Transmission line of power supply
Transmission line of power supply
With time, electric consumption has increased successively. Thus this leads to saturation of a transmission line and hence the lines reach critical points of ampacity and consequently sag. The carrying power capacity of these lines reduces. Other than constructing new transmission lines, which are hampered by the complexity of getting available passages to construct new overhead transmission lines, it is advisable to consider options of increasing power transmission capacity of the present transmission lines. The alternative of increasing the capacity in the already existing transmission lines provides a cheaper way out rather than constructing new underground transmission lines. Moreover, it is difficulty and demanding to acquire rights of way for new transmission lines.
With this increased power consumption, the transmission line may lack the required capacity forpower transmission. However, there are several ways of increasing the capacity in the already existing line. One way could be substituting old ACSR conductors with HTLS conductors is a method of increasing power transmission in the line thermal rating. HTLS conductors are capable of transmitting 1.6 to 2 times much current than ACSR conductors. When new HTLS conductors are installed, power rises in about 200-500 range (Grigsby 2001). Using AC transmission lines in DC power transmission increases the transmission capacity. Other advantages include stability of the power transmission, regulated emergency support and also there is no involvement with short circuit level. Thus power transmitted is raised by 3.5 times.
Saturation of overhead transmission lines
Saturation of overhead transmission lines creates restraints that restrict a system’s ability toconvey power and lower the use rates of the existing transmission network. Obviously, this reduces the capacity of such transmission lines. Because of the challenges associated with building of new overhead transmission lines, the main focus of counteracting the saturation is increasing the transmission capacity on existing lines and utilizing the existing transmission lines to the maximum through upgrading them. In cases where practicable, upgrading is the best alternative because it is economical and lead-times are few compared to construction of new transmission lines (Pansini 1998).
There are constraints that restrict the power transmission capacity in transmission lines. Power transmission capacity is characterized by switchgear characteristics whereby some transmission lines experience load capacity restrained by certain switchgear elements related with them. Here there is need to make out the element with lesser rated current in whichever end of the line. Still, the transmission capacity can be reduced because due to environmental specifications. In order to establish the load capacity in high voltage cables it is necessary to consider the thermal provisions of conductors of work like temperature, water availability and also electric conditions of the operation. There ought to be minimum safety distances and the voltages should be maintained and the network stability should be within appropriate limits.
Still power transmission capacity can be caused voltage drops. This comes about because in the network lines, transmission lines transport a lot of energy generated from the ends that are generating the power to the ends that are utilizing the power. Consequently, in case the ends that receive the power lack compensative reactive elements, the voltage drops below the limit securedby quality criterion. In such cases, it is appropriate to restrict the transmission of the concerned transmission lines to avoid exceptionally low voltages in the receiving ends and also so as to avert the likelihood of the transformer regulators collapsing due to a performance over their potentials (Mack 2002).
The stability of the whole electric system may affect the capacity of transmission lines. Incasethere are no reactive setbacks considered in specific zones, there are long interconnection lines between such zones. Therefore, voltages sustain normal tolerable limits but there could be conditions whereby strong power interchanges require extreme angular phase angle between locations of the generator rotors in each specific angular area. Thus this entails limitation of the power transmission in such transmission lines with object to avert stability loss and electric disjointing between these zones. Power transmission in such lines are detected by looking in things like maximum current foreseeable to be transported by the lines, maximum current of transmission the limits in these lines being thermal and lastly maximum acceptable current because of the switch gears present in these transmission lines (Mack 2002).
Solutions of inadequate capacity
Upgrading through voltage increment
Voltage is the gauge of the electromotive force required to uphold electric flow in thetransmission lines. Voltage vacillations can occur because of deviations in electricity demand or may be due to breakdowns on transmission lines. Limitations on the maximum voltage level are normally determined by how a specific transmission line is designed. In case the maximum limit is surpassed, noise is experienced; transformers and the equipments being used by the customers on the receiving end may be damaged. Low voltage makes the ones of the receiving ends experience insufficiency in their electrical operations and hence motors get destroyed. Thishence leads to the drop of the voltage in the transmission lines from the ends that send power to the ends that receive it. Voltage fall on the AC transmission lines is roughly proportional to the reactance power flows and transmission line reactance. The reactance within the transmission line rises with the extent of the line of transmission. Here, capacitors and inductive reactors are fixed, as necessary, on the transmission lines to partly regulate the quantity of voltage drop. This is very helpful since voltage levels and current levels decide the power that is transmitted to the customers. Still, these incapacitated AC transmission lines could be replaced with new compact AC lines. These two solutions increase the power transmitted through these overhead transmission lines and thus raising the rated voltage. This is achievable by making use of the experience obtained for HVAC transmission lines and allowing reduced safety margins in devising clearances. When installing the compact AC transmission lines, insulated cross arms and shorter span are used thus decreasing the sagging of the transmission line for a substantial rise in the power density to be attained.
Upgrading through current density increment
Every time the flow of electrons goes through a transmission line, there is heat production andthus the temperature increases. Thus there is need to increase the thermal rating to counter the decreased power capacity. This can be done through raising the maximum permissible operating temperature to 100°C. For example, if a transmission line is restricted to standard temperature of 50°C to 75°C and the electrical clearance is enough to permit a rise in sag for operation at higher temperature then the thermal rating of such transmission line can be raised. Still, the conductor responsible for power transmission can be reinstating with one that is larger one or with one that can operate constantly above 100°C. The main advantage is that it is cheap to install sincealuminum is easily available and has high conductivity with less density. Replacing the conductor with larger ones increase the load on the transmission lines because of increased power transmission. Thermal rating could be raised in existing transmission line can be raised by 50% through conductor replacement that has aluminum content twice as much of the original structure (Hughes 2003). The greater conductor doubles the transmission capability in the transmission lines. The disadvantage of using a larger conductor could be reduced by HTLS while still exhibiting steady tensile strength and skulk elongation properties. The main disadvantage is that replacing the conductor could shorten the life span of the transmission line.
Since there are numerous changes in the way the power transmission system is planned andmanaged, higher current densities in the existing transmission line ought to be reached. The different kinds of drawbacks that limit the power transmission should be analyzed for the upgrade potentiality to increase the transmission capability.
Grigsby, L., 2001, The Electric Power Engineering Handbook, CRC Press: USA.
Hughes, P., 2003, Networks of Power: Electrification in Western Society, The Johns Hopkins
University Press: Baltimore.
Pansini, E., 1998, Under grounding electric lines, Hayden Book Co: New York.
Mack, E., 2002, Electric power transmission patents, McGraw-Hill: California.