Viability of Permanent Single Phase Opening of Lines in Extra High Voltage un s. Paulo
-
Upload
devastathor -
Category
Documents
-
view
218 -
download
0
Transcript of Viability of Permanent Single Phase Opening of Lines in Extra High Voltage un s. Paulo
8/3/2019 Viability of Permanent Single Phase Opening of Lines in Extra High Voltage un s. Paulo
http://slidepdf.com/reader/full/viability-of-permanent-single-phase-opening-of-lines-in-extra-high-voltage 1/5
VIABILITY OF PERMANENT SINGLE-PHASE
OPENING OF LINES IN EXTRA HIGH VOLTAGE
SYSTEMS
PART I – SECONDARY ARC EXTINCTION
F. A.T. Siha, Member IEEE J,A, Jardini, FellowMember IEEE
e-mall fats@!peausp br e-mad Jarduu(jpea,usp.br
University of S50 PauloAv, Prof. Luciano Gualberto, 158– trav.3
05508-900 – S2ioPaulo, SP, Brazil
Abstract: This paper discusses the viability of permanent single-
phase opening of lines in extra high voltage systems as a system
planning criterion. To apply such criterion it is necessary that :
(i) the secondary arc that appears after a single-phase fault
clearing is quenched; (ii) after a single-phase opening, the
current unbalances of negative and zero sequence in the electric
system are compensated. Power electronics are used to meet
targets. Only the secondary arc extinction condition is analyzed
in this part.
Key words: single-phase opening, secondary arc, unbalances
I. INTRODUCTION
The most common practice when a fault in a transmission
line causes its tripping is the three-phase opening, even if the
problem is in one phase only. Once the fault is eliminated,
the line reclosure occurs after a certain dead time when the
extinction of the secondary arc current is expected.
If there are multiple circuits in a section and the permanent
fault is in one phase, there is no interruption in the flow of
tran:jmitted power even when the three phases are opened.However, there will be a reduction of the transmitted power
during a the initial period after the line opening. This
situation is even more critical when there is only one circuit,
between sections, because the three-phase opening will
interrupt the power flow completely.
The single-phase opening can thus be seen as a way to
minimize this problem, since most faults in Extra High
Voltage (EHV) lines are of single-phase type.
However, the arc extinction conditions are more critical at
the single-phase opening than at the three-phase opening. Inthe latter there will be arc current due to oscillations of the
trapped charges in the line capacitances with their reactors;
these oscillations decrease over the time. In single-phase
opening, voltages in untripped phases may maintain the
secondary arc in values above the extinction limit.
If the permanent single-phase opening is chosen (a
practice not fully established), the load flow disturbance is
smaller than three-phase opening; therefore, more favorable
for the system stability. On the other hand, in the permanent
single-phase opening, there will be distortions in the system
(upstream and downstream the disconnected line), where
negative and zero sequence current and voltage components
will appear. The zero sequence components are blocked in
AY transformer; however, they might interfere in the
protection system. The negative sequence components pass
through to generators and loads being responsible sometimes
for undesired heating at the machines that may be
disconnected by negative sequence protections.
As a conclusion, there are two aspects to be considered in
the use of a permanent single-phase opening (with or
without reclosingj: (i) the extinction of the secondary arc in
the faulty phase (even Z~there is no reclosing), and (ii) the
elimination of current distortions downstream and upstream
the faulted line.
0-7803-5938-0/00/$10.00 (c) 2000 IEEE
8/3/2019 Viability of Permanent Single Phase Opening of Lines in Extra High Voltage un s. Paulo
http://slidepdf.com/reader/full/viability-of-permanent-single-phase-opening-of-lines-in-extra-high-voltage 2/5
Fig. 1. 765 kV Transmission SystemSingleLine Diagram
‘Thisarticle discusses a methodology for the compensation
of the arc current. The compensation I minimization of the
distortions in the system upstream and dowmtrea~ the
disconnected line is discussed in another article pI also by the
use of Power Electronics.
‘This cmnpensation of the secondary arc k obtained by
inserting a voltage source in the reactor, in the same phase as
the faulty phase. This source is constituted by a capacitor and
power transistors, thus providing the control of the moduleand phase angle of generated voltage.
‘The simulations here reported were performed using the
ATP Alternative Transient Program. The test system has
similar characteristics to the real 6300 MV& 765 kValternating current (AC) system transmission from Itaipu to
Siio PauI~ Brazil, with”a detaded representation of the-first
section with an approximate length of310 km. An equivalent
impedance represents the two remaining sections and the
receiving system (Fig. 1).
IL FAULT AND ARC EVOLUTION
To have the phenomenon described, the following aspects
were considered:
- Singte-phase fault in bus B after 100ms steady state pre-fault condition;
- Single-phase opening (BI-B3) 50 ms after the fault
initiation, remaining the connection to earth in B;
- Elimination of the connection to earth in B, after 1000 ms
of the fault initiation instant;
The current value from B to earth is shown in Fig. 2 and
the voltage in B is shown in Fig. 3. The single-phase to earth
current peak r-s 16M* being high until the opening of
the circuit breakers at both ends of the faulty line. As fromthis instant there is still current from B to earth with muchlower level, the secondary arc. This swomlary arc current
results from the coupling of the sound phases with the faulty
phase and the transient of trapped charges at line
capacitances at the instant of the circuit breakers opening.
When the secondary arc extinguishes, a recovery voltage in
the faulty phase appears (Fig. 3). If this voltage is high the
arc regnishes.
*From this point ahead kV and A refer topeak values
D & ~>
-&l--+G’
a) Steadystate and short circuit– Oto 200 ms
‘ltl,
300 I
, “
‘I*,,!-..)m
1- ‘--,00
.,-
b)With uhme A of B1-B3 owned – 200to 1500~s.
Fi& 2. Clnnmt tiwmB to earth- single-phase fault am!s@le-phase opening
arc regnishes.
Note that this phenomenon is repeated at all arc current
crossing zero until extinction takes place, In Fig. 2 an arc
extinction was assumed at the instant 1100ms.
Fig. 4 shows the area as related to arc current and recove~
voltage, where the arc extinguishes [2].
III. TRANSIENT STADILI~Y
It is desired to comnare the effect in the system when a
single-phase or a three~phase breaker opening is adopted.
Therefore, the verification of influences of these types of
openings in power oscillations (transient stabili~), shall be
evaluated with proper program, However, a first insight can
“ ,,”,
O!---6,,
4,0
,00
20”
<“”
,0” J
r“-” ,..1Fig.3. Phaseto earth voltage at bus B
0-7803-5938-0/00/$10.00 (c) 2000 IEEE
8/3/2019 Viability of Permanent Single Phase Opening of Lines in Extra High Voltage un s. Paulo
http://slidepdf.com/reader/full/viability-of-permanent-single-phase-opening-of-lines-in-extra-high-voltage 3/5
180
i60
140
120
100
30
60
40
20
—
kV peak
!
10 20 30 40 50
Fig. 4 – Arc Extinction
Secondary arc current x Recovery voltage first peak
be c]btained by examining the power step at the instant just
after the three-phase or single-phase opening, without line
fault. The power variation is smaller when single-phase
opening is used as in the case of three-phase opening (813
MW against 410 MW arriving at Itaipu bus); therefore, better
for the system stability. However, currents (and voltages)
unbalances occur at the generator and at the receiving system
(Table I).Table I
Current from A to Itaipu at A
Positive sequence 4>70kA
I Negative sequence 0,35 kAI 7em seouence I (1
IV. CONDITION OF ARC EXTINCTION
For comparison the Base Case consisting of a single-phase
fault in B was run.
The three-phase line opening was simulated and it was
found that after 1600 ms the arc current is 35 A. Upon the arc
extinction the first peak of the recovery voltage at fault point
is 23 kV. The arc current and the recovery voltage valuesmeet the extinction criteria defined in Fig. 4.
With the single-phase opening the arc current remains 97
A (Fig. 2), and the first peak of the recovery voltage, (if the
arc extinguishes) 77 kV (Fig, 3). By the criterion defined on
Fig. 4 the arc is unlike to extinguish.
Note: Literature states that fast grounding switches mq
help arc extinction. It is also known that the
parameters represented in the simulation, like the
reactor resistance, may inruence the results. These
aspects will not be discussed here because this
work aims at using Power Electronics to get the
so-called extinction.
I,Al, ” B,
i
‘“~” –4 ‘-””4-”+ c-
+ ,3–~––-+--~ ; -
a..- .-
i
\
)--*+---”--
~)4 1 ;:“)[ H, - ‘:,( .-r _ _’H:-----
~1jc~.:~v=o”-’—Fig. 5. Arc compensation source scheme used forthe secondary arc
extinction
V. THE USE OF VOLTAGE SOURCE TO GET THE
SECONDARY ARC EXTINCTION
The aim is check the effectiveness obtained in the
reduction of the secondary arc current (Base Case single-
phase to ground fault – single-phase line opening condition)
by using a voltage source (arc compensation source) in series
with one of the reactors of the open line (Fig. 5).
A. Determination of the Voltage Source Characteristics
The Base Case was run, in steady state condition, andfollowed the procedures bellow described:
- With single-phase fault in B, and without arc compensation
source, the arc current was determined.
- The same case was run with generators (G1 and G2)
bypassed and with the voltage source on (connected to the
reactor in B1).
Testing different values, the source voltage (module and
phase) that feeds a current opposed to the arc current of the
previous step was determined. Note that, the principle of the
superposition of the sources (G1, G2 ~d VsouRcE ) was
therefore considered.
- Then the case with all system sources and with the presence
of VsOuRcE connected to the reactor at Itaipu was again run
so that the results in this step contain the new value of the arc
current modified by VsouRcE
This procedure was repeated for all other fault locations
down the line as for the arc compensation source connected
to the two line reactors, one at a time, The result with the arc
compensation source at B1 side is shown in Table II, being:
IARC= arc current without V~ouRc~
VsouRc~= voltage source determined for secondary arc
cancellation
I*Rc~= arc current with VSOUKE connected
IREACTOR= reactor cmrrentwithout VSOUKCE
0-7803-5938-0/00/$10.00 (c) 2000 IEEE
8/3/2019 Viability of Permanent Single Phase Opening of Lines in Extra High Voltage un s. Paulo
http://slidepdf.com/reader/full/viability-of-permanent-single-phase-opening-of-lines-in-extra-high-voltage 4/5
TABLE II
ARC CURRENT ANDVOLTAGE SOURCEFORSECONDARYARCEXTINCTION (CONNECTED AT B1 SIDE)
Fault location I~~c(A, “cl) VSOURCE (kV,Oel) IM,C,.(A, “cl) Iw~c~o~(A,”el)
B 97I@ 193Im 0,4 Im 14l=B1 95 Ifl 1811~ 0,7 IN 25 l=
B2 99 IQ 195 lx 3,0 IN 8 IW
l/4(B 1-B2) 96 Ifl 1891+J!WJ 0>6Ifi 19\w
3/4(Bl-B2) 100 I@ 195Im 0,3 Im o
Note that, in the table, the value of ( 360° +@IREACTOR,
where @~R~Ac-rO~s the phase angle Of IREACTOR is
closed to the desired V50URCE phase angle, and will be
referred here as Reference Phase.
B. Xensibi[ity analysis
The calculation was repeated with fault at various points
down the line.
The arc compensation source voltage applied was:
‘SOURCE = ‘13600+ ‘IREACTOR (1)
The reason for such angle choice was because it is closed
to the determined ideal value and that @ImAc~oRcan be
measured. The magnitude of E is to be determined. The
results are presented in Fig. 6.
Next, the sensibility to arc compensation source voltage
phme angle was determined by applying:
V50URCE= 200 kV 1360°+ @lREAcToR+ A@” (2)
Being: A@= variation of angle for the sensibility analysis
(in electrical degrees),
The 200 kV was chosen, because this value, is within the
range where the arc value is very low for the various
fauhlocations (Fig. 6).
The secondary arc current sensibility to the phase angle of
the source is shown in Fig. 7, to the arc compensation sourcekAULr
LO CA I ’1ON
1
“’%-5+-=J
125 175 225 275
E (kIJ)
From figures, one realizes that even with a t 20%
variation in E the arc current is bellow 50 A.
Similarly a + 20° variation in the arc compensation source
voltage phase angle as related to the Reference Phase does
not lead to arc current above 50 A.
C. Secondary Arc Extinction - Transient Analysis
For the performance analysis of the arc compensation two
tests were carried out: one using an ideal AC voltage source;
and then a power electronic based DC-AC source.
1) Ideal AC source : In the Base Case, at the instant t = 498 ms,
the ideal AC voltage source of 193 1201Q kV is
inserted inthe system. In an almost steady state condition the
arc current value is 32 A and the recovery voltage in the first
half cycle afler the arc extinction is 1.8kV. Therefore, the arc
current extinction is expected.
Having the same procedure repeated, but
V50URCE= 2001218° kV ( average value, passible of
adoption), the values 32 A and 25 kV for the arc current and
the recovery voltage, respectively, are obtained. Being also
satisfactory the conditions for arc extinction.
2) DC-AC Source : With a DC-AC inverter source, it is
possible to produce a device (Fig. 8) which generates a
sinusoidal waveform similar to the one of the ideal AC
source. This inverter has PWM (pulse width modulatecJ
control with a pulse frequency larger than the network’s. The
generated voltage therefore is not a pure sinusoidal waveFAULT
LOCATION
!
o—
!25 1/5 — 225 275 325
PHASE (degrees)
Fig. 7. Arc currentx Voltage source phase
(source in the reactor at Bl)Fig, 6. AJ-Ccurrent x Source voltagemodule(source in the reactor at B 1)
connected to the reactor at B1,
0-7803-5938-0/00/$10.00 (c) 2000 IEEE
8/3/2019 Viability of Permanent Single Phase Opening of Lines in Extra High Voltage un s. Paulo
http://slidepdf.com/reader/full/viability-of-permanent-single-phase-opening-of-lines-in-extra-high-voltage 5/5
rlTAIPU B, B B2 03 c
F’~+””+ -
b
7---”--”&R~---..
-. — .)
I
n “,.”,,,“1,...,;:S;1
T,II CH4!
-< ->
, r-t ‘“”o”’”_
~~.,
Fig. 8. DC-AC arc compensationsource
I1 1
1
Fig. 10. Current at the fault point (B to earth), phase a,Btie Casewith the insertionof Vs&acE= 153kV (DC).
The extinction can be facilitated when an opposed current
to the arc is injected through a power electronics based
device.
VII. ACKNOWLEDGMENTSx–a I
n–d
cl, m, a, .–a,
111 1dIGNALI
IT LnSIGNAL2 UI
~_...t (.s)
Fig. 9. SwitchingControl Signals
and contain different harmonics. Some harmonics can be
eliminated by selecting appropriate switching times @ing
angles) as shown in Fig. 9.
For a square wave of 153 kV (equivalent to AC source of
193kV peak) the arc current is of 40 A and the recovery
voltage is of 2.3 kV, satis~ing the condition for arc
extinction (Fig. 10).
The required power of this inverter is about 10 MVA (200
kV and 100 A). This device could be obtained by using a
10~200kV transformer ratio, with the source located in the
low voltage side supplying a 2 kA current.
VI. CONCLUSIONS
After single-phase opening in EHV AC systems, the
secondary arc current resulted fi-om the capacitive coupling
of the sound phases with the faulty phase, can reach values
where there is no guarantee of its extinction in due time.
The authors gratefidly acknowledge the contributions of
Edson H. Watanabe, Clovis Goldemberg and Carlos M. V.
Tahan for their suggestionsfor this work and the CNPQ for its
sponsorship.
VIII. REFERENCES
[1] F. A. T, Silva and J, A, Jardini, “Viability of permanent single-phase
opening of lines in extra high voltage systems, Part II – Unbalance
cancellation”. Submitted for publication, IEEE, PES, 1999.
[2] W. Sate, J, A. Lima and G, Borgonovo. “Interconnection ; An
alternative using static compensation”. In: SEMINARIO
NACIONAL DE PRODU@O E TRANSMISS~O DE ENERGIA
ELETRICA, 5. Recife, 1979.Anais. s.n.t. (inPortuguese)
[3]O. A. Ciniglio and D. P. Carroll “Improved power transfer during single
pole switching a symmetrical sequence filtering approach.” IEEETransactions on Power Delivery, v.8, n.1, p. 454-460, January
1993.
[4] E. W. Kimbark, “Suppression of ground-fault arcs on single-pole-switched EHV lines by shunt reactors”. IEEE Transactions onPower Apparatus and Systems, v.83, p, 285-290,March 1964.
[5] B, R. Shperling, A. Fakheri, and B. J, Ware. “Compensation scheme for
single-pole switching on untransposed transmission lines”. IEEE
Transactions on Power Apparatus and Systems, v.97, n.4, p.
1421-1429,July/August 1978.
[6]N. Knudsen “Single-phaseswitchingon transmis~ionlines using reactors
for extinction ofthe secondaryarc”, CIGRE, Report 310,1962.
0-7803-5938-0/00/$10.00 (c) 2000 IEEE