System integration in a changing world25 March 1998
Power system telecommunication (PST) engineering today encompasses a wide range of telecommunication disciplines. Systems are growing into large optical fibre networks with complex control architectures and integrated communication systems for users. The Java West Operational Telecommunications (JWOT) project in Indonesia and the Indian Southern Region System (ISRS) coordination and control project are typical examples of modern large power system telecom projects.
The communication requirements of power utilities are undergoing profound changes both in quantity and in nature. The pace of evolution in the power network as well as the widescale nature of rehabilitation projects in emerging countries render this transformation even more critical. Special attention must be given to the specification of requirements, dimensioning and the expandability of the structures in order to avoid saturation at an early stage. The task of system integration in this rapid evolution is of crucial importance.
Power system telecom rehabilitation projects in emerging countries are often financed through international loans with a rather long time between the definition and the implementation of the system. The JWOT project in Indonesia and the ISRS project presently in progress for PowerGrid Corporation in India are typical examples of large power system telecom projects.
The independent assessment of communication requirements is the most critical step in the definition of any communication project. With power system communications the task is even more difficult because of the varied nature of requirements, the long lapse of time between major network rehabilitations and the uncertainties as to the evolution of the applications.
Power networks in emerging countries evolve particularly fast. New power projects involve communication equipment at the site but generally no provision for overall communication network adaptations is made. A major power system telecom project must therefore allow almost costless power network extensions during the lifetime of the system.
The rapid and wide-scale introduction of information technology into the power network is leading to closer coupling of control centres and the power network elements. The domain of functionality of different devices has started to overlap and once separate functional blocks such as power plant and substation controls and network supervisory control are becoming integrated.
The resulting integrated process control communication network composed of a high speed wide area network (WAN) interconnecting local area networks (LAN) opens a never-ending technological race between information processing and data transmission capabilities. Consequently the estimation of the required capacity and quality of the communication channel becomes difficult when the communication system must live beyond the lifetime of the present power network automation architecture.
Another issue that must not be neglected is the utility office environment generating corporate telephone traffic routed through the public telecom network. The networking of office computer machinery for distributed database systems, remote sharing of resources and electronic mail are basic practices of the modern office.
Until recently, the extent of inter-office networking has been limited by the cost and possibilities of the telecom operator. The JWOT project produced a considerable reduction in the power company's telecom bills.
The diversity and the rapid evolution of technology is generally a source of confusion when specifying PST projects. The appropriate technology depends on the nature of the project, the required capacity, the geographical coverage and terrain characteristics and the type of traffic to be carried. One should distinguish between Backbone and Site Access technologies.
The saturation of existing resources, the requirement for higher capacities and electromagnetic compatibility problems have led power companies to integrate optical fibres into their transmission lines. In some companies, all new EHV lines are systematically equipped with optical fibres in the ground wire (OPGW). These isolated fibre links may be interconnected through the retrofit addition of optical cable to constitute a high capacity backbone.
The telecom deregulation in progress in many countries and the potential revenues from the leasing of surplus capacity (dark fibres, transmission channels) has further increased the preference of many power companies for a fibre backbone.
For retrofit applications, two cable technologies are considered at present as mature: self-supporting all-dielectic cable suspended from the transmission towers used at voltages up to 150 kV; and groundwire wrapped optical cable installed at any voltage if a groundwire exists.
Microwave radio has been used for a long time in many power utility communication networks. Digital microwave radio allows low cost, compact design and operation at lower transmit power levels than the older analog systems. Microwave radio allows the implementation of a network at low initial cost with no access requirements along the link but with a limited extension capacity and is subject to frequency availability and licensing.
Microwave communication is an adequate way to cross difficult terrain and to connect sites with no overhead transmission lines. Fast deployment microwave links can be used in case of transmission line or tower failures to preserve critical traffic during the system restoration.
The high capacity backbone cannot give access to all entities requiring communications. The diversity of access requirements gives a wide range of systems and services which may be used, consitituting a narrow band access level in the network.
The most widely spread transmission medium in PST remains the power line carrier. In a network with a digital high capacity backbone it is a cost-effective access solution when the distance to cover is large, the required channel capacity is small and the site is connected to the network through HV transmission lines.
The use of short and long distance microwave radio links and optical fibres at the access layer is cost-effective when the required capacity at a site is sufficiently high. The short haul microwave radio is also an attractive solution in the urban environment with the advantages of very compact design and small antenna size.
The point-to-multipoint TDM/TDMA radio systems in the 1.5/2.5 GHz band is particularly adapted to a group of sites spread across a relatively short distance. In this case, a group of digital channels (typically 30 or 60) is allocated to many sites in a radius of 200 to 300 km through time division multiplexing (down link) and time division multiple access (up link).
Mobile radio technology in recent years has undergone a tremendous growth and its effects on power utility mobile services are still to come. Trunking radio systems, allowing the use of several frequency bands to constitute a dynamic resource allocation system, benefit from the traffic characteristics of a large network and can be of extended coverage through a multicellular design. The implementation of a trunking system is especially cost-effective if it can be shared with some other users, hence the alternative for outsourcing or leasing to external users.
The local communications of the power utility can also be drastically simplified through the use of private radio paging systems, wireless PABX and wireless LAN solutions. For example, the telecom cabling of a power plant represents a large expense with no flexibility which can be avoided through the installation of a number of radio relays for full coverage. The DECT (Digital European Cordless Telephone) standard has been implemented by many manufacturers and is already operational in a number of industrial sites.
Implementing the network
Before proceeding to any detailed design of the target telecommunication system, it is necessary to assess the existing equipment. A site survey covering all the resources of the existing network is of great importance. It will lead to the decision whether the equipment can be reused with no modification, requires upgrading, must be relocated to the periphery or must be removed from the network.
The cost of upgrades, maintenance and relocations as compared to the replacement of equipment is an important factor in the optimization of project costs. A sound knowledge of the main existing equipment and their interfacing rules, as well as the applications which they vehicle is required in order to define any necessary hardware or software modifications during the intermediate steps or in the final configuration.
A widescale PST network is a large assembly of new and existing teleco subsystems generally from many different manufacturers. In order to assure the success of the project it is generally necessary to implement a system platform simulating all the interface points encountered in the system.
The migration path analysis, from the present state of the network to the target system, defines the project implementation steps. A 'make before break' strategy limiting interruptions to extremely short lapses of time is the general rule considering the critical nature of the power system communications.
Site performance testing to prove the adequacy of the total system, including the new, relocated and existing installations for each application is an essential activity in PST network integration.
The quality of service in a network depends not only on the implemented system but also on the ability to maintain the network adequately both on an immediate operational basis and on a long term basis.
The management of telecom networks includes a range of tasks to be carried out for the coordination, operation, maintenance and planning of the system in order to assure the optimal use of the network resources in all situations. These tasks are grouped into the following categories:Fault management Performance management Configuration management Accounting management Security management.
The management of a PST network is not only the implementation of powerful tools. The organization of the human resources into adequate functional and geographical structures, a widescale training programme and an adequate network information system, as well as and appropriate maintenance strategy are important tasks to be carried out during the implementation of the project.
TablesTable 1. Potential communication requirements for power companies