PERIODICA POLYTECHNICA SER. EL. ENG. VOL. 49, NO. 1, PP. 25–42 (2005)
ARCING TRANSIENTS ON MULTI-CIRCUIT LINES
National Power Line Company Ltd. (OVIT)
Received: Sept. 14, 2004
In several cases transmission line circuits with different nominal voltage levels run in parallel on
same towers. Becomes faulty the lower voltage (HV or MV) circuit it initiates a Single or Three
Phase Reclosing (SPR or TPR) during which the higher voltage (HV or EHV) circuits could cause a
low current (secondary) arc in the ionized plasma cloud generated by former primary fault arc as a
consequence of coupling with healthy phase conductors. Does not extinguish secondary arc till the
faulty phase(s) reclosing SPR or TPR will be inefficient.
One goal of the paper is to study electromagnetic transients during dead time of the AR
(Automatic-Reclosing) by simulation. Besides the author has invented and built a HV test circuit
from lumped components to analyse above-mentioned phenomena.
Article shows main results having got by simulation and confirmed by actual HV tests as well
as a plan of another HV circuit by means of which real network circumstances can be simulated
Inductive potential transformers and ZnO surge arresters are not disconnected from faulty
phase during AR. Analyzing influences by these units on studied phenomena has been also carried
escalation, test circuit, inductive potential transformer, ZnO.
EHV, HV, secondary arc, multi-circuit lines, EMTP, Automatic Reclosing, voltage
Importance of the multi-circuit lines increases in EHV long distance power trans-
electrical energy or to increase reliability of the operation of transmission lines.
Ownership of the land becomes more expensive in urbanised areas also in the
countryside additionally soitismore difficulttofindsuitable land tobuild overhead
lines in both areas. Running same or different nominal voltage overhead lines on
towers for each circuit. This is advantageous concerning lines reliability and urban
area site utilization but causes additional problems at the effective overvoltage-
protection and the successful AR performance versus single towers cases.
Let me take some definitions: common length (running on the same towers)
of the circuits with different nominal voltages calls sc; length of the lower nominal
voltage circuit running alone calls sa(see Fig. 1).
Fig. 1. The definition of scand sa
1.1. Secondary Arc in a Single Circuit Line
Arises SPR on a single circuit transmission line circuit breakers disconnect the
faulty phase at both ends of the line (see Fig. 2a)). After primary arc extinguishing
a hot, ionised, plasma leader remains in its place.
A secondary arc can develop in this plasma cloud supplied by healthy phases
being coupled with the faulty one. This low current (10÷150 A) secondary arc
andacapacitive onecausedbymutualcapacitances (CAB). Theinduced component
may usually be neglected because of its low amplitude. The equivalent circuit of
SPR  is shown by Fig. 2b).
CAB? ? CAC? ? CBC
C0=C0A? ? C0B? ? C0C
Fig. 2. Networkconfiguration(a))and equivalentcircuit (b))of the secondaryarc at single
Functions of the Fig. 2b) units are as follows: – UA/2 and 2CABare Thevenin
equivalent of the sound phases; C0represents the faulty phase earth capacitance;
Rarcisresistance ofthesecondary arc; theswitchsimulatesreignition andextinction
of the secondary arc by switching on and off.
ARCING TRANSIENTS ON MULTI-CIRCUIT LINES
Dielectric strength of the remanent plasma channel has to be increased to a
degree where switching-on-overvoltage that develops after the current-zero is not
able to breakdown plasma channel resulting inefficient SPR.Does not arise the sec-
ondary arc final extinguishing till circuit-breaker reclosing SPR will be inefficient.
Owing to consequences secondary arc is significant part of the SPR.
There are two types of the secondary arc:
Continuous: It generally exists immediately after primary arc, so arc channel
contains ionized gas in great quantities. Arc extinguishing happens directly
in neighbourhood of the 50 Hz current zero causing negligible current cut
off. Reignition occurs at small potential with low current, so it seems to be
a continuous arc (I = 20÷150 Apeak).
Intermittent: Arc channel is continuously getting cold including less and less
quantity ionised gas. Therefore arc will be extinguished at greater voltage
causing high current cut off and will be reignited at greater potential in every
50 Hz current zero breaking like as a well-known 50 Hz intermittent arc.
Secondary arc is influenced by several parameters. Some of them are de-
terministic (nominal voltage, length of the line, etc.); others are stochastic (wind
velocity, fault location, primary arc current and duration, etc.). Effects of some
parameters – mainly stochastic ones – are not cleared up exactly yet.
For evolving secondary arc length of its channel has to be equal at least to
the length of the primary arc channel which according to the current of about 5÷10
kA is much more energized than the secondary arc owing to a significant smaller
current. From these follows its pregnant thermal buoyancy on account of which
arc is forcefully influenced by the environmental parameters, especially by wind
velocity and wind direction (). In calm secondary arc can burn up to 20÷30
seconds what is greatly longer than dead timeof the SPRor TPR.Onthe other hand
it can extinguish in 3÷5 periods (60÷100 ms) if wind velocity is high (> 5÷6 m/s).
The shape of the arc channel is stochastic thus resistance, voltage, current of the arc
are changeful producing fluent heat quantity. The reason of the final extinguish is
that the voltage, which can sustain the arc, passes the potential-difference between
the earth and the conductor disconnected, so arc is not able to be reignited in the
next half period.
1.2. Multi-circuit Line Secondary Arc
Supply of the secondary arc is much more complex at this type of the lines than in
the former case. If one of the conductors becomes faulty arising SPR cycle own
healthy and the other circuit(s) phases supply secondary arc, each sound phase,
through its mutual capacitance (see Fig. 3a). To make an equivalent generator and
equivalent mutual capacitance every mutual path of the supply has to be added.
Thevenin equivalent of them are the UEQUand CEQUin Fig. 3b. If positions of
5.1. Inductive Potential Transformer
The inductive potential transformer is a galvanic connection between the earth and
the phase conductors. Based on characteristic of a 120 kV device  the nominal
current amountstoabout 0,2Aeffective. Whenthesepotential transformers takeon
both ends of the 120 kV part of the transmission line their current can be increased
pro rata on escalation voltages up to ∼7 A. The Uo,maxdecreases in a non-essential
rate (∼13 %) as a consequence of the conductor charge decrement due to increased
discharge by inductive potential transformer. The effect can be seen on Fig. ?? (see
label Potential transformer).
Fig. 16. The decreased potential caused by the inductive inductive potential transformer
on probability of unsuccessful reclosing is negligible.
5.2. ZnO Surge Arresters
Function of this circuit element is to protect devices on phase conductor from non-
allowable overvoltages. Derogation rate depends upon nominal voltage of the line,
rules of the standards and characteristic of the surge arrester. Reaches potential
of the disconnected phase caused by voltage escalation break point of the arrester
it takes off charge of the conductor. Its’ rate depends upon characteristic of the
arrester and of the conductor charge.
Taking a typical surge arrester  to either end of 120 kV line being part of a
420/120 kV double-circuit system voltage escalation cannot change as Uo,maxdoes
not reach break point (160÷170 kV) of the arrester. If, however, floating voltage is
higher (about 55 kV) Uo,maxwill also be higher as it is shown on simulated 750/120
kV line of Fig. 17 and arrester operates (see curve ‘MOV’). Tower shape of this
ARCING TRANSIENTS ON MULTI-CIRCUIT LINES
line is similar to 400/120 kV lines except insulation distances to earth and to higher
nominal voltage phase conductors.
Fig. 17. The influence of the ZnO surge arrester on the voltage escalation at the 750/120
kV transmission line
Difference between maximal values of the time functions is more significant
than in case of inductive potential transformer (∼50 kV ≈ 20 %). Even so ZnO
surge arrester cannot inhibit development of the phenomena studied and cannot
make pregnant dropping in probability of unsuccessful reclosing similar to the
action of the inductive potential transformer.
1. Contains secondary arc of the lower nominal voltage of the multi-circuit line
very short (∼50...800 µs) and high current impulses each transient current
zero causes great restriking voltages as a reason of the voltage escalation in
the faulty phase(s). Repetitive current impulses can ionise the remanent gas
cloud(s) continuously till the reclosing; consequently AR will be probably
2. AHVtestcircuit ismadeinwhichvoltageescalation phenomenon isverified.
3. Using results of the test carried out another HV test circuit is designed being
capable to simulate real network correctly.
4. Basing onsimulations bytheauthor itcanbeestablished: 4–5 ?circuit-units
are enough to map studied phenomena of the 120 kV phase conductor dis-
connected from the transmission line by an AR with permissible inaccuracy.
5. Two passive elements (inductive potential transformer and ZnO surge ar-
rester) having been not disconnected from the transmission line during AR
cannot disqualify voltage escalation but they can decrease its maximal value.
of  and of the National Power Line Company Ltd. for HV test possibilities.
 BÁN, G., Electromagnetic Transients of Electric Power Systems, book, 1986 in Hungarian.
 MIHÁLKOVICS, T.,The Effectof the Wind atthe Arc withstand Testsof High Voltage Insulator
Chains, Elektrotechnika, 1976/1, pp. 18–23.
 SZABÓ, SZ., Analysing HV Transmission Lines Secondary Arc Phenomena with Computer
Simulation diploma study, Budapest University of Technology and Economics, Dept. Electric
Power Engineering, May 2001 in Hungarian.
 Alternative Transient Program – Rule Book, Canadian/American EMTP User Group, USA,
 BÁN, G. – BÁNFAI, GY.– PRIKLER, L., The Commissioning Measurement of the 400 kV
Hévíz-Tumbri Interconnection at 1999, study, May 1999 in Hungarian,
 CSIDA, S. – KROMER L. I., An Improved Method for Determining Line Discharge through
Potential Transformers, IEEE PAS-97, 1978.
 The ABB EXLIM type ZnO surge arrester, description guide.
 VIZI, L., Development of Operating Frequency Arcs, PhD dissertation, 1998 in Hungarian.