ES2577881B2 - Distributed wireless system and procedure for the classification and location of faults in an underground electrical distribution network - Google Patents

Abstract

Distributed wireless system and procedure for the classification and location of faults in an underground electrical distribution network. The system comprises sensor devices (3), forming a network of wireless sensors (2), distributed in the underground electrical distribution network (1) and coupled to conductors (7) of the network (1) so that all sections of Drivers between branches have a sensor device (3) associated. The sensor devices (3) comprise means for measuring the current (34) that circulates through the conductor (7), being synchronized with each other and configured to identify the type of fault originated and the location thereof by exchanging messages, between the different sensor devices (3), with information on the synchronized current measurements and through the analysis of the fasorial information of said synchronized current measurements, taking into account the network topology.

Description

Field of the Invention The present invention falls within the field of methods and equipment for locating faults in electrical distribution lines, and more specifically in underground medium-voltage electrical distribution lines.

BACKGROUND OF THE INVENTION It is a fundamental task of electricity companies to guarantee the supply of energy to users in conditions of continuity and quality. Thus, the location of faults in power lines becomes a priority task for these companies. Once a fault has been detected, automatically estimating its position from the control center provides great advantages from the point of view of service quality, since both the restoration time and the number of maneuvers required are reduced. For this reason it is very attractive, in terms of quality and economy, the implementation of location systems of this nature.

The development and application of microprocessor-based systems in electrical engineering (lEOs) marks the emergence of the first automatic fault location techniques [1, 2]. Since then numerous methods of automatic fault location have been developed that are classified into four categories:

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Methods based on traveling waves ("traveling waves"). These types of methods analyze the high frequency signals (> 500kHz), in currents or voltages, produced by the impulses generated when the fault is triggered [3]. These impulses travel at high speeds through the power lines. The detection of the arrival of the impulse at two distant points allows to estimate the position of the fault. These techniques do not require complete knowledge of the characteristics of the lines, however, high wave speeds cause large errors in the location of the fault.

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Methods that use relatively high frequency components of voltages or currents. To estimate the position of the fault, these methods use the measurements obtained

with relatively high frequencies (> 10KHz), which are analyzed using techniques based on frequency domain analysis.

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Impedance methods. These methods use the fundamental components (appraisers) of tensions and intensities at endpoints of the line. They are the most used in locating faults in distribution networks and consist in calculating the impedances of the lines, as seen from the terminals of the same, before and during the fault. A good description of the different methods is found in [5] and its extensions to different cases of failure in [6].

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Methods based on punctual overcurrent detection. These methods are based on the use of Fault Circuit Indicators (FCI), as explained for example in US7023691 · B1. These elements are capable of detecting, locally, overcurrent events, memorizing them for a while or until the device is reset. Based on this information, in systems with radial distribution, it is possible to determine the section of line in which the fault originated. However, in systems with distributed generation where the flow of polency is not unidirectional, these systems are not able to perform the location. In these cases it is necessary to use directional FCls (as indicated for example in US7969155 · B2) which, using a measure of the voltage phase, are able to determine the direction of the power flow caused by the fault. Following these directions it is possible to determine the section under fault, even in these networks with distributed generation. The information generated by this type of devices is usually visual (light pilot or mobile element) that allow the operator to know, by direct inspection, the status of the device. There is a system with wireless communication on the market that allows access to information remotely. These systems are based on short distance radio links, or GSM or GPRS communications.

To date there are numerous patent documents related to fault location systems in power lines:

. W02007032697 · A1 presents a method for locating faults by dividing the lines of a transmission or distribution system into sections and assuming a hypothetical location in at least one of these sections, based on the measurements of the currents, in the fault conditions and also in pre · failure, in all seasons

system terminals, and also the measurement of the line voltage phase, in the fault and pre-fault conditions, in one of the system's terminal stations.

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AU2008200131-A1 describes a system for locating the point of failure, using several slave stations that collect data on the pre-failure situation of the distribution line and a master station, where all this information is received and processed, deducting a single point of failure, from a greater set of possibilities compatible with the measurements.

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W02013091028-A1 proposes a deployment of a sensor system for the registration of electrical parameters, in low voltage networks. These measuring elements use a GPS system for synchronization and will be connected at the ends of the distribution lines (one per line) and will communicate with the base station through a broadband connection.

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US20130205900-A 1 proposes an electrical distribution network management system, based on a deployment of sensors in aerial electrical distribution networks, recording information of an electrical and mechanical nature. Each of these sensors, communicates directly with a receiving station, which registers and processes the information of the nodes, trying to determine the characteristics of the installation, facilitating maintenance oppressions.

In the present invention, the use of a non-intrusive distributed system based on wireless sensor networks (WSN) is proposed as an alternative to locate faults in underground electrical distribution networks. A network of wireless sensors is made up of a series of small, low-power devices (nodes), capable of wireless communication between them and that collaborate to analyze a common phenomenon.

Sensor networks have many applications [71, the ubiquitous and pervasive monitoring of an environment being one of the main ones. The application of wireless sensor network technology in the field of electrical distribution networks is an emerging alternative, with numerous contributions in recent years, both of a general nature [8, 9], and of application in specific aspects, such as : airline surveillance [10]; monitoring of distributed generation systems [11], or management of charging systems for hybrid electric vehicles, etc. However, in no case has the networks been applied

from wireless sensors to the location of faults in underground power lines, which constitutes one of the novelties of the present invention.

Precisely, this is one of the points where there is an important innovation regarding the current fault location devices. So far, there are only two variants for these location systems: those that use local and isolated processing (based exclusively on local information) and those that use centralized processing (in which all information is concentrated and processed on a single node ). The present invention, on the other hand, is based on a collaborative processing between nodes, which gives the system the ability to detect, locate and classify faults in systems with distributed generation, based solely on current information, not requiring a measure of the phase of the tension (unlike the directional FCls that do need it), a measure that is inaccessible in shielded cables (customary in underground distribution lines). This fact shows the capacity of the collaborative system of the present invention, thanks to which a fault due to a fault in the internal insulation can be located (in which the return of the fault current is carried out by the mesh), and that solve the current FCI type systems.

Bibliographic references

[1] A. Girgis, C. Fallon, and D. Lubkeman, UA fault localization technique for rural distribution feeders, "Industry Applications, IEEE Transactions on, vol. 29, 1993, pp. 1170-1175.

[2] T. Takagi, Y. Yamakoshi, M. Yamaura, R. Kondow, and T. Matsushima, "Developmenl of a New Type Fault Locator Using the One-Terminal Voltage and Current Data," IEEE Transactions on Power Apparatus and Systems , vol. PAS-101, 1982, p. 2892-2898.

[3] Wenjin Dai, Min Fang, and Lizhen Cui, "Traveling Wave Fault Location System", Intelligent Control and Automation, 2006. WCICA 2006, p. 7449-7452.

[4] E. Rosoxllowski, J. Izykowski, B. Kasztenny, and M.M. Saha, ~ A new distance relaying algorithm based on complex differential equation for symmetrical components, "Electric Power Systems Research, vol. 40, Mar. 1997, pp. 175-180.

[5] J. Mora-Florez, J. Melendez, and G. Carrillo-Caicedo, ~ Comparison of impedance based fault location methods for power distribution systems, "Electric Power Systems Research, vol. 78, Abe. 2008, pp. 657 -666.

[6] R. Salim, M. Resener, A. Filomena, K. Rezende Caino de Oliveira, and A. Bretas, "Extended Fault-Location Formulation for Power Distribution Systems," Power Delivery, IEEE Transactions on, vol. 24, 2009, p. 508-516.

[7] Akyildiz, I.F .; Weilian Su; Sankarasubramaniam, Y .; Cayirci, E. in "A survey on sensor networks," Communications Magazine, IEEE, vol.4D, no.8, pp.1 02-114, 2002.

[8] V.C. Gungor, B.Lu and G.P. Hancke, UOpportunities and Challenges of Wireless Sensor Networks in Smart Grid, "IEEE Trans. Lnd. Electron., Val. S7, n.10, 2010.

[9] M.Erol-Kantarci and H.T. Mouftah, "Wireless multimedia sensor and actor networks tar the next generation power grid, ~ Ad Hoc Networks, val.g, n.4, 2011.

[10] Y_Yang, D.Divan, RG.Harley and T.G.Habetler, ~ Design and implemenlalion of power line sensornet tor overhead transmission lines, "IEEE PES General Meeting, 2009.

[11] I.S.AI-Anbagi, H.T. Mouftah and M. Erol-Kantarci, UDesign of a delay-sensitive WSN for wind generation monitoring in the smart grid, "24th Canadian Conference on Electrical and Computer Engineering (CCECE), 2011.

[12] Y.W.Hong and A.Scaglione, "A scalable synchronization protocol for large scale sensor networks and ils applications," IEEE J. Sel. Areas Commun., Vo1.23, n.S, pp. 1085-1099, 2005.

1131 A.Marco, R.Casas, J.L. Sevillana, V.Coarasa, J.L.Falco and M.S.Obaidat, "Multi-Hop Synchronization at the Application Layer of Wireless and Satellite Networks," IEEE Global Telecommunications Conference, 2008.

[14] D.F.Larios, J.M. Mora-Merchan. E. Personal, J.Barbancho and E. Leon, "Implemenling a Distributed WSN Based on IPv6 for Ambient Monitoring," Int. J. Distrib. Sens. Networks, 2013.

DESCRIPTION OF THE INVENTION The present invention relates to a system and method for locating faults in medium voltage electrical distribution underground lines. Specifically, it presents a system designed as a wireless sensor network with multiple non-embedded current sensors, which allows the detection, classification and location of faults.

The distributed wireless system for the classification and location of faults in an underground electrical distribution network comprises a network of wireless sensors distributed in an underground electrical distribution network. The wireless sensor network is formed by a plurality of sensor devices that constitute the sensor nodes of the network. Each sensor device is magnetically coupled to a conductor of the underground electrical distribution network to be monitored, the sensor devices of the network being distributed so that all sections of conductors between branches have at least one sensor device coupled.

Each sensor device has a wireless communication module for communication with other network sensing devices located within its reach, data processing means and means for measuring the current flowing through the conductor with which it is associated.

The sensor devices are synchronized with each other and configured to, once a fault event is detected, identify the type of fault originated and the point of the underground electrical distribution network where the fault has occurred through the exchange of messages, between the different sensor devices, with information on synchronized current measurements and by analyzing the fasorial information of said synchronized current measurements, taking into account the network topology.

To perform the fault location, the sensor devices are preferably configured to:

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determine the line segment in which the fault is found by comparing the input and output currents of the different segments that make up the underground electrical distribution network,

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classify the type of fault in the affected segment, determining the line or lines of the segment subject to failure and the type of insulation failure produced, and in particular if the fault is caused by a grounding or a loss of insulation in the cable inside;

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estimate the location of the fault within the segment in which the fault occurred taking into account its classification.

The sensor devices are preferably configured to perform the synchronization jointly using the zero-pass detection of the current measurements of the sensor nodes, and taking into account the situation of the sensor nodes within the underground electrical distribution network to be monitored and which The fasarial sum of currents in all nodes is equal to zero.

In a preferred embodiment the sensor devices have a power coil that surrounds the conductor and through which it receives the power supply.

The current measuring means of the sensor devices preferably comprise at least one Rogowski coil.

The sensor devices may be located in distribution network boxes

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underground electricity, in such a way that they allow monitoring all the power flow of the underground electrical distribution network.

The system may additionally comprise a control unit and a gateway with wireless communication capability configured to collect information from the wireless sensor network and transmit it to the control unit.

Another aspect of the present invention relates to a method of classifying and locating faults in an underground electrical distribution network. The procedure includes:

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establishing a wireless sensor network in an underground electrical distribution network, said wireless sensor network being formed by a plurality of sensor devices synchronized with each other and constituting the sensor nodes of the network; where each sensor device is associated with a conductor of the underground electrical distribution network to be monitored, the sensor devices of the network being distributed so that all sections of conductors between branches have at least one sensor device associated;

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measure, by each sensor device, the current flowing through the conductor to which it is associated;

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before the detection of a fault event, identify the type of fault originated and the location of the fault by exchanging messages, between the different sensor devices, with information on the synchronized current measurements and by analyzing the fasorial infonation of said synchronized current measurements, taking into account the network topology.

To achieve the detection and location of faults, in addition to the measurement of the current flowing through the lines, it is necessary that the sensor network provide two basic services: a method of training and routing of messages, and a mechanism of time synchronization that allows to share a global clock between all the devices. Both are classic problems of sensor networks, for which multiple solutions have been proposed [12, 13, 14], but even today it is not a closed line of research, since there are no optimal algorithms for all applications.

In order to synchronize the nodes, the present invention includes a method of global time synchronization using the distributed system of current measurements of the sensor network. Thanks to these distributed measures and through a collaborative method, a global clock can be estimated and calibrated for the sensor network that supports, among other things, the implementation of information routing methods that minimize the consumption of electrical energy.

The new system of location of faults in underground electrical distribution lines is therefore based on the collaborative analysis of the net flows of currents acquired through the use of a network of non-intrusive sensors that communicate wirelessly, forming a network of sensors wireless (WSN). The advantage of this approach with a sensor network is that it does not require any type of module and / or voltage phase information, parameters not accessible without drilling in the shielded cables usually present in the underground power distribution lines. The system only requires the current measurements acquired directly by the nodes, which, when exchanging information, are capable of detecting, classifying and locating faults, both in traditional distribution systems (with unidirectional current flows), and in systems with generation distributed, where the power flow can change direction. This is another advantage and innovation of the present method and system with respect to its predecessors.

As an additional advantage, no other system is required for the extraction of information from the network, that is, the system takes advantage of its own wireless communication structure, to inform the control center (on demand) of the different parameters of the network. However, the use of this technology has forced different aspects of the routing and synchronization of communications to be adapted to the characteristics of the

problem to solve. In the present invention, techniques based on the use of

implicit information to the electricity network itself to be monitored to obtain the route tables and time synchronization, which is a novel approach compared to the existing systems in the literature, which basically use only information obtained from the message exchange

The method of the present invention therefore allows the monitoring of a medium voltage underground electrical network by means of the use of a wireless sensor network that, with a non-intrusive procedure, allows the measurement of the currents that circulate through the network to be monitored. Using these measures of current and the exchange of messages, the network is able to monitor the status of the lines, as well as classify and locate the possible failures that may occur in them.

The system is made up of a deployment of sensor nodes, distributed in such a way that it is necessary to ensure that all sections of cables between branches have at least one current meter attached. The communications structure is automatically formed by exchanging messages, based on prior knowledge of the structure of the electricity grid.

The synchronization method of the sensor nodes takes advantage of the previous knowledge of the topology of the electrical network and the situation of the sensor nodes to synchronize, with high precision, a common global clock between all the nodes of the monitoring network. This time synchronization is necessary to be able to detect and locate possible faults or defects that may occur on the monitored underground power grid. To perform the synchronization, the system uses the knowledge that the phasor sum of the currents in all nodes is equal to zero. From this and assuming, in a first approximation, that the time lag in the reception of the messages is negligible among all the nodes of the fork, a mathematical model is established that uses the zero crossings of the current signal to calibrate, with high precision, the clocks of each of the nodes. The complete synchronization method is described in detail later.

The method for the classification and location of faults in underground electrical distribution lines allows to locate the fault once it has been detected (by means of the protection relay, located at the head of the line), based on the analysis of the phasor current information recorded by the different sensor nodes and

known the topology of the distribution network, including the location of each node within

the same. The location method based on this information is structured in three phases: determination of the line section between two transformation centers where the fault is found, classification of the type of fault and, finally, the estimation of the specific point of that section, in which the fault originated. The knowledge of this position allows the isolation of the fault and the restoration of the electricity supply to be carried out more quickly and accurately, considerably improving the continuity of the supply.

BRIEF DESCRIPTION OF THE DRAWINGS Next, a series of drawings that help to better understand the invention and that expressly relate to an embodiment of said invention that is presented as a non-limiting example thereof is described very briefly.

Figure 1 represents the general structure of a wireless sensor network.

Figure 2 shows the connection of a sensor node to the conductor to be monitored.

Figure 3 shows the internal structure of a sensor node.

Figure 4 shows the structure of a sensor network for monitoring the underground electrical network, where each cabinet can have one or more sensor nodes.

Figures 5A, 5B and 5C represent a model of the simple underground distribution network on which a deployment of nodes in the different boxes has been made. Figure 5C is a continuation of Figure 5B and this in turn is a continuation of Figure 5A.

DETAILED DESCRIPTION OF THE INVENTION The method and system of the present invention are based on the deployment of a wireless sensor network that allows the detection, classification and location of anomalies in underground electrical distribution lines.

Figure 1 shows a network of wireless sensors 2 distributed in an underground electrical distribution network 1 and formed by a plurality of low consumption sensor devices 3 (or sensor nodes), with wireless communication capability between them and collaborating to analyze a common phenomenon. The wireless sensor network 2 communicates with a control center 4, formed by a gateway 5 with

wireless capability (in communication with the sensor devices 3) and connected to a control unit 6 (e.g. a computer).

Each sensor device 3 of the network, also called sensor node, is designed to operate autonomously by acquiring its energy directly from the line, from a non-intrusive connection with it, since the device only has to be coupled around the conductor of the distribution network, without the need to drill or section it, as shown in Figure 2, which represents the way of connecting a sensor device 3 to the conductor 7 to be monitored.

Figure 3 shows the internal structure of the sensor devices 3. Each of these nodes is formed by a wireless communication module (i.e. a radio transceiver 30) that allows communication within the underground pipeline itself with other sensor devices 3; data processing means (for example, a microcontroller 31) that processes the information, a power supply 32 and an input-output subsystem 33, responsible for monitoring the environment through the different measurement systems that compose it. among them a current measurement module 34 that circulates through the conductor 7 of the distribution network, and an I / O interface for other sensors 35 useful for the distribution company (such as temperature sensor, humidity sensor, light intensity sensor, vibration sensor, sound sensor, etc.), which would provide more information about the environment or the working conditions of the installation. Thus, the sensor device 3 of the invention has the ability to integrate additional sensors for monitoring the installation, which allow the use of the communication infrastructure to provide additional information to the company that owns the installation. The sensor devices 3 are designed to, apart from being economical, allow rapid network deployment. Fundamentally the device network executes the following methods:

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Method for the calibration of the global clock of the system by means of a hybrid algorithm based on wireless communications and fasorial estimates of the currents that circulate through the conductors of the underground electrical network to be monitored.

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Collaborative method for the classification of faults in power lines based on the exchange of messages with the information of the net charge flows between the different nodes that form the electricity distribution network.

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Collaborative method for locating the rat on power lines based on the exchange of messages with the information with the synchronized current measurements of the nodes, and on the previous classification of the fault. This location allows to drastically reduce the number of maneuvers and the time of interruption of the service in the network, facilitating maintenance tasks (operators know exactly where they should perform repairs).

The following describes in detail the different devices that are part of the invention, and the functionality of said devices that allow the analysis of faults in the underground distribution lines, as well as the proper functioning of the communications between the devices.

The present invention raises a system whose development is deployed over a network of wireless sensors. The network is formed by a series of devices, called nodes, that are responsible for interacting with each other, so that through their interaction they allow monitoring of their environment. In the present invention the following components are distinguished:

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Control unit 6: It is an element, usually located in the control center 4, with which the user interacts and allows him to retrieve the information of the sensor nodes regarding the state of the underground electrical distribution network under analysis, indicating, in In the event of a breakdown, the section in which it has occurred and its location within it, thus making it easier for operators to insulate and repair the fault. In addition, it is responsible for storing the corresponding records of the detected fault records.

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Gateway 5: This element is a node that on the one hand allows communication with the control unit 6 through a standard port and on the other it integrates a radio transceiver compatible with that used in the other devices that make up the network. This device is responsible for redirecting operator inquiries through the wireless sensor network 2. Thanks to this device, the control unit 6 can collect information on the operating status of the underground electrical distribution network 1, as well as the internal status (remaining battery, error rate, etc ...) of each of the sensor devices 3. In addition, the gateway 5 is also responsible for making the necessary steps to ensure that the route tables of all the routes are kept updated network nodes, so that access is guaranteed through adequate retransmission using intermediate nodes to any element of the network.

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Sensor devices 3 or nodes: It is understood by sensor nodes, or simply nodes, the series of sensor devices 3 of low consumption and low cost that allow to interact with each other through the use of wireless communications and that allow monitoring a localized part of the problem solve, so that through their interaction you can find the global solution of the problem. The nodes proposed for the present invention consist of the following elements or subsystems (see Figure 3):

o Wireless communications subsystem: It will be composed of a low consumption radio transceiver 30. The frequency of the carrier signal will be chosen based on the network topology, seeking a minimization of transmission losses. Since the pipes that interconnect the boxes are surrounded by a plane of mass it can be assumed that for certain frequencies this channel will act as a waveguide, allowing a large range with low losses. These frequencies, together with an appropriate modulation, will be the one chosen for communications between all the elements that make up the network.

o Power subsystem: The sensor devices 3 receive the energy for proper operation through a power coil 36 (Figure 2) that surrounds the conductor 7, by means of which all circuits can be fed, together with suitable electronics. sensor electronics, including the radio transceiver, without the need to cut or puncture the insulation of the cable to which it is associated. Thanks to this, a very fast and non-intrusive deployment can be achieved, which does not damage the characteristics of the distribution network to be monitored.

In addition to the energy collection system, the power system consists of a backup energy storage system, such as a battery or a high capacity capacitor that will allow these devices to continue functioning after the appearance of a fault in the distribution network, situation in which there is no longer energy flow through the conductor and, therefore, the node could not be fed through the supply coil 36.

o I / O Subsystem 33; It allows the monitoring of the environment through the different measurement systems that compose it. In this case the most important magnitude is

the current through conductor 7 of the distribution network, measured through a current measurement sensor, preferably one or several Rogowski coils 37 (Figure 2), whose behavior is defined by:

or

;,,,,," (eleven )

Where n is the number of turns, To the area of the toroid section formed by the

coil and ~ o, vacuum permeability (4 "TT" 10- (V · s) / (A-m »

Thus, each coil allows the estimation of the current flowing through a conductor. Depending on the characteristics of the installation, nodes are provided with up to a maximum of one coil per conductor, typically three in conventional three-phase installations. However, for those installations whose topology requires it, the present invention can also be developed considering nodes with a single coil, so that several are installed per cassette, thus achieving greater redundancy in communications and, therefore, greater reliability of them.

o Processing subsystem: Preferably implemented by means of a microcontroller 31, it is responsible for the management of communications and the processing of the information necessary for the realization of the different methods or procedures described below. In addition, it is responsible for the aggregations of data necessary to minimize the use of the wireless communications channel, thereby increasing the reliability of the system.

In order to obtain the correct functioning of the system, the deployment of the sensor network is carried out within the boxes of the underground distribution lines to be monitored, preferably complying with the following premises:

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Both the power elements and the sensors are wrapped around the conductors 7 to be monitored (Figure 2), with no action required on it (eg, perforation or cutting of its insulator).

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A current measurement sensor is placed for each of the lines that cross the box 8. Thus, for example, in a three-phase system it is necessary to place three current sensors. Depending on the type of nodes used, this may require the installation of one or more nodes per cabinet.

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Sensor devices 3 are placed in all those boxes 8 (see Figure 4, which represents a structure of a sensor network) of the underground electrical distribution network 1 to be monitored that meet the following premises:

• When the separation between the box 8 with sensors before and after

the current box 8 exceeds the maximum coverage distance of the wireless communication system.

• When a fork of drivers occurs. In this case, sensor devices 3 must be placed at the exit of each fork although the coverage conditions do not require it. For example, in the case that a three-phase line is separated into two branches SO six sensor elements are necessary, three for each branch, placing one in each of the phases of the three-phase line.

To carry out the monitoring of a medium voltage underground electrical distribution network, it is necessary to know in advance the situation of the nodes and the topology of the electrical network to be monitored. Based on this information, the devices that make up the invention implement the following methods to monitor the power grid:

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Method for the formation of the network and its routes: The algorithm for network formation is based on a flood algorithm, which will begin on the bridge device of the gateway 5, generating a series of beacons that will be relayed to all nodes in order to obtain the number of minimum jumps for communication between all nodes. This process is called wireless network discovery, executing the following procedure:

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A given node, either at the request of the information system or because it takes a long time without exchanging information with other nodes, sends a message in redcast that will be received by a series of nodes, informing of its battery level.

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A series of nodes receive this message. These nodes are called neighboring nodes of the sender. With this information the nodes update their local route table, with which they determine the number of hops between the node that originated the message and the bridge or gateway device 5.

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Based on this information and assuming the physical topology of the electricity network to be monitored, the global map of routes to be used by the network is calculated by using a minimum weight overlay tree algorithm designed for wireless sensor networks. The weight of the covering tree takes into account various parameters, such as the topology of the electrical network to be monitored, the battery level of the nodes or the physical distance between sensor nodes to determine the optimal communication paths.

Cyclically, depending on the internal changes that occur in the nodes, the information system is responsible for updating these routes in case there are not enough communications in the network to keep the route tables updated,

maximizing network functionality and overall battery life.

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Time synchronization method: To correlate the information associated with different measurement points collected by different nodes, a time synchronization between them is necessary. For this, a method is used that combines the detection of zero steps of the current measurement, together with the sending of beacons and the prior knowledge of the status of the sensor nodes within the electrical distribution network to be monitored. The method implemented is as follows:

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The nodes are continuously measuring the current of the cable or cables to which they are associated. From the shape of the measured wave, each node calculates from a internal global clock a timestamp in which the positive crossing of the wave is zero-crossed. That is, the nodes are continuously measuring the current and processing it so that they always have in memory the magnitude and phase of the current, referred to their internal clock.

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If a request for synchronization of the information system occurs, or if a longer time has elapsed to Synchronized for synchronization, a node sends a synchronization message to the child nodes (those hierarchically

lower in the architecture of the electricity distribution network) and considers as synchronization time its last crossing through the zero of positive slope detected.

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Due to the lags and the operation of the radio transceivers, the broadcast time is unknown, but it can be assumed, due to the transmission speed of the communications via radio, that all the child nodes will receive the message in the Same instant of time.

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Each of the child nodes considers at this point the reception time as the origin of synchronization time, and they send to the parent node (that hierarchically superior in the architecture of the electricity distribution network, and which has originated the synchronization process) a message with the current module and the time lag between its last zero crossing of positive slope and the reception time of the synchronization message.

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The parent node, after receiving the information from all its child nodes, fasorially adds the current magnitudes of all these and determines the phase resulting from the aggregation. With this information, the error introduced due to the unknown time of receipt of the message is estimated from the time lag between the aggregate phase and the phase considered as time source.

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Once that phase is measured, the parent node sends a message in redcast to the child nodes informing of the overall time in which the reception of the message originated.

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Each of the child nodes uses that information to calibrate their internal global clock.

With this algorithm, a high-precision time synchronization can be ensured, taking advantage of the fact that the architecture of the electricity distribution network is known and that the time difference in the reception by the child nodes of a message spread by the parent node is negligible.

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Method for the classification and location of faults in underground electrical distribution lines: Once a fault event has originated, it is analyzed by means of

.

Analysis of the fasorial information recorded by the different nodes and known the topology of the network identifies what type of fault has originated and it is estimated at which point of the network this has occurred. As an example, Figure 5 (which due to its extension has been subdivided into Figure 5A -which includes the substation and the first and second segment-, Figure 58 -which includes an intermediate segment f and Figure is -which includes the last segment z-) represents a simple underground electrical distribution network 1, without bifurcations, in which the deployment of the sensor network has been carried out in the different boxes 8. The underground electrical distribution network 1 shown in Figures SA, 5B And 5e comprises a substation 9, a plurality of segments 10 (one segment is the section of power line that separates two transformation centers 11) with their respective transformation centers 11. In the segment f a fault is located. The location is carried out collaboratively by all the nodes of the network, while the classification is carried out by the nodes that are right in front of the transformation centers. The procedure implemented is divided into the following phases:

• Determination of the segment in which the fault originated, segment f.

This first stage consists in comparing the input currents of segment f with the output currents of segment f. The input current of segment f is calculated from the current data measured by the sensor devices 3 of the segment immediately before the transformation center {-1, segment {-1, and the own consumption of the transformation center {-1 . The output currents of the segment {is calculated from the current input values of each of the transformation centers that hang from that line section, including the transformation center itself f. Additionally, another way to calculate the output currents of segment f would be through the consumption recorded by the nodes of the next segment f + 1, adding the current that is derived from the transformation center f. Thus, if the difference between this input and output current to segment f exceeds a threshold, the detection of the fault in segment i is considered as defined in the following equation:

I (lsm.> :( f-I) -1 <'"7".> :( f_I)) - (I sr, N.> :( f + l) + I (T.>: F) 1

"" {Missing detected in

OR

> threshold (2)

segment f

(!. 'I · /; N.> :( f -1) -lel ".. (f-1)) -: 2 .: lel" .. (j)

'Vx = a, b, c

of

Where I SENxU-l) -ICTxU-l) is the current entering segment f,

(ISENX (f + l) + ICTxf) or IJCTX (j) are two different ways of calculating the current

} = f

leaving the segment f; where x is the concrete line being analyzed, ISEN K (I

5 1) is the current measured by any of the sensor nodes of the segment (f-1) of the line x, ISEN) ({f + l) is the current measured by any of the sensor nodes of the segment (f + 1) for line x, leT) (1-1) is the current measured at the transformation center (f-1) for line x, and finally j takes all the values from f to z, to add in the summation all the streams derived by the centers

10 of transformation hanging from segment f. This analysis is carried out for each of the phases (A, B and e) independently, to know the existence of a fault.

• Once segment 10 is determined to be missing (segment f in Figure 58)

15, based on the input and output data of the segment, the type of fault can be classified according to the lines (phases A, B, e) affected and the type of fault that has occurred in the insulation. This analysis is divided into two parts:

Q

Determination of missing lines: this overcurrent analysis

20 allows to determine that line x is subject to failure. From the evaluation of (3) on the different lines, we can determine simple typologies (a single affected line), double (two affected lines) or triple typologies (the three affected lines) of the fault.

11SFNx (f _1) -I! "" I "X (f -1) 1> threshold)

Missing on the

o =:> (3)

{line x

1 ('· HN.l "(f + 1) + I (" r.l "m l> threshold

o Determination of the type of insulation fault: In this phase it is distinguished whether the fault is caused by a grounding, originated at the same point of the fault, or on the contrary is due to a loss of insulation inside the cable and returning the current through the

30 mesh Based on Figure 58, Ix (represents the current that would circulate

by the conductor of the line x cable, in the segments of segment f before the

missing point. ISx1 represents the current that would circulate through the wire mesh of line x, in the segments of segment f before the point of failure, IFx represents the fault current in line x (null if the fault is internally insulated), e ILsx represents the current that is derived from the conductor of the line x to its mesh. Similarly, l'xI and I'sxl represent the currents that would clrculate through the conductor and the wire mesh of the line x, in the segments of segment f after the point of failure. This analysis can be done through the collaborative analysis of the sensors of the affected segment f. If the return of the current is through the mesh, all these sensors have to measure approximately the same (equation 4),

(I, f + I ",,) - (I; f + I; 'f) ~ I, ~ O} 1SEN x (f, y) -l! Tf + 1 Sxf ~ 11SD (~ {f, Y) -ISEN ~ (f, y ') 1 <threshold (4) ISEN ~ {f, y') = 1 '1tf + l'SJt.f

In equation (4) I.'IIiNX (f, y) represents any of the currents measured by the sensing devices 3 located in the segments f segment, prior to the point of lack of line x, and I. "¡; NX (f, y ') represents any of

the currents measured by the sensor devices 3 located in the segments f segment, after the point of lack of the line x. Therefore, if this condition defined in (4) is met for all sensors in segment f, it is determined that the fault is due to a failure in the internal insulation, otherwise, it is determined that the fault is due to a direct derivation grounded at the point of failure.

• Once the segment under fault is determined and its type determined, the next step is to estimate the point at which the fault is within the segment. In this respect, two important variants are distinguished:

o Insulation fault with grounding at the point of failure (negative case of the condition defined in equation 4): In this circumstance the determination of the section under fault is reduced to be evaluating the current measurement of each node, in each arc of segment f, with the measurement recorded by the next node. For an x line, when there is a difference between these two currents greater than a threshold (equation 5),

can clearly determine that the fault is among the subsegment

defined between those nodes i and i + 1.

Missing detected in the subsegment (~ 'JiNx fi -ISHNx fi + l> threshold :::::>... (5)

I (.) I

(.) defined between boxes 1 and 1+ 1

o Insulation fault without grounding at the point of failure (return of current through the mesh, affirmative of the condition defined in equation 4): In this circumstance the segment sensors do not detect the ILsx current (current that it is derived from the conductor of the line x to its

10 mesh) caused by the fault (equation 6), because the net current flow is zero. For this alternative, the use of a method based on the calculation of the resistance of the anterior (p · RSh) and posterior ((1-p) -RSh) mesh to the point of failure (equation 7), where RSh represents the total resistance of the mesh in the segment of segment r, ISxf and I'sxf represent the 15 currents that would circulate through the mesh of the line x cable in the segments of segment f anterior (1M) and posterior (I'sxf) to the point of failure, respectively,

Vfx represents the tension (referred to mass) that appears in the mesh at the point of failure, on the line x. Finally, to determine the normalized position Mp "of the fault within segment f (equation 8).

I.o; .rf =!. "'/ INx (f, y) - (!.,' /: NX (f-l) + I CrX (f _l»)} (6)

!. ~ f = 1,% 'N, «f, y') - (1." HNX (f-l-l) -ICJ'X (f-l-l »)

Vf --p'R '/}

X -ShSxf RI. l RI '

Vf = (1-) K.¡ '. =: '-p'. ~ '~, = (-p} ",'.", (7)

x P .v, Sxf

(8)

This planning is not only valid for simple topologies (for example, that of Figure 5), it is also extensible to distribution lines that have bifurcations. In these more complex topologies it would only be necessary

add to the described approach the equations derived from these electrical knots.

Thanks to the use of all these methods or functionalities, the monitoring network 5 can easily determine the operating status of the underground electricity network.

Claims (11)

1. Distributed wireless system for the classification and location of faults in an underground electrical distribution network, characterized in that it comprises a network of wireless sensors (2) distributed in an underground electrical distribution network (1), said wireless sensor network ( 2) being formed by a plurality of sensor devices (3) that constitute the sensor nodes of the network; where each sensor device (3) is coupled to a conductor (7) of the underground electrical distribution network (1) to be monitored, the sensor devices (3) of the network being distributed so that all sections of conductors between branches have connected at least one sensor device (3), each sensor device (3) having: • a wireless communication module (30) for communication with other sensor devices (3) of the network located within its range;

•

data processing means (31);

•

means for measuring the current (34) that circulates through the conductor (7) to the

that is coupled; the sensor devices (3) being synchronized with each other and configured to, once a fault event is detected, identify the type of fault originated and the point of the underground electrical distribution network (1) where the fault occurred through the exchange of messages, between the different sensor devices (3), with information on the synchronized current measurements and by analyzing the fasorial information of said synchronized current measurements, taking into account the network topology 2. System according to claim 1, characterized in that to perform the fault location the sensor devices (3) are configured to:

-

determine the line segment (10) in which the fault is found by comparing the input and output currents of the different segments that make up the underground electrical distribution network (1),

-

classify the type of fault in the affected segment, determining the line or lines of the segment (10) subject to the fault and the type of insulation failure produced, and in particular if the fault is caused by a grounding or a loss of insulation inside the cable;

-

estimate the location of the fault within the segment (10) in which the fault occurred taking into account its classification.

3.

System according to any of the preceding claims, characterized in that the sensor devices (3) are configured to perform the joint synchronization using the zero-pass detection of the current measurements of the sensor nodes, and taking into account the location of the nodes sensors within the underground electrical distribution network (1) to be monitored and that the sum of charges of currents in all nodes is equal to zero.

Four.

System according to any of the preceding claims, characterized in that the sensor devices (3) have a supply coil (36) that surrounds the conductor (7) and through which it receives the power supply.

5.

System according to any of the preceding claims, characterized in that the current measuring means (34) of the sensor devices (3) comprise at least one Rogowski coil (37).

6.

System according to any of the preceding claims, characterized in that the

Sensor devices (3) are located in boxes (8) of the underground electrical distribution network (1), in such a way that they allow monitoring the entire power flow of the underground electrical distribution network (1).

7.

System according to any of the preceding claims, characterized in that it further comprises a control unit (6) and a gateway (5) with wireless communication capability configured to collect information from the wireless sensor network (2) and transmit it to the control unit. control (6).

8.

Classification and fault location procedure in an underground electrical distribution network, characterized in that it comprises:

-

establishing a wireless sensor network (2) in an underground electrical distribution network (1), said wireless sensor network (2) being formed by a plurality of sensor devices (3) synchronized with each other and constituting the sensor nodes of the net; where each sensor device (3) is coupled to a conductor (7) of the underground electrical distribution network (1) to be monitored, the sensor devices (3) of the network being distributed so that all sections of conductors between branches have associated at least one sensor device (3);

-

measure, by each sensor device (3), the current flowing through the conductor (7) to which it is associated;

-

before the detection of a fault event, identify the type of fault caused and the location of the fault by exchanging messages, between the different sensor devices (3), with information on the synchronized current measurements and by analyzing the tax information of said synchronized current measurements, taking into account the network topology.

9. Method according to claim 8, characterized in that the location of the fault comprises:

-

determine the line segment (10) in which the fault is found by comparing the input and output currents of the different segments that make up the underground electrical distribution network (1),

-

classify the type of fault in the affected segment, determining the line or lines of the segment (10) subject to the fault and the type of insulation fault produced, and in particular if the fault is caused by a grounding or a loss of insulation inside the cable;

-

estimate the location of the fault within the segment (10) in which the fault occurred taking into account its classification.

10.

Method according to any of claims 8 to 9, characterized in that the sensor devices perform the joint synchronization using the zero-pass detection of the current measurements of the sensor nodes, taking into account the situation of the sensor nodes within the network of underground electrical distribution (1) to be monitored and that the rasorial sum of currents in all nodes is equal to zero.

eleven.

Method according to any one of claims 8 to 10, characterized in that the sensor devices (3) are arranged in boxes (8) of the underground electrical distribution network (1), in such a way that they allow monitoring the entire power flow of the underground electrical distribution network (1).