METHOD FOR OPERATING A SWITCHGEAR AND SWITCHGEAR

Description

[0001] Method for operating a switchgear and switchgear The invention relates to a switchgear, in particular for medium and / or high voltages.

[0002] A common source of faults in switchgear is the bolted connections within the switchgear, especially those assembled on-site. The bolted connections to the busbar and high-voltage cable play a particularly important role. These connections can deteriorate over time, causing additional localized heating that can ultimately lead to a fault. Early identification of such faults allows for proactive fault correction.

[0003] From US 2017 / 0148300 A1 and DE 10 2019 204 307 A1, it is known to compare absolute temperature values ​​between the individual phases of the switchgear in order to detect a possible defect. It is assumed that such a defect occurs in only one phase.

[0004] It is also known to relate the temperature increase relative to the ambient temperature to the quadratic current using a linear equation. Subsequently, the change in this linear equation is considered to assess the state of the system.

[0005] A disadvantage of the known methods is that comparisons of the temperature between phases require a symmetrical current load and the influence of some errors on the absolute temperature is small, making error detection difficult.

[0006] The object of the invention is to provide an improved method for determining the state of a switchgear and a corresponding improved switchgear.

[0007] This problem is solved by a switchgear system having the features of claim 1.

[0008] In the operating method according to the invention for a switchgear, signals from two temperature sensors arranged in the switchgear are recorded. Furthermore, a function that models a ratio of the temperature profiles at the temperature sensors determines the ratio of two thermal time constants for temperature changes at the temperature sensors. Finally, an alarm signal is generated if the ratio of the thermal time constants falls within an error range.

[0009] The switchgear according to the invention comprises a temperature sensor and an evaluation unit, the evaluation unit being configured to carry out the method. The evaluation unit is thus configured to receive signals from two temperature sensors arranged in the switchgear, to determine, by means of a function that models a ratio of the temperature profiles at the temperature sensors, a ratio of two thermal time constants for temperature changes at the temperature sensors, and to generate an alarm signal if the ratio of the thermal time constants lies within an error range.

[0010] The switchgear can be an air-insulated switchgear (AIS) or a gas-insulated switchgear (GIS).

[0011] Advantageously, the present invention does not compare absolute temperature values, but rather considers time constants that allow the temperature to adjust after a change in thermal influences, particularly after a change in current. By determining these time constants by fitting them to a function, signal noise and other statistical influences are automatically minimized. Furthermore, the time constants are visible even with small changes in thermal influences and are not dependent on the current load being symmetrical across different phases.

[0012] A particular advantage of this method is that by calculating the ratio of the two considered time constants, two influencing factors can be neglected: the ambient temperature and the electrical losses of the switchgear, which lead to the temperature change. Since these are not necessarily known or available as measured values, considering the ratio of the time constants results in a simplified and improved fitting process, leading to more reliable results.

[0013] Advantageous embodiments of the method and the switchgear according to the invention are described in the dependent claims. The embodiment of the independent claims can be combined with the features of one of the dependent claims or, preferably, with those of several dependent claims. Accordingly, the following additional features can be provided: The error range can include all values ​​for the ratio of the time constants that are further away than a minimum distance of 1 or further away than a minimum factor of 1. For example, the error range can include all ratios that lie outside the interval from 0.8 to 1.2; here, the minimum distance is 0.2. Alternatively, the error range can include, for example, all ratios that lie outside the interval from 0.8 to 1.25; here, a minimum factor of 0.8 is used.

[0014] The function can describe the temperature profile under the assumption that the temperature sensors are connected to an ambient temperature via a first-order thermal network, each with a thermal mass and a thermal resistance, while the ambient temperature is disregarded in the function.

[0015] Preferably, a safety measure is implemented upon receipt of an alarm signal. This could involve, for example, reducing the current flowing through the switching system, particularly through an affected phase, shutting down the switching system, or initiating maintenance. The urgency or severity of the safety measure can, for instance, depend on the degree of deviation below the reference value.

[0016] The switchgear can include one phase or multiple phases, in particular three phases, and can further include a temperature sensor for each phase.

[0017] Preferably, the temperature sensors are located in a thermally tightly coupled system, for example in the cable connection room.

[0018] The temperature sensors are preferably designed to measure the temperatures of bolted joints. For this purpose, they are preferably arranged close to such bolted joints. Since thermal time constants of thermal adaptation are determined, it is not necessary for the temperature sensors to be arranged directly on the bolted joints; however, it is advantageous if they are arranged so close to them that the thermal influence of a fault in the bolted joint clearly outweighs the influence of other bolted joints, for example, those of other phases.

[0019] The temperature sensors can be located, for example, at a busbar connection, a cable connection, an upper outlet, a lower outlet or a feedthrough.

[0020] As an alternative to performing the fitting process directly in the switchgear itself, the switchgear can also be coupled to a computer system located remotely, particularly as a cloud service. In this case, the switchgear is appropriately designed to transmit the available measured values, at least the temperature profile, to the computer system. The computer system, in turn, is designed to perform the fitting process using at least the temperature profile. The advantage here is that the data is processed centrally, and the computing and storage capacity of the computer system is typically much higher than that of a switchgear system, since switchgear systems are usually equipped with a microcontroller at best, whereas computer systems operate with microprocessors.

[0021] The invention will now be described and explained in more detail with reference to the exemplary embodiments shown in the figures. The figures show: Figure 1 shows an air-insulated switchgear assembly with a temperature sensor, Figure 2 shows a thermal model for the switchgear assembly, Figure 3 shows a T-connector of a switchgear assembly with placement options for a temperature sensor. Fig. 1 Figure 1 shows an exemplary embodiment of a switchgear assembly 1 in a cross-sectional view. The switchgear assembly 1 is designed as an air-insulated switchgear assembly in this case; however, the invention can also be applied to gas-insulated or other switchgear assemblies for low-, medium- or high-voltage applications.

[0022] Switchgear 1 of Fig. 1It has four different compartments, separated from each other by partition walls. A busbar compartment 4 houses a set of busbars 14 (usually one busbar per phase of the power network), via which electrical energy is distributed between several adjacent switchgear units. The respective busbar compartments 4 can be directly connected to each other, thus forming a common busbar compartment, or they can be separated from each other.

[0023] The busbars 14 arranged in the busbar compartment 4 are connected via connecting conductors 16 to upper outputs 12 of a switching device 10 located in an equipment compartment 2, whereby, for example, so-called contact tulips or finger contacts can be used to provide detachable contacts for easy replacement of the switching device 10. Switching devices 10 can include, for example, circuit breakers, load switches, short-circuiting devices, earthing switches, fuses, and the like.

[0024] The lower outputs 13 of the switching device 10 are connected in a corresponding manner via connecting conductors 16 to cables 15 located in a cable connection room 3, which can serve as inputs or outputs of the electrical energy distributed by the switching system 1.

[0025] The connecting conductors 16 are electrically connected to the switching device 10 via feedthroughs 11 between the equipment compartment 2 on the one hand and the busbar compartment 4 or the cable connection compartment 3 on the other.

[0026] A low-voltage compartment 5 can house control electronics, measuring and signaling devices, and other such low-voltage auxiliary equipment. This low-voltage auxiliary equipment can read measured values ​​from the various current-carrying and voltage-bearing components and forward them to remote devices for control and protection purposes, and / or display them locally and / or evaluate them automatically. To provide such measured values, current and voltage transformers are typically mounted on the busbars and cables, and their measuring outputs are connected to the low-voltage auxiliary equipment.

[0027] The connections between the upper and lower outputs 12, 13 and the switching device 10, between the upper and lower outputs 12, 13 and the bushings 11, between the bushings 11 and the connecting conductors 16, and between the connecting conductors 16 and the busbars 14 or the cables 15 can be made using friction-fit connections such as screw or clamp connections. Increased heat generation can therefore occur at these points if the quality of such an electrical contact is insufficient.

[0028] Therefore, in this example, three temperature sensors 18a...c are arranged in the cable connection compartment 3 near three analog screw connections, each part of a phase. The temperature sensors 18a...c are thus very close to their respective screw connections and also close to each other – compared to the size of the switchgear 1. The temperature sensors 18a...c are communicatively connected to an evaluation unit 17, which in this case is shown as part of the switchgear 1. The evaluation unit 17 is located in the low-voltage compartment 5 and can be part of other low-voltage auxiliary equipment. In other embodiments, the functionality of the evaluation unit 17 can also be located outside the switchgear 1, for example, in a separate computer or in a cloud service. In all cases, there is at least an indirect data connection between the temperature sensors 18a...c and the evaluation unit 17, through which measured values ​​from the temperature sensors 18a...c can be transmitted to the evaluation unit 17.

[0029] The communication link between the temperature sensors 18a...c and the evaluation unit 17 can be established via an electrical or optical data line, a wireless communication link, or near-field communication. In the latter case, the temperature sensors 18a...c are electromagnetically excited via antennas (not shown) in the cable connection compartment 3 of the switchgear 1 and their readings are determined based on their response to the electromagnetic excitation. This offers the advantage that the temperature sensors 18a...c can be galvanically isolated from the evaluation unit 17 and, moreover, can be installed without batteries to power a wireless communication link.

[0030] If the current flowing through switchgear 1 changes, the power loss occurring in the switchgear also changes according to PV = I² < * R, where I is the current flowing and R is the electrical resistance present in switchgear 1. This causes a change in the temperature in switchgear 1, which is reflected in the sensor signal of the temperature sensors 18a...c. The entire switchgear 1 forms a complex thermal system in which temperature changes propagate. The temperature changes that occur close to the temperature sensor 18a...c are most quickly visible in the signal of that sensor, particularly temperature changes caused by the screw connection in whose immediate vicinity the temperature sensor 18a...c is located.

[0031] Typical time constants for temperature adjustment after a change in current are approximately 1 hour. If the screw connection in question is faulty and causes a significant additional heat input, this manifests itself in a reduced time constant for the temperature change.

[0032] It is possible to determine the time constants through an evaluation, for example, a fit to the measurement data. The functional relationship results from a model that is in Figure 2 The functional relationship is shown in a model that is presented in Figure 2This model simplifies the superposition of many thermal time constants and power losses into a simple model structure with a single heat source, which is connected via a first-order thermal network to an RC element consisting of a thermal mass 21 and a thermal resistance 22, with the outside temperature 23 acting as a heat sink. In the event of a fault, the superposition is dominated by the faulty screw connection 20.

[0033] For the first-order thermal network as in Figure 2 The following relationship is shown: T Amb t = τ ⋅ T ˙ t + T t − P Loss t ⋅ R

[0034] Here, TAmb is the ambient temperature 23, TA is the temperature of a respective temperature sensor 18a...c, PLoss is the power loss, and R is the thermal resistance 22. The parameter τ is the desired time constant for the temperature adjustment of this temperature sensor 18a...c. It is evident that, with a constant ambient temperature and constant power loss, a step change in power loss results in an exponential temperature T. However, it cannot be generally assumed that these values ​​are constant.

[0035] Furthermore, it cannot be assumed that the ambient temperature values ​​are even known. On the one hand, the switchgear may be designed in such a way that it does not have a sensor for this. On the other hand, in some embodiments of the invention, the evaluation may not take place in the switchgear itself, but, for example, in a cloud server where ambient temperature measurements are not available because they are not transmitted. The same applies to the electrical losses Ploss of the switchgear.

[0036] It is therefore advantageous to combine the relationships for two of the temperature sensors 18a...c: T Amb t = τ 1 ⋅ T ˙ M 1 t + T M 1 t − P Loss t ⋅ R 1 T Amb t = τ 2 ⋅ T ˙ M 2 t + T M 2 t − P Loss t ⋅ R 2

[0037] The indices M1 and 1 denote the values ​​belonging to a first temperature sensor 18a...c, and the indices M2 and 2 denote the values ​​belonging to a second temperature sensor 18a...c. After rearranging and normalizing to the respective maximum temperature TM1max and TM2max, the following results: 0 = τ 1 ⋅ T ˙ M 1 t T M 1 max + T M 1 t T M 1 max − P Loss t + T Amb t R 1 ⋅ R 1 T M 1 max 0 = τ 2 ⋅ T ˙ M 2 t T M 2 max + T M 2 t T M 2 max − P Loss t + T Amb t R 2 ⋅ R 2 T M 2 max

[0038] Further rearrangement yields an expression for the relation of the two time constants τ 1 and τ 2 : τ 2 = T M 2 max T ˙ M 2 t ⋅ τ 1 T ˙ M 1 t T M 1 max + T M 1 t T M 1 max − T M 2 t T M 2 max + B τ 2 = T M 2 max T M 1 max ⋅ T ˙ M 1 t T ˙ M 2 t ⋅ τ 1 + T M 2 max T ˙ M 2 t ⋅ T M 1 t T M 1 max − T M 2 t T M 2 max + B With B = − P Loss t + T Amb t R 1 P Loss t = t 1 + T Amb t = t 1 R 1 + P Loss t + T Amb t R 2 P Loss t = t 2 + T Amb t = t 2 R 2

[0039] By normalizing the data and considering the two time constants or their relative slopes, term B can be neglected while still achieving sufficient accuracy to identify errors. This eliminates the need for additional current or ambient temperature measurements, a key advantage of this method. Since the parameters τ₁ and τ₂ are unknown, a fitting process is employed. Instead of determining separate values ​​for τ₁ and τ₂, only the relationship τ₁ / τ₂ is established. This relationship provides a sufficient indicator for comparative state determination. While the relationship could also be determined by separately calculating τ₁ and τ₂ through a fitting process, in that case, term B could not be neglected. This fitting process does not require waiting for a specific point in time; it can be performed continuously within a rolling time window of the measurement data.The method benefits from the fact that the sensors under consideration are closely coupled with respect to ambient temperature due to their spatial proximity.

[0040] The resulting ratio of τ₁ and τ₂ is close to 1 if the switchgear 1 has no faults in the immediate vicinity of the two temperature sensors 18a...c, i.e., if the screw connections on which the temperature sensors 18a...c are located do not cause significant heat input. In this case, all heat sources of the switchgear 1 are approximately equidistant from the two temperature sensors 18a...c, since the temperature sensors 18a...c are located close to each other, for example, on directly adjacent screw connections. As a result, changes in current have approximately the same effect on both temperature sensors 18a...c, and the resulting time constants are nearly identical, thus having a ratio of approximately 1.

[0041] If, however, one of the screw connections is faulty, it causes heat input. Since this heat input now occurs very close to one of the two temperature sensors 18a...c – compared to the distance between them – the effect on the time constant of the two temperature sensors 18a...c differs, and the ratio of the time constants now deviates significantly from 1. Experiments have shown that the resulting ratios are, for example, around 0.6.

[0042] The size of the ratio can therefore be used as a criterion for determining whether a fault has occurred. This is done by comparing the ratio's deviation from 1 with a predefined threshold, for example, 0.2. If the deviation from 1 exceeds the threshold, an alarm signal is triggered and / or a safety measure, such as a shutdown, is initiated. In this example, an alarm signal is triggered if the ratio is greater than 1.2 or less than 0.8. Alternatively, a factor can be used to determine how the ratio deviates from 1, ensuring that faults in both bolted connections are treated mathematically equally. For example, if 0.8 is used as the factor, an alarm signal is triggered if the ratio is less than 0.8 or greater than 1 / 0.8 = 1.25.

[0043] In addition to comparing the ratio to an absolute threshold, its trend can also be analyzed to identify errors. If the ratio rises or falls significantly over time, for example by 10% within a given period, an error can be assumed, triggering an alarm and / or initiating a safety measure such as a shutdown.

[0044] In a gas-insulated switchgear, the temperature sensors 18a...c can be arranged, among other things, in or on a T-connector. Figure 3Figure 40 shows a cross-sectional view of such a T-connector with multiple possible positions 41...44 for the temperature sensor 18a...c. The positions differ in their distance from the screw connection and thus in their response to current changes. For a position very close to a potential fault, such as position 43, the thermal response can be well described by a first-order thermal network, whereas for a position further away from the fault, such as position 42, a second-order thermal network better represents the temperature profile. Reference sign

[0045] 1 Air-insulated switchgear 2 Equipment room 3 Cable connection room 4 Busbar room 5 Low-voltage room 10 Switching device 11 Bushings 12 Upper output 13 Lower output 14 Busbar 15 Cable 16 Connecting conductor 17 Evaluation unit 18a...c Temperature sensor 20 Screw connection 21 Thermal ground 22 Thermal resistance 23 Outside temperature 40 T-connector 41...45 Positions for the temperature sensor

Claims

1. Method for operating a switchgear installation (1), in which - signals from two temperature sensors (18a...c) arranged in the switchgear installation (1) are recorded, characterized in that - a ratio between two thermal time constants for temperature changes is determined at the temperature sensors (18a...c) by fitting a function, which models a ratio between the curves of the temperatures in the temperature sensors (18a...c), to the signals, - an alarm signal is generated when the ratio of the thermal time constants is within a fault range.

2. Method according to Claim 1, in which the fault range includes all values for the ratio between the time constants that are further away than a minimum distance of 1.

3. Method according to Claim 1 or 2, in which the function describes the temperature curve on the assumption that the temperature sensors (18a...c) are connected via a first-order thermal network to a thermal mass (21) and via a thermal resistance (22) to an ambient temperature (23), wherein the ambient temperature (23) is not taken into account in the function.

4. Method according to any one of the preceding claims, in which a safety measure is carried out in response to reception of the alarm signal.

5. Method according to Claim 4, in which the safety measure comprises reducing a flowing current, shutting down the switchgear installation (1) or initiating a maintenance measure.

6. Switchgear installation (1) having at least two temperature sensors (18a...c) and an evaluation device (17), wherein the evaluation device (17) is designed to carry out a method according to any one of the preceding claims.

7. Switchgear installation (1) according to Claim 6 having a plurality of phases or switching panels, in particular three phases, and a temperature sensor (18a...c) for each phase or each switching panel.

8. Switchgear installation (1) according to Claim 6 or 7, in which the temperature sensors (18a...c) are designed to measure temperatures of screw connections.

9. Switchgear installation (1) according to Claim 8, in which the temperature sensors (18a...c) are arranged on a busbar connection, a cable connection, an upper outgoing circuit (12), a lower outgoing circuit (13) or on a bushing (11).

10. System having a switchgear installation (1) and a computer system, designed in particular as a cloud service and separate from the switchgear installation (1), in which the computer system is designed to carry out a method according to any one of Claims 1 to 5 and the switchgear installation (1) is designed to transmit the temperature curve to the computer system.