Technical field

The invention is an Intelligent Link Box with early warning system for online monitoring of sheath bonding system and high voltage cable accessories. This invention will be used in high voltage cable systems.

Prior art

As stated in PCT applications WO2016190823A1 and WO2019194754; a sheath bonding system is a system to minimize the induced circulating current and to protect insulation of HV cable outer sheath against overvoltages from lightning, switching, and fault surges. Link boxes as main part of sheath bonding system are the enclosures in which bonding and grounding of sheathes of HV cable joints or terminations made through removable links. Link boxes also may contain sheath voltage limiters (SVL) to limit lightning or switching overvoltages. Link boxes are installed close to HV cable joints or terminations and may be installed in places such as underground manholes, aboveground structures/pedestals, or tunnel walls.

Any failure in link box proper performance can lead to failure of costly HV cable system. The link box may fail due to exposure to the harsh environment, including moisture, heat, UV, manufacturing defect, or mechanical impact. Common failures that can be inspected externally include corrosion, physical damages, and moisture ingress. Many utilities would require that SVLs be housed in explosion proof link boxes to withstand short-circuit conditions. Some utilities have experienced some damage to their systems due to the failure of SVLs under short circuit conditions. Inappropriate selection of SVL in bonding system is a main cause of link box failure and damage to sheath of EHV cable during short circuit and transient voltages.

It is more cost efficient to prevent failures with regular maintenance, than to perform corrective maintenance after a failure has occurred. Offline maintenance methods (not energized HV cable system) including periodic visual inspection, contact resistance test, DC withstand test and SVL integrity tests are the common practices in HV cable industry. These methods are not able to detect the failures between periodic intervals because these periodic inspections are performed in yearly intervals (making the whole system offline is a costly and complex procedure) so any problem in cable system will be will be detected one year later in these methods. Online methods (energized HV cable system) including measuring sheath currents, fiber optic embedded SVL monitoring or measuring SVL leakage current, use of DTS (Distributed Temperature Sensing) data to check condition of bonding system, visual or thermal images have been used in some practices. These methods also suffer from being high cost and complexity of installation and operation.

On the other hand, diagnostic testing of new or service- aged installed high voltage power cable systems using partial discharge (PD) detection, measurement and locating, has a long history. Online PD monitoring of EHV cable systems has received more attention in recent years. Some utilities now require continuous real time PDM (partial discharge monitoring) system in high voltage cable systems. There are many commercial partial discharge monitoring systems available in market but most of them suffer from high cost, complexity of installation & operation and need to highly experienced staff to operate whole system and interprete collected data.

As a result, due to the above-mentioned disadvantages and the inadequacy of the existing solutions, an improvement in the relevant technical field was required. New method should be able to detect the any problem instantly and warn the cable system owner to make corrective action, also new method should be simple to install & operate and also cost effective.

Purpose of the invention

The invention aims to provide a method with different technical characteristics which brings a new perspective in this field, unlike the embodiments used in the present art.

Main purpose of the invention, compensating the lack of a special online monitoring system for link boxes as integral part of sheath bonding system of high voltage cable systems.

Another purpose of the invention, any failure of link boxes (e.g. water ingress etc.) will be detected immediately and alarmed to control center for further investigation and required onsite action. Another purpose of the invention, intelligent link box would be equipped with a simple to operate partial discharge alarming system for online monitoring of high voltage cable accessories (joints and terminations).

There is no equal or similar product for intelligent Link Box. Intelligent Link Box can be used to continuously monitor & alarm different parameters of link box including current & voltage of sheathes, number of impulse voltage incidents, water ingress, temperature & humidity, internal pressure, link box lid status, and partial discharge level of HV cable accessories. Thanks to embedded advanced decision-making algorithms, final user will only deal with simple alarms not complex data. Simple user interface integrated to SCADA system enables the operator to receive alarms concerning unusual behaviour before catastrophic failure of link boxes and cable accessories.

In order to fulfill the above-described purposes, the invention is an intelligent link box with early warning system for online monitoring of sheath bonding system and high voltage cable accessories characterized by comprising;

• An enclosure body which is a base frame for mounting internal parts and protection of internal parts against environmental conditions,

• An enclosure cover which is a cover for protecting internal components from environmental conditions,

• Bonding cables for connection of metallic sheath of high voltage cable joints or cable termination to the intelligent link box,

• A Disconnectable link bar for cross bonding of high voltage cable sheathes,

• Partial discharge sensors to pick up partial discharge pulses, measurement of induced AC voltages in the intelligent link box, counting number of lightning impulses passing through sheath voltage limiters,

• At least one current transformer to measure the induced AC currents in bonding system,

• At least one water sensing sensor to detect water ingress into intelligent link box,

• At least one temperature & humidity sensor to evaluate condensation issues or other abnormal condition inside intelligent link box,

• At least one mechanical switch to show the open/close statues of lid,

• At least one pressure sensor to detect any increase of internal pressure of link box due to internal arc, • An analog conditioning board to convert received signals from Partial discharge sensors and current transformer to readable data for main processing unit (MPU),

• A partial discharge measuring board for conditioning, filtering, and amplification of the high frequency partial discharge signals,

• A main processing unit to process all incoming data from sensors, conditioning board and partial discharge measuring board,

• A battery pack to supply power for whole electronic components,

• A junction box to unify input cables and protection of signals,

• Multiple core signal cable for transmission of signals between lower and upper compartments,

• Fiber optic cable for fiber optic data transmission,

• A fiber optic media converter to convert standard data to optical data to be transmitted to control center,

• A terminal box for local partial discharge measurements.

The structural and characteristic features and all advantages of the invention will become more apparent from the following figures and the detailed description made with reference to these figures, and therefore the evaluation should be made with reference to these figures and detailed description.

Brief description of the figures

Figure 1, schematic view of invention in High Voltage cable system.

Figure 2, complete set up of invention.

Figure 3, internal view of invention.

Figure 4, base plate of upper compartment.

Figure 5, complete setup of invention (closed lid).

The drawings do not necessarily have to be scaled and details which are not necessary to understand the present invention may be omitted. Furthermore, elements which are at least substantially identical or at least substantially identical functions are designated by the same number.

Reference list

100 Intelligent link box 101 Cable joint

102 Termination

104 Control center

105 FO line

106 GSM antenna

201 Enclosure body

202 Enclosure cover

203 Bonding cables

204 Cable glands

205 Disconnectable link bar

206 Sheath Voltage Limiters

207 Partial discharge sensors

208 Current transformer

209 Water sensing sensor

210 Temperature & humidity sensor

211 Mechanical switch

212 Pressure sensor

213 Analog conditioning board

214 Partial Discharge measuring board

215 Main processing unit (MPU)

216 Battery pack

217 Junction box

218 Multiple core signal cable

219 Fiber optic cable

220 Fiber optic media convertor

221 Terminal box

Detailed description of the invention

In this detailed description, preferred embodiments of the invention are explained for better understanding of the subject matter and with no limiting effect.

The invention is an intelligent link box (100) with early warning system for online monitoring of sheath bonding system and high voltage cable accessories. Fig.1 shows overall structure of intelligent link box alarming & monitoring system. It can be seen that intelligent link box (100) are installed close to cable joint (101) and terminations (102). Bonding cables (203) are used to connect sheath of high voltage cables to intelligent link box (100). Two remote data communication methods (between on-site intelligent link box (100) and SCADA database in control center (104)) can be used according to target project requirements. A fiber optic communication method can be used when the project owner can allocate a FO line (105) for alarming system (new cable projects). If this option is not feasible then a wireless GSM/GPRS communication method can be used for intelligent link box (100). In this method it is necessary to install a GSM antenna (106) outside of link box where the GSM signals can be reached.

Fig. 2-4 shows components of the present invention. Intelligent link box (100) includes a stainless-steel enclosure body (201) and stainless-steel enclosure cover (202). Enclosure body (201 ) can be seen as a base frame for mounting internal parts and protection of internal parts against environmental conditions. Bonding cables (203) are entered into link box inside through cable glands (204). Then Cross bonding of cable sheathes made by disconnectable link bars (205). These cables are star connected via sheath voltage limiters (206) inside the link box.

There are different sensors inside intelligent link box (100). Three partial discharge sensors (207) are insulator type PD sensor with built-in HV divider which has been described in WO2019194754. This sensor contains a soft ferromagnetic core with primary and secondary winding to pick up PD signals from disconnectable link bar (205) of link box connected to high voltage cable sheath. This sensor also contains a HV voltage divider for measuring induced voltages in bonding system. This output also can be used to provide synchronization signals for partial discharge measuring board (214). Also, output of this divider can be used for counting number of lightning impulses passing through Sheath Voltage Limiters (206) inside link boxes so condition monitoring of SVL is possible. Three 20/0.1 ratio epoxy current transformers (208) are used to measure the induced currents circulating inside link boxes so sheath current monitoring of bonding system will be made. Any increase or unbalance in sheath currents will be monitored. These sensors are mounted around bonding cables (203) inside link box and are designed to measure the sheath currents during normal operating of bonding system and abnormal conditions (e.g. SVL failure that can lead to increased or unbalanced currents). A water sensing sensor (209) is used inside link box to detect water ingress into link box. A temperature & humidity sensor (210) is used to evaluate condensation issues or other abnormal condition inside linkbox. A mechanical switch (211 ) is embedded in lid of enclosure body (201) to show the open/close statues of lid, this data can be used to check the unauthorized opening of link box. A pressure sensor (212) was used to detect any increase of internal pressure of link box due to internal arc. All output data of these sensors are directly sent to main processing unit (MPU) (215) of intelligent link box (100).

An analog conditioning board (213) was used to convert received signals from AC HV voltage divider (207) and AC current measuring sensors (208) to readable data for main processing unit (MPU) (215). The conditioning board also contains a synch voltage selection circuit to provide appropriate synch signal for partial discharge measuring board (214).

The partial discharge measuring board (214) has three input channels connected to the insulator type partial discharge sensors (207). An input protection stage is followed by signal conditioning, filtering, and amplification of the high frequency partial discharge signals from partial discharge sensors (207). It also receives the synch signal from the conditioning board (213) to synchronize the measured PD signals with AC voltage of bonding system. The board includes an ethernet output port to communicate with main processing unit (MPU) (215). Special attention has been made to develop a noise discrimination algorithm to reduce the false alarming due to received background noise.

Providing energy for all electronic components of intelligent link box (100) is critical for a reliable system. A Ni-MH battery pack (216) charging from solar panel or street lighting line has been selected. A microprocessor based MPPT charger was used to ensure long life (10 years) operation of battery pack.

An ARM Cortex M type (microcontroller) main processing unit (215) (which is low-cost and energy-efficient) has been selected to process all incoming data from sensors (207-212), analog conditioning board (213) and partial discharge measuring board (214). An advanced decision-making algorithm for alarming has been embedded in this unit. Alarming algorithms and triggering levels can be customized in SCADA user interface according to project specifications. Two remote data communication methods (Fiber optic or GSM/GPRS) can be used according to project requirements.

All sensitive electronic components have been placed in upper separate compartment in lid of enclosure body (201) to be isolated (shielded) from HV side of link box (lower compartment). All electronic components are mounted on a removable baseplate in upper compartment. All sensor output cables are entering a junction box (217) on wall of lower compartment. All signal lines are protected by surge protection devices inside junction box. Connection between upper compartment (electronic devices) and junction box made via a multiple core signal cable (218) as well as a fiber optic cable (219). This fiber optic cable (219) is output of fiber optic media convertor (220) which converts standard data to optical data to be transmitted to SCADA control center. By removing these cables, the lid of link box (as well as all electronic devices) can be pulled out for any setting or maintenance work on site. There is small terminal box (221) on top of upper compartment. There are three PD output in this terminal box as well as a synch output for local partial discharge measurement on site. This option is useful to perform deep investigations of partial discharge measurements when an alarm has been received from intelligent link box (100).