PERFORMANCE WITH CONDENSER SUPPLEMENTARY CONTROLS
5. Typical response to flicker under lighting.
9.5. Saturated-Reactor Compensators 325 Neglecting any phase change between E and (which in practice is
small anyway), the supply current is constant. The voltage at all points upstream of the tapped reactor is therefore constant and free from fluc- tuations. In particular, since E
-
= the voltage at the supply end of the tapped reactor is constant and is given byThe voltage supplied to the primary of the furnace transformer is now given by Equations 19, 21, and 23 as
which is of the voltage E (or and is determined exclusively by the compensator and the furnace current.
A disadvantage of the plain arrange-
ment described so far is that the furnace open-circuit voltage is reduced to (see Equation 24 with from its original level which was inter- mediate between E and V, (depending on the other loads connected at the PCC and elsewhere), At the same time the short-circuit reactance is
increased from
+
to Both of these effectsreduce the furnace power. In order to restore the furnace supply to the condition it had without the compensator, the voltage boosting winding shown in Reference 8 has been successfully used. The alternative of reducing k by means of a capacitor in series with the saturated reactor is not used because it delays the response of the The power
factor is also reduced by the compensa-
tor, and capacitors are generally connected at the supply end of the tapped reactor. These are usually divided into banks and combined with linear air-core reactors to make harmonic filters to absorb harmonic currents from the furnace as well as from the compensator, and to avoid resonances. Filters for frequencies up to the 15th have been
9.5.2. The Polyphase Harmonic-Compensated Reactor Compensator
A second type of saturated-reactor compensator, quite distinct from the tapped-reactor arrangement described in Section 9.4.1, is the polyphase harmonic-compensated reactor. Sometimes called a compensator (because it can be connected directly to the furnace without the need for a tapped series reactor!, this compensator was developed by
Friedlander (see Figure 38 of Chapter Two main variants are monly used, the twin-tripler and treble-tripler reactors.
The basic principle is the same as that of the
Reactive and the Arc Other Consumers Furnace
T
T
Saturated Shunt Filters18. General for flicker with busbar-type of saturated- reactor compensator.
iron core to approximate an ideal constant-voltage reactive characteristic. In the twin- and treble-tripler reactors, however, the three phases are mutually coupled on a multiple-limb core in a
multiplying arrangement which results in the elimination of harmonic currents up to orders 1, where is the number of "phases" pro- duced the pulse-multiplication techniques used in rectifiers). In the twin-tripler = 6, and the lowest-order harmonic currents are the th and 13th. In the treble-tripler and the lowest-order
currents are are the 17th and 19th under balanced conditions. By loading the main reactor with a tuning reactor." which itself is loaded with a short-circuited delta-connected winding, the lowest-order harmon- ics can be further suppressed, leaving negligible residual harmonics below the 23rd and 25th in the twin-tripler and the 35th and 37th in the tripler under balanced conditions (1-1.5% and 2-4% respectively).
Shunt Capacitors
FIGURE 19. V-I characteristic of saturated- reactor of the busbar-type with and without shunt capacitors.
Current
References 327
Both of these harmonic suppression techniques have the additional effect of improving the linearity and flatness of the V-I characteristic to within over the normal range of currents from about 10% to 100% of rated current).'"' However, the linearity as well as the of the iron core can be unfavorabiy affected unless the slope is kept above about 7%. In arc furnace applications this residual slope reduces the effective compensation ratio. The obtainable flicker suppression ratio is somewhat less than what is obtainable with the
reactor compensator.
The internal harmonic canceiation in the saturated reactor
under unbalanced conditions, but the harmonic currents which apuear are usually not excessive in the presence of current harmonics from the arc furnace.
Shunt capacitors are usually provided for overall power-factor correc- tion. and these may be divided up into harmonic filters, typically for or- ders 3, 5, 7 and sometimes also for 4 and 6 and a "high-pass" branch
(Figure The shunt capacitors modify the resulting characteristic as shown in Figure 19. Compensators rated up to 177 have been applied at voltages up to 70 for rolling mills and other highly variable large loads as well as for arc furnaces.
REFERENCES
G. J. "Electric Furnace Succeeds in Technology and Profit." to MP-18, February 4, 1980.
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E. R. Freeman and J. E. Medley, Use of Power Electric Arc
Proc. February 1978.
H. Frank and "Raising the Production of Arc Furnaces by the Voltage with Thyristor-Switched Capacitors," ASEA J. 50 9-16 (1977).
Sundberg, "The Arc Furnace as a Load on the Network," A S M 49 75-87 L. E. Bock and A. H. Moore, "Application of Capacitors Arc Furnace Power Systems," Power 19 18-23. September 1976.
L. Dixon, E. Friedlander, R. Seddon, and Young, "Static Shunt for Voltage-Flicker Paper 7, IEE Symposium on Transient,
and Distorting Loads and Effect on Power and
February 1963. IEE Conference Report Series No. 8 "Abnormal Loads on Power Systems."
E. Friedlander, A. Telahun. and J. Young, "Arc-Furnace Flicker in Ethiopia," GEC 32 2-10 (1965).
328 Reactive Compensation and the Electric Arc Furnace
9. Berry et "Saturated Reactor Compensator Achieves Major Reduction of Flicker Caused by Arc Furnace Installation." presented at CEA Spring
Toronto, March 22-24, 1976.
M. Kennedy. Loughran, and D. J. Young, of a Suppressor to Reduce Voltage Fluctuations Caused by a Multiple Arc Furnace IEE
130-137, April 22-24, 1974.
E. A. J. Heath, and I). Young, Statrc Compensator for the BSC Anchor Project." IEE 110, April 22-24, 1974.
H. George and R. Gosselin. "Static Compensators of Simplified Construction as a Remedy to Power System Disturbances," 110, April 22-24. 1974.
13. C. G . Cooksley et "The Compensation of Voltage Dips and at Brrtish Steel Corporation's Anchor IEE 110. 124-129. April 22-24, 1974.
14. C. B. Cooper. E. Friedlander and D. J. Young, "Requirements and Compensatron Methods for Scrap Melting Arc Furnaces," Prrbl. 146-150, April 22-24, 1974.
15. R. Coates and G . L. Brewer, "The Measurement and Analysis of Waveform Caused by a Large Multi-Furnace Arc Furnace IEE 110.
April 22-24, 1974.
16. H. S. Brown, Hunter Memorial Lecture, November 1978, IEE, Elecrr. Power Appl., 2 99-107. June 1979.
R. Armstrong, "Predicting the Electrrcal Performance of Arc Furnaces." Proc. Elecrr. Appl. 1 (3). 86-90, 1978.
G. F. L. Dixon and G. "Supply to Arc Furnaces: Measurement and of Supply-Voltage Fluctuation," IEE 119 (April
C. Concordia, L. G. Levoy, and C. H. Thomas. "Selection of Buffer Reactors and Svnchronous Condensers on Power Systems Supplying Arc-Furnace Loads," AIEE
76, July 1957.
20. C. Concordia. "Voltage Dip and Synchronous-Condenser Swings Caused by Furnace Loads," AIEE 74. October 1955.
M. Black and L. F "The Application of a Series to a Synchro- nous Condenser for Reducrng Voltage Flicker," AIEE . 70, 145-150
A. Seki, J. and K. Murotani. "Suppression of Flicker Due to Arc Furnaces hv a Thvrrstor-Controlled Compensator," Paper A78 Summer Meet-
-, - *
Los Angeles, 1978.
23. M. Chanas, "Perturbations on Industrial and Systems Compen- sation by Static Means," Pt. 1, Rev. Electr. 87 December 1978, (in 24. M. Lemoine. Op. Pr. 2.
25. Charles, Op Electr. 88 49-57. January 1979.
26. M. and G 4, 58-72.
27 E. Wanner and W. "Static Power Factor Compensators for use with Arc Fur-
naces," 790
28. W E. and R. "Flicker Caused by UHP Arc Furnaces Using Scrap and Directly Reduced paper presented to CNBE-Brazilian Nattonal
References
29, E. and C. G. Robinson. "Report on Ultra-high Elec- tric Steel Furnaces," J. Metals. 67-75.
"Survey of Arc Furnace Installations on Power and Resulting Flicker." AIEE Trans., 1957.
J. Survey, Symposium on
Arc Furnaces, 1973.
32. A. and Gaussens. pur du Flicker,"
Elecrr. 7 Mav 1957.
33. Depenbrock. "Compensation of Rapidly Currents." 98,
June 1977. (in German).
34. G. Klinger. "Control and Regulation of a Self-Guiding Com- mutator Connection," 98, 411-414 (1977).
35. Klinger. "Tolerance Band Single-Phase Circuits with Selection of Control Values." 87-90. February 1976.
36. E. Friedlander. "Voltage-Flicker Compensation with AC Saturated Reactors.'
29 107-114
3 7 E. "Flicker Suppression for Single-Phase Resistance-Welding Machines," GEC Scr. 32 79-84 (1965).
38. E. and R. W. Lye, "A Compensator for Flicker Control on the Saskatchewan Power System," Presented to Canadian Electrrcal
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Chapter 10
dc wtnding
R3
winding
By Fourier analysis the ac waveform of Figure be decomposed into the following series of harmonic components:
sin
---
5- ---
7 11 13sin
...
+-
6
where is the rms value of the fundamental component of the ac line current (equal to and is the order of the harmonic. An alter- native transformer connection is shown in Figure with the primary winding in delta. The current in the secondary or winding is the same as in Figure but the 30' phase shift introduced by the deltalwye connection produces the stepped line current waveform of Figure 2d. Fourier analysis of this primary current wave yields the following of harmonics: