TEMPERATURE MONITORING FOR SWITCHGEAR

Description

Technical area

[0001] The invention relates to a method for operating a switchgear and a switchgear operable according to the method. Technical background

[0002] In switchgear, such as that used in high- and medium-voltage technology, but also in high-voltage and low-voltage systems, current-carrying components are often bolted together or connected in some other form of force-fit connection. Unlike a material connection, these force-fit connections can become loose during operation due to vibrations, cold / hot cycling, or material fatigue. Contamination or oxidation of the conductors can also occur at the contact points. In both cases, the contact resistance increases, resulting in increased heat generation. This heat generation can lead to accelerated oxidation of the conductors, so that the condition of the contact deteriorates at an increasing rate. In extreme cases, this can lead to the destruction of the switchgear.

[0003] US 2014 / 0145849A1 discloses measuring conductor temperatures at multiple points along the phase conductors, as well as other operating parameters such as the ambient temperature and the currents flowing in the phase conductors. Based on the latter two parameters and known properties of the switchgear, a forecast of the expected temperatures is created, which is then compared with the measured temperature values. If the measured temperature values ​​deviate significantly from the forecast, an alarm can be triggered. Patent documents EP 3 171 469 A1 and EP 1 537 647 B1 relate to the background of the present invention.

[0004] The known method is complex to implement and requires in-depth knowledge of the switchgear to be monitored, which is why the present invention sets itself the task of introducing a simple method for temperature monitoring of switchgear that nevertheless allows the detection of inadequate contact states. Summary of the invention

[0005] A first aspect of the invention solves this problem by a novel method for operating a switchgear assembly with at least three phases carrying a load current. The method according to the invention comprises at least the following steps: Measuring a conductor temperature at a respective measuring point of each of the at least three phases to obtain respective phase temperature measurement values; selecting a subset of the phase temperature measurement values, wherein the subset comprises a plurality of phase temperature measurement values ​​and wherein a residual set of the phase temperature measurement values ​​remains; averaging the subset of the phase temperature measurement values; comparing the phase temperature measurement values ​​of at least the residual set of the phase temperature measurement values ​​with the mean value of the subset of the phase temperature measurement values; and generating an alarm signal if one of the compared phase temperature measurement values ​​deviates from the mean value of the subset of the phase temperature measurement values ​​by more than a predetermined alarm threshold.

[0006] The method according to the invention can be carried out with little effort and is based on the insight that multi-phase switchgear has, to a certain extent, built-in redundancy. Due to the generally similar loading of the phases and their at least almost identical design, all phase conductors of the switchgear should therefore have identical temperatures if the switchgear is in proper working order. By selecting a subset of the phase temperature measurements for which an average is calculated, measurement errors and different loading of the phases are at least partially compensated. At least the phase temperature measurements of the remaining set of phase temperature measurements can then be compared with the average value, whereby an excessively hot phase temperature can be reliably detected. In some embodiments of the invention, in addition to the phase temperature measurements of the remaining set, those of the subset can also be compared with the average value.A measurement of the currents or the ambient temperature can be omitted or does not need to be taken into account, whereby the computational complexity of the method according to the invention is very low.

[0007] An example of a switchgear assembly with more than three phases is also understood herein to include a switchgear assembly in which at least the connections (busbars and / or cables) of each electrical phase are implemented multiple times in parallel, for example with two or more busbars and / or two or more cable connections. This is done, for example, in gas-insulated switchgear assembly that carries particularly high load currents in order to provide the required conductor diameters while keeping the components required for this manageable (flexibility and weight of cables, load-bearing capacity and gas tightness of bushings, etc.). In such switchgear assembly, an additional step of averaging the phase temperature measurements obtained from the multiple-execution parts can be carried out before the average values ​​thus obtained are fed to the method according to the invention as phase measurement temperature values.In addition, an alarm signal can be issued if the phase temperature measurements obtained on the parts that have been executed multiple times differ from each other by more than a second alarm threshold.

[0008] Accordingly, the term "phase" and its derivatives, such as "phase temperature," "multiphase," etc., should not be understood to imply that one "phase" must be distinguished from another "phase" by a voltage shifted in time by a portion of the period of a sinusoidal oscillation. Rather, individual conductors in a parallel circuit can also be referred to as "phases," even if they all carry the same voltage without phase shift. An example of a multiphase switchgear in this expanded sense is a switchgear for the electrical supply of rail vehicles via an overhead line. If large currents are to be switched, the single phase (in the traditional sense) can be divided among several parallel conductors (phases in the expanded sense).

[0009] In an easy-to-implement embodiment of the invention, the subset of phase temperature measurements can be formed by selecting the remaining N-1 phase temperature measurements as a subset for each of N phase temperature measurements, and then comparing the respective phase temperature measurement with the mean of the N-1 phase temperature measurements. Accordingly, the relevant steps of the method are executed N times.

[0010] However, a similarity criterion can also be applied in the step of selecting the subset of phase temperature measurements, so that the subset contains those phase temperature measurements that satisfy the similarity criterion or satisfy it most. This type of subset selection makes it possible to identify so-called "outliers" among the phase temperature measurements and evaluate them by comparing them with the mean of the subset. The similarity criterion can, for example, be a distance between the phase temperature measurements, with the similarity criterion being best satisfied by those phase temperature measurements that are closest to one another.It is also conceivable that a quadratic weighting criterion is applied to obtain a reference phase temperature value and the remaining set of phase temperature measured values ​​is formed from the phase temperature measured value that has the greatest distance from the reference phase temperature value.

[0011] Preferably, a safety measure is implemented upon receipt of the alarm signal. This could include, for example, reducing the load current, shutting down the switchgear, or initiating maintenance. For example, the urgency or severity of the safety measure can be determined by the extent to which the alarm threshold is exceeded.

[0012] The predetermined alarm threshold can preferably be predetermined depending on the switchgear's load current. For example, a higher alarm threshold can be provided for a higher load current, since heat generation is proportional to the square of the load current. Therefore, with constant contact quality and increasing load current, correspondingly larger deviations between the phase temperature measurements can be expected. To avoid false alarms at high load currents and the absence of an alarm at low load currents, a higher alarm threshold can be predetermined for a higher load current than for a lower load current.

[0013] The predetermined alarm threshold can also be predetermined based on the mean value of the subset of phase temperature measurements. In this case, the measurement of the load current can advantageously be omitted compared to the embodiment of the invention just explained, since it can be assumed that the mean value of the subset of phase temperature measurements is largely determined by the flowing load current.

[0014] Alternatively or additionally, the predetermined alarm threshold can also be predetermined depending on the ambient temperature of the switchgear. At a high ambient temperature, less heat can be dissipated from the switchgear, which is why the mean value of the subset of phase temperature measurements increases. This can lead to a falsified assessment of the condition of the contacts based on the comparison of the individual phase temperature measurements with their mean value. This is even more likely if the alarm threshold is also predetermined depending on the mean value of the subset.

[0015] In principle, it is also possible within the scope of the invention to make the alarm threshold variable and predeterminable. This means that, depending on installation parameters such as the installation altitude above sea level and / or the specific configuration of a switchgear, a different alarm threshold is predetermined, with which the individual switchgear is then operated.

[0016] The respective measuring point for each of the three phases can be arranged, in particular, at a busbar connection, a cable connection, an upper outgoing terminal, a lower outgoing terminal, or at a bushing. Temperature sensors can preferably be provided at several or all of the aforementioned measuring points in a switchgear assembly. In such a case, the respective connections can be assessed individually, with respective mean values ​​preferably being calculated for respective subsets of the phase temperature measured values ​​measured at the same measuring point but on the different phases, with which the phase temperature measured values ​​or their residual amounts are then compared.

[0017] Preferably, the alarm signal includes information about the respective measuring point and / or the respective phase for which the deviation of the one compared phase temperature measurement value from the mean value of the subset of phase temperature measurements was determined to be greater than the predetermined alarm threshold. This simplifies the localization of the insufficient contact. The alarm signal can, for example, be transmitted to a remote control center, from where appropriate safety measures can be initiated if necessary.

[0018] In embodiments of the invention, different degrees of damage to a contact, or different types of safety measures or different urgency of these safety measures, can also be detected. For example, a warning signal can be generated if one of the compared phase temperature measurements deviates from the mean of the subset of phase temperature measurements by more than a predetermined warning threshold, which is lower than the alarm threshold. In response to the warning signal, a longer-term or less drastic safety measure can then be provided than upon receipt of the alarm signal. It is conceivable to provide additional thresholds that accordingly provide different information about the quality of a contact.

[0019] A second aspect of the invention relates to a switchgear assembly with at least three phases, temperature sensors arranged at respective measuring points of each of the at least three phases, and a control unit connected to the temperature sensors. The temperature sensors are designed to measure conductor temperatures to obtain phase temperature measurements. The control unit is designed to carry out the method of the previous aspect of the invention. Short description of the characters

[0020] The invention is explained in more detail below with reference to exemplary embodiments. They show: Fig. 1 shows an embodiment of a switchgear assembly according to the invention; and Fig. 2 shows an embodiment of the method according to the invention for operating a switchgear assembly. Detailed character description

[0021] Fig. 1 shows an embodiment of a switchgear assembly 1 according to the invention in a cross-sectional view. The switchgear assembly 1 is designed as an air-insulated switchgear assembly, but the invention can also be applied to gas-insulated or other low-, medium-, or high-voltage switchgear assembly.

[0022] The switchgear 1 of Fig. 1 has four different compartments separated from each other by partition walls. A busbar compartment 4 houses a set of busbars 14 (usually one per phase of the power grid), via which electrical energy is distributed between several switchgear systems arranged side by side. 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 outgoing terminals 12 of a switching device 10 located in a device compartment 2. For example, so-called contact tulips or finger contacts can be used to provide detachable contacts for easy replacement of the switching device 10. Circuit breakers, load switches, short-circuiters, earthing switches, fuses, and the like can be used as the switching device 10.

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

[0025] The connecting conductors 16 are electrically connected to the switching device 10 via bushings 11 between the device 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 accommodate control electronics, measuring and signaling devices, and other such low-voltage auxiliary devices. These low-voltage auxiliary devices can read measured values ​​from the various current-carrying and voltage-carrying components and transmit 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, with their measuring outputs connected to the low-voltage auxiliary devices.

[0027] Maintenance personnel can access the equipment room 2 and the low-voltage room 5 through respective access doors 7 and 8. Rooms 2, 3, and 4 are connected to a hot gas duct 6, which can collect hot gases generated during a malfunction such as an arc in the switchgear, divert them away from the switchgear, and release them into the environment at a location that is safe for any personnel nearby.

[0028] The connections between the upper and lower outgoers 12, 13 and the switching device 10, between the upper and lower outgoers 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 force-locking connections such as screw or clamp connections. Increased heat generation can therefore occur at these points if the quality of an electrical contact established in this way is too low, which is why one, several, or all of the aforementioned points, depending on the particular design of a switchgear 1, can be considered as measuring points for the application of the method according to the invention. Accordingly, respective temperature sensors 18 can be arranged at these points on each phase of the switchgear, which are communicatively connected to a control unit 17.The communicative connection between the temperature sensors 18 and the control unit 17 can be implemented via an electrical or optical data line, a wireless communication link, or via near-field communication. In the latter case, the temperature sensors 18 are electromagnetically excited via antennas (not shown) in the compartments 2, 3, and 4 of the switchgear 1 and read based on their response to the electromagnetic excitation. This offers the advantage of being able to design the temperature sensors 18 galvanically isolated from the control unit 17 and, moreover, without batteries for powering a wireless communication link.

[0029] The control unit 17 is presently arranged in the low-voltage compartment 5 and can be part of another low-voltage auxiliary device. The control unit 17 is designed to carry out the method according to the invention.

[0030] The invention can also be readily applied to gas-insulated switchgear. Cable connections are particularly suitable as a measuring point for phase temperature measurements, as these are often located outside the gas-insulated compartment and can therefore be easily equipped with temperature sensors. However, the use of passive wireless temperature sensors also allows monitoring of additional measuring points located inside the gas-insulated area in gas-insulated switchgear, without the expense of installing infrared-permeable and gas-tight inspection windows.

[0031] Fig. 2 shows an embodiment of the method according to the invention for operating a switchgear, for example a switchgear 1 as in Fig. 1 shown in the form of a flowchart. The method begins in a start step S0 and continues in a step S1, in which a conductor temperature is measured at a measuring point of the switchgear to obtain the respective phase temperature measured values. Since a switchgear is usually designed with three phases, step S1 is executed three times, once for each phase. It is of course also possible to read out phase temperature measured values ​​for all three phases simultaneously in a single execution of step S1. Step S1 can also be repeated for other measuring points of the switchgear.

[0032] In a subsequent step S2, a subset of the phase temperature measured values ​​is selected, wherein the subset comprises a plurality of phase temperature measured values, leaving a residual set of phase temperature measured values. In a three-phase switchgear system, the subset will typically contain two phase temperature measured values, and the residual set will typically contain one phase temperature measured value.

[0033] In step S3, an average value of the subset of phase temperature measurements selected in step S2 is calculated. This average value is then compared in step S4 with the phase temperature measurement(s) of at least the remaining set. A check is carried out to determine whether the compared phase temperature measurement deviates from the average value of the subset of phase temperature measurements by more than a predetermined alarm threshold. In particular, a check is carried out to determine whether a phase temperature measurement of the remaining set is greater than the average value of the subset of phase temperature measurements plus the predetermined alarm threshold. Or, expressed as a formula, a check is carried out to determine whether: T R > T ¯ T + ΔT ,

[0034] where T R the compared phase temperature measurement of the residual quantity, T T the mean of the phase temperature measurements of the subset and ΔT designate the predetermined alarm threshold. If this is the case for the compared phase temperature measurement, an alarm signal is generated in step S5. Otherwise, step S5 is skipped. As explained in detail above, the predetermined alarm threshold can be predetermined depending on further parameters or measured values, in particular a load current of the switchgear, the mean value of the phase temperature measurements, or an ambient temperature of the switchgear.

[0035] In the present exemplary embodiment, steps S2, S3, S4, and S5 are carried out for each of the three phases of the switchgear, like step S1, whereby the statements above regarding simultaneous or sequential execution also apply here. In embodiments in which a similarity criterion is applied, the multiple execution of steps S2 to S5 can also be omitted. For example, in a three-phase switchgear, the two phase temperature measurements that have the smallest temperature difference can be selected as a subset. An average value is then calculated from these two phase temperature measurements, which is compared with the remaining phase temperature measurement. In such embodiments of the method according to the invention, the temperature monitoring of the switchgear can be carried out with just a single comparison.

[0036] The procedure of Fig. 2may end in step S6 or, if necessary after a waiting period has elapsed, return to step S0.

[0037] The method according to the invention for operating a switchgear and the switchgear according to the invention allow a reliable detection of bad or deteriorated connections in the switchgear without the need for complex modeling of the switchgear and its operation.

[0038] The invention has been explained in more detail with reference to preferred embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention, which is defined exclusively by the following claims. List of reference symbols

[0039] 1Air-insulated switchgear 2Equipment room 3Cable connection room 4Busbar room 5Low-voltage room 6Hot gas duct 7, 8Access doors 9Access direction 10Switching device 11Plug-ins 12Upper outgoing circuit 13Lower outgoing circuit 14Busbar 15Cable 16Connecting conductor 17Control unit 18Temperature sensor

Claims

1. Method for operating a switchgear installation (1) having at least three phases carrying a load current, wherein the method comprises at least the following steps of: measuring a conductor temperature at a respective measurement point of each of the at least three phases in order to obtain respective phase temperature measured values; selecting a subset of the phase temperature measured values, wherein the subset comprises a plurality of phase temperature measured values, and wherein a residual set of the phase temperature measured values remains; forming an average value of the subset of the phase temperature measured values; comparing the phase temperature measured values of at least the residual set of the phase temperature measured values with the average value of the subset of the phase temperature measured values; and generating an alarm signal when one of the phase temperature measured values compared differs from the average value of the subset of the phase temperature measured values by more than a predetermined alarm threshold value.

2. Method of the preceding claim, in which, in the step of selecting the subset of the phase temperature measured values, a similarity criterion is applied and the subset contains those phase temperature measured values that satisfy or best satisfy the similarity criterion.

3. Method of the preceding claim, in which the similarity criterion is a spacing between the phase temperature measured values, wherein the similarity criterion is best satisfied by those phase temperature measured values which have the smallest spacing between one another.

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

5. Method of the preceding claim, in which the safety measure comprises reducing the load current, shutting down the switchgear installation (1) or initiating a maintenance measure.

6. Method of one of the preceding claims, in which the predetermined alarm threshold value is predetermined on the basis of the load current, the average value of the subset of the phase temperature measured values and / or an ambient temperature of the switchgear installation (1).

7. Method of one of the preceding claims, in which the respective measurement point of each of the three phases is arranged on a busbar connection, a cable connection, an upper outgoing circuit, a lower outgoing circuit or on a bushing (11).

8. Method of one of the preceding claims, in which the alarm signal comprises information about the respective measurement point and / or the respective phase, for which the deviation of the one compared phase temperature measured value from the average value of the subset of the phase temperature measured values by more than the predetermined alarm threshold value was determined.

9. Method of one of the preceding claims, in which a warning signal is generated when the one compared phase temperature measured value deviates from the average value of the subset of the phase temperature measured values by more than a predetermined warning threshold value which is less than the alarm threshold value.

10. Switchgear installation (1) having at least three phases, temperature sensors (18) which are arranged at respective measurement points of each of the at least three phases and are designed to measure conductor temperatures in order to obtain phase temperature measured values, and a control unit (17) connected to the temperature sensors (18), characterized in that the control unit (17) is designed to carry out the method of one of the preceding claims.