With the rapid development of information technology (IT), utilities in developed countries are facing an increased customer demand for improvements in the quality and reliability of power supply. Until recently, Japanese utilities provided exclusive retail service for the customers in their respective service areas. A retail electricity market, introduced in March 2000, gave customers with more than 2 MW contracted capacity and connected to systems above 20 kV the freedom to select service providers other than conventional utility companies. Therefore, it is crucial that utilities realize both advanced customer service and competitive electricity price. Kansai Electric Power Co. Inc. (Kansai EP) supplies power to more than 12 million customers in the major Japanese cities of Kyoto, Nara and Osaka as well as the beautiful harbor city of Kobe. Kansai EP energy sales are the second highest in Japan — 17% of the nation's total — with a service area of only 8% of the national land area (Fig. 1).

Over the past 40 years, Kansai EP continuously invested in new technology to upgrade its distribution system to improve system reliability. Following from a conventional Distribution Automation System (DAS), the Advanced Distribution Automation System (ADAS) employs the latest IT to further improve customer services.

Generation Capacity	37,800 MW
Energy Sales	140,403 GWh
Number of customers	12,630,000
System peak demand	32,230 MW
Number of employees	26,248
	(As of March 2000)

Distribution Network Design

In the mid-1970s, Kansai EP introduced a time-sequential reclosing system for pole-mounted vacuum switchgears to reduce the duration of circuit interruptions. This consists of automated sectionalizing switchgear equipped with remote terminal units (RTUs). The system enables isolation of the faulted section of the network, allowing restoration of customers connected to sound sections in minimum time by a combination of automatic circuit reclosure at the source substation and lockout operation at each switchgear (Fig. 2).

This reclosing initiative significantly improved the reliability of power supply, reducing the Kansai EP SAIDI (System Average Interruption Duration Index) from 60 minutes to nearly five minutes (Fig. 3). For those customers affected by the fault, it was necessary for system operators to find the best process of power restoration, including on-site manual switching. This system does not require any communication facilities, thus it can be operated locally with less initial investment than a system remotely controlled via communication lines. As a result, it exhibited competitive cost benefit during the transition period before Kansai EP introduced a DAS.

The Kansai EP typical overhead distribution system designs are a radial configuration with interconnections to adjacent primary feeders through normally open tie switches. The underground distribution cables placed in conduits facilitate quick power restoration. Pad-mounted multicircuit switchgears minimize power-interrupted sections.

The Kansai EP distribution network comprises major primary feeders designed as a 6.6-kV three-phase three-wire ungrounded delta system. This is supported by the later introduction of 22- and 33-kV feeders to meet increasing power demands with improved levels of reliability and higher quality of supply standards.

Kansai EP undertook measures to improve distribution-system reliability. It began in the 1960s by replacing bare overhead conductors with insulated conductors. This action secured public safety and avoided power interruptions caused by trees. By the mid-1980s, Kansai EP completed this replacement program.

In the Kansai EP service territory, lightning is one of the most critical causes of faults. To restrict power interruptions caused by lightning, the standard installation now required arresters and shield wires. Previously, arresters and shield wires installations occurred on those circuits subject to frequent lightning storms based on the isokeraunic level.

To minimize the number of faults in underground cables, Kansai EP took a look at specific manufacturing techniques. For example, to prevent water tree failures, the company now only uses XLPE-insulated cables manufactured with three different insulation layers molded simultaneously (instead of individually formed layers).

Failures of customer's equipment directly connected to primary distribution feeders cause distribution system faults. Kansai EP recommends customers install pole-mounted air switches with a ground- or earth-fault relay at the connection point with the distribution system. The company offers consultation services to minimize faults attributable to customers' equipment.

Distribution Automation System

DAS makes it possible to remotely operate the distribution system by monitoring and controlling automated sectionalizing switchgear, and by observing the status of equipment at distribution substations. It automatically executes system operations such as automatic power transfer to distribution circuits outside the area affected by the faulted section. It comprises a central processing unit (CPU) at a customer service office, slave units at substations, automated sectionalizing switchgear and the RTUs. The CPU in the customer service office holds the system surveillance information and executes calculations to remotely control the system. Slave units at a substation and pole-mounted switches transmit data to the CPU.

Need for DAS Upgrade

To operate the distribution system with a higher utilization factor, it is necessary to upgrade the functions related to automatic power restoration of DAS in the event of a fault. Kansai EP introduced advanced IT to develop a more efficient system at a lower cost. The system is interconnected with a broad computer network, both inside and outside customer service offices, to construct a distributed data-processing system with open specifications.

Originally, DAS and the business computerization system (One Stop Service [OSS] system) were developed as independent system configurations. Now ADAS is interconnected with OSS to integrate data management. This makes it possible to save data maintenance works and to provide customers with real-time power-outage information through OSS.

ADAS helped Kansai EP secure a competitive edge for the liberalization of the retail power market. Because of the system interconnection with the distribution substations control system Kansai EP restores power supply quickly in case of a transmission system fault while streamlining the power-system operation process.

Configuration of ADAS

The previous DAS used a centralized processing system that included a dedicated mini-computer system. To introduce ADAS, Kansai replaced the CPU at the customer service office with a distributed data-processing system. The company adopted a general-purpose UNIX server and a Windows NT client to reduce installation costs and realize compact system size.

The client OSS also used Windows NT to provide a user-friendly environment for operators accustomed to handling personal computers. This helped Kansai EP restrict the cost for developing programs related to Human Machine Interface (HMI).

To interconnect DAS with the existing business-processing system, it was necessary to ensure that real-time processing, such as calculation for power restoration, would not be affected as a result of any data access by other systems. An offline server holds the general relational database, information such as measured current or voltage from substations or RTUs, as well as the distribution system data. The data in the offline server is open to other systems and is easily accessible, securing the possible extension of the computer network. Kansai EP installed servers developed by different vendors using the market mechanism to reduce costs for the latest technologies.

Multistep Interchange Calculation

Kansai EP's DAS automatically restores power to sound sections by switching to adjacent distribution feeders. This happens when a fault occurs at a substation or on the distribution system. The current DAS calculates up to a three-step interchange to display the process of power restoration. The “interchange” allows compensation for the insufficient back-up capacity of adjacent feeders. Increasing the number of steps increases the average current or utilization factor. This increases the restoration time for the multistep interchange (Fig. 5). Therefore, Kansai EP developed a fast calculation method for multistep interchange to make further reserve capacity available for quick power restoration.

This method combines the newly developed GA method with a conventional artificial intelligence (AI) method. This system completes the whole calculation in less than 1 minute, even when a power outage because of a substation fault causes a wide-scale loss of supply. ADAS is able to realize a five-step interchange compared with the three-step interchange with DAS. In practice, the AI method completes the main iterations, as it is superior to the GA method in preferable solutions. The GA method is a more valuable tool for executing larger power interchanges and primarily backs up the AI solution.

Interconnection with OSS

All Kansai EP service areas employ the OSS system, enabling the utility to manage distribution system data and customers on a mapping system, to design the distribution system with Computer Aided Design (CAD), and to register data automatically following completion of field work. The interconnection of OSS to DAS achieved integrated data management, thus reducing the volume of maintained data. The linkage of the DAS data related to distribution systems and customers with OSS allows for automatic updating of similar data in the DAS. Furthermore, the power-outage information retained in DAS can be transmitted to the OSS terminal, thus Kansai EP succeeded in improving customer services. Call operators easily can check on the situation outage when responding to customers' inquiries.

System Information Exchange

Kansai EP operates transmission systems, including the grid substations, at power control stations that are under the transmission division while the distribution network-engineering group is responsible for the distribution systems. Thus, there is a need to exchange system information between the control stations and customer services offices during contingency or normal operation. The development of an online function interconnects DAS with power-system supervisory and control systems so the T&D systems operate as a united system.

The operational procedures to restore the power system (including substations and distribution systems) execute automatically, therefore reducing the duration of power interruptions. The automatic data-transfer function that links the customers to the power-system supervisory and control systems has cut the time sales representatives need to handle customer inquiries.

33-kV and 22-kV UD Feeders

Kansai EP has yet to adopt DAS for totally underground systems. These systems are not equipped with automated sectionalizing switchgear, comparable to those installed on overhead distribution systems. Kansai EP plans to introduce an automatic surveillance/control system for the underground distribution system between the substation and the customers' premises on 33-/22-kV distribution systems. The intent of these designs is to reduce the duration of power outages and to provide customers with additional services.

Further Development

The ADAS has been on trial in Kansai EP's customer services office in Kobe since April 2000 and was installed in two other customer service offices by September 2000. Based on the results of these trial installations improvements in system functions will be made before extending ADAS to the remaining 38 customer service offices during the next three years.

ADAS has made it possible to enhance system performance while reducing operation costs. It comprises a distributed data-processing system with open specifications that can be interconnected with virtually any type of computer system. Kansai EP can identify the increasing needs of customers, including their reliability concerns and local information, by disclosing information of DAS for the business-processing system or the power-control systems being operated by other departments. Kansai EP is committed to build and operate integrated supply networks of electric power and data communication, gearing to meet the deregulated future. Additionally, Kansai EP plans to develop extended system functions to realize a complete customer support service in which ADAS will make a major contribution.

Hirofumi Tayama earned the MSEE degree from Kyoto University and joined Kansai Electric Power Co. in 1973. Tayama has held several senior managerial positions in distribution engineering, strategic distribution business planning and distribution system operations. Currently, Tayama is general manager of the Distribution Network Engineering Group.

The Definition of Reliability Indices

System Average Interruption Duration Index (SAIDI)
= Sum of customer interruption durations/Total number of customers served

System Average Interruption Frequency Index (SAIFI)
= Total number of customer interruptions/Total number of customers served