Distribution automation (DA), a system that enables an electric utility to monitor, coordinate and operate distribution components in real time from remote locations, first emerged in the 1980s. Nowadays, DA plays a significant role in power distribution network operation and power quality. New distribution equipment such as reclosers and feeder switches are designed and manufactured with DA support using a variety of protocols and standards for remote monitoring and control.
However, many utilities still have large populations of pre-1980 equipment in operation without automation facilities as it is not cost-effective to replace this equipment and provide the necessary communications infrastructure. The majority of distribution utilities defer the large investment in wide-scale automation until their time-expired equipment fails in service and is replaced by units designed with automation capability.
Fault indicators are just one of many distribution network components installed for fault detection on the 20-kV overhead line circuits on the Mashhad Electric Energy Distribution Co. (MEEDC) network in Iran. In the event of a fault, field crews are dispatched to locate the fault by visual inspection, disconnect the faulted section and prepare the network for repair. This time-consuming activity has a major impact on network-reliability statistics in terms of the length of customer interruptions.
MEEDC examined the performance of its fault indicators and saw the need for improvement. The utility designed and developed in-house a cost-effective, reliable and remote monitoring system to extend the operational life of fault indicators installed on its distribution network.
Fault Indicator Communications Protocols
The design of MEEDC's fault indicators typically employs power-line carrier and fixed radio-frequency networks, but both communications systems have disadvantages. With power-line carrier, there is a lack of conformity with local distribution networks and the possibility of losing information. Establishment of a radio-frequency network requires having many different elements like collector towers and repeaters, which increases the total investment.
The majority of MEEDC's fault indicators are old and unable to support automation, but, conversely, the utility realizes the importance of fault indicator automation and network monitoring to create a more reliable distribution network. To address the need for improved reliability, MEEDC established a research and development (R&D) pilot project to design a reliable and remote monitoring system for its old fault indicators.
MEEDC has installed different types and models of fault indicators, with different features and specifications, on its distribution network during the last 20 years. CableTroll 2500 from the NorTroll Co. is just one of the types installed. These units have the ability to remotely monitor and control using several existing terminals as a digital input and output, which is why they were chosen for the fault locating system to be developed. In addition to light-emitting diodes and an optional Xenon flash unit, the CableTroll 2500 has a pair of relay contacts (120 V dc/1 A) that give a 1-sec pulse as soon as a fault is sensed, and the interface module only needs to check the status of this contact to detect a fault occurrence.
Fault Location Automation
The piloted fault locating system has a graphical user interface to show the position of the fault location on a screen in the control center. Furthermore, it is able to send a text message to a predefined mobile phone number to inform the user of the fault occurrence on the network. MEEDC takes advantage of the global system for mobile/general packet radio service (GSM/GPRS) communications standard, which is a high-speed data-handling technique. By using GPRS, it is possible to send information to users in a packet form. It has many other advantages that emphasize its usage value, including vast coverage, improved data transmission quality, low running costs and fast switching times.
In the piloted system, each fault indicator uses the GSM/GPRS communications standard to connect to the server. Each fault indicator has a unique Internet protocol (IP) address, which also is used as a unique identity (ID) that is able to send the time and date of a fault to the server. Since the aim of this project was to add monitoring ability to past-generation fault indicators installed on the MEEDC network, the design had to keep to as few configuration changes as possible and have a relatively simple installation procedure.
The piloted system has two different parts, including hardware and software. The hardware comprises a contact relay circuit using an Atmel ATmega32 microcontroller and a GSM/GPRS module. When a fault occurs on the network, the relay output contact changes its mode for 1 sec. The microcontroller-based circuit acts as an interface between the fault indicator, and the GSM/GPRS module detects this change in the output mode as a 1-sec pulse and then sends one data packet, including the fault indicator IP address, time and date of the fault, to the server. The system continues sending the packet until it receives an acknowledgement from the server, when it then reverts to a waiting mode to observe the next pulse from the relay. It also sends a short message service (SMS) with the fault location and time information of the fault to a set of predefined mobile phone numbers.
The software designed for the server includes two main parts. The first is responsible to receive and store data sent from the GPRS, and the second is responsible for showing the data on the screen and providing a report on the on-line fault indicators. Designed to be compatible with Esri's ArcGIS software standard, the software updates its map through the computer network. It also works cooperatively with other software used by MEEDC.
There also are several tools in the software for reporting and performing basic statistical operations. The screen presentation shows all the fault indicators in yellow when in normal mode, but in the event of a fault on the network, the data packet that includes a unique code, the time and the date of the fault is sent to the server through the GPRS module, and immediately the yellow on the screen starts to blink red.
In 2010, MEEDC recorded 587 faults sensed by fault indicators on its 20-kV overhead lines. The maximum restoration time in 2010 was 191 minutes, with the overall average being 60 minutes. Whether a fault occurred during or outside of traffic rush hours had a marked influence on the restoration time. In general, two-thirds of the restoration time was spent patrolling lines to locate a fault; having a central fault locator system would immediately reduce this wasted time.
The GPRS-based fault locator system developed was installed on MEEDC's 20-kV overhead lines in the city of Mashhad. Reports from the field crews and staff in the control center monitoring the network confirmed the average time to locate and repair a fault on the network was reduced from 60 minutes to 20 minutes. The benefit of using this system for locating a fault instead of through visual inspection, especially in areas with a dense population and heavy traffic, was significant. In addition to reducing the fault location time and, consequently, the fault outage time, the traveling time and number of vehicles associated with line patrols were reduced, thereby reducing fuel consumption and its destructive environmental effects.
The design and implementation of the GPRS-based fault locator system was undertaken by MEEDC's R&D center for a pilot region. The zone 8 region network had 20 old fault indicators in circuit and each was suitably equipped with an interface module. After a period of six months, feedback was received from the managers and field crews responsible for this region. The result showed using this system had a significant influence on reducing restoration times; furthermore, it reduced the non-distributed electric energy supplied, an important factor in view of the impact on MEEDC's profit.
Encouragement by Success
The success of this pilot project encouraged MEEDC to implement this system for all fault indicators on the network. However, since MEEDC is not an electronic devices manufacturer, the utility signed a contract with SAMA Sanat Toos for the development and upgrading of a commercial fault locator product using the experience gained during the pilot research project.
This fault locator system has been implemented by connecting a small GSM/GPRS interface module to the old generation of fault indicators and installing software in MEEDC's automation servers. It has proved to be an inexpensive method, compared with the alternative of substantial capital investment in new distribution equipment with automation features. This cost-effective solution now provides a fast response to fault detection that has significantly improved the reliability of MEEDC's distribution network.
Mohsen Zabihi ([email protected]) is vice president of Mashhad Electric Energy Distribution Co. and serves as the deputy supervisor for planning and operations and as a member of the R&D committee. Zabihi is the author and co-author of two books and several technical papers. He holds a BSEE degree from Ferdowsi University in Mashhad, Iran.
Naser Nakhodchi ([email protected]) is a senior engineer at Mashhad Electric Energy Distribution Co.'s R&D center, whose research interests include control and automation of electricity distribution networks and related electronic devices. Nakhodchi has a BSEE degree in branch control from Ferdowsi University in Mashhad, Iran, and a master's degree in industrial information from Skovde University in Sweden.
Saeed Alishahi ([email protected]) is the manager of Mashhad Electric Energy Distribution Co.'s R&D center as well as a member of the utility's R&D committee. In addition to being responsible for all research projects and activities in MEEDC, he also is the author of more than 50 international and national papers and articles in the field of electricity distribution. Alishahi holds a BSEE degree.
Mohammad Hossein Yaghmaee ([email protected]) is an associate professor at Ferdowsi University in Mashhad, Iran, and a research consultant at Mashhad Electric Energy Distribution Co. He holds a bachelor's degree in communications engineering from Sharif University of Technology in Tehran, Iran, a master's degree in communication engineering from Tehran Polytechnic (Amirkabir) University of Technology and a Ph.D. in communications engineering from Tehran Polytechnic University of Technology. Yaghmaee has published more than 120 international conference and journal papers, and his research interests are in communications networks and Internet engineering.
Atmel | www.atmel.com
Esri | www.esri.com
NorTroll | www.nortroll.no
SAMA Sanat Toos | www.sama-eg.com