With ever increasing demand of electric power, the existing transmission networks are found to be weak resulting in poor quality of unreliable supply. Also, it is realized that for expanding or enhancing the power transfer capability of the present transmission networks, huge sum of finances are required and sometimes even difficulties are encountered in finding right-of way for the new [...]
DC transmission possesses many technical and economic advantages over ac transmission. Some of the advantages are given below: Advantage # 1. Cheaper in Cost: Bipolar HVDC transmission lines require two-pole conductors while ac system requires 3 conductors to carry power. HVDC transmission can utilize earth return and, therefore, does not require a double circuit while EHV-AC transmission always requires a [...]
HVDC transmission is a strong alternative to EHV-AC transmission in some of the applications such as long distance high power transmission by overhead lines, under water transmission, transmission by underground cables, system interconnection by means of overhead lines or underground cables or back-to-back HVDC coupling stations, frequency conversion (50/60 Hz) and hence preferred. On the basis of applications, HVDC transmission [...]
The high voltage dc links may be classified into: 1. Monopolar Link 2. Bipolar Link 3. Homopolar Link. Type # 1. Monopolar DC Link: As the name suggests, monopolar link has only one conductor and return path is provided by permanent earth or sea. The line usually operates with negative polarity with respect to ground so as to reduce corona [...]
Modern trend is to use extra high voltage (EHV) and ultra-high voltage (UHV) for transmission of huge blocks of power over long distances. The reasons for adopting of EHV/UHV range for transmission purposes are given below: 1. Reduction of Electrical Losses, Increase in Transmission Efficiency, Improvement of Voltage Regulation and Reduction in Conductor Material Requirement: For transmission of given amount [...]
The major problems associated with EHV transmission are discussed below: Problem # 1. Corona Loss and Radio Interference: The corona is not only a source of power loss but it is also a source of interference with radio and television. The corona loss depends on various factors such as system frequency, system voltage, air conductivity, air density, conductor radius, conductor [...]
There are certain limitations in the transmission of power by EHV ac system. These limitations and design aspects are discussed below: 1. Stability Considerations: Power transferred is expressed as: if resistance and shunt leakance of the transmission line are neglected. For equal terminal voltages (i.e. VS = VR = V) Maximum steady state transfer of power takes place theoretically for [...]
In this article we will discuss about:- 1. Introduction to HVDC Transmission 2. Principle of HVDC Transmission 3. Power Control 4. Ground Return 5. Earth Electrode and Station Earth 6. Transient Overvoltages and Insulation Coordination 7. Corona 8. Circuit Breaking 9. Comparison with EHV-AC Transmission 10. Limitations. Contents: Introduction to HVDC Transmission Principle of HVDC Transmission Power Control in HVDC [...]
In HVDC transmission system or HVDC back-to-back coupling station, ac is converted into dc by means of a combination of converter-transformers and concerter valves. The conversion of ac into dc is called rectification. At the receiving end of the HVDC transmission line, dc is converted back to ac by means of converter valves and and converter transformers. The conversion of [...]
For drawing a overhead line, different accessories like pole, conductor, etc. are required. A brief discussion is given here about varieties of accessories available in the market and their use in different jobs:- 1. Electric Poles or Supports 2. Overhead Line Conductors 3. Insulators 4. Cradle Guard 5. Lightning Arrestor 6. Horn-Gap Lightning Arrestor. Accessory # 1. Electric Poles or [...]