#26- Enhancement in Power Transmission System
1. Installation of New Transmission Line:
This is usually the first option that comes to mind whenever a transmission line is limited in the amount of power it can transmit, so as to alleviate overloading by providing additional paths for power flow. It is beneficial by increasing the reliability of the transmission system. However, it has to pass through economic, political and environmental hurdles.
2. Reconductoring Transmission Line/Terminal Equipment Replacements:
A line can be reconductored with a larger conductor with more power-carrying capability if the original transmission line conductor is inadequate to carry expected power flows, provided that the transmission line towers do not need to be significantly altered to support the heavier conductor. In addition, some terminal equipment may need to be upgraded to match the desired rating.
3. Conversion from single circuit to double circuit:
This involves making necessary modifications to the existing transmission towers and adding a second transmission line to the structure. This option extensively reduces the line impedance and increases current-carrying capacity of the line, thereby increasing power transmission capacity of the line.
4. Voltage Upgrade:
Another option is to increase the operating voltage of the transmission line, such as upgrading the voltage from 132 kV to 330 kV. In this instance, for example, the nominal rating of the line maybe drastically increased while using the same conductor. This type of improvement may require upgrading the transmission towers to meet National Electric Safety Code (NESC) clearance levels. In addition, the switching stations and substations must also be upgraded with higher voltage circuit breakers, switches, transformers, and other related equipment.
5. Reactive Power Compensation:
Addition of reactive power compensation devices (especially FACTS devices) in the form of series compensation, shunt compensation or the combination of the two, (depending on the nature of the line and its identified deficiency and need) to the transmission line is also another means of enhancing the performances of a transmission line. The addition of compensation modifies the electrical impedance of the line and therefore increases the power flows across the line. This can be an effective and economical means of increasing the transmission capability as a whole, by taking advantage of transmission lines that are not loaded to their thermal limits.
6. Phase Shifting:
Inequality in line impedances of a double circuit transmission line can bring about imbalance in load sharing between the circuits of the line: a situation where one circuit suffers overload while the other is under loaded. This is because electric current naturally flows through the path of least impedance. Addition of phase shifting device in the line helps to regulate and to better control the power flows on the system to optimize the existing transmission capability by distributing the power flows across the transmission lines.
