Energy and Power Engineering, 2013, 5, 1456-1462
doi:10.4236/epe.2013.54B276 Published Online July 2013 (
Energization of a Half-Wavelength Transmission Line -
Pr e-Operational Transients Studies
Camilo Machado Jr1, Marcelo Maia2, Eden Carvalho Jr3, Maria C. Tavares4,
João B. Gertrudes5, Elson C. Gomes4, Walmir Freitas4, Marcos A. Paz5, Fernando A. Moreira6,
Carlos A. Floriano1, Vanderlei G. Machado1, Aniela M. Mendes1
1ELETRONORTE -Brasília, Brazil
2CHESF, Recife, Brazil
3ENTE, São Paulo, Brazil
4University of Campinas, Campinas, Brazil
5State University of Feira de Santana, Feira de Santana, Brazil
6Federal University of Bahia, Salvador, Brazil
Received April, 2013
In the present paper the main results of the pre-operational studies related to the energization maneuver of a
Half-Wavelength Transmission Line (AC-Link), are presented. The simulations were performed in PSCAD with actual
Brazilian system data. Specifically the following studies were performed: electromagnetic transient studies of energiza-
tion maneuver considering no fault and the occurrence of fault along the trunk; dynamic analysis of generator units that
will energize the AC-Link; TRV on the circuit-breaker that will energize the trunk. The main conclusion is that the
AC-Link energization experiment can be implemented without jeopardizing or causing time-life reduction of the
equipment involved in the experiment, which comprises the generator unit that will energize the trunk, the step-up
transformer, the arresters that will be kept during the experiments, as well as the circuit-breaker that will energize and
then trip the AC-Link.
Keywords: Electromagnetic Transients; Half-wavelength Transmission; AC-Link; Energization Test; Dynamic
Analysis; TRV; Faults
1. Introduction
According to Brazilian Institute of Geography and Statis-
tics (IBGE) on the last 10 years Brazilian population has
grown 1.17 % per year, totalizing 12.48 % for the last
decade. This growth aligned to the Brazilian industrial
advance has generated an increasing demand for electri-
cal energy, and hence a higher need for new energy re-
Nowadays, it is important to find renewable resources
to avoid the environment degradation. A huge hydroelec-
tric potential exists on the North of Brazil, on the Ama-
zon Region, with amounts of 100 GW not yet used, as
presented in [1].
However, this potential is located very far from the big
Brazilian load centers with distances higher than
2500 km. These long distances bring some extra difficul-
ties to transmit such huge blocks of energy.
In 2008 the Brazilian Electrical Energy Regulatory
Agency (ANEEL) proposed a so called Strategic R&D
Project to be supported by utilities and coordinated by
universities named: “Half-Wavelength transmission line
experiment". According to the call: "it is considered of
great relevance to the Brazilian Electrical System the
execution of field tests to confront with theoretical and
computational results, especially the ones related to
overvoltages derived from line energization and the vol-
tage profile along the line without reactive compensation,
for the half-wavelength transmission system." [2-5]. And
even more: "This effort has the main objective of evalu-
ating the possibility of including the line with a little
more than half-wavelength in the studies of future inte-
gration of the forthcoming hydro plants to the Brazilian
Integrated Electrical System" [6].
In 2011 the research project began, technically and fi-
nancially supported by the Brazilian Utilities: ELE-
and ENTE, being executed by the following universities:
Copyright © 2013 SciRes. EPE
C. M. JR ET AL. 1457
Specifically the project main objective is the imple-
mentation of the energization maneuver in a set of Bra-
zilian system composed of 500 kV transmission lines that
when connected in series will form a 2600-km long trunk
[7]. That corresponds to a little more than half-wave-
length for 60 Hz electrical system.
The proposed circuit will use the existing interconnec-
tions North-South 1, North-South 2 and part of North-
east- Southeast, totaling 2600 km [8].
The test trunk, here called AC-Link for being an AC
point-to-point transmission, has economical advantages
when compared with AC conventional interconnection
that are heavily compensated, as this alternative needs
neither intermediate substations nor reactive compensa-
tion (series or shunt) [9]. The AC-Link is also a competi-
tive alternative when compared with HVDC Link as its
terminal substations only have ordinary AC transformers
and no harmonic filters are needed [9]. That is an impor-
tant feature as there is no Power Electronic Technology
involved [1].
For the experiment the heavily compensated line sec-
tions will have the series compensation by-passed and
the shunt compensations removed. The circuit breakers
(CB) of the intermediate substations will be locked in
closed position and the one at the remote end substation
will be locked at opened position. Only the CB at the
sending end will be in use. With this a 2600-km long
500-kV trunk is obtained. The energization maneuver
will be implemented through the 500 kV CB at the send-
ing end. All the protection schemes at intermediate sub-
stations should be out-of-service so that no CB changes
position during the test.
The main electromagnetic transient results are pre-
sented in the following sections.
2. Analyzed System Description
The transmission system used in the study is formed by
three 500 kV interconnection trunks that have similar
characteristics and will be connected to form the AC-
Link [7,8]. The characteristics of the transmission lines
are summarized in Tables 1 to 3 where the sequence
components of longitudinal and transversal parameters
per unit length were calculated assuming ideally trans-
posed lines, for 60 Hz.
These trunks have same terminal substations which
allow connecting them in series. During the test the Bra-
zilian electrical system will become practically discon-
nected, for the North and Northeast systems will remain
connected to the Southeast, South and Central systems by
only a single 500 kV interconnection trunk instead of the
three normally in service.
It is a major concern that the test has the shortest dura-
tion possible. In order to reduce the setup time for the
test and afterwards, to recompose the system, all surge
arresters at lines terminals will be kept in service. As the
transient overvoltages are expected to be very low, the
arresters will not operate during the test and their pres-
ence will not impact the validity of the test. The sin-
gle-phase diagram with the substations and lines in-
volved is depicted in Figure 1.
The energization will be performed from Serra da
Mesa substation (sending end – SE) in one shot, what
means that the entire trunk will be energized at a single
shot using a pre-insertion resistor circuit-breaker (CB).
This was identified as the most adequate procedure for
AC-Link, as the controlled switching is not effective [7].
Table 1. Longitudinal and Transversal Parameters Calcu-
lated at 60 Hz - North-South I.
Sequence Unitary
Zero 0.37138 4.11662 0.00725
Positive/Negative0.01589 0.70700 0.01612
Table 2. Longitudinal and Transversal Parameters Calcu-
lated at 60 Hz - North-South II.
Sequence Unitary
Zero 0.34822 3.74452 0.00946
Positive/Negative0.01602 0.71089 0.01634
Table 3. Longitudinal and Transversal Parameters Calcu-
lated at 60 Hz - North East-South East.
Sequence Unitary
Zero 0.34821 3.75767 0.00934
Positive/Negative0.01602 0.72403 0.01603
Figure 1. Single-phase diagram of AC-Link Test - 500 kV.
Copyright © 2013 SciRes. EPE
The Brazilian ISO (ONS) will identify when the lines
that will form the AC-Link can be disconnected without
jeopardizing the Brazilian electrical system. The period
when these interconnections have low power flow will be
chosen to perform the test. As explained, the test is
planned to be as short as possible and it should not last
more than 2 to 3 hours, comprising the experiment setup,
the sequence of energization and finally the system res-
Traditional soil representation was applied during the
tests, specifically the soil resistivity was considered con-
stant with frequency over the entire length of the
AC-Link trunk with value of 4000 .m due to high soil
resistivity in these regions [10].
3. Electromagnetic Transient Studies
For the implementation of the energization maneuver the
regular transient studies were performed in PSCAD, as
described in the following sections.
Due to the line length the overvoltages are expected to
be much lower than the ones observed in regular trans-
mission lines of few hundreds of kilometers long. This
occurs because the traveling waves are attenuated as they
travel along the line, mainly the zero sequence one.
The lines were modeled with the phase domain model
which properly represents the line longitudinal parame-
ters frequency dependence.
3.1. Line Energization Without Faults
The insulation level of the 500 kV lines and the equip-
ment connected in the test system were not surpassed
during the energization tests.
The surge arresters that were kept connected during
the simulations did not affect the AC-Link behavior as
the results were similar to the configuration when they
were considered just in the AC-Link terminals.
The overvoltage levels observed and the surge arrest-
ers energy consumption during the energization were
very low, far below the equipment limits. In Figure 2 the
line-to-ground voltage at AC-Link terminal is presented.
Figure 2. Voltage at receiving end during AC-Link
energization - Pre-switching terminal voltage of 0.9 pu and
no pre-insertion resistor.
When the number of generator units was varied for the
line energization the lower overvoltage levels were ob-
tained when more units were used. However it was pos-
sible to energize the link with any number of units avail-
able at the SE substation. The simulation results showed
that the overvoltage levels and the sustained voltage were
within the system capability.
It was also verified that it is possible to perform the
maneuver with or without the pre-insertion resistor. The
resistor is designed to remain in service for 8-10 ms and
that is not adequate to mitigate the AC-Link overvoltages
[5]. For an AC-Link the resistor should be kept for 20 ms
so the traveling waves could reach the opposite terminal
and return at least once. As this would entail important
device modification the other alternative would be the
resistor bypass. However that would affect the test setup
As the overvoltages with the resistor kept for 10 ms
and without the resistor were not important the test shall
be implemented with the resistor operating as originally
3.2. Line Energization with Fault
Some simulations were performed supposing occurrence
or existence of single line to ground faults and three-
phase faults, involving or not the ground, during the
AC-Link energization test.
Although the experiment will be performed with fine
weather in the majority of the AC-Link, due to its length
there is a possibility of rain in part of the Link. However,
due to the short duration of the experiment the probabil-
ity of occurring a fault during the test is very low. Nev-
ertheless, the equipment involved in the test, namely the
generator unit, the step-up transformer, the circuit-
breaker and the line sections with their arresters should
not be damaged and should be put back into service in
the following hours after the experiment.
The faults were represented along the Link, at each
line section terminal and in the middle of each section.
When the fault caused important overvoltage this interval
was reduced. The fault was represented by a 20- resis-
The simulations consisted of energizing the line with
fault and removing the fault after 100 ms.
The voltage at SE terminal for single phase fault (SLF)
is presented in Figure 3.
The measured overvoltages due to SLF were limited to
2.0 pu along the line as the surge arresters were repre-
sented. In order to observe the transient severity the ar-
rester energy was analyzed. The energy was not impor-
tant except for faults occurring between 85 and 90 % of
the AC-Link length measured from the SE. If a fault oc-
curs in this region the arrester located at the remote end
absorbs high amount of energy. An additional arrester
Copyright © 2013 SciRes. EPE
C. M. JR ET AL. 1459
could be installed for the test at that location. However
the probability of occurring a fault in that specific region
during the short duration of the experiment is extremely
low. The existent relay was used in RTDS study and the
protection operation time prevented this severe arrester
energy consumption [10].
The maximum overcurrent observed in the CB oc-
curred for terminal fault and was of 2.6 kA. The highest
fault current was produced for a fault at 70 % of the Link
length reaching 2.9 kA. The transformer neutral current
reached a maximum value of 2.9 kA.
The results for isolated and grounded three-phase
faults (3LF) were similar. The overvoltages and overcur-
rents vary with the fault location, being more severe if
the fault occurs between 65% and 95 % of the AC-Link
The critical regions for both SLF and 3LF are related
to the sequence impedances seen by the SE. For instance,
the SLF critical region occurs at multiples of quarter
wavelength of zero sequence seen from the terminal. The
network at this terminal will also influence the quasi-
resonance region, but in this experiment the major effect
will be the AC-Link itself as the terminal is just formed
by the generation unit and the transformer (this is an iso-
lated system).
For the 3LF the critical regions corresponds to multi-
ple of quarter wavelength positive sequence seen from
the SE. At these regions sustained overvoltage may be
produced and have to be mitigated promptly.
For 3LF the overvoltage increases in an accentuated
rate, as the positive sequence attenuation for 60 Hz is
very small. A common mistaken analysis seen in a large
number of researches that deal with AC-Link is the ex-
tremely high overvoltage for three-phase faults, far be-
yond the line insulation level. The simulations cannot
produce voltages along the line supposing flashovers will
not happen. There is no meaning in obtaining 4.0 pu
overvoltage as before that a flashover will occur. When
the flashover occurs the AC-Link will immediately be
removed from the quasi-resonance condition and the
Figure 3. Maximum transient overvoltages measurured at
Sending End terminal for single-phase fault.
voltages that will arise will depend on the new fault loca-
In order to mitigate the stresses produced by 3LF at
critical locations it was proposed to use a mitigation me-
thod called Reduced Insulation Distance (RID) [11]. This
method, applied for the no-load test study, consists in
reducing the insulator string length in a selected tower in
order to provoke the flashover in that specific location.
The RID was installed in a tower near Imperatriz substa-
tion (km 1306 – 40% distant from the SE).
The RID was prepared to disrupt at 1.6 pu (line to
ground), for:
- This voltage is much higher than the transient
overvoltage at this location during energization without
any faults (maximum transient value of 1.2 pu);
- During no-load steady state the sustained voltage
is very low at this location (0.54 pu);
- 3LF produces no severe overvoltages or overcur-
rents along the AC-Link when it occurs this location.
With this method the severe overvoltages/overcurrents
are not established and the severe condition is immedi-
ately eliminated. Using RID the overvoltages due to 3LF
are below withstand levels and regular thermal capability
arresters can be used. The maximum current levels ob-
tained in CB, transformer neutral and RID are, respec-
tively, 3.11 kA, 2.41 kA and 8.32 kA. The RID current
value is lower than the electric discharge current that can
reach more than 30 kA and, therefore, it will not damage
the insulator string.
In Figure 4 the maximum voltages measured at SE
during grounded 3LF are presented. In Figure 5 the
maximum currents measured at CB are during grounded
3LF are shown.
This RID will not act for SLF as the voltage at this lo-
cation will not reach 1.6 pu. It will only operate for 3LF
at the severe region. If the RID operates for a lower vol-
tage for SLF this will not be a severe condition.
Figure 4. Maximum transient overvoltages at sending
terminal for grounded 3LF along the Link with RID.
Copyright © 2013 SciRes. EPE
3.3. Generator unit Performance During
Energization without Fault
The AC-Link can be energized from 1, 2 or 3 power
units. The requirements of the generators are greater if
only one machine is used. However the measured values
do not compromise the equipment integrity or reduces its
In Figure 6 the active power is presented for energiza-
tion without pre-insertion resistor.
3.4. Generator unit Performance during
Energization with Faults
Simulations were performed considering the occurrence
of faults along the AC-Link during the energization Test.
If a single-phase fault occurs the stress will not dam-
age the generator unit. Specifically, if a fault occurs in
the critical region for SLF the generator will send 1.5 pu
of active power and 0.5 pu of reactive power. These val-
ues do not affect its unit due to the short duration of this
In case of three-phase fault, grounded or isolated, the
stress again will not damage the generator. Specifically,
if a fault occurs in the critical region RID will operate
immediately, protecting the generator. During the tran-
sient the current in the generator will reach 3.0 pu, re-
ducing promptly to 0.7 pu. After the transient the ma-
chine injects 0.1 pu active power and 0.60 pu reactive
3.5. Line Tripping without Faults
The opening of no-load AC-Link results in very low ca-
pacitive current and the voltage between the breaker
poles is not severe and attenuates very fast, as presented
in Figure 7. The results showed that it is possible to open
the AC-Link using the existing CB at Serra da Mesa sub-
station (SE). The capacitive current through CB poles
and the voltage across its terminals are much lower than
its capability.
Figure 5. Maximum transient current at circuit-breaker for
grounded 3LF along the Link with RID.
Potência ativa
0.0 1.0 2.0 3.0 4.0 5.0
PG (pu)
PG 1
Figure 6. Active power injected by 1 generator unit during
energization without fault – Pre switching voltage: 0.9 pu –
Without pre-insertion resistor.
Figure 7. TRV of pole A during AC-Link no-load tripping
after energization without fault.
3.6. Line Tripping with Faults
The simulations consisted of energization and subsequent
tripping considering terminal fault, short-line fault and
remote fault. The faults analyzed were SLF and 3LF.
For remote faults the fault location was varied in order
to verify the behavior in critical regions. As there is no
standard for such a long trunk tripping, simulations were
performed comparing the AC-Link with the line for
which the CB was designed for terminal and short-line
faults. The actual line is 256 km long with shunt com-
pensation in both terminals.
It was observed that:
- The terminal fault current is similar to the one ob-
served for shorter lines even when shunt compensated, as
presented in Figure 8;
- The short-line-fault for AC-Link is less severe than
for similar lines of hundreds of kilometers, as in the latter
the inductance of the shunt compensation will produce
higher TRV;
- The highest current to be interrupted is not defined
by terminal fault, but rather by three-phase fault in spe-
Copyright © 2013 SciRes. EPE
C. M. JR ET AL. 1461
cific location which varies with the short circuit power
(Ssc) of the terminal network. These locations can be
from 60 to 85 % of the line length for low and high Ssc,
respectively, measured from the circuit breaker;
- The voltages at the circuit breaker contacts for re-
mote 3LF faults are not severe when RID mitigation
procedure is applied;
The TRV produced by remote SLF are not severe.
4. Conclusions
In the present paper electromagnetic results concerning
an energization of an AC-Link trunk formed by existing
500 kV lines are presented.
The use of Reduced Insulation Distance (RID) at a
tower near Imperatriz substation (1306 km) will mitigate
the overvoltages that are produced when a three-phase
fault occurs in a specific region (65 to 95 % of Link
length measured from SE). This method is adequate for
the energization maneuver but is not a straightforward
solution to be used during normal operation.
With RID the 3LF is not a sever condition for the
AC-Link energization. The SLF does not produce high
overvoltages, but the energy absorbed by the arresters at
the remote end can become excessive if protection does
not operate as designed [10]. In that case an additional
arrester or a higher thermal capacity arrester may be
Regarding the generator units, the requirements for
normal operation and operation under faults did not re-
sult in special requirements, and the actual machine can
cope with the experiment without damaging or reducing
its life-time.
The actual circuit-breaker designed for a highly shunt
compensated 256-km long line was capable of opening
Figure 8. TRV across pole A during AC-Link tripping after
energization under SLF terminal fault.
the no-load AC-Link and also tripping the AC-Link un-
der SLF and 3LF (terminal, short-line and remote). Even
for the critical region for SLF and 3LF the CB suffered
no special stress.
It can be stated that the AC-Link energization test can
be implemented in the analyzed system without impact-
ing the equipment involved (specifically generator unit,
transformer, circuit-breaker, line surge arresters and line
structure). There will be no damage to the devices in-
volved and their life-time will not be reduced due to the
stresses imposed by the experiment.
The HVAC-Link is a reliable and technically robust
solution for very long transmission trunks and due to its
constant terminal voltage for all load profile, it should
also be carefully analyzed for intermittent power transfer
as the ones produced by alternative energy sources, as
large solar and wind power plants.
In [11, 13] some results regarding line protection are
presented. Ongoing research on Single-Phase Auto Re-
closing will be presented in a near future. As the AC
Link cost is attractive for very long transmission, proper
technical solution can be developed if necessary to solve
specific needs.
5. Acknowledgements
This work was supported CNPq, CAPES and FAPESP in
Brazil. The results presented in this paper are partial re-
sults from the project supported by ELETROBRAS/
as part of ANEEL (Brazilian Electrical Energy Regula-
tory Agency) strategic project 2008 (proc. 4500072477).
The project was coordinated by UNICAMP with the par-
ticipation of UFBA and UEFS.
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