Technical field

The application relates generally to a monitoring system for underground trans mission cables.

Background

Wireless measurement systems have been used to measure an operation of above-ground electric power transmission lines and obtained measurement results have been transmitted to an operator that is responsible for a monitoring of the operation of a transmission line system remotely and a maintenance of the moni tored system.

Strict demans for increasing the reliability of electric power transmission have however forced electrical distribution companies to change the transmission lines from above ground to underground, whereupon an installation of known wireless measurement devices in connection of underground transmission cables has be come impossible.

In order to monitor the operation and condition of underground transmission lines in real-time, operators have installed the known measurement systems in connec tion of above-ground components of the underground transmission lines, e.g. in distribution substations or cabinets. This has decreased accuracy and coverage of the measurement systems because of long distances, e.g. several kilometers, be tween the above-ground components.

Summary

An object of the invention is to withdraw the drawbacks of known solutions and to provide an accurate monitoring system for underground transmission cables that covers a whole underground transmission cable grid.

A object of the invention is fulfilled by providing the system, cable joint, methods, computer program, and computer-readable medium according to the independent claims.

Embodiments of the invention are specified by the system, cable joint, methods, computer program, and computer-readable medium according to the independent claims. A monitoring system for underground transmission cables comprises a transmis sion cable joint and a system monitor. The transmission cable joint comprises at least a casing and a coupler. The casing encompasses the coupler, which is con figured to couple wires of the transmission cables. The transmission cable joint fur ther comprises a measurer and a radio communicator encompassed by the cas ing. The measurer is configured to measure at least a current and a voltage from a coupled transmission cable belonging to the transmission cables. The radio com municator is configured to transmit parameter values relating to the current and the voltage wirelessly to the system monitor in order to monitor at least an opera tion of the transmission cables remotely.

A monitoring method for monitoring underground transmission cables comprises a step of coupling, by a coupler of a transmission cable joint, wires of the transmis sion cables to each other. The method further comprises a step of encompassing, by a casing of the transmission cable joint, the coupler, a measurer of the trans mission cable joint, and a radio communicator of the transmission cable joint. The method further comprises a step of measuring, by the measurer, at least a current and a voltage in a coupled transmission cable belonging to the transmission ca bles. The method further comprises a step of transmitting, by the radio communi cator, parameter values relating to the current and the voltage wirelessly to a sys tem monitor in order to monitor at least an operation of the transmission cables remotely.

A transmission cable joint for monitoring underground transmission cables com prises at least a casing and a coupler configured to couple wires of the transmis sion cables. The casing encompasses the coupler. The transmission cable joint further comprises a measurer and a radio communicator encompassed by the cas ing. The measurer is configured to measure at least a current and a voltage in a coupled transmission cable belonging to the transmission cables. The radio com municator is configured to transmit parameter values relating to the current and the voltage wirelessly outside the transmission cable joint in order to enable at least a monitoring of an operation of the transmission cables remotely.

Another monitoring method for monitoring underground transmission cables com prises a step of coupling, by a coupler of a transmission cable joint, wires of the transmission cables to each other. The method further comprises a step of en compassing, by a casing of the transmission cable joint, the coupler, a measurer of the transmission cable joint, and a radio communicator of the transmission ca ble joint. The method further comprises a step of measuring, by the measurer, at least a current and a voltage in a coupled transmission cable belonging to the transmission cables. The method further comprises a step of transmitting, by the radio communicator, parameter values relating to the current and the voltage wire lessly outside the transmission cable joint in order to enable at least a monitoring of an operation of the transmission cables remotely.

A computer program comprises instructions, which, when the computer program is executed by a computer, which is in accordance with the previous cable joint, cause the computer to carry out at least the steps of the another monotoring method.

A tangible, non-volatile computer readable medium comprises the computer pro gram, which is in accordance with the previous computer program.

Brief description of the figures

The embodiments of the invention are explained below with reference to the ac companying figures: fig. 1 presents a monitoring system of an underground transmission cables fig. 2 presents operational parts of a transmission cable joint

Detailed description of the figures

Fig. 1 presents a monitoring system 100 for an underground medium voltage (MV) transmission (delivery) cable grid (system) 102 that comprises a plurality of MV transmission (delivery) cables 104, which are typically 1-100 kV, e.g. 10, 15, 20, or 30 kV, cables.

The system 100 comprises at least one portable underground transmission cable joint (connection enclosure) 106 that is suitable to be buried in the groud, where it couples (connects) the feeder-side and load-side cables 104 to each other in an underground MV transmission line of the grid system 102 by coupling each wire of the feeder-side cable 104 to a respective wire of the load-side cable 104, when it is not possible to use one continuous cable 104 between transformer stations 108 because of e.g. distance or obstacles. The at least one cable joint 104 comprises one, two, three, four, or more transmission cable joints.

Each cable joint 106 comprises a portable casing (casket) 210 that encompasses other components 212, 214, 216, 218, 222 of the cable joint 106 in order to shelter the components 212, 214, 216, 218, 222 during the handling of the cable joint 106 and in the underground conditions from e.g. external pressure and moisture caused by surrounding soil. The casing 210 has been manufactured at least partly from a highly heat-conductive material, e.g. aluminum, copper, or any other heat- conductive material, to enable a cooling of the cable joint 106.

The casing 210 comprises first (upper) and second (lower) casing parts with bolt flanges. The casing parts are designed (shaped) so that the casing parts, which are attached to each other, establish a component space that enables to install the components 212, 214, 216, 218, 222 inside the casing 210. The casing parts are sealed watertightly by a watertight seal material between the casing parts and at tached to each other by fasteners, e.g. bolts or screws, through the bolt flanges. The fasteners may be unfastened and the casing parts may be separated from each other so that the casing 210, which has an openable structure, is open and it is possible to maintain or to repair the components 212, 214, 216, 218, 222 if nec essary.

Additionally, the casing parts are designed so that, when the casing parts are at tached to each other, the casing 210 establishes a feeder cable opening to one end of the casing 210 for the feeder-side cable 104 and a load cable opening to another end of the casing 210 for the load-side cable 104. The openings, which are sealed watertightly by the watertight seal material, allow the feeder-side and load-side cables 104 to enter into the component space, inside the casing 210, so that the coupling of the feeder-side and load-side cables 104 is sheltered.

The casing 210 also comprises one or two handlebars so it is possible to carry the portable cable joint 106 by one or two persons and one or two lifting bars so that it is possible to hoist the cable joint 106.

Each cable joint 106 also comprises a coupler 212 that couples the wires of the feeder-side and load-side cables 104. The feeder-side cable (cabling) 104, which comes from a transformer station 108, is coupled to a feeder (primary)-side of the coupler 212 (connection terminals) and the load-side cable (cabling) 104 to a load (secondary)-side of the coupler 212 so that the wires of the feeder-side cable 104 are coupled to the feeder-side of the coupler 212 and the wires of the load-side cable 104 to the load-side of the coupler 212. Each wire of the feeder-side cable 104 is coupled to a respective wire of the load-side cable 104.

Each cable joint 106 also comprises a measurer 214 that is configured to measure a current I and a voltage V from at least one coupled wire of the feeder-side cable 104, e.g. from one, two, or three wires; from at least one coupled wire of the load- side cable 104, e.g. from one, two, or three wires; or from at least one coupled wire of each coupled cables 104, e.g. from one, two, or three wires. If both the feeder-side cable 104 and the load-side cable 104 comprise e.g. three coupled wires, the measurer 214 is configured to accomplish three-phase current and volt age measurements. The measurer 214 is also configured to measure earth fault current and voltage measurements. The measurer 214 comprises at least one measurement transformer for a current measurement and for a voltage measure ment. The at least one measurement transformer comprises one, two, three, four, or more measurement transformers. The measurer 214 comprises e.g. a meas urement transformer for each parameter (current, voltage) value I, U to be meas ured so that it is possible to measure the previously explained measurements from the cable(s) 104. The measurer 214 provides a measured current value I as a re sult of the current measurement and a measured voltage value U as a result of the voltage measurement.

The measurer 214 may also measure (determine) at least one of temperature in side the casing 210, temperature outside the casing 210, a vibration of the feeder- side cable 104, a vibration of the load-side cable 104, and a location of the cable joint 106. Then, the measurer 214 comprises a thermometer for a inside tempera ture measurement when the measurer 214 measures the inside temperature, a thermometer for an outside temperature measurement when the measurer 214 measures the outside temperature, a vibration transducer for a vibration meas urement when the measurer 214 measures the vibration of the cable(s) 104, and a locator for the location when the measurer 214 locates the cable joint 106.

The measurer 214 provides a measured inside temperature value Ti _n as a result of the inside temperature measurement, a measured outside temperature value T _out as a result of the outside temperature measurement, a measured vibration value VB for the cable(s) 104 as a result of the vibration measurement, and a deter mined location (value) LO as a result of the location determination, if the measurer 214 is able to measure such value.

The thermometer for the outside temperature measurement, if measurer 214 com prises such, is installed outside the casing 210 opposite the other components 212, 214, 216, 218, 222 of the cable joint 106 so that it is able to measure the out side temperature. Each cable joint 106 also comprises a controller 216 that processes each meas ured value I, U, Ti _n , T _out , VB, LO from the measurer 214 as respective parameter values I, U, T, _n , T _out , VB, LO.

The cable joint 106 also comprises a radio communicator 218 that communicates (transmits) at least the obtained parameter values I, U relating to the current and the voltage wirelessly outside the cable joint 106. The radio communicator 218 may also communicate each of the parameter values Ti _n , T _out , VB, LO relating to the temperatures, vibration(s), and location, if such has been obtained as above has been explained, wirelessly outside the cable joint 106. The obtained parameter values I, U, Tin, Tout, VB, LO are communicated outside by radio transmissions through a wireless radio communication network 120 so that the monitoring system 100 is enable to use the communicated values I, U, Tin, Tout, VB, LO for monitoring the operation of the transmission cables 104 as well as the whole underground grid system 102 remotely. Each cable joint 106 or at least one of the cable joints 106 in the grid system 102 may also comprise a compensator (inductance limiter) 222 that compensates (lim its, minimizes) a reactive current, a capacitive earth fault current, or both currents when the coupled transmission cables 104 produce such current(s) by establishing inductance that compensates a capacitive feature of the produced current(s). The compensator 222 comprises a ZN (ZigZag) transformer that is coupled (con nected) with the coupler 212 parallely to the coupled transmission cables 104. The compensator 222 is connected internally to the casing 210, which operates as a grounding point, from from its neutral side so that the solid connection, which is in side the casing 210, operates as a grounding point and an inductance for limiting the produced current(s).

The compensator 222 compensates the produced current(s) during use and faults so that it is not necessary to any other, expensive, system. One example of the compensator 222 has been explained in patent publication FI128488.

The system 100 also comprises at least one transformer (station) 108 that con- verts the voltage from other transmission line to a different voltage for one of the transmission cables 104 or from one of the transmission cables 104 or to the dif ferent voltage for other transmission cable 104 or circuit. The at least one trans former station 108 comprises one, two, three, four, or more transformer stations. At least one transformer station 108 comprises at least one high voltage (HV)/MV transformer station, at least one MV/low voltage (LV) transformer station, or both transformer station(s).

Each transformer station 108 comprises a measurer that measures at least a cur rent I and a voltage U at least from the feeder-side cable 104, from the load-side cable 104, 105, or from both ones correspondingly as the measurer 214. The measurer may also measure at least one of temperature Ti _n inside a casing of the transformer station 108, temperature T _out outside the casing, a vibration VB of the feeder-side cable 104, a vibration VB of the load-side cable 104, 105, and a loca tion LO of the transformer station 108.

Each transformer station 108 also comprises a controller that processes measured values I, U, Tin, Tout, VB, LO relating to the current, voltage, and other other possi bly measured quantities as the respective parameter values I, U, Tin, Tout, VB, LO and a radio communicator that communicates the obtained parameter values I, U, Tin, Tout, VB, LO wirelessly outside by radio transmissions through the network 120 so that the monitoring system 100 is enable to use also these communicated val ues I, U, Tin, Tout, VB, LO for monitoring the operation of the transmission cables 104 and the grid system 102 remotely.

Each transformer station 108 or at least one of transformer stations 108 may be an underground transformer station that is suitable to be buried in the groud, where upon it also comprises a casing that encompasses the actual transformer and the above explained components of the transformer station 108 in order to shelter those from mechanical impacts and from underground pressure and moisture conditions.

The system 100 also comprises at least one underground distribution cabinet 123 at an end of LV cable 105 from the MV/LV transformer station 108 that enables to distribute electric power to customers. The at least one distribution cabinet 123 comprises one, two, three, four, or more distribution cabinets.

Each distribution cabinet 123 comprises a measurer that measures at least a cur rent I and a voltage U correspondingly as the measurer 214 at least from the feed er-side LV cable 105, from the load-side connections, or from both ones. The measurer may also measure at least one of temperature Ti _n inside distribution cab inet 123, temperature T _out outside distribution cabinet 123, a vibration VB of the feeder-side LV cable 105, a vibration VB of load-side connections, and a location LO of the distribution cabinet 123.

Each distribution cabinet 123 also comprises a controller that processes measured values I, U, Ti _n , T _out , VB, LO relating to the current, voltage, and other other possi bly measured quantities as the respective parameter values I, U, Tin, T _ou t, VB, LO and a radio communicator that communicates the obtained parameter values I, U, Tin, Tout, VB, LO wirelessly outside by radio transmissions through the network 120 so that the monitoring system 100 is enable to use also these communicated val ues I, U, Tin, Tout, VB, LO for monitoring the operation of the grid system 102 re motely.

Each distribution cabinet 123 or at least one of distribution cabinets 123 may be an underground distribution cabinet that is suitable to be buried in the groud, where upon the distribution cabinet 123 also comprises a casing that encompasses its above explained components 108 similarly as the casings of the cable joint 106 and the transformer station 108.

The underground installation of the cable joints 106, transformer stations 108, dis tribution cabinets 123, and other underground components of the grid system 102 provides stable temperature conditions for the components 106, 108, 123 because of slow ground temperarure changes.

The system 100 also comprises a system monitor (computer) 124 that monitors the operation of the transmission cables 104 and the grid system 102 remotely. It receives the communicated parameter values I, U, T, _n , T _out , VB, LO from each ca ble joint 106 and the communicated parameter values I, U from each transformer station 108 through the network 120. The monitor 124 communicates update files to computer programs 236, 238, 240, 242 of the components 106, 108 and opera tion commands, e.g. a disconnection command in order to disconnect a faulty transmission line, to the transformer station(s) 108.

The monitor 124 produces at least one indicator, which represents the operation in the grid system 102, on the grounds of the received parameter values I, U, Ti _n , Tout, VB, LO. If the monitor 124 identifies on the grounds of the indicator(s) that a certain transmission cable 104, cable joint 106, transformer station 108 or any other grid component has a problems, is broken, or needs service, it communi cates through the network 120 or through other network a service indication SE to the service (computer) 126, which then arranges a relevant service to the grid sys tem 102.

Fig. 2 presents the cable joint 106 that is able to operate in the grid system 102 and in the network 120 as above has been explained.

The cable joint 106 comprises the casing 210, coupler 212, measurer 214, and the compensator 222 as above has been explained.

The cable joint 106 also comprises the controller 216 that controls operations of its parts 214, 216, 218 so that the cable joint 106 operates as above has been ex plained.

The controller 216 comprises a processor (processor part) 228 that performs op erator-initiated and/or computer program-initiated instructions, and processes data in order to run computer programs (applications). The processor 228 may com prise at least one pro-cessor, e.g. one, two, three, four, or more processors.

The controller 216 also comprises a memory (memory part) 230 in order to store and to maintain data. The data may be instructions, computer programs, and data files. The memory 230 comprises at least one memory, e.g. one, two, three, four, or more memories.

The cable joint 106 also comprises the radio communicator 218 as above has been explained and an antenna 232 that the controller 216 uses in order to send data, e.g. the parameter values I, U, Ti _n , T _out , VB, LO, to at least one of entities in the system 100, e.g. the monitor 124 and, possibly, the service 126, via the anten na 232. The radio communicator 218 may also receive commands, requests, and data from at least one of entities in the system 100, e.g. the monitor 124 and, pos sibly, the service 126, via the antenna 232. The communication between the radio communicator 218 and other entities in the system 100 is provided through the an tenna 232 wirelessly.

The cable joint 106 also comprises a power supplier 234 that comprises compo nents for powering the cable joint 106, e.g. a battery and a regulator.

The memory 230 stores at least a measurement application 236 for operating (controlling) a measurer 214, a radio communicator application 238 for operating the radio communicator 218, and a power supplier application 240 for operating the power supplier 234. The memory 230 also stores a computer program (computer software, computer application) 242, which uses at least one of parts 214, 218, 228, 230, 232, 234 in order to perform at least the operations of the cable joint 106 as above has been explained, when it is executed (run) in a computer, e.g. in the cable joint 106, by the controller 216.

The computer program 242 may be stored in a tangible, non-volatile computer- readable storage medium, e.g. a Compact Disc (CD) or Universal Serial Bus (USB) -type storage device.