New Technologies for Electric Power Distribution Systems

1 New Technologies for Electric Power Distribution Systems 158 New Technologies for Electric Power Distribution Systems to Unify Protection/Control Units so They Can Be Incorporated into IntelligentSubstations OVERVIEW: Recently, due to concerns about the liberalization of electricitysupply, deregulation, and global impact on the environment, securing areliable Power supply has become an important social need worldwide. Toensure this need is fulfilled, detailed investigations and developments are inprogress on Power Distribution Systems and the monitoring of are on (1) digital technology based on the application ofsemiconductor high-speed elements, (2) intelligent substations applying IT(information technology), and (3) system configurations aimed at high-speedcommunication.

2 Incorporated in these are demands for the future intelligentcontrol of substations, protection, monitoring, and communication systemsthat have advantages in terms of high performance, functional Distribution ,information-sharing and integrated Power Distribution management. Today sconventional apparatus also requires streamlining of functions,improvements in sensor technology, and standardized interfaces. Bypromoting these developments, the following savings for the whole systemcan be expected: (1) reduced costs in remote surveillance in the field ofapparatus monitoring, operation, and maintenance, (2) reduced maintenancecosts based on the integrated management of equipment, and (3) reducedcosts due to space saving as a result of miniaturizing KashiwazakiTakayuki WakidaMasakazu SatoYasuo SatoINTRODUCTIONTHE upgrading of our 500-kV trunk transmissionsystem has almost been completed, and the electricitysystem has been considerably improved.

3 Yet, costreductions are required to cope with the entry of IPP(independent Power producer) and the introduction ofpower source distributors caused by the deregulationof Electric utilities. To achieve this, each electricitysupply company is decreasing expenditure byefficiently using equipment, improving operations, andeffectively controlling plant-and-equipmentinvestment. The Power Distribution system alsorequires reductions in initial investments, such as theunit price of apparatus and miniaturization, andreduced costs for the whole life cycle, including theoperation/maintenance costs of the substation construction of a new Power Distribution systemhas been considered to meet these requirements.

4 It willadopt digital technology and IT-relatedtechnology, which has made rapid advances in system aims at minimizing the total cost, notonly reducing of the unit price but also the cost ofinstallation, construction, operation, and article discusses the construction of intelligentsubstations in the Power Distribution system, as wellas protection/control-unified equipment as examplesof the new SUBSTATIONC oncept of Intelligent SubstationsIn conventional substations, substation apparatus,such as switchgear and transformer, control, protectionand monitoring equipment is independent of everyother device, and connection is based on the signalscoming through the cable.

5 On the other hand, anintelligent substation shares all information onapparatus, control, protection, measurement andapparatus monitoring equipment through one bus byapplying both digital technology and IT-relatedtechnology. Moreover, high efficiency andminiaturization can be achieved because the localcubicle contains unified control/protection andmeasurement equipment that is one integrated systemHitachi Review Vol. 51 (2002), No. 5 159(see Fig. 1). Since an optical bus shares the informationbetween the apparatus and equipment, the amount ofcable is sharply reduced.

6 Moreover, as internationalstandards (IEC 61850 and 61375 etc.) are adopted andthe system conforms to the telecommunicationsstandard, equipment specifications can be standardizedfor different Monitoring SystemAll the data from each monitoring and measuringdevice is transmitted and used for a higher-levelmonitoring system via an optical bus. The requireddata is accessed through the Intranet or the Internet atthe maintenance site of an electricity supply companyor a manufacturer and the apparatus can be monitoredfrom a remote location. The construction, analysis anddiagnosis of the database including trend managementand history management also become possible.

7 As aresult, signs of abnormalities can be checked out wellin advance, and prompt action can be taken in timesof emergency. Maintenance plans can also be draftedto ensure reliability, by inspecting revision descriptionand parts management, efficient maintenance planningand reliability maintenance are also THAT CAN CONTRIBUTE TO ANINTELLIGENT SUBSTATIONS witchgear and TransformerThe burden can be drastically decreased becausethe sensor signal from the PCT is digitized at the sensoroutput edge and the load on the PCT only reaches thatof an A-D (analog-to-digital) converter.

8 Rogowski coilsare used as the current sensors and capacitive potentialdividers are used as the voltage sensors. These sensorsdrastically reduce the size of the switchgear (see ).Fig. 1 Intelligent Substation System Configuration (Image).The whole substation system is combined by optical LAN, andapparatus composition is 2 Gas Combined SwitchgearMiniaturization by DigitalCorrespondence GCS (gas combinedswitchgear) is shown as an company s maintenance siteManufacturer s maintenance sitePublic circuit/InternetSupervisory controlSerial busInterfacePCArtificial satelliteGPSTime serverWeb server terminal cardWeb server terminal cardProtection cardMeasuring cardControl cardApparatus monitoring cardMobile terminal cardOptical serial process busOptical serial process busPCT sensor/optical conversionApparatus control sensor/optical conversionApparatus monitoring sensor/optical conversionSubstation apparatusLocal cubicleGPS: global positioning systemPCT.

9 Potential current transformer5,160 mm7,340 mm9,740 mm8,050 mm(a) Conventional PCT(b) Digital PCT with polymer bushing to reduce main parts7,350 mmPTCT9,060 mm7,880 mm1,780 mm3,650 mm1,575 mmGCBCTPTGCBGCB: gas circuit breakerCT: current transformerPT: potential transformerNew Technologies for Electric Power Distribution Systems 160 Present studies on miniaturizing conventionalequipment have so far been aimed at standardizingseries. Advanced miniaturization will be attempted bydigitizing this system, corresponding to its and ControlIntelligent substations require protection andcontrol equipment to be installed outdoors and thisneeds to be compact so that the local cubicle is able tocontain them.

10 Outdoor installation requiresimprovements in insulation against heat andairtightness besides parts reliability. Compactprotection and control equipment will generate demandfor unified fabrication of protection/control and high-density components. The current protection/controlsystem that uses compact equipment is PROTECTION AND CONTROLSYSTEMT rends in Protection and Control SystemsDue to the rapid progress in today s informationfield, applying digital technology and adding ITfunction to the protection/control system are possible,to support stable Power supply, and improvemaintenance.