Line Compensation

Line Compensation

With increase in load demand, it becomes necessary to make use of high voltage transmission lines for transmitting the power over long distances. With improved design and other technical consideration, the high voltage lines can be used for transmitting power for maximum possible length of line. But this may turn out to be expensive in certain cases. In such cases the alternative is to increase the transmission capability of EHV transmission systems.

The capacity of these power transmission lines can be increased by using conventional methods such as choosing higher transmission voltages, higher speed breakers, intermediate switching stations and reduced reactances of generators and the transformers. The transient stability limit can be increased using high speed excitation systems. The series impedance of the line can be reduced by the use of bundled conductors which increases the stability limits.

The modem technique of artifically reducing the series reactance and shunt susceptance of the lines by using series capacitors and shunt susceptance of the lines by using series capacitors and shunt reactors is called compensation. With this compensation the system stability is improved. Similarly the power transmission efficiency is increased along with voltage control. It also helps in reducing transient overvoltages.

If series capacitors are used the line reactance is compensated directly and losses are reduced. The voltage conditions will be improved instantaneously with wide fluctuating loads. Power transfer ability is improved along with power factor.

With shunt capacitors the phase angle between the voltage and the current is reduced which has various advantages.

When total reactive power obtained from series and shunt compensation is known then the maximum power transfer capability, voltage control conditions and efficiency of line depend on number, location and circuit arrangements of series capacitor and shunt reactor.

For long transmission line it is required to find the most appropriate location for capacitors and reactors in addition to compensation required for a particular line. The optimum possible solution must be obtained. 

Thus in summary we can say that for getting better voltage profile, for correction of power factor and for load balancing compensation is required.

Review Question

1. Briefly explain about the shunt and series line compensation.