, by the measuring and / or control unit 37 of the Fig. 1 can be measured. The typical temporal profile of the drive current shown extends over a period of less than 10 seconds in usual applications, for example over 3 to 5 seconds. At a time t0, the electrical auxiliary drive is activated, whereupon a very high drive current is established up to a time t1, the rate of increase being limited by the inductance of the motor windings of the electric motor 32. The rapidly rising drive current builds up a magnetic field in the motor windings, which is the cause of the motor movement. At time t1, the electric motor 32 begins to rotate, whereby a generator effect of the rotation creates a counter voltage that counteracts the cause, which is why the drive current decreases again when the electric motor 32 begins to rotate at time t1.After the electric motor 32 starts up, the drive current decreases and then remains at a plateau until a time t2, which characterizes the electric motor 32 still running without mechanical load, i.e., before the clamping work begins. The current applied during this period is necessary to overcome losses in the electric motor 32, the gear box 32, and the other moving components connected to the electric motor 32. Accordingly, drive current measurements taken during the plateau contain information about the condition of these components.

[0034] From time t2, the drive current increases again to reach a (local) maximum at time t3. The increase in the drive current is caused by the additional torque required to tension the drive spring 34. At time t2, the actual tensioning of the drive spring 34 begins, i.e., from this point in time, spring energy is introduced into the drive spring 34 by the auxiliary electric drive 31. The drive spring 34 continues to be tensioned until the auxiliary electric drive 31 is deactivated at time t4. This point in time can be determined in particular by the position of the drive spring 34 or a component mechanically connected to the drive spring 34, such as the electric motor 32 itself.For example, an auxiliary switch can be actuated directly or indirectly by the drive spring 34 when it has reached a predetermined end position, whereby the auxiliary switch interrupts the drive circuit of the electrical auxiliary drive. However, it is also conceivable to select a fixed time t4 for a given stored-energy spring drive and to assume, for the operation of the medium-voltage switchgear, that the drive spring 34 is sufficiently tensioned at this time.

[0035] After deactivating the auxiliary electric drive at time t4, the drive current drops rapidly until it reaches zero at time t5. Current flowing during this time, for example, can flow in an arc in the aforementioned auxiliary switch, sustained by the inductance of the motor windings, until the motor windings are demagnetized.

[0036] The control unit 37 can measure the drive current of the electric auxiliary drive 31 in different ways. For example, in particularly simple embodiments, it is possible to measure the drive current only once at a predetermined time after activation of the electric auxiliary drive, for example at a time t3', which corresponds to the expected time of occurrence of the (local) maximum of the drive current (time t3 in Fig. 2). If the drive current value measured at this time deviates from an expected value, this could indicate, for example, fatigue of the drive spring (less drive current is required to tension the drive spring), an increase in friction losses in the electric motor and / or gearbox (more drive current is required to tension the drive spring), increasing mechanical play in the electric auxiliary motor (the local maximum is only reached later), and other aging effects. Since some of these effects are counteracting, they can mask each other when occurring simultaneously, so repeated measurements are beneficial.

[0037] The measurements can be repeated periodically, for example, at least every 50 milliseconds. In practical embodiments, the drive current is measured at intervals of 1 millisecond or less, for example, with a sampling frequency of 8 kilohertz.

[0038] As an alternative to the single or periodic measurement, several measurements of the drive current can also be carried out that are not evenly distributed over time, namely at the expected times of occurrence of one or more of the characteristic times described as t1 to t5. For example, at a time that is likely to occur between times t1 and t2, the Fig. 2 in order to obtain a measured value characteristic of the load-free operation of the electric auxiliary drive 31. Subsequently, a measured value can be measured at the time t2 and t4 of the Fig. 2, in order to obtain a measured value from which a measure of the clamping work applied by the electric auxiliary drive 31 can be obtained. Such a method is simple to implement, but already offers a more reliable detection of various aging effects than a single measurement of the drive current.

[0039] It is also possible to perform a series of measurements within a time span around the expected times of occurrence of the characteristic times to be considered for a specific embodiment of the operating method according to the invention and then interrupt the measurements until the next (expected) characteristic time approaches. Within each series of measurements, the respective maximum or minimum with the associated measurement time can then be considered as the actual characteristic time and used for the evaluation. This reduces the number of measurements and the data to be processed for the evaluation compared to a continuous or periodic measurement of the drive current, but still achieves a comparable reliability for detecting aging effects in the spring-loaded drive.

[0040] In Fig. 2, the area under the time profile of the drive current corresponds to the integral of the drive current, which in turn represents the total energy required to tension the drive spring. This integral can be divided into two Fig. 2 parts indicated by different hatching, of which part I (first part of the integral of the drive current) indicates the spring energy actually introduced into the drive spring and part II (second part of the integral of the drive current) indicates the losses in the electric motor 32, gear 33, etc. Part I is distinguished from the rest in that, from time t2 onwards, only the parts of the drive current which are above the instantaneous value of the drive current at time t2 are taken into account for part I, until the current falls below this instantaneous value again or until the electrical auxiliary drive is deactivated.

[0041] For the evaluation, the integral and / or its parts can be considered. It is also possible to relate the integral or its parts to each other and consider these relationships in the evaluation.

[0042] Regardless of the details of the evaluation of an embodiment of the method according to the invention, an evaluation data set is created that describes the current state of the spring-loaded actuator as meaningfully as possible and is then compared with an expectation, for example, an older evaluation data set, a corresponding data set obtained during an initial measurement during production of the spring-loaded actuator, or a data set typical for the type of spring-loaded actuator. Depending on the result of the comparison, a maintenance signal can then be output. For example, the need for maintenance action can be indicated if the evaluation data set or individual data of the evaluation data set deviate from the expectation by more than a predetermined error tolerance.Depending on the implementation of the procedure, the type of probable fault and / or the affected component can also be signaled by the maintenance signal.

[0043] Fig. Figure 3 shows an embodiment of a method according to the invention for operating the spring-loaded drive. The method begins in a start step S0 and then continues with a step S1, in which the electric auxiliary drive is activated. After activating the electric auxiliary drive, a step S2 is repeatedly executed, in which the drive current of the electric auxiliary drive is measured while the drive spring of the spring-loaded drive is tensioned. This measures the temporal progression of the drive current.

[0044] It should be noted here that it is not important in principle whether the measurement of the drive current is started at the same time as the activation of the electric auxiliary drive, before or after it, or even carried out continuously independently. In this respect, the Fig. 3 only to illustrate an embodiment and for a better understanding of the invention.

[0045] In step S3, an integral of the drive current is determined. This step can be performed instead of Fig. 3, after measuring the entire time course, can also be carried out in parallel with step S2 by continuously accumulating the individual measured values. Subsequently, in step S4, the Fig.2, the first part of the integral is determined, and in a step S5 the second part of the integral. The order of steps S4 and S5 can of course be interchanged. It is also possible to determine a value from the integral, the first part of the integral, and the second part of the integral by calculating the sum or difference of the other two values. In step S6, an evaluation data set is created that can contain any combination of the measured values, the integral, its parts, and / or their ratio(s), or even just a single one of the values ​​mentioned. In step S7, this evaluation data set is compared with an expectation, and finally, in a step S8, a maintenance signal is output depending on the result of the comparison. The method is then terminated in a final step S9 until the next tensioning of the drive spring.In response to the maintenance signal, a suitable maintenance measure can be planned and the medium-voltage system can be temporarily taken out of service at a convenient time for carrying out the maintenance measure.

[0046] The invention has been explained in more detail with reference to illustrations of exemplary embodiments. These exemplary embodiments are not intended to limit the scope of the invention, which is defined solely by the following claims, but serve merely to facilitate understanding. List of reference symbols 10 medium-voltage switchgear 20 switches 21 Moving contact 22 Counter contact 30 spring-loaded drive 31 electric auxiliary drive 32 electric motor 33 gearboxes 34 Drive spring 35 triggers 36 Implementation 37 Measuring unit, control unit 38 signal receivers

Claims

[1] A method for operating a spring-loaded drive (30) of a medium-voltage switchgear (10) comprising the steps: - measuring a time profile of a drive current of an electrical auxiliary drive (31) for tensioning a drive spring (34) of the spring-loaded drive (30) of the medium-voltage system (10); - tensioning the drive spring (34) with the auxiliary electric drive (31); - Creating an evaluation data set as a function of the measured time profile of the drive current, wherein an integral of the time profile of the drive current is determined and wherein a first component of the integral is determined which indicates a clamping work performed by the auxiliary drive; - comparing the evaluation data set with an expectation; and - Outputting a maintenance signal depending on a result of the comparison. [2] The method of the preceding claim, wherein a second portion of the integral is determined which indicates drive losses of the auxiliary drive (31). [3] The method of the two preceding claims, in which the first and second parts of the integral are related to each other. [4] The method of one of the preceding claims, wherein at least one characteristic time (t1, t2, t3, t4, t5) is determined when creating the evaluation data set and wherein in the step of comparing the evaluation data set the at least one characteristic time (t1, t2, t3, t4, t5) and / or a drive current measured at the at least one characteristic time (t1, t2, t3, t4, t5) is compared with an expected value associated with the at least one characteristic time (t1, t2, t3, t4, t5). [5] The method of the preceding claim, wherein the at least one characteristic time (t1, t2, t3, t4, t5) is a time selected from the start of a current flow through the auxiliary drive (31), the start of tensioning of the drive spring, the occurrence of a local or global maximum of the drive current, the switch-off time of the auxiliary drive (31) and the end of a current flow through the auxiliary drive (31). [6] The method of any preceding claim, wherein the expectation is a historical data set or a predetermined data set specific to a type of spring actuator. [7] A spring-loaded drive (30) for a medium-voltage switchgear (10) and with an electrical auxiliary drive (31) which is designed to tension a drive spring (34) of the spring-loaded drive (30), and a measuring unit (37) which is designed to measure a drive current of the auxiliary drive (31) and to transmit a measurement result to a control unit (37) for carrying out the method according to one of the preceding claims. [8] A medium-voltage switchgear (10) with a switch (20) having a moving contact (21) and a spring-loaded drive (30) according to the preceding claim, which is designed to move the moving contact (21) of the switch (20) in response to a control signal. [9] A data storage device with a computer program which, executed by a control unit (37), for example a control unit (37) of a spring-loaded drive (30), a medium-voltage switchgear (10), a digital protection device or a remote control center, carries out the method of one of claims 1 to 6.

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