Digital Computer Analysis eled switches chopping inductive current that causes
31.8.2 Digital Computer Analysis eled switches chopping inductive current that causes
numerical oscillations. The use of artificial RC “snub- The main type of program employed for studies is an elec-
bers” helped to alleviate some of these problems. The tromagnetic transients program (EMTP) that solves sets of
choice of the snubber capacitor was a function of differential equations by step-by-step integration methods.
the magnitude of the current to be chopped and the The digital program must allow for the modeling of both the
timestep size.
linear and non-linear components (single- and three-phase)
3. The use of the trapezoidal integration method results and of the topological changes caused; for example, by valve
in numerical oscillations when the network admittance firing or by circuit-breaker operation. Detailed modeling of the
matrix to be inverted becomes singular. This is the converter control system is necessary depending on the type
direct result of modeling switches as truly either ON of study.
or OFF without representation of their intermediate The EMTP has become an industrial standard analysis tool
non-linear characteristics.
for power systems and is widely used. The program has had a
4. The requirement of a one-timestep delay between the checkered history and numerous variants have appeared. Ini-
main program and the transient analysis of control tially, the development of the program was supported by the
systems (TACS) subroutine for controls simulation. Bonneville Power Administration (BPA). Some of the draw-
5. The use of new VSCs with multiple switching per cycle backs in the capabilities of EMTP became more pronounced
made the problem of switching “jitter” much more as the modeling of FACTS with power electronic switches and
evident.
VSCs became more desirable.
6. The lack of user-friendly input and output processors.
848 V. K. Sood
A B vd_rec
C scope id_rec
scope
vd_rec
id_rec
VC 1 2 3 firing_inv_star
+ RL2 VC VC 4 VC 5 VC VC 6 f1 2 1 YY2 1.1572,22.58mH
f2
L=44 mH
3-phase 6-pulse bridge
REC_STAR_PLUS
dc_neg
INV_STAR_PLUS Bridge
6p_Bridge
f3 f4
f6 f5 4 5 10M + 6 230/205.45 220.0kVRMSLL /_67.43 ?v
1 + ?v 239kVRMSLL /_67.43
R8
dc_pos
firing_rec_star gates
V_pri_inv_a
10M
scope
v_pri_inv_b v_pri_inv_a v(t) p3 1
Gamma Detector
v_pri_inv_c
Rectifier AC Filters Gamma_min
REC_DELTA_PLUS
1 2 6-pulse bridge
V.K.Sood
gamma_min_star
C1 230.5/205.45 DC Filter
5.0143uF
RLC RLC 12.536uF
1 2 3 4 5 6 firing_inv_delta +
+ C2 10M
R9
dc_neg VC VC VC VC VC VC f1 f3 f2 3 2 1 Inverter AC
f4 4 1 YgD_3 2 1.062mH system
11th 13th 250.0 L3 + R2
firing_rec_delta
gates
DC Line
R7
Bridge 6p_Bridge
p2 v(t)
v_pri_rec_a v_pri_rec_b
scope V_pri_rec_a
10M
dc_pos INV_DELTA_PLUS
f5 f6 5 6
v_pri_rec_c
Rectifier AC system
REC_DELTA_MINUS
1 2 6-pulse bridge
VV1 Gamma Detector
gamma_min_delta Inverter AC Filters
amplitude 1.0 pu 2 width 200 ms
VV3 VV4
Gamma_min
V.K.Sood
RLC RLC 12.536uF C20 + C19
gates
time shift 300 ms
f2 R12 +
firing_rec_delta
f1 1 firing_inv_delta 11th 13th 250.0 L6 +
+ 1 + cSW1
a REC_STAR_MINUS
f4 f3 2 3 YgD_4
1.062mH
1 YY3
2 3-phase 6-pulse bridge +
195.4mH L8
10.35 R14
R18
dc_neg
1 Ph fault
dc_pos INV_DELTA_MINUS
Bridge
6p_Bridge
DC Filter
Gamma Detector
firing_rec_star
350mH
+ 2.5 VV1 VV2 VV3
Gamma_min
gamma_min_delta_minus
VV4
VV6 VV5
V.K.Sood
firing_inv_star Bi-polar 12p HVDC transmission system
f5 f4 4 5 1 YY4 2 Inverter: +/- 490 kV, 1.5 kA, Gamma = 18 degs, Ld = 350 mH
Things to do:
R15
1 2 3 4 5 6 f1 1
1. Add DC line
dc_neg VC VC VC VC VC VC f2 Rectifier: +/- 500 kV, 1.5 kA, Alpha = 18 degs, Ld = 350 mH 2 10M Bridge 6p_Bridge f3 3
230/205.45 AC:
f6 Following tests have been pre-programmed and tested: 6
+ 2.5 + 350mH
dc_pos INV_STAR_MINUS
Transformers with 10% Leakage Reactance per phase. 230 kV L-L on Line Side; 205.45 kV L-L on Valve Side.
R19 + Thevenin Sources At Rec and Inv.
2. 10% step change in Gamma order at inverter 1. 10% step change in I order at rectifier
Gamma Detector
DEV1
10M Timestep = Use 25 micro-sec.
3. Commutation failure at inverter
4. Single phase fault at rectifier showing mode shift
Gamma_min
gamma_min_star_minus
For information: V.K.Sood, [email protected]
V.K.Sood
FIGURE 31.33
A sample of the graphical input file of EMTP RV.
In recent years, considerable effort has been made by the The models used in the simulators and digital programs EMTP Development Coordination Group (DCG) to restruc- depend on the assumptions made and on the proper under- ture the program. This has resulted in the latest version called standing of the component and system characteristics; there- the EMTP RV (restructured version) (see www.emtp.com). fore, they require care in their usage to avoid unrealistic results The entire code of the program has been re-written and in inexperienced hands. graphical input and output processors have been added.
A sample of the graphical input file is shown in Fig. 31.33. The main advantage of digital studies is the possibility of correct representation of the damping present in the system.
31.9 Concluding Remarks
This feature permits more accurate evaluation of the nature and rate of decay of transient voltages following their peak The HVDC technology is now mature, reliable, and accepted levels in the initial few cycles, and also a more realistic assess- all over the world. From its modest beginning in the ment of the peak current and total energy absorption of the 1950s, the technology has advanced considerably and main- surge arresters. The digital program also allows modeling of tained its leading edge image. The encroaching technology stray inductances and capacitances and can be used to cover a of flexible ac transmission systems (FACTS) has learned and wider frequency range of transients than the dc simulator.
gained from the technological enhancements made initially The main disadvantage of the digital studies is the lack of by HVDC systems. The FACTS technology may challenge adequate representation of commutation failure phenomena some of the traditional roles for HVDC applications since with the use of power electronic converters. However, with the the deregulation of the electrical utility business will open increasing capacity of computers, this is likely to be overcome up the market for increased interconnection of networks [7]. in the future.
HVDC transmission has unique characteristics, which will
31 HVDC Transmission 849
provide it with new opportunities. Although the traditional References
applications of HVDC transmission will be maintained for bulk power transmission in places like China, India, South
1. E.W. Kimbark, Direct Current Transmission – Volume I, Wiley America, and Africa, the increasing desire for the exploita-
Interscience, USA, 1971, ISBN 0-471-47580-7. tion of renewable resources will provide both a challenge
2. J. Arrillaga, High Voltage Direct Current Transmission, 2nd Edition, and an opportunity for innovative solutions in the following
The Institution of Electrical Engineers, UK, 1998, ISBN 0-85296-941-4. applications:
3. K.R. Padiyar, HVDC Power Transmission Systems - Technology and System Interactions, John Wiley & Sons, India, 1990, ISBN • Connection of small dispersed generators to the grid.
0-470-21706-5.
• Alternatives to local generation. 4. D. Melvold, HVDC Projects Listing, Prepared by IEEE DC and Flexible • Feeding to urban city centers.
AC Transmission Subcommittee.
5. J. Ainsworth, “The Phase-Locked Oscillator – A New Control Sys- tem for Controlled Static Converters,” IEEE Transactions on Power Apparatus and Systems, Vol. PAS-87, No. 3, March 1968, pp. 859–865.
Acknowledgments
6. A. Ekstrom and G. Liss, “A Refined HVDC Control System, “ IEEE Trans. on Power Apparatus and Systems, Vol. PAS-89, No. 5/6, The author pays tribute to the many pioneers whose vision
May/June 1970, pp. 723–732.
of HVDC transmission has led to the rapid evolution of the 7. V. K. Sood, HVDC and FACTS Controllers – Applications of Static power industry. It is not possible here to name all of them
Converters in Power Systems, Kluwer Academic Publishers, Canada, individually. April 2004, ISBN 1-4020-7890-0.
A number of photographs of equipment have been included 8. L. Carlsson, G. Asplund, H. Bjorklund, and H. Stomberg, “Recent and in this chapter, and I thank the suppliers (Mr. P. Lips Future Trends in HVDC Converter Station Design,” IEE 2nd Interna- tional Conference on Advances in Power System Control, Operation
of Siemens and Mr. R. L. Vaughan from ABB) for their and Management, Hong Kong, December 1993, pp. 221–226. assistance.
9. C. Gagnon, V.K. Sood, J. Belanger, A. Vallee, M. Toupin, and
I also thank my wife Vinay for her considerable assistance M. Tetreault, “Hydro-Québec Power System Simulator”, IEEE Canadian in the preparation of this manuscript.
Review, No. 19, Spring-Summer 1994, pp. 6–9.
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Flexible AC Transmission Systems
E. H. Watanabe
32.1 Introduction......................................................................................... 851
Electrical Engineering Department,
32.2 Ideal Shunt Compensator ........................................................................ 852
COPPE/Federal University of Rio de Janeiro, Brazil, South America
32.3 Ideal Series Compensator ........................................................................ 853
32.4 Synthesis of FACTS Devices ..................................................................... 856
32.4.1 Thyristor-based FACTS Devices • 32.4.2 FACTS Devices Based on Self-commutated Switches
M. Aredes
32.5 Voltage Source Converter (VSC)-Based HVDC Transmission ......................... 873
Electrical Engineering Department, Polytechnic School and COPPE/
References ............................................................................................ 876
Federal University of Rio de Janeiro, Brazil, South America