What are the major problems associated with EHV transmission?
some of the major problems associated with EHV transmission are:-
**Corona loss and radio interference**: The corona is a phenomenon that occurs when the electric field at the surface of an energized conductor exceeds a certain threshold, causing a partial discharge of air molecules. This results in a loss of power and a generation of electromagnetic noise that can interfere with radio and television signals. The corona loss depends on various factors such as system frequency, system voltage, air conductivity, air density, conductor radius, conductor surface, load conditions, atmospheric conditions, etc. The problem is more severe in EHV transmission lines, as they operate at higher voltages and electric fields. To reduce the corona loss and radio interference, some possible solutions are increasing the spacing between the conductors, increasing the diameter of the conductors, using hollow or ACSR conductors, or using bundled conductors¹²⁴.-
**Line support**: EHV transmission lines require heavy supporting structures to withstand the mechanical stresses due to wind and snow loading, as well as the electrical stresses due to high voltages. The design and erection of these structures are both difficult and expensive. Moreover, the line support also affects the aesthetics and environmental impact of the transmission lines¹⁴.-
**Insulation requirements**: EHV transmission lines require high insulation levels to prevent flashovers and breakdowns due to high voltages. The insulation requirements depend on various factors such as system voltage, switching surges, lightning surges, soil resistivity, etc. The insulation design must also consider the thermal and mechanical stresses due to load variations and environmental conditions. The insulation requirements are higher for underground cables than for overhead lines¹²⁴.-
**Erection difficulties**: EHV transmission lines pose many challenges in terms of erection and installation. The transportation and handling of heavy conductors and structures are difficult and costly. The alignment and sagging of conductors must be done with precision and care. The jointing and termination of underground cables must be done with special tools and techniques. The testing and commissioning of EHV transmission lines require sophisticated equipment and procedures¹²⁴.-
**Power station and substation equipment**: EHV transmission lines require special equipment at the power stations and substations to handle the high voltages and currents. These equipment include transformers, circuit breakers, isolators, surge arresters, reactors, capacitors, etc. The design and operation of these equipment must consider the effects of overvoltages, harmonics, transients, etc. The cost and maintenance of these equipment are also high¹⁴.-
**High short circuit current**: EHV transmission lines can carry large amounts of power over long distances. However, this also means that they can generate high short circuit currents in case of faults or disturbances. These currents can cause severe damage to the equipment and pose a risk to the system stability and security. Therefore, EHV transmission lines require fast and reliable protection systems to isolate the faulted sections and minimize the impact on the rest of the system¹⁴.-
**Surge arrestor**: EHV transmission lines are exposed to various sources of overvoltages such as switching surges, lightning surges, temporary overvoltages, etc. These overvoltages can exceed the insulation strength of the line and cause flashovers or breakdowns. To protect the line from overvoltages, surge arresters are installed at strategic locations along the line. Surge arresters are devices that limit the voltage across them by diverting the excess current to ground¹⁴.-
**Single pole switching and auto reclosing**: EHV transmission lines often use single pole switching and auto reclosing schemes to improve the system reliability and availability. Single pole switching means that only one phase of a three-phase circuit breaker is opened or closed at a time. This reduces the switching surges and transient recovery voltages that can cause insulation failures or restrikes.
Auto reclosing means that a circuit breaker is automatically closed after a predetermined time interval following an opening operation due to a fault or disturbance. This allows the line to resume normal operation if the fault is temporary or cleared by other means¹⁴.