Long distance bulk power transfer:The need to economize investments in generation reserves, sharing of benefits in utilizing variability in generation mixes and load pattern have given rise to interconnection of neighboring power systems and development of large power grids.
Rapid increase of load (which is the case in developing countries like India), remote generation and system interconnections have made it necessary to transmit more power over longer distances efficiently and easily. Long distance bulk power transfer is possible only with Extra High Voltage (EHV) and Ultra High Voltage (UHV) transmission lines.
Research and Development activities:Priority is given to research and development activities for the optimization of cost of power transmission, efficient utilization of existing Right of Way (ROW) and increased power transfer capability. The recent technological developments and application of power semi-conductor devices, digital electronics, control equipments and satellite communication have increased the capabilities of EHV and UHV AC transmission lines.
Modern Trends in AC Transmission:
The modern trends in AC transmission are:
1. To utilize Flexible AC Transmission Systems (FACTS) employing power electronic based and other static controllers to enhance the controllability and capability of AC transmission lines.
2. To opt for higher transmission voltages exceeding the EHV range. Transmission voltage of 765 kV AC has been introduced in India in the year 2007. Research and development is going on for the next higher voltage of 1200 kV UHV AC transmission system. In this regard a 1200 kV test station and test line at Bina (Madhya Pradesh) is in advanced stages of research and development.
3. To deploy satellite imagery technique (which is supposed to enhance the transmission line survey). Survey techniques are improved through GIS and Airborne Laser Terrain Mapping (ALTM) or Light Detection and Ranging (LiDAR). Laser mapping produces the detailed elevation measurements at a faster rate and accuracy. It can be used at locations where the approach is limited or restricted. With this technique, long transmission corridor can be mapped with speed to determine the exact location of towers. The same data can be used for monitoring the transmission lines, for it's repair and modification activities.
4. Tall and multi-circuit towers are increasingly being used to avoid deforestation, protection of wild life and effective utilization of existing ROW.
5. Recent trend is to use multi-conductor bundled conductors having four, six, and eight sub-conductors.
6. To use high temperature endurance conductors for increased loading and higher power transfer capability.
7. More and more use of compact gas insulated substations of 765 kV and 1200 kV class.
8. Use of high strength polymer insulators.