Power Engineering Guide Transmission and Distribution (1)

This Power Engineering Guide is devised as an aid to electrical engineers who are engaged in the planning and specifying of electrical power generation, transmission, distribution, control, and utilization systems. Care has been taken to include the most important application, performance, physical and shipping data of the equipment listed in the guide which is needed to perform preliminary layout and engineering tasks for industrial and utility-type installations.

The equipment listed in this guide is designed, rated, manufactured and tested in accordance with the International Electrotechnical Commission (IEC) recommendations. However, a number of standardized equipment items in this guide are designed to take other national standards into account besides the above codes, and can be rated and tested to ANSI/ NEMA, BS, CSA, etc.

General Introduction

Energy management systems are also important, to ensure safe and reliable operation of the transmission network.

Distribution

In order to feed local medium-voltage distribution systems of urban, industrial or rural distribution areas, HV/MV main substations are connected to the subtransmission systems. Main substations have to be located next to the MV load center for reasons of economy. Thus, the subtransmission systems of voltage levels up to 145 kV have to penetrate even further into the populated load centers. The far-reaching power distribution system in the load center areas is tailored exclusively to the needs of users with large numbers of appliances, lamps, motor drives, heating, chemical processes, etc. Most of these are connected to the low-voltage level. The structure of the low-voltage distribution system is determined by load and reliability requirements of the consumers, as well as by nature and dimensions of the area to be served. Different consumer characteristics in public, industrial and commercial supply will need different LV network configurations and adequate switchgear and transformer layout. Especially for industrial supply systems with their high number of motors and high costs for supply interruptions, LV switchgear design is of great importance for flexible and reliable operation. Independent from individual supply characteristics in order to avoid uneconomical high losses, however, the substations with the MV/LV transformers should be located as close as possible to the LV load centers.

The compact load center substations should be installed right in the industrial production area near to the LV consumers. The superposed medium-voltage system has to be configured to the needs of these substations and the available sources (main substation, generation) and leads again to different solutions for urban or rural public supply, industry and large building centers. In addition distribution management systems can be tailored to the needs, from small to large systems and for specific requirements.

Despite the individual layout of networks, common philosophy should be an utmost simple and clear network design to obtain

_ Flexible system operation

_ Clear protection coordination

_ Short fault clearing time and

_ Efficient system automation.

The wide ranges of power requirements for individual consumers from a few kW to some MW, together with the high number of similar network elements, are the main characteristics of the distribution system and the reason for the comparatively high specific costs. Therefore, utmost standardization of equipment and use of maintenance-free components are of decisive importance for economical system layout.

Siemens components and systems cater to these requirements based on worldwide experience in transmission and distribution networks.

Protection, operation, control and metering

Safe, reliable and economical energy supply is also a matter of fast, efficient and reliable system protection, data transmission and processing for system operation. The components required for protection and operation benefit from the rapid development of information and communication technology.

Modern digital relays provide extensive possibilities for selective relay setting and protection coordination for fast fault clearing and minimized interruption times. Remote Terminal Units (RTUs) or Substation

Automation Systems (SAS) provide the data for the centralized monitoring and control of the power plants and substations by the energy management system. Siemens energy management systems ensure a high supply quality, minimize generation and transmission costs and optimally manage the energy transactions. Modularity and open architecture offer the flexibility needed to cope with changed or new requirements originating e.g. from deregulation or changes in the supply area size. The broad range of applications includes generation control and scheduling, management of transmission and distribution networks, as well as energy trading. Metering devices and systems are important tools for efficiency and economy to survive in the deregulated market. For example,

Demand Side Management (DSM) allows an electricity supply utility from a control center to remotely control certain consumers on the supply network for load control purposes. Energy meters are used for measuring the consumption of electricity, gas, heat and water for purposes of billing in the fields of households, commerce, industry and grid metering.

Overall solutions – System planning

Of crucial importance for the quality of power transmission and distribution is the integration of diverse components to form overall solutions.

Especially in countries where the increase in power consumption is well above the average besides the installation of generating capacity, construction and extension of transmission and distribution systems must be developed simultaneously and together with equipment for protection, supervision, control and metering. Also, for the existing systems, changing load structures, changing requirements due to energy market deregulation and liberalization and/ or environmental regulations, together with the need for replacement of aged equipment will require new installations.

Integral power network solutions are far more than just a combination of products and components. Peculiarities in urban development, protection of the countryside and of the environment, and the suitability for expansion and harmonious integration in existing networks are just a few of the factors which future-oriented power system planning must take into account.