23-06-2012, 12:54 PM
Compensator rating for radial distribution lines
[attachment=25223]
Abstract
34% of the South African population is still without
electricity. Most of these people stay in deep rural areas where
the cost of electrification is very high. Radial lines are
characteristic of rural networks and methods to stretch existing
lines or constructing cost-effective new networks are of high
priority. Cheap conductors with large voltage drops and voltage
regulating network devices are on the forefront of research in
rural electrification.
INTRODUC’TION
omost people electricity is a given commodity. Socioeconomically,
electricity is seen as a basic necessity for
creating wealth. However, 34% of the South Atiican
population is still without electricity [16]. Approximately 50’%0
of these households are in deep rural areas where the cost of
electrification is very high due to large plot sizes and long
distances between dwellings. Electrification is so important
that the government and the South Afkican utility, Eskom,
allocated a budget of RI billion per annum over the next 15
years for electrification [16].
STWTCHING THE NETWORK
Stretching the network refers tc~the use of existing lines
beyond their traditional capacity. Line capacity is determined
by the voltage regulation across the line impedance and the
thermal rating of the line. The line current determines both the
voltage regulation and heating of the line; however, poor
voltage regulation occurs long before the thermal limit of
reticulation networks is reached. If a line is driven beyond
traditional voltage limits a compensator is needed to boost the
line voltage to acceptable levels. Such a compensator is
usually inserted where a load is connected at a point of poor
voltage regulation. This point is known as the point of
common coupling (PCC).
ANALYSIS OF VOLTAGE REGULATION
Residential loads, whether in rural areas or cities, are
primarily constant impedance loads (e.g. geysers, heaters,
stoves and incandescent lamps). It is therefore a fair
approximation to treat all loads along a residential line as
constant impedance loads. Assuming balanced three phase
networks, the whole network before the PCC can be
represented by a single TMvenin equivalent source, as shown
in Fig. 1. Ei%cient methods to calculate Vs and <Yfrom the
actual network parameters (which can be a vast number) are
documented in [14].
CATHEDRAL PEAK CASE STUDY
The Cathedral Peak case study shows a practical situation
where the network is stretched to accommodate new loads.
Due to the rugged Dr&ensberg terrain, a 45 km long 11 kV
radial line feeds the Cathedral Peak Hotel, which is right at the
end of the line. Various other customers are also connected
along the line. Currently the voltage regulation at the hotel is
just within limits, but loads in the area are increasing rapidly.
Load-growth studies of this region indicate a voltage
regulation problem in 2005. The projected network for 2005
is shown in Fig. 3 [2].
CONCLUSION
All compensators maintained the required voltage regulation
at both the PCC and PCCS. The series compensator achieved
this only for limited ranges of d For the series-shunt and in-
Iine compensators the power factor at PCCS needed to be
regulated at 0.98 (leading) to maintain the required voltage
regulation. This is an advantage as it reduces the reactive
power demand tlom the sending end.
[attachment=25223]
Abstract
34% of the South African population is still without
electricity. Most of these people stay in deep rural areas where
the cost of electrification is very high. Radial lines are
characteristic of rural networks and methods to stretch existing
lines or constructing cost-effective new networks are of high
priority. Cheap conductors with large voltage drops and voltage
regulating network devices are on the forefront of research in
rural electrification.
INTRODUC’TION
omost people electricity is a given commodity. Socioeconomically,
electricity is seen as a basic necessity for
creating wealth. However, 34% of the South Atiican
population is still without electricity [16]. Approximately 50’%0
of these households are in deep rural areas where the cost of
electrification is very high due to large plot sizes and long
distances between dwellings. Electrification is so important
that the government and the South Afkican utility, Eskom,
allocated a budget of RI billion per annum over the next 15
years for electrification [16].
STWTCHING THE NETWORK
Stretching the network refers tc~the use of existing lines
beyond their traditional capacity. Line capacity is determined
by the voltage regulation across the line impedance and the
thermal rating of the line. The line current determines both the
voltage regulation and heating of the line; however, poor
voltage regulation occurs long before the thermal limit of
reticulation networks is reached. If a line is driven beyond
traditional voltage limits a compensator is needed to boost the
line voltage to acceptable levels. Such a compensator is
usually inserted where a load is connected at a point of poor
voltage regulation. This point is known as the point of
common coupling (PCC).
ANALYSIS OF VOLTAGE REGULATION
Residential loads, whether in rural areas or cities, are
primarily constant impedance loads (e.g. geysers, heaters,
stoves and incandescent lamps). It is therefore a fair
approximation to treat all loads along a residential line as
constant impedance loads. Assuming balanced three phase
networks, the whole network before the PCC can be
represented by a single TMvenin equivalent source, as shown
in Fig. 1. Ei%cient methods to calculate Vs and <Yfrom the
actual network parameters (which can be a vast number) are
documented in [14].
CATHEDRAL PEAK CASE STUDY
The Cathedral Peak case study shows a practical situation
where the network is stretched to accommodate new loads.
Due to the rugged Dr&ensberg terrain, a 45 km long 11 kV
radial line feeds the Cathedral Peak Hotel, which is right at the
end of the line. Various other customers are also connected
along the line. Currently the voltage regulation at the hotel is
just within limits, but loads in the area are increasing rapidly.
Load-growth studies of this region indicate a voltage
regulation problem in 2005. The projected network for 2005
is shown in Fig. 3 [2].
CONCLUSION
All compensators maintained the required voltage regulation
at both the PCC and PCCS. The series compensator achieved
this only for limited ranges of d For the series-shunt and in-
Iine compensators the power factor at PCCS needed to be
regulated at 0.98 (leading) to maintain the required voltage
regulation. This is an advantage as it reduces the reactive
power demand tlom the sending end.