design consideration for the eddy county static var compensator
TRANSCRIPT
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8/9/2019 Design Consideration for the Eddy County Static Var Compensator
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EEE
Transactions
on
Power
Delivery Vol 9
No.2
April
1994
DESIGN CONSIDERATIONS FOR THE
EDDY COUNTY STATIC VAR COMPENSATOR
757
H.
K.
Tyll, Member G. Huesmann K. Habur K.Stump,Sr. Member
W. H.
Elliott, Member
F.
E.Trujillo, Sr. Member
Siemens AG Siemens E&A Southwestern Public Services
ErlangeqGermany Atlanta, GA, USA Amarillo, TX, USA
KEYWORDS
SVC, thyristor controlled reactor (TCR), thyristor swit-
ched capacitor (TSC), reactive power compensation,
voltage control, filter design
ABSTRACT
This paper describes the steps for the design of the
Static VAR Compensator (SVC) Eddy County. The
specified system requirements on operating range, loss
evaluation and harmonic performance led
to
an SVC
configuration which contains one TSC branch, one TCR
branch for continuous reactive power control and two
double tuned filter branches. The system voltage
of
the
SVC secondary bus was optimized to 8.5 kV based on thy-
ristor equipment capabilities. The paper shows the voltage
and current stresses of the thyristor valves taking into
account system faults for the TCR branch and misfiring
effects on the TSC branch. The approach for filter design
considering the harmonic performance requirements and
resulting component ratings are shown. The Eddy County
SVC commenced commercial operation in April 1992.
INTRODUCTION
System studies conducted by Southwestern Public Ser-
vice indicated the need for reactive compensation between
50 MVAr (inductive) and
+
100 MVAr (capacitive). A Static
VAR Compensator system covering this range has been
designed and installed at the 230
kV
Eddy County sub-
station located in the southwest corner of the SPS system.
Figure 1 shows the SPS system in the area of Eddy Coun-
ty. Significant features of the Eddy County substation are
that it contains a back to back HVDC converter (rated 200
MW)
to
transfer power between the
SPS
system and
western New Mexico, it has a 345 kV connection
to
a
major generating station at Tolk, and it has a 230 kV con-
nection to generators in the Cunningham
/
Maddox area.
The purpose of this SVC is
to
provide voltage support for
the system and allow most efficient use
of
the generators
in the system.
This paper presents the SVC designed for the Eddy
County substation and highlights the main SVC design con-
siderations and procedures. The SVC secondary voltage is
optimized
to
take full advantage of the thyristors as proven
by type tests for the selected thyristor design. The circuit
configuration and SVC physical layout are presented. Filter
design considerations and techniques are discussed.
93 SM
450 7
PWRD
A
paper recommended and approved
by the IEEE Substations Committee of the IEEE Power
Engineering Society for presentation at the IEEE/PES
1993 Summer Meeting Vancouver B.C. Canada July
18- 22 1993. Manuscript submitted August 28 1992;
made available for printing April 5 1993.
PRINTED IN USA
NEW
MEXICO
\--- .
Roswell
Lubbock
Eddy County Cunningham DenverCity
To
EPE
Maddox
TEXAS
4
A
atisbad
345 V
230 kV
115
kV
Legend: - - -
- - -
HVDC Ba ck-to-Back
Station
Fig. 1 Location of the Eddy County Substation
NETWORK REQUIREMENTS
System characteristics:
Normal voltage
Max. cont. voltage
Min. cont. voltage
Max. phase voltage unbalance
Transient overvoltage
Normal base frequency
Normal frequency deviation
Min. cont. frequency
Max. cont. frequency
Short circuit power range
System harmonic requirements
Individual Voltage Distortion
Total Voltage Distortion (THD)
230 kV
1
.O
pu)
242 kV (1.05 pu)
219 kV (0.95 pu)
2
o
345 kV (1.5 pu)
60
Hz
20.02Hz
59.5 Hz
60.5 Hz
1.1
...2.0
GVA
1.O
1.5%
SVC basic data requirements
Design points
Rated inductive power -50 MVAr 1
.O
pu voltage
Rated capacitive power 1OOMVAr 1.O pu voltage
Operating range
Continuous cap. operation
0.85
to 1.1 pu voltage
Continuous ind. operat ion
0.9 to
1.1 pu voltage
Full inductive operation at voltages above
1.1
pu
0885-8977/94/$04.00 993 IEEE
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The data listed above results in a V
/ I
characteristic as
shown in Figure
2.
Below
0.85
pu voltage the SVC shall
operate at its capacitive limit. At voltages above
1.1
pu the
SVC shall operate at its inductive limit. The operation at
1.5
pu voltage is a limited period of
3
cycles. Within the
voltage range of
0.85 to 1 . 1
pu, any operating point else-
where in the shadded area is permitted.
I
TSC+TCR+FC
I
I
I
I I I
I
I 1
I
I 1
I I
I 1
100 50
I
I 1
design point design point
TCR+FC I
I
I
I
50
Oprim
in
MVAr
Continuous
V
operation
4
1 o 0.5
0 0.5
b r i m
in PU+
~leurCaf ivofi
-
apacitive
Operation
Fig.
2: V / I
diagram of the SVC Eddy County
as seen on the HV side
4
Capacitive
Range
SVC DESIGN
Inductive
Range
Basic configuration
Figure 3 shows a single line diagram of the SVC confi-
guration selected
to
meet requirements outlined in the
previous section. SVC capacitive requirements are met by
a
76
MVAr TSC branch and a 24 MVAr filter. The filter is
chosen to shunt away harmonic currents produced by the
TCR
so
that the harmonic distortion limits
of
the system
are satisfied. The TCR branch is rated for approximately 74
MVAr to compensate the filter and absorb the required
50
MVAr from the system. The MVAr figures are referred
to
the
230
kV bus and include the effect of the
12
SVC
transformer.
The TSC branch includes two surge arresters. An arres-
ter labeled CC in Figure
3
is connected across the capa-
citor to limit voltage in case the thyristor misfires at the
worst possible time. A second surge arrester labeled SR in
Flgure
3
connected across the TSC valve and reactor
protects the thyristor against overvoltages. Neither of these
arresters operate during normal SVC operation. They
protec the TSC branch from faults and misfiring transients.
Figure
4
shows the SVC operating diagram. There is an
overlap range of approximately
10
degrees where the TSC
may be either off or on depending upon past history. This
overlap is controlled by a hysteresis type effect and avoids
control instability at the TSC switching time even for the
case of large system frequency deviations as specified.
230 kV, 60 Hz
TSC
DF1
A
LTSC = 0.58 mH
C T ~ C
765 pF
LI = 0.81 mH
L2 = 73pH
C1
= 10000 pF
Cp
= 368pF
I
DF2
TCR
A
L3 =
0.20
mH
4 = 50pH
C3
= 1753 pH
C4 = 441 pH
R
= 7.5 Q
LTCR = 7.5 mH
Fig. 3: Single line diagram and data
of the SVC Eddy County
Fig.
4:
Operating diagram of the SVC Eddy County
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The TCR reactors consists of two coils per phase in-
stalled in a double stack arrangement. Reactors for the
TSC are installed
side by side. The filter arrangement
consists of two double tuned filters (DF). The first is tuned
to the 3rd and 5th harmonics and the second is tuned to
the 7th and ll.5th harmonics. The second DF includes a
resistance to achieve a high pass characteristic for the
higher harmonics.
Filter branches are tuned very accurately to keep the
harmonic distortion to a minimum and within specified
limits. Filter reactors have been designed with taps to
enable the inductance to be adjusted. This allows initial
mistuning due to reactor and capacitor manufacturing
tolerances to be compensated. Filter reactors are installed
in a triple stack arrangement. Hence, it is very important to
consider the influence of mutual coupling between coils to
achieve proper tuning. More information about the filter
design procedure is given in the Filter Design section.
Operatinq losses
formula.
The SVC losses are evaluated according
to
the following
LOSS-Cost
=
$Cl
x
A + $C2 x B + $C3 x C
A, B, C
$C l, $C2, C3
operating ranges
/
points
cost figures for A, B, C
$C1 = $1800
$C2
=
$56
$C3 = $56
A Average power loss in kW for SVC output on 230 kV
bus from max. inductive range to
0
MVAr
B Maximum power loss in kW for SVC output on 230 kV
from 0 MVAr to the net filter range
C Average power
loss
in kW for SVC output on 230 kV
from the net filter range to 100 MVAr.
Figure 5 shows the operating losses of the SVC as a
function of its reactive power output. The average losses of
the overall operating range based on the nominal ca-
pacitive power are 0.45%. The cost of losses evaluated
according the given formula amounts to
$
0.5 Mio. A loss
versus reactive power characteristic is shown in Figure 5
as dorred line. Comparable average losses would amount
to 0.43
Y
which is only slightly lower.
But converted to loss cost according the given formula
an amount of $ 1.1 Mio would arise. The difference of $
0.6 Mio justifies the higher installation cost using a TSC
branch.
Losses
1 F 100 Ind.
00 80 60 40 20 20
40
60
Reactive
Power
[MVAr]
Fig. 5: Operating losses
of
the SVC Eddy County
Physical Layout
Figure 6 shows the physical layout of the SVC system.
The branches (TCR, TSC and filters) are connected
to
the
secondary bus by removable links. This arrangement
allows failed branches to be disconnected
so
that SVC
operation can be resumed in a degraded operating mode.
Removable links used for branch connections allow a
lower cost design than disconnect switches. In addition to
lower hardware costs, removable links require less space
in the station than switches. Total area for the SVC equip-
ment is only 50
m
by 44.5 m.
Filters
k
Fig. 6: Layout of the SVC Eddy County
The SVC control building contains the open loop control
(PLC), closed loop control (regulation)[4,5], protection
system consisting of main and back-up protection, thyristor
valves with Valve Base Electronic (VBE), cooling system
for the thyriztor v&es and AC
/
DC distribution which
includes a battery unit. In addition the building contains
switchgear control cubicles and a transient fault recorder
from the
SPS
Company. The control room is airconditioned
and the thyristor valve rooms are ventilated to keep the
temperature within the allowed limits.
The thyristor valve cooling system is a single circuit
cooling system with outdoor water
/
air recooler fan banks.
To avoid freezing
of
the water during extreme cold weather
conditions a water
/
glycol mixture is used. The glycol con-
tent is approx. 30 . This will prevent the cooling system
from freezing at temperatures down to 5 degree F when
the SVC is not in operation. The cooling system includes
redundant pumps
(100
o redundancy). Two water / air
heat exchangers provide 100
oo
redundancy for
temperatures up to 92 degree F.
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DesiQncalculations for the thyristor valves
49.7 V.
25 kV
valve voltage
- 25 kV1
10 kA
29.0 V'
-
22.5
kA
15.8 kV
0 kV
10
kAr
T 7
Nominal secondary voltage for the SVC was chosen as
8.5 kV to make optimum use of the thyristor capabilities.
Three phase thyristor valves consist of three thyristor
modules stacked one above the other. Figure 7 shows a
three phase TSC valve. The Eddy County TSC valve con-
tains
14
hyristor levels and the TCR valve contains
7
thy-
ristor levels. The thyristors each have a current carrying
capacity of
4200
Arms and a peak blocking voltage of
5.6
kV. In the Eddy County design, rated TSC current is 3200
Arms
and rated TCR current is
3300
Arms. These design
ratings are below the
4200
Arms capability of the thyristors
and allow for additional stress due
to
short time overloads
and thyristor misfiring [l] In all cases, the junction
temperature remains well below 120 degrees C.
Thyristor modules applied in the Eddy County SVC
design have been extensively type tested for other
applications
[2].
est values are based on a draft paper of
the ClGRE working group
14.01
TF
02.
hat proposes tests
which are more applicable
to
real SVC valve stresses than
those which have been proposed by IEC
146.
F r u n t
v i e S i d e V i e w
, W a t e r t u b e s
n u b b e r c a p a c i t
W a t e r o o l e d
snubber
r e s i s t
Thyristor electronics
Fig.
7:
Drawing of a three phase TSC valve
Valve stresses in the Eddy County SVC have been cal-
culated with the NETOMAC
[3]
digital electromagnetics
program. Worst current, recovery voltage, and di
/
dt
stresses for the TSC valves occur during a misfiring event.
Misfiring calculations were based on the worst case
sequence of events as follows:
- The SVC is in full capacitive operation. This leads
to
the
maximum voltage on the secondary side of the SVC
transformer.
During this operation the TSC valves are blocked and
then the valve in the TSC leg with the highest capacitor
voltage is misfired.
-
The instant of misfiring is chosen at the time of
maximum blocking voltage across the TSC valve. This
results in maximum current magnitude and highest di
/
dt stresses.
Figure
8
shows the voltages and currents in the TSC
branch for this misfiring. The magnitude of the current
pulse was below 23 kA. Recovery voltage across the
blocked valve remained below
50
kV. This is well below
the blocking voltage of the
14
hyristor level TSC valve.
-
24.4 V
20kVL
I
\
10 kA
capacitor voltage
i30.1 kV
capacitor current, 22.5
kA
Fig. 8: Voltage and current stresses of a TSC branch
due to a valve misfiring
40 k V
4 k q -valve current AB
n
n
rq
w v
valve voltage
AB
9.35kA
valve voltage
CA
Fig. 9: Voltage and current stresses of a TCR branch
due to a three phase system fault
The worst stresses for a TCR valve occurs during a three
phase fault on the high voltage bus. Voltage and current
stresses for this case are shown in Figure 9. Note that
these traces show valve current when the valve is
conducting and voltage when the valve is blocked. The
sequence of events for Figure
9
were as follows:
- Full inductive operation at 1.5per unit voltage
- Fault initiation at the time when one TCR current is at a
peak
-
Fault clearing between
4
and 5 cycles after initiation
- TCR valve blocking at the first current zero after fault
clearing.
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that components are rated properly and not overstressed
in the extreme conditions.
The network impedance as a function of frequency must
be known for proper filter performance design. The
impedance versus frequency characteristics
of
the Eddy
County bus were computed for many system conditions.
The following parameters were varied during the system
impedance evaluation study:
-
range of generation
-
range of load
- various steps of HVDC compensation
- system configuration (lines out).
Figure 12 shows the system impedance boundary that
was determined from the impedance versus frequency
calculations. For all frequencies and system conditions, the
network impedance is somewhere within the shaded area.
Data given on the figure quantitatively defines the network
impedance region.
equiv
-
The TCR currents decay on the long time constant of the
TCR branches. Clearing of the fault at the most
unfavorable time adds an additional peak to the thyristor
currents in phases AB and CA. The TCR current in one
phase (CA in Figure 9) may be prolonged because of
delayed zero crossings. Junction temperature must remain
below 120 degrees C in this extreme case for the thyristors
to remain undamaged. Oscillation in the TCR current
during the decay period is due
to
the natural frequency of
the filters and the SVC transformer leakage inductance.
Figures 10 and 11 are examples from the thyristor type
tests which were performed at the CESl laborities in
Milano, Italy [2]. Figure 10 shows the resutts of a fault test
which is equivalent to a thyristor misfiring. Figure 11 shows
the result of a DC trapped current decay test. These tests
are more sever than the stresses computed for the Eddy
County thyristors in the TSC and TCR branches.
Calculation of the thyristor junction temperature verified
that it remains below 120 degrees C at the end of current
flow when the valve is required
to
withstand the recovery
voltaae. Hence, it is concluded that the thyristor valves in
Iv TCR
-
(Fault current test)
Fig.
11
Test results of the TCR valve type test
(DC trapped current)
Filter desiqn
Filter design is one of the most important steps in the
SVC design process. The first step in proper filter design
must ensure that the specified distortion limits are not
exceeded. The second step in filter design is
to
ensure
Fig. 12: Network impedance equivalent area
The equivalent circuit for all harmonic calculations is
shown in Figure 13. The TCR is represented as the
harmonic current source. In parallel the SVC filter and TSC
branches are connected. The TSC branch may be
switched off according
to
the SVC operation conditions.The
LV bus is connected via the transformer impedance
to
the
230
kV
system. At the 230 kV bus the HVDC filters and the
equivalent network impedance are represented. The HVDC
filter branches can be regarded according to the HVDC
operation.
Fig. 13: Equivalent circuit for harmonic calculations
At a first step without knowledge about the system
impedance only a filter tuned
to
fifth harmonic was
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assumed. Afterwards a two double tuned filter arrangement
had
to
be selected, but the total fundamental power for the
filter branch was not changed.
The worst resonance condition between the network
impedance boundary and the harmonic filters was
assumed for the calculation of the individual harmonic
voltage distortion. Harmonic voltage distortion was also
computed with the network circuit open. The total harmonic
distortion (THD) was computed with the two highest
individual harmonic distortion values from the worst case
network resonance conditions and the remaining harmonic
distortions determined with the network open circuited.
This yields to the worst possible THD results.
Harn
nonic performance is based on:
Nominal system voltage
Maximum initial mistuning due
to
tolerances
Detuning according temperature range
Assuming ma . magnitudes of TCR harmonic current
independant on firing angle
Negative sequence voltage content which gives rise
to generation of triple harmonics outside the delta
Firing angle unsymmetry which results in generation
of even harmonics
Loss of capacitor units of up to alarm level
Operating ranges of the TCR
Rating calculations for the filter components are done
seperately from the performance calculations. They are
based on similar conditions as above with the addition that
the following conditions are imposed:
- Maximum system voltage of 1.1 pu
- Increase of harmonic currents by 10°/~
- Extended detuning effect due to loss of capacitor
units up to trip level.
I -
Ambient harmonics
In principal the same equivalent circuit was used. The
limitation of the impedance area by the straight lines was
increased to 80”. The maximum impedance was set to
infinity. This leads to higher amplification factors and
results in higher safety margins for the components. The
influence
of
ambient harmonics on filter component rating
is considered assuming the infeed of harmonics from the
HVDC station at the 230 kV busbar.
kV
Fig. 14: Voltage and current stresses of the components
in the parallel circuit of DF 3
/ 5
Rating values of the components have also been
checked for transient conditions of:
- SVC energization
- Three phase system fault and voltage recovery.
-
Saturation by neighbor transformers
Figure 14 shows worst case stresses of the 3
5
DF
components during the condition of a three phase fault and
volta e recovery. Harmonic currents generated by the
HVD8 and SVC transformer results in extreme high
stresses for the filters. The voltage and current stresses of
the parallel circuit of the DF in this case determine the
actual rating values for these components.
CONCLUSION
A Static Var Compensator meeting the, -50 MVAr to
+
100 MVAr compensation range required by the
Southwestern Public Service Company has been designed
and installed at the Eddy County substation near Artesia,
New Mexico. Basic requirements on voltage and reactive
power were determined for Eddy County by computer
studies and project ions of future SPS needs. Costumer
load, fuel expense, voltage regulation, generation, energ
losses, and system reliability were considered in the SV
design specification.
A basic configuration consisting of a TSC branch, a TCR
branch and two double tuned filter branches has been
designed to meet the system requirements. An econo-
mical and efficient design has been achieved by applying
thyristors with surge arrester protection, where necessary,
that have been previously type tested for conditions more
severe than those that can exist in the Eddy County SVC.
Loss curves and evaluation has indicated favourable SVC
efficiency. Filter branches in the SVC were designed to
meet the SPS performance specifications and component
ratings were selected to exceed stresses imposed by the
system. Close working cooperation between Southwestern
Public Service Company and the SVC supplier during all
stages of the project (studies, design, installation and
commissioning) made it possible to meet all SVC
requirements and
to
put the SVC into commercial
operation within the scheduled time frame.
REFERENCES
G.Thumm, H.Tyll, ”A Closer Look at Thyristors in
SVC applications”, Siemens Energy and Automation,
Vol. 1 pp. 12-17, 1989
B. Endres, G . Thiele,
I.
Bonfanti, G. Testi, ”Design
and Operational Testing on Thyristor Modules for the
SVC Kemps Creek”, IEEE Transaction on Power
Delivery, Vol.
5,
No
3,
July 1990, pp. 1321-1328
W.Baver. K. H. Kruaer. D. Povh. B. Kulicke. ”Studies
for HVDC and SVC ‘Using the NETOMAC Digital
Program System”, IEEE CSEE Joint conference on
High Voltane Transmission Systems in China, 1987,
Paper 873C-32
H. Tyll, K. Leowald, F. Labrenz, D. Mader, ”Special
Features of the Control Svstem of the Brushv Hill
SVC”
,
Canadian Electrical Association, Power Sistem
Planning and Operation Section, Spring meeting,
Toronto 1989
K. Bergmann, B. Friedrich, K. Stump, W. Elliot,
Digital Simulation, Transient Network Analyzer and
Field Tests of the Closed Loop Control of the Eddy
County SVC”, IEEE 93
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BIOGRAFIES
763
Frank E. Truiillo was born in Deming,
New Mexico, on July 17, 1954. He
William H. ( Bill ) Elliott was born in Bird
City, KS on June
1,
1942. He received a
bachelor of sience degree in electrical
engineering from Kansas State
University, Manhattan, Kansas in 1965.
He joined Southwestern Public Service,
Amarillo, TX in 1965. Mr. Elliott’s
activities have been in the field of
system and transmission operation,
system engineering and planning.
~
Currently he is working as Principal
Engineer in Electrical Operation’s. Mr. Elliott is member of
the Institute of Electrical
&
Electronic Engineers (IEEE), the
Texas Society of Professional Engineers ( TSPE ) and the
National Society of Professional Engineers NSPE
).
Klaus Habur was born in Furth, Bavaria,
Federal Republic
of
Germany on April 8,
1952. He received his education at the
Ohm-PolytechnikumiNurnbergand at the
DAG-TechnikumMlurzburg. He joined
Siemens AG 1980 as a design engineer
for electrochemical plants. Previous to
this work, he was with a consulting
engineers company. In 1985 he joined
the Reactive Power Compensation Sales
Department and worked as a project
engineer and project manager for various SVC projects.
Gabriele Huesmann was born in
Munster, Westfalia, Federal Republic of
Germany on March 18, 1963. She joined
Siemens in 1982 and received an
education as engineers assistant. After
two years work in the Transportation
Systems department, she joined the
network planning department. Since
1986 she is active in the field of
programming, SVC design and harmonic
system analysis.
Keith B. Stump was born in Richmond,
Indiana, on February 12, 1941. He
received a bachelor of Science de ree
in electrical engineering from 8hio
University in 1963, and a Master of
Science degree in electrical engineering
from Purdue University in 1965. He was
employed by Allis-Chalmers Corp. in
Milwaukee, WI, from 1965 through 1977.
He then transferred to Siemens-Allis,
Inc. in 1978 which became Siemens
Energy &Automation, Inc., Atlanta,
GA.
Mr. Stump is
currently working in the Power Systems Technology
department in the area of system simulation and analysis.
Mr. Stump is a member of the IEEE Power Engineering
Society and vice chairman of the IEEE Surge Protective
Devices Committee.
received a Bachelor of Science Degree
in Electrical Engineering from New
Mexico State University, Las Cruses,
New Mexico in 1976. He joined
Southwestern Public Service, Amarillo,
TX in 1977. Mr Trujillo’s activities have
been in the field of system engineering.
Currently he is working as Senior Design
Engineer in the System Engineering
group for SPS. Mr. Trujillo is a Senior member
of
IEEE.
Heinz
K.
Tyll was born in Hof, Bavaria,
Federal Republic of Germany on May
15, 1947. In 1968 he graduated in
Electrical Engineering from Coburg
Polytechnikum. In 1974 he received the
diplom degree from the Technical
University of West-Berlin. After joining
Siemens AG, he worked in their High
Voltage Transmission Engineering
Department since 1975 in the field of
SVC system analysis with transient net-
work analyzer and di ita1 programs. Since 1988 with the
System Engineering &oup of the HVDC and SVC Sales
Department he is responsible for SVC design and
transmission system analysis. He is member of IEEE,
ClGRE WG 38 TF 04 and 05 and also IEC WG 22F TF
05.