Abstract
M.Ing. (Electrical and Electronic Engineering)
Shunt reactors are used in power system amongst other things, to suppress overvoltages in the
network during network switching, auto reclosing of transmission lines and under low
loading condition of the network. Traditionally, shunt reactors of fixed type have been used
and these have been permanently connected to the system.
This research work investigated the feasibility of replacing the fixed shunt line reactors with a
reactor, whose parameters are automatically varied depending on the system reactive power
requirements, in a mature power system overlaid with high voltage lines to improve amongst,
other things voltage stability.
However, in a mature system overlaid with parallel higher voltage lines, power tend to flow
on the matured system rather than higher voltage system as predetermined by various
impedances of the power system. It is therefore desirable that loading of higher voltage lines
be increased because of their higher power transfer capability and fact that higher voltage
networks generate capacitive power which is substantially more than for each line at the
original voltage.
However, replacing a large number of fixed line reactors, at low loadings of higher voltage
lines, even when system collapse is averted by increasing the number of reactors inserted into
the system, overvoltage problems may still be an issue, until a certain number of must-run
reactors, operating at full reactance, are put into service. If too much inductive reactance is
removed from the system when the loading levels are extremely low, the power system will
collapse.
Therefore, there was no economic benefit in replacing all the fixed shunt line reactors with
controllable type when the loading was still relatively low. Thus, the majority of the
converted reactors were operating in their full rating as there was still more reactive power to
be absorbed.
However, when the power was diverted to flow on the higher voltage system through the use
of series compensation of the higher voltage system, there was a possibility of making some
fixed shunt line reactors on the higher voltage network controllable. This also allowed more
power to be transferred in the higher voltage system thus improving its utilisation. Also, a
positive impact on active system losses was realised.