EP3765826A1

EP3765826A1 - Apparatus and method for monitoring temperature of cable joint of cable connected to gas insulated switchgear

Info

Publication number: EP3765826A1
Application number: EP18909982.3A
Authority: EP
Inventors: Xin Zhang; Genhuang ZHUANG
Original assignee: ABB Schweiz AG
Current assignee: ABB Schweiz AG
Priority date: 2018-03-12
Filing date: 2018-03-12
Publication date: 2021-01-20
Also published as: WO2019173949A1; CN111602039B; EP3765826A4; CN111602039A

Abstract

An apparatus and a method for monitoring a temperature of a cable joint (201) of a cable (200) connected to a gas insulated switchgear (300). The apparatus comprises an adaptor (101) adapted to be coupled to a cable socket (31) of the switchgear, the cable socket being provided with a mounting hole (311) for connecting the cable joint, the mounting hole being provided at a mounting surface (312), wherein the adaptor, when coupled to the cable socket, is situated at the mounting surface and outside the mounting hole; a temperature sensor (102) arranged in the adaptor and configured to detect a temperature of the adaptor; and a processor (103) configured to determine the temperature of the cable joint based on the detected temperature of the adaptor. Then the temperature of the cable joint may be determined conveniently and precisely.

Description

APPARATUS AND METHOD FOR MONITORING TEMPERATURE OF CABLE JOINT OF CABLE CONNECTED TO GAS INSULATED SWITCHGEAR

FIELD

Embodiments of present disclosure generally relate to the field of electrical equipment, and more particularly, to an apparatus and a method for monitoring a temperature of a cable joint of a cable connected to a gas insulated switchgear (GIS) .

BACKGROUND

GIS is widely used in high-voltage distribution application. In use, a cable is typically connected to the GIS through a cable joint so as to transmit electrical power to the GIS. If the connection between the cable joint and the GIS is poor, a large contact resistance may occur at the cable joint. Thus, a temperature of the cable joint may increase greatly when a current flows in the cable. Currently, the demand for monitoring the temperature of the cable joint is getting high gradually. However, the difficulty of monitoring the temperature of the cable joint lies in that the cable used in the GIS is an all-insulation cable and there is no extra space for any temperature sensors to be installed to the cable joint.
Therefore, there is a need for a new solution for monitoring the temperature of the cable joint conveniently and precisely.
SUMMARY
In a first aspect of the present disclosure, an apparatus for monitoring a temperature of a cable joint of a cable connected to a gas insulated switchgear is provided. The apparatus comprises an adaptor adapted to be coupled to a cable socket of the switchgear, the cable socket being provided with a mounting hole for connecting the cable joint, the mounting hole being provided at a mounting surface, wherein the adaptor, when coupled to the cable socket, is situated at the mounting surface and outside the mounting hole; a temperature sensor arranged in the adaptor and configured to detect a temperature of the adaptor; and a processor configured to determine the temperature of the cable joint based on the detected temperature of the adaptor.
In some embodiments, the adaptor comprises: a first part coupled to the cable socket at the mounting surface; and a second part configured to accommodate the temperature sensor.
In some embodiments, the cable socket comprises a threaded hole at the mounting surface, and the first part is a threaded rot adapted to be inserted into the threaded hole.
In some embodiments, the second part comprises a receiving hole in which the temperature sensor is arranged and sealed by pouring sealant.
In some embodiments, the apparatus further comprises a current sensor configured to detect a current in the cable, wherein the processor is further configured to determine the temperature of the cable joint further based on the current in the cable.
In some embodiments, the processor is configured to determine the temperature of the cable joint by: in response to detecting that the current in the cable increases, determining the temperature of the cable joint based on the detected temperature of the adaptor and a first relationship between temperatures of the cable joint and the adaptor; and in response to detecting that the current in the cable decreases, determining the temperature of the cable joint based on the detected temperature of the adaptor and a second relationship between temperatures of the cable joint and the adaptor, the second relationship being different from the first relationship.
In some embodiments, determining the temperature of the cable joint further based on the current in the cable comprises: in response to an instantaneous increase of the current in the cable exceeding a first threshold, increasing a value of the determined temperature of the cable joint by a first compensation value; and in response to an instantaneous decrease of the current in the cable exceeding a second threshold, decreasing a value of the determined temperature of the cable joint by a second compensation value.
In a second aspect of the present disclosure, a method for monitoring a temperature of a cable joint of a cable connected to a gas insulated switchgear is provided. The method comprises detecting a temperature of an adaptor by a temperature sensor arranged in the adaptor, the adaptor being adapted to be coupled to a cable socket of the switchgear, the cable socket being provided with a mounting hole for connecting the cable joint, the mounting hole being provided at a mounting surface, wherein the adaptor, when coupled to the cable socket, is situated at the mounting surface and outside the mounting hole; and determining the temperature of the cable joint based on the detected temperature of the adaptor.
In some embodiments, the cable socket comprises a threaded hole at the mounting surface, and the adaptor comprises: a first part constructed to be a threaded rot adapted to be inserted into the threaded hole; and a second part configured to accommodate the temperature sensor.
In some embodiments, the second part comprises a receiving hole in which the temperature sensor is arranged and sealed by pouring sealant.
In some embodiments, the method further comprises: detecting a current in the cable by a current sensor; in response to detecting that the current in the cable increases, determining the temperature of the cable joint based on the detected temperature of the adaptor and a first relationship between temperatures of the cable joint and the adaptor; and in response to detecting that the current in the cable decreases, determining the temperature of the cable joint based on the detected temperature of the adaptor and a second relationship between temperatures of the cable joint and the adaptor, the second relationship being different from the first relationship.
In some embodiments, the first relationship is obtained by performing linear fitting on at least two pairs of temperatures of the cable joint and the adaptor, the second relationship is obtained by performing linear fitting on at least three pairs of temperatures of the cable joint and the adaptor, and the at least three pairs of temperatures comprises at least a pair of transient temperatures of the cable joint and the adaptor.
In some embodiments, determining the temperature of the cable joint further based on the current in the cable comprises: in response to an instantaneous increase of the current in the cable exceeding a first threshold, increasing a value of the determined temperature of the cable joint by a first compensation value; and in response to an instantaneous decrease of the current in the cable exceeding a second threshold, decreasing a value of the determined temperature of the cable joint by a second compensation value.
In a third aspect of the present disclosure, a gas insulated switchgear comprising the apparatus according to the first aspect of the present disclosure is provided.
According to various embodiments of the present disclosure, the temperature sensor is arranged in the adaptor coupled to the cable socket of the switchgear and the temperature of the cable joint may be determined based on the temperature of the adaptor. Since the location of the adaptor is close to the cable joint, the temperature of the cable joint may be determined conveniently and precisely. Moreover, through the adaptor, the temperature sensor is easy to be installed and maintained.
DESCRIPTION OF DRAWINGS
Through the following detailed descriptions with reference to the accompanying drawings, the above and other objectives, features and advantages of the example embodiments disclosed herein will become more comprehensible. In the drawings, several example embodiments disclosed herein will be illustrated in an example and in a non-limiting manner, wherein:
Fig. 1 schematically illustrates a gas insulated switchgear according to an example embodiment;
Fig. 2 schematically illustrates an apparatus for monitoring a temperature of a cable joint according to an example embodiment;
Fig. 3 schematically illustrates an example arrangement of the apparatus for monitoring the temperature of the cable joint relative to the cable socket;
Fig. 4 schematically illustrates an adaptor and a temperature sensor of the apparatus as shown in Fig. 3 in an enlarged view;
Fig. 5 is a schematic cross sectional view of a cable socket as shown in Fig. 3;
Fig. 6 schematically illustrates an apparatus for monitoring the temperature of the cable joint according to another example embodiment;
Fig. 7 is a graph schematically illustrating real temperatures of the adaptor and the cable joint when a current in the cable varies;
Fig. 8 is a graph schematically illustrating a first fitting relationship between the temperatures of the cable joint and the adaptor when the current in the cable increases;
Fig. 9 is a graph schematically illustrating a second fitting relationship between the temperatures of the cable joint and the adaptor when the current in the cable decreases;
Fig. 10A is a graph schematically illustrating the real temperature and the determined temperature of the cable joint in phase A;
Fig. 10B is a graph schematically illustrating the real temperature and the determined temperature of the cable joint in phase B;
Fig. 10C is a graph schematically illustrating the real temperature and the determined temperature of the cable joint in phase C;
Fig. 11A is a graph schematically illustrating an error between the determined temperature and the real temperature of the cable joint without compensating for the determined temperature;
Fig. 11B is a graph schematically illustrating the error between the determined temperature and the real temperature of the cable joint after compensating for the determined temperature; and
Fig. 12 is a flow chart of a method for monitoring a temperature of a cable joint of a cable connected to the switchgear according to embodiments of the present disclosure.
Throughout the drawings, the same or similar reference symbols are used to indicate the same or similar elements.
DETAILED DESCRIPTION OF EMBODIEMTNS
Principles of the present disclosure will now be described with reference to several example embodiments shown in the drawings. Though example embodiments of the present disclosure are illustrated in the drawings, it is to be understood that the embodiments are described only to facilitate those skilled in the art in better understanding and thereby achieving the present disclosure, rather than to limit the scope of the disclosure in any manner.
As discussed above, the difficulty of monitoring the temperature of the cable joint lies in that the cable used in the GIS is an all-insulation cable and there is no extra space for any temperature sensors to be installed to the cable joint. According to embodiments of the present disclosure, a temperature sensor is arranged in an adaptor coupled to the cable socket of the switchgear and the temperature of the cable joint may be determined based on the temperature of the adaptor.
The above idea may be implemented in various manners, as will be described in detail in the following paragraphs. Figs. 1-12 illustrate example manners for implementing the principles of the present disclosure and corresponding test results. Hereinafter, the principles of the present disclosure will be described in detail with reference to Figs. 1-12.
Fig. 1 schematically illustrates a gas insulated switchgear 300 according to an example embodiment. As shown, the switchgear 300 includes a cable socket 31. A cable 200 may be connected to the cable socket 31 through a cable joint 201 so as to transmit electrical power to the switchgear 300. In use, if the connection between the cable joint 201 and the cable socket 31 is poor, a large contact resistance may occur at the cable joint 201. In this situation, a temperature of the cable joint 201 may increase greatly when a current flows in the cable 200. In order to capture the temperature change of the cable joint 201 timely, the switchgear 300 may further include an apparatus 100 for monitoring the temperature of the cable joint 201. Hereinafter, example configurations of the apparatus 100 will be described in detail with respect to Figs. 2-6.
Fig. 2 schematically illustrates an apparatus 100 for monitoring the temperature of the cable joint 201 according to an example embodiment, and Fig. 3 schematically illustrates an example arrangement of the apparatus 100 relative to the cable socket 31. As shown, the cable socket 31 is provided with a mounting hole 311 for connecting the cable joint 201. The mounting hole 311 is provided at a mounting surface 312 of the cable socket 31.
In an embodiment, as shown in Figs. 2 and 3, the apparatus 100 may include an adaptor 101, a temperature sensor 102, and a processor 103. The adaptor 101 is connected to the cable socket 31 at the mounting surface 312 and situated outside the mounting hole 311. Along the mounting surface 312, the adaptor 101 is spaced from the mounting hole 311 by a distance. The temperature sensor 102 is arranged in the adaptor 101 to detect the temperature of the adaptor 101. Based on the detected temperature of the adaptor 101, the processor 103 may determine the temperature of the cable joint 201 through a predefined relationship between temperatures of the adaptor 101 and the cable joint 201.
Fig. 4 schematically illustrates the adaptor 101 and the temperature sensor 102 as shown in Fig. 3 in an enlarged view, and Fig. 5 is a schematic cross sectional view of the cable socket 31 as shown in Fig. 3.
In an embodiment, as shown in Fig. 4, the adaptor 101 may include a first part 111 and a second part 112. The first part 111 may be coupled to the cable socket 31 at the mounting surface 312 of the cable socket 31. The temperature sensor 102 may be arranged in the second part 112. The temperature sensor 102 may be connected to the processor 103 through a wire 115 and a terminal 116. A value of the detected temperature of the adaptor 101 may be provided to the processor 103 via the wire 115 and the terminal 116.
In an embodiment, the first part 111 may be a threaded rot. Accordingly, as shown in Fig. 5, the cable socket 31 may include a threaded hole 313 at the mounting surface 312. The threaded hole 313 is spaced apart from the mounting hole 311 along the mounting surface 312. Through thread mating between the threaded rot and the threaded hole 313, the first part 111 may be screwed into or out of the threaded hole 313. In this way, the temperature sensor 102 is easy to be installed and maintained.
In other embodiments, the first part 111 may be coupled to the cable socket 31 in other manners. As an example, the first part 111 may be adhered or soldered to the cable socket 31. It is to be understood that the first part 111 may be coupled to the cable socket 31 in any other suitable manners. The present disclosure does not intend to limit the coupling manners between the first part 111 of the adaptor 101 and the cable socket 31.
In an embodiment, as shown in Fig. 4, the second part 112 may include a receiving hole 113. The temperature sensor 102 may be arranged in the receiving hole 113 and sealed by pouring sealant 114. With such an arrangement, the temperature of the adaptor 101 may be detected precisely by the temperature sensor 102. It is to be understood that the temperature sensor 102 may be arranged in the adaptor 101 in any other suitable manners. The present disclosure does not intend to limit the arrangement of the temperature sensor 102 in the adaptor 101.
With the above embodiments of the present disclosure, the temperature sensor 102 may be conveniently arranged in the adaptor 101 coupled to the cable socket 31 and the temperature of the cable joint 201 may be determined based on the temperature of the adaptor 101. Since the location of the adaptor 101 is close to the cable joint 201, the temperature of the cable joint 201 may be determined precisely.
Fig. 6 schematically illustrates an apparatus 100 for monitoring the temperature of the cable joint 201 according to another example embodiment. The apparatus 100 as shown in Fig. 6 is similar to the apparatus 100 as shown in Fig. 2. Hereinafter, only the difference between the apparatuses 100 of Figs. 6 and 2 will be described in detail, and the description regarding the same portions will be omitted.
In the embodiment as depicted in Fig. 6, the apparatus 100 further includes a current sensor 104 for detecting a current in the cable 200. The processor 103 may determine the temperature of the cable joint 201 further based on the current in the cable 200. In order to determine the temperature of the cable joint 201 further based on the current in the cable 200, the variation of temperatures of the adaptor 101 and the cable joint 201 over the current in the cable 200 will be described in detail in the following with reference to Figs 7-11B.
Fig. 7 is a graph schematically illustrating real temperatures of the adaptor 101 and the cable joint 201 when a current in the cable 200 varies. As shown, when the current in the cable 200 increases, for example from 200A to 2110A, the real temperature of the cable joint 201 may increase gradually and the real temperature of the adaptor 101 may increase accordingly. When the current in the cable 200 decreases, for example from 2110A to 450A, the real temperature of the cable joint 201 may decrease gradually and the real temperature of the adaptor 101 may decrease accordingly. However, the increase process of the temperature of the adaptor 101 is different from the decrease process of the temperature of the adaptor 101, since there is a temperature gradient field between the adaptor 101 and the cable joint 201. Specifically, when the temperature of the cable joint 201 increases, the temperature of the adaptor 101 may increase substantially synchronous with the temperature of the cable joint 201. However, when the temperature of the cable joint 201 decreases, the temperature decrease of the adaptor 101 may lag behind the temperature decrease of the cable joint 201. Thus, the relationships between the temperatures of the cable joint 201 and the adaptor 101 when the current in the cable 200 increases and decreases are different.
In an embodiment, in response to detecting that the current in the cable 200 increases, the processor 103 may determine the temperature of the cable joint 201 based on the detected temperature of the adaptor 101 and a first relationship between temperatures of the cable joint 201 and the adaptor 101. With respect to the first relationship, Fig. 8 illustrates an example fitting process.
Fig. 8 is a graph schematically illustrating a first fitting relationship between the temperatures of the cable joint 201 and the adaptor 101 when the current in the cable 200 increases. As shown, multiple pairs of temperatures of the cable joint 201 and the adaptor 101 may be plotted in the chart. In an embodiment, for each current as shown in Fig. 7, two pairs of temperatures of the cable joint 201 and the adaptor 101 in a stable state may be plotted in the chart. Through a least square method, the first relationship may be fitted as a linear relationship. In another embodiment, in addition to the two pairs of temperatures of the cable joint 201 and the adaptor 101 in a stable state, one or more pairs of transient temperatures of the cable joint 201 and the adaptor 101 may be plotted in the chart. With more temperature points, the fitting relationship between the temperatures of the cable joint 201 and the adaptor 101 may be more precise. It is to be understood that the first relationship may be fitted in any other suitable manners. The present disclosure does not intend to limit the fitting manners of the first relationship.
In an embodiment, in response to detecting that the current in the cable 200 decreases, the processor 103 may determine the temperature of the cable joint 201 based on the detected temperature of the adaptor 101 and a second relationship between temperatures of the cable joint 201 and the adaptor 101. In an example, the second relationship is different from the first relationship. With respect to the second relationship, Fig. 9 illustrates an example fitting process.
Fig. 9 is a graph schematically illustrating a second fitting relationship between the temperatures of the cable joint 201 and the adaptor 101 when the current in the cable 200 decreases. As shown, multiple pairs of temperatures of the cable joint 201 and the adaptor 101 may be plotted in the chart. In an embodiment, for each current as shown in Fig. 7, at least three pairs of temperatures of the cable joint 201 and the adaptor 101 may be plotted in the chart. The at least three pairs of temperatures may include at least a pair of transient temperatures of the cable joint 201 and the adaptor 101. As an example, for each current as shown in Fig. 7, three temperatures of the adaptor 101 TR _stable, TR _{stable_under_last_current}, and TR _transient may be determined for plotting in the chart. TR _stable represents the stable temperature of the adaptor 101 for a specific current in the cable 200, for example 1500 A. TR _{stable_under_last_current} represents the stable temperature of the adaptor 101 for the last current, for example 2110A. TR _transient represents a transient temperature of the adaptor 101 for the specific current in the cable 200, for example 1500 A. In an embodiment, TR _transient may be selected according to the thermal response time equation:
wherein e represent natural constant. With TR _stable and TR _{stable_under_last_current}, TR _transient may be calculated according to the above equation. Hence, for each current as shown in Fig. 7, three pairs of temperatures of the cable joint 201 and the adaptor 101 may be obtained and plotted in the chart.
With the at least three pairs of temperatures of the cable joint 201 and the adaptor 101, the second relationship may be fitted as a linear relationship through least square method. Through more temperature points, the fitting relationship between the temperatures of the cable joint 201 and the adaptor 101 may be more precise when the current in the cable 200 decreases. It is to be understood that the second relationship may be fitted in any other suitable manners. The present disclosure does not intend to limit the fitting manners of the second relationship.
In the following, test results of the determined temperature of the cable joint 201 will be described in detail with respect to Figs. 10A-10C. In an example, the switchgear 300 may be connected to a plurality of cables 200 of three phases A, B, and C. For each cable 200, the temperature of the cable joint 201 may be determined in the manners described herein. Fig. 10A is a graph schematically illustrating the real temperature and the determined temperature of the cable joint 201 in phase A, Fig. 1 0B is a graph schematically illustrating the real temperature and the determined temperature of the cable joint 201 in phase B, and Fig. 10C is a graph schematically illustrating the real temperature and the determined temperature of the cable joint 201 in phase C. As shown, for the cables 200 in each phase, the real temperature and the determined temperature of the cable joint 201 substantially conform to each other as time varies. Thus, the test results show that, with embodiments of the present disclosure, the temperature of the cable joint 201 may be determined precisely.
Fig. 11A is a graph schematically illustrating an error between the determined temperature and the real temperature of the cable joint 201 without compensating for the determined temperature. As shown, most of time, the error between the determined temperature and the real temperature of the cable joint 201 is below 5 ℃. However, at the beginning of sharp change of the current in the cable 200, the error would get to 10 ℃. The reason of this phenomenon is that when the current in the cable 200 changes sharply, the temperature of the cable joint 201 can follow this sharp change, but it would spend some time for this change in influencing the temperature of the adaptor 101 because of the temperature gradient field between cable joint 201 and the adaptor 101.
In an embodiment, in response to an instantaneous increase of the current in the cable 200 exceeding a first threshold, the processor 103 may increase a value of the determined temperature of the cable joint 201 by a first compensation value. With the first threshold, the instantaneous increase of the current may be found. In various embodiments, the first compensation value may be a fixed value or a time-varying value. Through increasing the value of the determined temperature of the cable joint 201 by the first compensation value, the error between the determined temperature and the real temperature of the cable joint 201 may be compensated when the current in the cable 200 increases. Thus, the temperature of the cable joint 201 may be determined more precisely when the current in the cable 200 increases.
In an embodiment, in response to an instantaneous decrease of the current in the cable 200 exceeding a second threshold, the processor 103 may decrease a value of the determined temperature of the cable joint 201 by a second compensation value. With the second threshold, the instantaneous decrease of the current may be found. In various embodiments, the second compensation value may be a fixed value or a time-varying value. Through decreasing the value of the determined temperature of the cable joint 201 by the second compensation value, the error between the determined temperature and the real temperature of the cable joint 201 may be compensated when the current in the cable 200 decreases. Thus, the temperature of the cable joint 201 may be determined more precisely when the current in the cable 200 decreases.
Fig. 11B is a graph schematically illustrating the error between the determined temperature and the real temperature of the cable joint 201 after compensating for the determined temperature. As shown, after compensating, the error is substantially below 5 ℃.
Fig. 12 is a flow chart of a method for monitoring the temperature of the cable joint 201 according to embodiments of the present disclosure. The method 900 can be carried out by, for example the apparatus 100 for monitoring the temperature of the cable joint 201 as illustrated in Figs. 2-6.
At block 910, a temperature of an adaptor 101 is detected by a temperature sensor 102 arranged in the adaptor 101. The adaptor 101 is adapted to be coupled to a cable socket 31 of the switchgear 300. The cable socket 31 is provided with a mounting hole 311 for connecting the cable joint 201. The mounting hole 311 being provided at a mounting surface 312. The adaptor 101, when coupled to the cable socket 31, is situated at the mounting surface 312 and outside the mounting hole 311.
In some embodiments, the cable socket 31 comprises a threaded hole 313 at the mounting surface 312, and the adaptor 101 comprises: a first part 111 constructed to be a threaded rot adapted to be inserted into the threaded hole 313; and a second part 112 configured to accommodate the temperature sensor 102.
In some embodiments, the second part 112 comprises a receiving hole 113 in which the temperature sensor 102 is arranged and sealed by pouring sealant 114.
At block 920, the temperature of the cable joint 201 is determined based on the detected temperature of the adaptor 101.
In some embodiments, the method 900 further includes: detecting a current in the cable 200 by a current sensor 104; in response to detecting that the current in the cable 200 increases, determining the temperature of the cable joint 201 based on the detected temperature of the adaptor 101 and a first relationship between temperatures of the cable joint 201 and the adaptor 101; and in response to detecting that the current in the cable 200 decreases, determining the temperature of the cable joint 201 based on the detected temperature of the adaptor 101 and a second relationship between temperatures of the cable joint 201 and the adaptor 101, the second relationship being different from the first relationship.
In some embodiments, the first relationship is obtained by performing linear fitting on at least two pairs of temperatures of the cable joint 201 and the adaptor 101, the second relationship is obtained by performing linear fitting on at least three pairs of temperatures of the cable joint 201 and the adaptor 101, and the at least three pairs of temperatures comprises at least a pair of transient temperatures of the cable joint 201 and the adaptor 101.
In some embodiments, determining the temperature of the cable joint 201 further based on the current in the cable 200 includes: in response to an instantaneous increase of the current in the cable 200 exceeding a first threshold, increasing a value of the determined temperature of the cable joint 201 by a first compensation value; and in response to an instantaneous decrease of the current in the cable 200 exceeding a second threshold, decreasing a value of the determined temperature of the cable joint 201 by a second compensation value.
It should be appreciated that the above detailed embodiments of the present disclosure are only to exemplify or explain principles of the present disclosure and not to limit the present disclosure. Therefore, any modifications, equivalent alternatives and improvement, etc. without departing from the spirit and scope of the present disclosure shall be included in the scope of protection of the present disclosure. Meanwhile, appended claims of the present disclosure aim to cover all the variations and modifications falling under the scope and boundary of the claims or equivalents of the scope and boundary.

Claims

An apparatus (100) for monitoring a temperature of a cable joint (201) of a cable (200) connected to a gas insulated switchgear (300) , comprising:

an adaptor (101) adapted to be coupled to a cable socket (31) of the switchgear (300) , the cable socket (31) being provided with a mounting hole (311) for connecting the cable joint (201) , the mounting hole (311) being provided at a mounting surface (312) , wherein the adaptor (101) , when coupled to the cable socket (31) , is situated at the mounting surface (312) and outside the mounting hole (311) ;

a temperature sensor (102) arranged in the adaptor (101) and configured to detect a temperature of the adaptor (101) ; and

a processor (103) configured to determine the temperature of the cable joint (201) based on the detected temperature of the adaptor (101) .
The apparatus (100) according to claim 1, wherein the adaptor (101) comprises:

a first part (111) coupled to the cable socket (31) at the mounting surface (312) ; and

a second part (112) configured to accommodate the temperature sensor (102) .
The apparatus (100) according to claim 2, wherein the cable socket (31) comprises a threaded hole (313) at the mounting surface (312) , and the first part (111) is a threaded rot adapted to be inserted into the threaded hole (313) .
The apparatus (100) according to claim 2, wherein the second part (112) comprises a receiving hole (113) in which the temperature sensor (102) is arranged and sealed by pouring sealant (114) .
The apparatus (100) according to claim 1, further comprising a current sensor (104) configured to detect a current in the cable (200) , wherein the processor (103) is further configured to determine the temperature of the cable joint (201) further based on the current in the cable (200) .
The apparatus (100) according to claim 5, wherein the processor (103) is configured to determine the temperature of the cable joint (201) by:

in response to detecting that the current in the cable (200) increases, determining the temperature of the cable joint (201) based on the detected temperature of the adaptor (101) and a first relationship between temperatures of the cable joint (201) and the adaptor (101) ; and

in response to detecting that the current in the cable (200) decreases, determining the temperature of the cable joint (201) based on the detected temperature of the adaptor (101) and a second relationship between temperatures of the cable joint (201) and the adaptor (101) , the second relationship being different from the first relationship.
The apparatus (100) according to claim 5, wherein determining the temperature of the cable joint (201) further based on the current in the cable (200) comprises:

in response to an instantaneous increase of the current in the cable (200) exceeding a first threshold, increasing a value of the determined temperature of the cable joint (201) by a first compensation value; and

in response to an instantaneous decrease of the current in the cable (200) exceeding a second threshold, decreasing a value of the determined temperature of the cable joint (201) by a second compensation value.
A method (900) for monitoring a temperature of a cable joint (201) of a cable (200) connected to a gas insulated switchgear (300) , comprising:

detecting a temperature of an adaptor (101) by a temperature sensor (102) arranged in the adaptor (101) , the adaptor (101) being adapted to be coupled to a cable socket (31) of the switchgear (300) , the cable socket (31) being provided with a mounting hole (311) for connecting the cable joint (201) , the mounting hole (311) being provided at a mounting surface (312) , wherein the adaptor (101) , when coupled to the cable socket (31) , is situated at the mounting surface (312) and outside the mounting hole (311) ; and

determining the temperature of the cable joint (201) based on the detected temperature of the adaptor (101) .
The method (900) according to claim 8, wherein the cable socket (31) comprises a threaded hole (313) at the mounting surface (312) , and the adaptor (101) comprises:

a first part (111) constructed to be a threaded rot adapted to be inserted into the threaded hole (313) ; and

a second part (112) configured to accommodate the temperature sensor (102) .
The method (900) according to claim 9, wherein the second part (112) comprises a receiving hole (113) in which the temperature sensor (102) is arranged and sealed by pouting sealant (114) .
The method (900) according to claim 8, further comprising:

detecting a current in the cable (200) by a current sensor (104) ;

in response to detecting that the current in the cable (200) increases, determining the temperature of the cable joint (201) based on the detected temperature of the adaptor (101) and a first relationship between temperatures of the cable joint (201) and the adaptor (101) ; and

in response to detecting that the current in the cable (200) decreases, determining the temperature of the cable joint (201) based on the detected temperature of the adaptor (101) and a second relationship between temperatures of the cable joint (201) and the adaptor (101) , the second relationship being different from the first relationship.
The method (900) according to claim 11, wherein the first relationship is obtained by performing linear fitting on at least two pairs of temperatures of the cable joint (201) and the adaptor (101) ,

the second relationship is obtained by performing linear fitting on at least three pairs of temperatures of the cable joint (201) and the adaptor (101) , and

the at least three pairs of temperatures comprises at least a pair of transient temperatures of the cable joint (201) and the adaptor (101 ) .
The method (900) according to claim 11, wherein determining the temperature of the cable joint (201) further based on the current in the cable (200) comprises:

in response to an instantaneous increase of the current in the cable (200) exceeding a first threshold, increasing a value of the determined temperature of the cable joint (201) by a first compensation value; and

in response to an instantaneous decrease of the current in the cable (200) exceeding a second threshold, decreasing a value of the determined temperature of the cable joint (201) by a second compensation value.
A gas insulated switchgear (300) comprising the apparatus (100) according to any of claims 1-7.