The present invention relates to link boxes which is electrically and mechanically integral accessories of cable bonding system. The invention especially relates to a link box with built-in partial discharge sensor for partial discharge measurement in high voltage cable joints and terminations.

State of the Art High voltage cables are always designed with metallic sheath to controls the electric field stress in the cable insulation and also providing return path for fault current. During normal operation of cable system, AC voltages may be induced on metallic sheath due to electromagnetic coupling between core and the metallic sheath. In order to limit the magnitude of sheath voltages and also to minimize the flow of circulating currents, special bonding and grounding methods such as single point bonding and cross bonding are used in high voltage cable systems.

Link boxes are the metallic enclosures in which bonding and grounding of sheathes of high voltage cable joints or terminations made through removable links. Link boxes also may contain sheath voltage limiters to limit lightning or switching overvoltages of cable system. Link boxes are installed close to high voltage cable joints or terminations and may be installed in places such as underground manholes, aboveground pedestals or tunnel walls and etc. Diagnostic testing of new or service-aged installed high voltage power cable systems which include cable, joints, and terminations, using partial discharge detection, measurement and locating, has a long history. After-laying partial discharge testing on newly installed cable system is an efficient method to find defects in accessories, e.g. improper positioning, cuts or scratches, contaminations etc. Partial discharge testing on service-aged cable systems is a useful indicator of insulation degradation. Partial discharge testing may be carried out on-line (at normal service voltage) or off-line (by an external voltage source). Moreover, continuous on-line monitoring of cable systems has received more attention in recent years. Partial discharge measurement on long high voltage cable systems can be carried out by three different methods including ¹ Partial discharge detection at cable end using coupling capacitor, ² Partial discharge detection at cable accessories using embedded sensors inside the joints or terminations ³ Partial discharge detection at link boxes using inductive sensors (e.g. high frequency current transformers).

According to current practices, off-line partial discharge measurement during commissioning tests at existing link boxes carried out by installation of temporary partial discharge sensors around sheath bonding cables or cross bonding links of link boxes. Test procedure includes installing temporary high frequency current transformers, protection circuit setup and connection of cables to portable partial discharge test device. These steps can be time- consuming procedure. Furthermore, there is a commonly encountered problem for online partial discharge measurement at link boxes. In such cases, split-core high frequency current transformers are needed. Also, mounting these sensors during online conditions requires live-working on energized link box which may be dangerous for test stuff. Also, this procedure is time & labor consuming in long HV cable systems with a great number of link boxes.

Another problem is encountered when installing permanent high frequency current transformers as a part of online partial discharge monitoring systems. According to current practices, high frequency current transformers are installed around sheath bonding cable itself. This method is not an engineering solution because these sensors are subjected to environmental conditions during its service life or may be damaged due to faults in cable system.

Having been encountered as a result of the technical researches, the Application No. CN 202443038 U relates to high-voltage cable intelligence earth box. Another application which has been encountered as a result of the technical researches is the Patent No. CN 103308832 A which relates to a partial discharge test device for high-voltage cable insulation middle joint and use method. However, neither of the applications have a novelty which aims to solve the aforementioned drawbacks.

As a result, due to the drawbacks mentioned above and the inadequacy of the existing solutions regarding the subject matter, it is required to make a development in the related technical field. Objects of the Invention

The invention, configured by being inspired by the current conditions, aims to solve the above mentioned drawbacks.

Present invention introduces an all-in-one solution for above mentioned problems of partial discharge measurement in link boxes.

The object of the present invention is to avoid unexpected high induced voltages by short circuits which may occur during offline commissioning tests or online tests using this type of link boxes and performing partial discharge testing easily, just by connecting portable partial discharge test device to its terminal box through spark gap protection box.

Increased safety of test stuff and reduced time and labor work during partial discharge test at link boxes are the main advantages of present invention.

Moreover, detected partial discharge signals can be sent out of the link box via signal cables through sealed glands. This alternative is very useful in online partial discharge monitoring systems that permanent installation of high frequency current transformers is required. By using present invention, partial discharge sensors shall be installed inside a sealed box so they are not affected by environmental conditions or any other hazards.

To achieve the aforementioned objects, the present invention is a link box which provides bonding and grounding of sheathes of voltage cable joints or terminations and comprises · an enclosure body which all other components are placed inside and protects the all components from environmental effects,

• an enclosure cover which is upper part for the link box,

• cable glands through which provide entering into enclosure body of earthing cable and coaxial bonding cables,

· disconnectable crossing bars which provide a cross connection of coaxial bonding cables inside the link box characterized in comprising;

• partial discharge sensors placed inside link box around coaxial bonding cables or disconnectable crossing bars which act as primary winding for partial discharge sensor and provide detection of partial discharge in high voltage cable joints and terminations,

• an additional housing located on the enclosure cover which pulses of partial discharge signals are transmitted using signal cables connecting partial discharge sensors to protection box and provides carrying out of partial discharge measurement during partial discharge test just only by opening the housing cover without opening enclosure cover,

• a protection box located in additional housing intended for connecting partial discharge test device and also provides protection of test circuit using spark gaps inside.

In another preferred embodiment of the present invention, said link box is comprising sensor cable glands which provide sending of detected partial discharge signals out of the link box and monitoring them.

The structural and characteristic features and all the advantages of the present invention will be more clearly understood thanks to the figures below and the detailed description written with reference to those figures, therefore; the evaluation needs to be done by taking said figures and the detailed description into consideration.

Figures for a Better Understanding of the Invention

Figure 1 shows components of the present invention.

Figure 2 shows top view present invention in detail.

Figure 3 shows schematic view of a high voltage cable system during offline and online partial discharge test.

Figure 4 shows arrangement of current invention when it used for online monitoring.

The drawings do not need to be scaled and the details that are not necessary for understanding the present invention may have been ignored. In addition, the elements that are at least identical to a great extent or at least have identical functions to a great extent are referred with the same number.

Description of the Part References 1. Enclosure body 2. Enclosure cover

3. Cable gland

4. Coaxial bonding cable

5. Earthing cable

6. Additional housing

7. Housing cover

8. Gasket

9. Protection box

10. Partial discharge sensor

11. Signal cable

12. Sensor cable gland

13. Threaded cap

14. Input socket

15. Output socket

16. Cable termination

17. Cable joint

18. Disconnectable crossing bar

19. Sealing gasket

100. Link box

Detailed Description of the Invention

In this detailed description, the preferred embodiments of the invention are described only for a better understanding of the subject without any limiting effect.

The invention relates to a link box (100) with built-in partial discharge sensor (10) for partial discharge measurement in high voltage cable joints and terminations (17, 6).

Fig.1 shows components of the present invention. Link box (100) includes a stainless steel enclosure body (1) and stainless steel enclosure cover (2). Enclosure body (1) can be seen as a base frame for mounting internal parts and protection of internal parts against environmental conditions. Three coaxial bonding cables (4) are used to connect metallic sheath of high voltage cable joints (17) to link box (100). Earthing cable (5) is connected to earthing busbar inside the link box (100) and then it's ready to be connected to earthing electrode outside of the link box (100). Sealed penetration of coaxial bonding cables (4) and earthing cable (5) into enclosure body (1) made by cable glands (3). Partial discharge detection is made by three partial discharge sensors (10) (high frequency current transformers) placed around main conductor of coaxial bonding cables (4) or disconnectable crossing bars (18), which are used to provide a cross connection of coaxial bonding cables (4), located inside the link box (100) which act as primary winding for partial discharge sensor (10). Pulses of partial discharge signals are induced to secondary of partial discharge sensor (10) and then transmitted to additional housing (6) using signal cables (11).

Fig.2 shows top view of present invention in detail. Detected partial discharge signals enters a sealed additional housing (6) located on the enclosure cover (2). Sealing of this additional housing (6) made by a gasket (8). This additional housing (6) contains a protection box (9) with protective spark gaps inside. There are also three BNC input and three output sockets (14, 15) in additional housing (6) for connection of signal cables (1 1) and also connecting portable partial discharge test device to the protection box (9). Although, there is a galvanic isolation between primary and secondary side of partial discharge sensors (10), but electromagnetic induction on signal cables (11) and BNC input sockets (14) may occur during transient conditions. So this protection circuit is necessary to prevent any danger to portable test device or test stuff during tests.

As shown in Fig.3, offline or online partial discharge testing in present invention is possible just only by opening the housing cover (7) and connecting partial discharge test device to protection box (9). Opening the enclosure cover (2) of link box (100) is not required in this case. It is to be noted that underground link boxes (100) are generally installed in small manholes with limited space so opening of enclosure cover (2) is not done easily. Moreover, opening-closing of enclosure cover (2) may lead to lifetime reduction of sealing gasket (19).

As shown in Fig.4, it is possible to use present invention as a part of online partial discharge monitoring systems. Detected partial discharge signals are sent out of the link box (100) toward monitoring system through sealed small sensor cable glands (12). When this option is not used, sensor cable glands (12) shall be covered by threaded caps (13).