CA2082056C - An electrically variable current limiting reactor for precipitators - Google Patents

Abstract

An electrically variable current limiting reactor (24) which is usable in association with a power supply (14-22) for an elec-trostatic precipitator (10, 58) is disclosed herein. The current limiting reactor (24) is capable of having the inductance value there-of varied responsive to system operation conditions. Most particularly the inductance of the current limiting reactor (24) can be modified responsive to the form factor of the sinusoidal AC input current to the power supply transformer. Additionally, the in-ductance of the current limiting reactor (24) can be controlled responsive to the fractional conduction of the full wave rectified current waveform at the output of the full wave rectifier of the power supply. Other conditions can be monitored to control the inductance value of the current limiting reactor (24) such as physical system parameters. An automatic operating control may modify the inductance of the current limiting reactor responsive to the current entering the primary of the transformer of the pow-er supply.

Description

-~0~205~
~. .
AN ELECTRICALLY VARIABLE CURRENT LIMITING
REACTOR FOR ~K~;cL~l~lATORS
DESCRIPTION
BACKGROUND OF THE INVENTION
5 1. Field Of The Invention Continuing ~ ~-c; q on environmental quality and recent new ,' ~cic on air quality in particular have resulted in increasingly stringent regulatory control of industrial .omi Ccif)nc~ One technique which has proven 10 highly effective in controlling air pollution is the removal of undesired particulate matter from a gas stream by electrostatic precipitation.
An electrostatic precipitator is an air pollution control device designated to electrically charge 15 and collect particulates generated from industrial processes such as those occurring in cement plants, pulp and paper mills and utilities. Particulate-laden gas flows through the precipitator where the particles acquire a charge. These charged particles are attracted to, and 20 collected by, oppositely-charged metal plates. The cleaned process gas may then i~e further processed or safely discharged to the atmosphere.
The electrostatic precipitation process involves several complicated, interrelated physical - -h~n;rmc:
25 The creation of a nonuniform electric field and ionic current in a corona discharge; the ionic and el~ctronic *

Pcr/ussl/0l74s ~2~
charging of particles moving in ~: ' in~d electro- and hydrodynamic fields; and the t~lrblllf~nt transport of charged particles to a collect~Dn surf ace . Because of J
this, many practical considerations can act to reduce 5collection ef f iciency .
To maximize the particulate collection, a precipitator should operate at the highest practical usahle energy level, increasing both the particle charge and collection ~ ~r~hi 1 i tles of the system. At the same 10time, there is an energy level above which arcing or "sp~rkin~", a temporary short which creates a conductive gas path, occurs in the system. M~cimi7.in~ the efficiency of an electrostatic precipitator re auires operating the system at the highest poseihle usahle energy level.
Ideally, the electrostatic precipitator should operate constantly at its point of greatest f~f f ~ c~-~r~ry.
Unfortunately, conditions unaer which an electrostatic precipitator operates, such as temperature, comhustion rate, and the rhf~mJc~l composition of the particles heing 20collected, change constantly. This ~ tes calculating parameters critical to a precipitator ' s operation .
2. Description Of The ~rior Art This invention relates to electrostatic 25precipitators in general and cp~cifi~lly to precipitator power supplies. Prior art precipitator power supplies have used either saturahle core reactors or silicon-controlled rectif iers ( SCRs ) paired with a f ixed-value current-limiting reactor (CLR). This invention relates to 30 an illl~L~ V~..~llt of the CLR.
Prior art ~:LRs have an inductance of f ixed value with several taps for selecting other values. The number of taps available is limited, typically to three.

WO 92/16302 ~Cr/US91/0174S
~ 2~21~

Adjusting the inductance of the CLR requires that the precipitator f ield section be powered down and taps manually changed.
A CLR of the correct value contributes to 5 protecting the precipitator power supply f rom the destructive ef f ects of arcing or spark currents and ensures greater electrical and particulate collection Pf f i ~-iPn~iPc .
Prior art devices useful for voltage and current 10 control of power supplies have been disclosed in various patents i n~ 1in g U.5. Patent No. 1,372,653 issued March 22, 1921 to F. Dessauer on an Electrical Transformer System; U.S. Patent 1,702,771 issued Feb. 19, 1929 to Y.
Groeneveld on an Amplifying Transformer; U.S. Patent No.
1,73Z,715 issued Oct. 22, 1929 to F. ~PcsAllpr et al on an Electromagnetic Induction ApRaratus; U. S . Patent No.
1,896,480 issued Fel:. 7, 1933 to A. Christopher on a BAlAnrPd Inductance Device; U.S. Patent No. 2,878,455 issued March 17, 1959 to C. Lamberton et al on a Three 20 Winding Transformer; U.S. Patent No. 3,483,499 issued Dec.
9, 1969 to L. Lugten on an Inductive Device; U.S. Patent No. 4,020,438 issued April 26, 1977 to A. MAnir^-lPthU on an Autotransf ormer With Series And Tertiary Wlndings Havlng Same Polarity T _~'An-~e; U.S. Patent No. 4,513,274 issued April 23, 1985 to M. Halder on a Current Transformer For Measuring In:,LL, -ts; U.S. Patent No.
4,590,453 issued May 20, 1986 to A. Weissman on an Autotransformer With Common Winding Having Oppositely Wound Sections; U.S. Patent No. 4,916,425 issued April 10, 30 1990 to N. Zabar on an Ele~ n~otic Device and U.S.
Patent No. 4,973,930 issued November 27, 1990 to U. Mai et al on a Twin Coil.
An alternative to the silicon-controlled rectif iers paired with a f ixed-value current limiting WO 9~16 302 PCr/US91~01745 ;~a~205~ ~
. ~

reactor is a saturable core reactor. The saturable core reactor ( or saturable reactor ) was originally developed in Germany and was used in the United States extensively from 1945 foreward. The principal application has been to 5 control the power applied to heating elements. Saturable reactors are electrically and ~hiln;c~lly rugged. In recent years, their ~unctions have been largely taken over by silicon-controlled rectifiers; as a consequence, the saturable reactor has been relegated to obscurity.

SUM~ARY OF T~IE INVENTION
The present invention generally provides a current limiting reactor f or use within a power supply system for a electrostatic precipitator wherein the 15 inductance of the current limiting reactor can be electrically, automatically and cont~n~lollcly modified responsive to system conditions. By continuous monitoring of the correct system conditions the variation in the inductance of the current limiting reactor can increase 20 the average voltage and current within the precipitator f ield . The ultimate result of this more caref ul and accurate control is that the destructive effects of spark currents on equipment are minimi7ed and the electrical and particle collection eff;r!i~nc~c are ~nh~n~-r~d.
2 5 Furthermore the overall average voltage and current in the precipitator fields can be increased before spark over actually occurs such as to permit a higher overall power level bef ore spark over . Fur~hf~ _ e it is particularly important that the variable currer~t limiting reactor of 3 0 t~e present invention be constructed such as to automatically attain its maximum inductance value if an open circuit condition occurs in the control circuit or control wlnding. In this manner the automatic protection WO 92/l6302 PCr/US9l/0174S
ag20~

of equipment will be achieved if excitation of the control winding is lost.
The basic precipitator power supply i n~ c a silicon controlled rectifier stack which preferably - 5 includes two individual silicon control rectif iers connected in an inverse parallel conf iguration in series between a line voltage power source and the current limiting reactor. An automatic control can be operative to modify the output of the silicon control rectifier stack to modify the power output of the silicon controlled rectif ier stack . When operated at maximum power the silicon controlled rectifier stack output ;n~]ll~ c a sin--cr);~lAl AC current waveform. However when operated below the rating thereof there is a naturally occurring deterioration of the wavef orm in addition to the power output .
The current limiting reactor is positioned in series with respect to the silicon controlled rectif ier stack . In prior art conf igurations this current limiting reactor was of a fixed inductance value or had various taps to allow some element of modif ication of the inductance thereof between fixed values. Changing of the inductance value normally required powering down the system in order to make the change in the current limiting reactor. With the present invention this current limiting reactor is dynamic and continuously responsive to system parameters in order to vary the inductance thereof.
The operative current limiting reactor is connected to a transf ormer rectif ier set . Initially the primary of the transformer receives the low voltage and high current signal an~ transforms this to a high voltage and low current signal in the secnnA~ry of the transformer. The output of the step-up trans~ormer s~ n~l~ry is provided to a rectifier which provides a high 16302 PCr/US91/0174 208~056 6 voltage DC signal to the precipitator to f acilitate collection of particulate matter.
In one conf iguration of the dynamic current limiting reactor of the present invention the control winding is cQnnected to a variable DC power source. This control windlng is adapted to vary the inductance of the current limiting reactor responsive to variations in the DC power source . With this conf iguration electrical coupling between the control winding and the inductor winding or windings of the current limiting reactor is achieved through a magnetic core. In the preferred physic21 configuration two identical inductor windings are wound about a magnetic core. ~he core extending through each inductor winding extends throus~h the control winding in opposite directions to yield a resultant instantaneous f lux through the control winding of zero . As such with this conf iguration the inductance of the CLR control device is a function of the magnitude of the DC current passing through the control winding.
Operation of the control winding can be automatic responsive to sensed system conditions such as the dynamic variables wlthin the precipitator f ield .
These dynamic variables can depend upon the type of material being precipitated, the temperature or ~les:-uL~
conditions or other various dynamic conditions. Variation in the DC power source can be achieved manually by an operator responsive to visual reading of the parameters or can be automatically variable.
Pref erably variation in DC power supply to the control winding is responsive to the shape of the AC
waveform at the input of the primary of the transformer rectif ier set or is responsive to the shape of the rectif ied AC wave at the output of the transf ormer rectifier set. Both the maintenance of a low form factor 16302 PCI/US9l/01745 ,. ~2Q~2056 and the maintenance of a high secondary f ractional cor~luct i nn have been shown to be excellent parameters f or maintaining accurate control o_ variations in the inductance of the current limiting reactor as will be 5 shown in more detail below.
As an alternative conf iguration the present inventiorl can include a somewhat 'i f; Pfl automatic system for controlling the inductance of the current limiting reaetor wherein a eurrent transformer utilizes the primary 10 current passing in series from the silicon controlled rectif ier to the transf ormer rectif ier set as the primary with a transformer secondary winding extending thereabout.
The output signal of the current transformer sec--n~lAry winding is rectified by a conventional full wave bridge 15 rectif ier and is provided to the control winding of the current limiting reactor control winding. The DC current through this control winding will then modify the inductance of the inductor winding which is in series between the silicon controlled rectif ier stack and the 20 current transformer primary. In this manner the inductance value of the inductor winding of the current limiting reactor will be proportionally responsive to the current at the primary of the transf ormer rectif ier set .
It is an object of the present invention to 25 provide an electrically variable current limiting reactor wherein utilization with an electrostatic precipitator is greatly PnhAn-'Pd.
It is an object of the present invention to provide an electrically variable current limiting reactor 30 wherein variation in the inductance therein is made possible responsive to system parameters.
It is an object of the present invention to provide an electrically varlable current limiting reactor particularly usable with a power supply for an WO 92/16302 PCr/US91/01745 2~8~6 8 electrostatic precipitator wherein a low f orm f actor of the input current signal at the primary of the transformer rectifier set is maintained. , It is an object of the present invention to 5 provide an electrically variable current limiting reactor particularly usable with a power supply f or an electrostatic precipitator wherein a high q~f-nn~lAry fractional conduct~on at any power level is achieved at the output of the full wave rectifier o~f the transformer lO rectifier set.
It is an object of the present invention to provide an electrically variable current limiting reactor particularly usable with a power supply for an electrostatic precipitator wherein the destructive effects 15 of arcing or spark currents are minimized.
It is an object of the present invention to provide an electrically variable current limiting reactor particularly usable with a power supply for an electrostatic precipitator wherein greater electrical and 20 par~;c1~lAte collection eff;c~i~nr;~ are achieved.
It is an object of the present invention to provide an electrically variable current limiting reactor particularly usable with a power supply f or an electrostatic precipitator wherein '; f i ~Ations of the 25 inductance of the current limiting reactor can be achieved without having the precipitator field powered down.
It is an object of the present invention to provide an el~c~rin~lly variable current limiting reactor particularly usable with a power supply for an 3 0 electrostatic precipitator wherein the overall average voltage and current in the precipitator f ield is increased before spark over occurs thereby permitting a higher overal~power level before spark over.
It is an object of the present invention to Wo 92~16302 PCl'tUS91/01745 9 208205~ -provide an electrically variable current limiting reactor particularly usable with a power supply for an electrostatic precipitator wherein the current limiting reactor automatically goes to maximum inductance value responsive to an open circuit occurring within the control circuit or the control winding.
It is an object of the present invention to provide an electrically variable current limiting reactor particularly usable with a power supply f or an electrostatic precipitator wherein automatic protection of all e~auipment is provided if the control winding excitation is lost.
BRIEF DESCRIPTION OF T~IE DRAWINGS
While the invention is particularly pointed out and distinctly claimed in the conrll~Ai n~ portions herein, a preferred ~ i t is set forth in the following detailed description which may be best understood when read in connection with the ~ ying drawings, in which:
Figure 1 is a schematic illustration of a typical precipitator power system;
Figure 2 is a graph of a conventional ~:~n~lcoiiii-wavef orm;
Figure 3 is a vector diagram for ~et~rm;n;n~ the ;mp.or-7i~nf~ of the current limiting reactor;
Figure 4 is a graph of kilovolts vs. m; l l; i 5 showing the advantages of the variable current limiting reactor over the prior art f ixed current limiting reactor;
- Figure 5 iE a schematic of an: ' -';- t of an automatic electrically variable current limiting reactor;
- Figure 6 is a schematic illustration of an embodiment of the general coil and core conf iguration f or l6302 PCr/US91/0174 20820~

an electrically variable current limiting reactor;
Figure 7 is a perspective illustration of an ; `,oAir^nt of the electrlcally variable current limiting reactor shown in Figure 6;
Figure 8 is a perspective illustration of an ~ho~l; r t of the general eoil and core eonf iguration f or an electrically variable current limiting reactor; and Figure 9 is a graph of a transfer function of an electrically variable current limiting reactor.
DETAILED DESCRIPTION OF T~E ~ ;KK~ ~M72f~DIM~T
The present invention is designed to provide a precipitator f ield 10 where particulate matter is actually collected. It is made up of collecting plates connected to one side of the precipitator power supply. The other 15 side of the supply is conneeted to discharge electrodes 58 which are l~n; fnrmly spaeed from the colleetion plates.
The field, in effeet, forms a capacitor, two conduetors separated by an insulating material. The precipitator power supply is operated at a very high direet-current 20 voltage which charges particulates e~tering the field as well as causing them to be attracted to the collecting plates. As the voltage of the preeipitator power supply is increased, particulate collection increases. The voltage cannot be increased infinitely, however; the 25 practical high-voltage ceiling is limited by the electrical ratings of the e~uipment and by the occurrence of sparking in the f ield.
Sparking in the f ield occurs when the voltage is high enough to ionize the gas between a discharge 30 electrode and a collectlng plate. Ionized gas is a conductor, so the result is a localized eleetrical breakdown of the gas causing energy stored in the 02 PCr/US91/01745 11 - 2~2~56 capacitive f ield to be discharged through the breakdown, somewhat like lightning. This event defines the maximum energy level that can be sustained in the precipitator f ield at the time it happens . When a spark occurs, it is 5 effectively a short across the se~nfl~ry of the transformer-rectifier (TR) set 22. If the precipitator power supply is not interrupted when a spark occurs, the spark may be maintained, caus ing current f low in the precipitator to become very high as energy is gained rom 10 the power supply. Spark currents are wasted energy; they do not contribute to the collection of particulates.
Uncontrolled, they damage precipitator system c, ~e~ts, both mechanical and elcctrical, and greatly reduce collection ef f iciency .
To determine the size of the precipitator field, many factors must be considered: The type of material being collected, the size and resistivity of the particles, and the operating temperature are principal among them. In most industrial pr~cipitators, more than 20 one ield is used. A typical application will ind precipitator fields arranged one behind another as inlet ield, second field, third field, outlet field, etc.
A transformer rectifier (TR) set 22 is a combination step-up transformer and full-wave rectifier.
25 The transformer transforms the primary voltage to a very high secondary voltage and transf orms the primary current to a low se~ontl~ry current. The rectifier converts the alternating current (AC) output from the ~er~nfl~ry of the transformer to full-wave rectified DC. A typical TR set 30 used in a precipitator application is filled with oil or cooling and insulation. T~pical ratings might be:
RMS Primary voltage: 400 VAC
RMS Primary current: 240 Amps (A) Average secondary voltage: 45,000 VDC

wo 92/16302 PCI~/US91/01745 f~l?82D56 ~

Average secnnAAry current: 1500 m~ l l i Ar-,rq (mA) Transformer turns ratio: 1:135 This example of a typical TR set will be used in much of S this document. ~
The same factors cnnqi ~ red in sizing the precipitator field affects the selection of a TR set, along with the size of the field itself. In most industrial precipitators, one TR set is connected to one 10 or two precipitator f}~l~ sections.
Eower control for a precipitator is accomplished by silicon-controlled rertifiPrs 16 and 18 (SCRs). An SCR
is a solid-state device that acts like a switch because it has a "gate" that allows it to be turned on electrically.
15 A f irst silicon-controlled rectif ier 16 and a second sill~on co~LLolled rectifier 18 are connected in an inverse-parallel conf iguration in series between the line voltagQ power source 14 and ahead of the current-limiting reactor 24 and the precipitator high voltage transformer.
20 Each SCR conducts alternately, one on the positive half-cycle, the other on the negative half-cycle. some form of automatic SCR voltage control 20 ( typically miuLu~ ucessor-based) de~-~rmi n~q which SCR is switched on and at what point in the half -cycle of the wavef orm . An 25 SCR which is switched on remains on until the current f lowing through it decays below what is called the ~holding current", usually at or near the end of the half-cycle; it cannot be switched of f in any other manner .
A complete sine ~sinusoidal) wave cycle 28, one 30 positive followed by one negative half-cycle, is measured in its progress by degrees from zero to 360 (Figure Z~. A
half-cycle is measured in its progress ~rom zero to 180 degrees. The point at which an SCR is turned on, or "fired", is measured in degrees from the b~inn~ng of the .

l6302 PCr/US91tO1~4 .

half -cycle and hence is called the f iring angle . The part of the half-cycle during which the SCR conducts is also measured in degrees from the firing point until confll~ctit n ceases and is called the conduction angle. Power control - 5 is achieved with SCRs by varying the point in the half-cycle at which each SCR is switched on. The nature of the SCR device is such that the output f rom the stack is no longer a sine wave 28 because each half-cycle is "chopped"
at the point in that cycle where an SCR is "fired" or switched into a conductive state.
Det~rminin3 the SCR stack rating also involves several considerations. The SCRs 16 and 18 must each have a current rating that exceeds that of the TR set 22 with which they will be used. ~he blocking voltage of each SCR
must be approximately three times the line voltage to prevent inadvertent conduction of the SCR resulting f rom voltage breakdown. The rate of change of voltage with respect to time ( expressed as dv/dt ) must also be sufficient to prevent inadvertent conduction. "Snubber"
circuits are normally used on the SCR stack in precipitator applications to reduce or "snub" the dv/dt to a level d~ u~l iate to commercially-available SCRs .
The SCR automatic voltage control ~ AVC ) measures the primary and seconflAry voltages and currents ( some also monitor form factor and se~r)nflAry fractional conduction), and is connected to the SCR stack 12. The AVC provides the triggering pulses which f ire the SCRs, putting them into a state of conduction. It detf~rmi n~.C where in the electrical half-cycle to fire a particular SCR, thereby achieving power control. For example, if the AVC fired each SCR 16 or 18 at 90 degrees into the electrical half-cycle, the firing angle would be 90 degrees, the conduction angle would be 90 degrees, and exactly half of =
the AC power would be applied to the TR set 22. It is in PCr/l)S91/0174 208~ 14 this manner that the AVC 20 provides power control to ensure operation within the electrical limits of the equipment . Further, if the AVC does not f ire an SCR f or a half-cycle, then the output of the precipitator power 5 supply is interrupted for that half-cycle. This permits interrupting or "quenching" sparks when the AVC detects them .
The current-limiting reactor 24 ( CLR) of prior art is an inductor of f ixed value . ~any CLRs used in lO precipitator `A~Flic~t;r~nc have taps which can be changed manually to provide a limited selection of inductance values .
The CLR 24 limits the current flow during sparking. If a spark occurs while an SCR is conducting, 15 the spark continues until the SCR stops conducting near the end o~ the half-cycle. During this time, the TR set 22 effectively has a short on its secr~n~Ary due to the spark and this is ref lected into the primary. A properly t1e.ci qn~ TR set 22 has some circuit i ~ nre, even with a 20 spark, but it is not enough to significantl~ limit the current. Since the SCR 12 is fully turned on and the TR
set 22 presents a low 1~re~lAnre due to the spark, the only circuit element r i n 1 nq to control current f low is the CLR. Because of this, it is important that the CLR 24 25 have the right inductance value to control spark currents.
Another function of the CLR 24 is to shape the voltage and current waveforms. For optimum electrical and collecting ef f iciencies, the wave shape of the voltage and current presented at the primary of the TR set 22 must be 30 a sine wave 28. Because the SCRs 16 and 18 chop and thereby distort the current waveform, the CLR 24 is needed to ~ilter and restore the waveform to some approximation of the sine wave. Selecting the proper inductance value Qf the CLR 24 is important ~or this function as well.

6302 PCr/l lS91/01745 .
.2~82056 Flistorically, the inductance value of the CLR 24 has been detsrm;n~sd by using a figure of 50 percent of the -~9nre of the TR set 22. Vector analysis of the voltages in the primary circuit of the TR set 22 illustrates this in Figure 3.
The voltage on the primary of the TR set 22 is assumed to be at a zero-degree phase angle such that TR
set 22 is purely resistive. The voltage is set at its maximum value, which is the primary voltage rating of the example TR set 22, or 400 VAC. The voltage across the CLR
24 is assumed to be at a 90-degree phase angle such that the CLR 24 is purely inductive. The voltage is to be det~rm; ne~.
Since the CLR 22 and TR set voltages are in a 90-degree phase angle relationship to one another, the problem presents itself as a right triangle. The voltage output from the SCR stack 12 forms the hypotenuse of the triangle. If the SCRs 16 and 18 are assumed to be at or near full conduction, i.e., a zero-degree firing angle and a 180-degree conduction angle, the magnitude of the hypotenuse will be approximately equal to the line voltage. For a 460 to 480 VAC line, 450 VAC can be assumed .
The Pythagorean theorem is used to f ind the unknown side of a right triangle with the formula c2-a2=b2. In this instance, substitution provides 4502_ 4002=CLR voltage2, and the CLR voltage is found to be the square root of 42,500, or 206 volts, approxlmately half the voltage on the TR set primary.
Next, it is nsc~o~sAry to determine the inductance of the CLR 24 that will yield the calculated voltage. Since the voltage across the CLR 24 is half that across the primary of the TR set 22, the i _-1Anre of the CLR 24 is approximately half that of the TR set 22.

-02 PCr/US9l/01745 ~.
~08~ 16 The i -~Ar~p of the TR set 22 is de~ermi nP~ by dividing the primary voltage rating by the primary current rating. In this example, that is 400V/240A=1.67 ohms.
Half of this figure, about 0.84 ohms, is the desired 5 ; -~Ant~P . The needed irductance is detPrm; nPtl by calculating the inductive reactance using the f ormula L=XI~/ ( 27rf ) . By substitution, this becomes L=0 . 8 4 / ( 2x3 . 1 4 16x6 0 ), giving an inductance I L ) of 2 . 2 mi llihenr ie s ( mH ) .
If the ef_ect of a CLR 24 with a value of 50 percent of the i - 'Ance of the TR set 22 at spark-level currents is PY~mi~d, it is found that, at the rated TR
set current limlt, the ;~re~1An~ e of the TR set 22 is x and the i -'An~e of the CLR 24 is 0.5x. These ;rpP~An~eS are not in time phase an~ cannot be added arithmetically, so the total circuit ;~re~Ant~e in the primary is l.llx. When a spark occurs, the TR set; ~ 'An-'e iS assumed to drop to zero f or all practical purposes, and the resulting circuit nre is now 0.5x. Since the im7P~Anre in the primary dropped by a factor 1.11/0.5, or 2.22, the primary current would increase by a factor of 2.22. In fact, since the TR
set 22 still has some i - 'An~P, the current does not actually increase that much, but a significant increase does occur.
The CLR value has been selected f or operation at the current limit rating of the example TR set. For operation at a lower current, a correspon~i; nqly larger inductance value could be used. This would have the practical e_fect o~ reducing spark currents, si~n;fi~Antly lengthening the lif~s of e~auipment. However, this would also limit the amount of current that could be applied to the TR set 22 and therefore restrict its output to a lower current. ~qany TR sets 22 are operated below their rated limited .

WO 92~
16302 PCr/US9l/01745 2~82û~

Measuring Resultant Precipitator Wave Shapes -Once the values and ratings of the c, - Ls of the precipitator power supply are det~rm; n~d, the characteristics of the primary and secondary voltages and 5 currents can be measured to determLne if those values and ratings are correct. Recall that the CLR inductance value was calculated to provide nearly full conduction of the SCR stack output when the TR set is operating at its maximum ratings. This will provide a primary current wave 10 shape that will be very nearly a sine wave 28. The secontlAry current wave shape will be very nearly a full-wave rectif ied sine wave . Two electrical measurements can be made to determine how closely the wave shapes correspond to the desired sine waveform.
One measure of how closely the primary current waveform approximates a sine wave 28 is the primary current form factor. The form factor is de~erm;n~d by measuring both the root-mean-square (RMS) and average primary current and then dividing the RMS value by the average. Expressed as an equation, this means ~orm factor=RMS/Average. For an ideal sine wave 28, these are the relat;onch;p-c between R~S and average values and form f actor:
RMS value: 0.707 of peak value Average value: 0.636 of peak value Form factor: 0.707/0.636=1.11 Precipitator power supplies operating at maximum ratings are normally designed to operate at a form factor of 1.2.
How closely the s~on~l~ry current waveform approaches a rectified sine wave is the secondary current fractional conduction. This is det~r~in~d by measuring the duration of the 5~ nn~1~ry current waveform and dividing it by the maximum possible duration. For a line frequency of 60 Hertz (Hz), the maximum pocc;hl~ duration WO 92/16302 PCr~US9l/01745 208205~ 18 is 8.33 m;lli~ nnfl~ (ms), the period of a single half-cycle . Hence, secondary f ractional conduction=t/T, where t is the duration of the secondary current waveform and T
is the maximum pQ':~; hl ~ duration . Precipitator power 5 supplies operating at maximum ratings are normally designed to operate with a ~ n~Ary fractional conduction of 0.86. Secondary fractional conduction relates to form factor as secondary fractional conduction=(1.11/Form factor ) 2 .
Importance Of Precipitator Wave Shapes - To illustrate the importance of precipitator wave shapes, the , r L values and ratings for a precipitator electrical system, and particularly the CLR 24, were selected for operation at the maximum ratings of the equipment. The 15 table presents actual, measured values for a precipitator power supply, t n~ nq form factor and ~ nn~Ary fractional conduction data. These indicate how closely the waveforms approximated a sine wave 28 at the primary of the TR set 22 and a full-wave rectified sine wave on 20 the s~c~n~Ary. The T~ set 22 has the ratings presented on page 13, and a turns ratio of 1:135.
RMS Primary Amps 40 80 120 160 200 220 RMS Primary Volts 152 203 243 282 312 327 Avg .cF~c~nt~Ary Mi 11; i _ ~ 158 369 609 873 1155 1307 25Avg 5~Qn~lAry Kilovolt 25 27 29 30 32 33 Form Factor 1.79 1.56 1.44 1.35 1.29 1.26 Fractional Conduction 0 . 33 0 . 45 0 . 54 0 . 63 0 . 76 0 . 81 SCR Firing Angle 130 115 103 92 82 77 ( in degrees ) 30SCR cr~n~lc~ n Angl 50 65 77 88 98 103 ( in degrees ) For each point, multiplying the average 6302 PCr~US91/01745 20820~6 secondary current by the turns ratio of the TR set 22 and the form factor will equal the RMS primary current. As an eSIuation, this is represented as Average secondary current x Turns ratio x Form factor = RMS Primary current. This demonstrates clearly that the secondary current output varies directly with the form factor. Maximum electrical ef f iciency occurs when there is maximum output f rom minimum input. As the table shows, maximum electrical efficiency occurs when the form factor is lowest, at 1.2.
As the f orm f actor increases, the output decreases with respect to its input.
Because of this, it is a primary objective of this invention to maximize electrical Pffiri~nry by devising a variable CLR and CLR control 26 for the purpose of maintaining a low forrn factor and a high ce~n~lAry f ractional conduction at any given power level, thereby increasing the average voltage and current in the precipitator field for a given input.
The 5P~nr~rlAry voltage is not subject to coL~ ding analysis because of the capacitive nature of the precipitator f ield . ~owever, the voltage-current ( VI ) graph ( Figure 4 ) illustrates that the se~ n~l~ry voltage also increases as the form factor decreases. The graph on Figure 4 is f or a precipitator power supply used in a refuse bur~ing application. Its ratings are:
R~S Primary Voltage: 460VAC
RMS Primary Current: 6 l A
Average Se~ n~lAry Voltage: 50 ,000 VDC
Average Seron~Ary Current: 400 mA
There are two plots on the graph. The first shows the voltages and currents in the precipitator f ield with the f ixed-value CLR supplied by the manuf acturer . At the primary current limit of 61A, the se~ n~lAry current limit of 400 mA could not be attained. The maximum 6302 PCr/US91/01745 ~ ~8~0~6 20 c~cnn~Ary current possible was 332 mA.
The second plot shows the voltages and currents in the precipitator field with a prototype variable CLR.
An increase of both secondary current and voltage across 5 the operatlng range is clearly indicated, as well as the fact that the secnr~Ary current limit could be achieved.
It is therefore a primary objective of this invention to maximize particulate collection efficiency by devising a variable CLR f or the purpose of malntaining a lO low form factor and a high secondary fractional conductlon at any given power level, thereby increasing the average voltage and current in the precipitator f ield. This in turn will cause more particulate collection to occur because the particle charge is increased, as is the 15 attraction to the plates.
The practical limit to which the high voltage can be raised is governed by the electrical ratings of the eçluipment or by sparking in the precipitator f ield.
Sparking will occur when the spark-over voltage is 20 reached. This voltage is determined by several actors, ; nn] ~ ng gas chemistry. When this voltage level is reached, voltage cannot be raised beyond Lt. An ideal precipitator power supply will apply power in such a manner that the peak value of the s~cnn~iAry voltage and 25 current are near the average value. This will produce the maximum average secondary voltage and current before spark-over occurs.
If the precipitator wavef orms have very high peaks and very low averages, measuring the precipitator 30 wave shapes will show a high form factor and a low cenOn~lAry fractional conductlon. ~rArkin~ will occur on the peaks and the field will have little average s~cnn~9Ary voltage and current needed for particulate collection.
Therefore, this invention is designed to PCI~/US91/0174~i .
21 ' 2082 maximize particulate collection efficiency by devising a variable CLR 24 for the purpose of maintaining a low form factor and a high ser~n~lAry fractional conduction at any given power level, thereby increasing the average voltage - 5 and current in the precipitator field before spark-over occurs .
As it has been demonstrated, sparking in the precipitator field, energy management, or any condition that causes operation of the TR set below its rated limits will cause an increased form factor and a decreased secondary fractional conduction, resulting in operating ineffiri~nri~s~ The voltage level at which a spark occurs changes constantly because of dynamics of the gas chemistry, temperature, and other related precipitator parameters. To maintain the desired electrical and particulate collection ~ffiriF~nr;~q, the imn~ nre of the CLR 24 must be dyn rAlly adjustable.
It is therefore a primary objective of this invention to maximize electrical and particulate collection effir; ~nrj~s by devising a variable CLR 24 that can be dynA-n; rA l l y adjusted by being varied electrically and automatically f or the purpose of maintaining a low form factor and a high secon~l~ry fractional conduction at any power level.
This precipitator power supply is designed to have a full-wave rectified sine wave output from the TR
set 22. This will contribute to the electrical and particulate collection effir;~nr;es. SCRs 16 ana 18 paired with a f ixed-value current limiting reactor 24 have been shown to be superior to saturable core reactor systems . However, even SCR-CLR systems become inef f icient when operated at any power level other than the limits f or which the - -~nts were rated. This is because at any lower power level the SCRs have a reduced conduction angle -O PCr~US91/01745 2~8'~

resulting in a high f orm f actor and a low secondary fractional conduction. It is therefore the objective of this invention to create current limiting reactor 24 that can be varied electrically and/or automatically for the 5 purpose of overcoming these inef f iciencies .
The electrically variable current-limiting reactor (EVCLR) is an improvement over the prior art f ixed-value CLRs and saturable reactor systems . The EVCLR
is much like a ~t~1r~hl e reactor. Both devices have a lO control winding 32 which is connected to a source of DC
energy. Both devices are h~;c~lly inductors, the i~re-l~n- e of which can be varied electriaally. The speed at ~ which a change applied to the control winding appears as a change in the i -~n~-e of the device is slow in both 15 devices. The range of variability of the inductance of the EVCLR is not as great as that of the saturable reactor .
The principal advantage of the EVCLR over the saturable reactor is that the EVCLR causes virtually no 20 distortion to the primary current waveform, while the saturable reactor causes much distortion. The distortion caused by the EVCLR can be held to low values, on the close order of less than one percent.
Since the EVCLR is slow like the saturable 25 reactor and has a limited range of inductance adjustment, it is not suitable as a control element if used by itself.
However, in precipitator systems that use SCRs paired with a fixed-value CLR, the EVCLR can replace the fixed-value CLR and yield c~n~ r~hl ~ advantage. In this 30 application, adjustment of the CLR can now be accomplished electrically and automatically. This accomplishes all of the objectives of the invention.
The concept of EVCLR operation that is contemplated is that the ;~r~lAn~-e of the EVCLR would be 16302 PCr/US91/01745 208205~

ad~usted to its minimum i n~ tAn~-e value when the TR set 22 is operating at its rated limit. This would be approximately 50 percent of the T~ set i _-~An~'e, and would provide the optimum form factor of l. 2 and s~ Ary - 5 fractional conduction of 0. 86 . When the TR set 22 is operated below its rated limit, the EVCLR can be ad~usted electrically to increase its inductance, thereby maintaining a low form factor and a high ~ ror~lAry fractional conduction. This configuration will have the following advantages:
l ) It will increase averag~ voltage and current in the precipitator field, thereby increasing parti ~1l1 Ate collection;
2) It will minimi2e the destructive effect of spark currents on eS~uipment;
3) It will increase electrical efficiency by delivering maximum electrical output for minimum input;
and 4 ) It will increase the average voltage and current in the precipitator field before spark-over occurs .
The basic configuration of the EVCLR is as shown in Figures 6 and 7. In the schematic shown in Figure 6 the control winding 3 2 is operatively connected with respect to a variable DC power source 42. The control winding is coupled with respect to the inductor winding means 30 which preferably takes the form of a first inductor winding means 34 and a second inductor winding means 3 6 which are basically identical with respect to one another. The first inductor winding means 34 as shown best in Figure 7 is wound about a f irst core 3 8 . In a similar manner the second inductor winding means 36 is wound about a second core 40. Preferably both the first core 38 and the second core 40 extend through the control PCI/US9l/01745 p~,820~6 winding 3 2 in opposite directions to eancel the instantaneous 1ux therein. This is shown further below.
This conf iguration results in the inductanee of the EVCLR
device being a f unction of the magnitude o the DC current 5 passing through the control winding which itself is variable responsive to different types of controls.
various controls for modifying the DC current through the control winding 32 can include a manual adjustment which is based upon manual reading of form 10 factor and/or se~nn~i~ry fractional conduction readings.
This manual adjustment furthermore eould be based upon any applieable physical signal or combination of physical signals sueh as boiler load, eoal type or temperature, etc. Furthermore the adjustment of the DC power source 42 15 and thus the eontrol o the amount of DC eurrent passing through eontrol winding 32 ean be varied by an automatic adjustment responsive to the same above-identified parameters . In another possible ronf i~ration as shown in Figure 6 an automatie electrieally variable eurrent 20 limiting reactor can be designed Uti 1 i 7:1 n~ the eurrent at the primary of the transformer reetifier set 22 as the power souree.
In the EVCLR as shown in Figures 6 and 7 as the DC power souree 42 eonneeted to the eontrol wlndlng 32 is 25 reduce~, the inductance increases. I a fault condition occurs which causes a loss of control winding excitation, the inductor 3 0 def aults to its maximum inductance value .
This limits the primary current f low to its lowest and safest value. Therefore, it is a primary ob~ective of 30 this invention to devise a variable current limiting reactor which will automatically attain its maximum value o ; n~ tAnre to provide automatic protection of equipment if a fault occurs which causes a loss of control winding excitation .

WO 92/16302 PCr/US9l/01745 25 ` ~` `2`~82~
The automatic elect}ically variable current-limiting reactcr 44 (AEVCLR) can be constructed according to schematic illustrated in Figure 5. The primary windin~
48 of a current transformer 46 is placed in series with the AEVCLR. The sPco~lAry winding 50 of the current transformer is connected to a full-wave bridge rectifier 52. The DC cutput of the full-wave bridge rectifier is connected to the control winding 56 of the AEVCLR.
This conf iguration provides f or automatic adjustment of the current-limiting reactor 24. The inductance will be inversely proportional to the primary current. As the primary current increases, the DC signal to the control winding 56 increases. This causes a proportional decrease in the inductance of the CLR
inductcr winding means 54 of the current limiting reactor.
Conversely, as the primary current decreases, the DC
signal to the control winding 56 decreases. This causes a proportional increase in the inductance of the CLR
inductor winding 54 of the current-limiting reactcr.
This configuration will automatically adjust the inductance of the AEVCLR 44 by responding to changes in operating conditions of the TR set 22, thereby maintaining a low form factcr and a high secondary fractional conduction at any given power level and thus achieving all of the stated objectives of this invention.
Design And Construction Of The EVCLR - The design considerations for an electrically-varlable current limiting reactor (EVCLR) are:
Nominal system voltage;
3 0 Rated current;
Inductance required at rated operating current;
Inductance re~[uired at cne-half of rated operating current;
Maximum temperature rise of the EVCLR;

302 PCr/US9l/01745 20820~6 ~

Non-saturation of the inductor when the full primary voltage is impressed across it;
The inductance over the general operating range (from one-half to full operating current) shall be Lnversely proportional to the operating current, ensuring that the inductance is nearl~ optimal; and Distortion should be kept at a minimal level over the entire operating range.
The design procedure for a representative EVCLR
is shown in Figures 6, 7 and 8. Figures 6 and 7 present the general coll and core configuration of the device.
Two identical inductor windings 34 and 36 are mounted on two cores 38 and 40 and connected in parallel as shown.
Alternating currents in the lnductor windlngs 30 result in an alternating f lux in each core . The windings are connected so that the instantaneous f lux coupled to the control winding, which is common to both cores, is always zero. Hence, if everything is bAlAr~ d, there is no induced voltage in the control winding. In actual practice, the center leg of the core can be magnetically coupled. ~wo separate core structures are not reguired.
A magnetomotive force caused by DC current in the control windlng 3 2 does, however, cause e~ual magnetic drops in both cores 38 and 40. These drops cause changes in reluctance of the magnetic paths and hence changes in inductance. As such, the inductance value of the device is a function of the magnitude of the direct current in the control winding 32.
It should be noted that the E~CLR as illustrated is two inductors in parallel, each of which conducts half of the load current . Each individual inductor, theref ore, must be designed f or twice the reguired inductance and half of the rated current.

pCr/US91/01745 27 2~2056 The EVCLR must be ~tF~c; qn~d not to saturate when the full primary voltage Ls impressed across it. During sparking, the full primary voltage appears across the EVCLR. In this example, the maximum AC flux density will 5 therefore be limited to 16 kilogauss (one kilogauss equals 1000 lines of flux per square centimeter) at full primary voltage for M-6 29-gauge electrical steel. This density ( B ) can be calculated as f ollows:
B=3875Ep/NAf 10 where Ep is the system primary voltage, N is the number of turns, A is the inductor core area in square inches, and f is the line frequency in Hertz ~cycle per second).
The individual inductors must be ~t~ nf~d f or half the maximum continuous current expected.
Generally, a 110-degree Celsius (C) temperature rise is acceptable for this type of device. For a 110-degree rise, it is important to use a 180-degree insulation system. This allows for a rise of llO-degree rise above a 40-degree ambient temperature as well as a 20 30-degree "hot spot". For higher ambient temperatures, adj ustments must be made ln the design .
The choice of ~1 ; or copper f or windings is entirely discretionary. If ~1 t is used, a current density of approximately 1000 amps (A) per square inch is 25 a good starting point. For copper, the figure should be 1450A/in2. Coil watt-densities for either conductor should be approximately 0 . 4 watts per square inch at 20 degrees Celsius . It should be noted that signif icant losses will occur in the windings owing to fringing around 3 0 the gaps under the inductor windings .
The general requirement for inductance for the example EVCLR will be 1. 5 x mH at rated current and 3 . 0 x mH at one-half of rated current, providing a desirable and usable control range.

PCI'/US91/01745 2 0 ~ ~ 2 8 To accomplish "automatic control", the AC line current in the lines is transf ormed to a suitable level, then rectified. This DC signal is supplied to the control winding of the EVCLR. The DC signal has little ripple because of the high inductance inherent in the control winding. The control current is therefore proportional to the average of the primary load current. However, it should be noted that the control current is proportional to the R~S of the load current only if the form factor remains constant. To operate effectively, the EVCLR must also be operated in the more linear portion of its range as shown in the graph in Figure 8. As illustrated, the design range for the example inductor must be approximately 4 to l . The inductance will, theref ore, be four times as high with no control current ( 0 amps ) as it is when the device is fully saturated.
To meet the above requirements and still ensure low harmonic distortion, the inductor is constructed with two dif f erent air gaps . Figure 8 shows the general construction used. Each of the pair of inductors has two large air gaps and two small ones.
The general design criteria are:
AX/AU--2 . 4 lc/lgx~60 lc/lgu~500 where lc is the mean length of the magnetic path ( steel), lgx and lgu are the lengths of the air gaps in the X and U
portions of the core, respectively, and Ax and Au both are the area of steel in the x and u portions, respectively.
The inductance range can then be calculated to be from sectiD~s u and X both being completely unsaturated (high relative p~rlT~'~Ahi 1~ ty) to section U being completely saturated. In this condition, it is as if ~ section u does not exist.

02 PCr/US9l/01745 20820~

Derivation of the design equations proceeds in this manner:
L = N~/I
~ = NI/R
where N is turns, ~b is total f lux lines, I is current and R is reluctance ( magnetic resistance ) by substitution:
L = N2/R
for an air gap, iron-core circuit;
R = ( lC/~Uo~rAc ) + ( lg/iUoAC ) where lc is the core mean length, lg is the air gap length, JUO is the p~ -h;l;ty free space (3.19 x 10-8 H/IN" ), iur is the relative permeability of steel, and Ac is the core area Thus, the general inductance equation:
L=(3.19xlO=8)N2Ac/[lc/~ur)+lg]
For the purposes here, ,ur will be con~ red either very high ( inf inite ) or very low ( zero ) .
The inductance equation can then be simplified to L=( 3 . l9xlO=8 )N2/lg/AC
This equation will be used to calculate the two extreme conditions of inductance: Section U completely saturated, and sectlon u not saturated.
Let Ru=lgu/Au and Rx=lgx/Ax Since reluctance in magnetic circuits is analogous to resistance in electrical circuits, 3 o RT=RuRx/ ( Ru+Rx ) The high and low inductance limits are now calculated using the following equations in conjunction with previously-cited general criteria:
~in=(3-19X10 8)N /Rx 6302 PCr/US9l/01745 , 2082aS~ 30 where Rx=lgx/Ax and LmaX=( 3 . l9x10-8 )N2~RT
where RT=RURX/ ( RU+Rx ) = ( lgulgx/Au~x ) / [ lgU/AU ) + ~ lgX/AX ) ]
It is important to recall that the goal of this sequence is to achieve a relationship f or the example 10 inductor wherein Lmax is 4 x Lmin~
The control winding must be ~ nP~l and matched to the primary load current with several factors,borne in mind:
Temperature rise of control wlnding;
Correct ampere-turns for proper full-current inductance; and AvaLlable current transformer.
Design assumptions:
Load current f orm f actor of 1. 2 .
For 100 degrees (C) temperature rise, 0.55 watts per square inch at 20 degrees should be used on the control winding.
The DC current should be calculated by using:
B = ( 0 .155NIDC) / ~ 313lgu) Use B - 20 kilogauss.
While particular ~mhor~; ts of this invention have been shown in the drawings and described above, it will be apparent, that many changes may be made in the form, arrangement and positioning of the various elements 30 of the combination. In con~ ration thereo~ it should be understood t~at preferred ~mhQ~ ts of this invention disclosed herein are intended to be 1~ l ustrative only and not intended to Iim~t the scope of the invention.
.

Claims (39)

I CLAIM:

1. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator comprising:
a) a silicon controlled rectifier stack electrically connected to an AC input voltage line;
b) a SCR voltage control means operatively connected with respect to said silicon controlled rectifier stack to control voltage output therefrom;
c) a transformer rectifier set in series with respect to the output of said silicon controlled rectifier stack, said transformer rectifier set including a TR input signal and a TR output signal, said transformer rectifier set including:
(1) a step-up transformer means adapted to receive said TR input signal and increase voltage and decrease current thereof;
(2) a full wave rectifier means adapted to receive an AC signal from said step-up transformer means for rectifying thereof, said full wave rectifier means adapted to generate said TR output signal; and d) a current limiting reactor positioned electrically in series between said silicon controlled rectifier stack and said transformer rectifier set, said current limiting reactor being electrically variable, said current limiting reactor including a CLR control means to vary the inductance of said current limiting reactor, said current limiting reactor including:
( 1 ) a core means defining a gap means therein to enhance linearity of said current limiting reactor, said gap means comprising a plurality of individual gaps within said core means, said individual gaps being of at least two different sizes;
(2) an inductor winding means extending around said core means and around said gap means defined therein to reduce distortion of said current limiting reactor, said inductor winding means being electrically in series between said silicon controlled rectifier stack and said transformer rectifier set;
(3 ) a control winding means extending around said core means to be electrically operatively coupled with respect to said inductance winding means to control the inductance thereof responsive to current flow through said control winding means.

2. A variable inductance current limiting reactor having low distortion, characteristics for use with an electrostatic precipitator as defined in Claim 1 wherein said current limiting reactor achieves maximum inductance responsive to deactivation of said CLR control means.

3. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator as defined in Claim 1 wherein said silicon controlled rectifier stack comprises two silicon controlled rectifiers electrically connected in an inverse-parallel relationship in series between the AC
input voltage line and said current limiting reactor.

4. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator as defined in Claim 1 wherein said inductor winding means comprises a first inductor winding and a second inductor winding both extending about said core means to be electrically connected in parallel with respect to one another.

5. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator as defined in Claim 4 wherein said core mean further comprises:

a) a first core with said first inductor winding mounted thereon; and b) a second core with said second inductor winding mounted thereon, said first core and said second core also extending through said control winding means in opposite directions to eliminate induced voltage and instantaneous flux in said control winding means.

6. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator as defined in Claim 5 wherein said first core and said second core are magnetically coupled within said control winding means.

7. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator as defined in Claim 1 further comprising a variable DC power source electrically connected with respect to said control winding means to vary power applied thereto and facilitate control of the inductance of said inductor winding means.

8. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator as defined in Claim 7 wherein said inductor winding means is operative to achieve maximum inductance responsive to loss of excitation of said control winding means.

9. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator as defined in Claim 7 wherein an increase in the power output of said variable DC power source will cause a reduction in the inductance of said inductor winding means.

10 . A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator comprising:
a) a silicon controlled rectifier stack electrically connected to an AC input voltage line, said silicon controlled rectifier stack including two silicon controlled rectifiers electrically connected in an inverse-parallel relationship in series with respect to the AC
input voltage line;
b) a SC voltage control means operatively connected with respect to said silicon controlled rectifier stack to control voltage output therefrom;
c) a transformer rectifier set in series with respect to the output of said silicon controlled rectifier stack, said transformer rectifier set including a TR input signal and a TR output signal, said transformer rectifier set including:
(1) a step-up transformer means adapted to receive said TR input signal and increase voltage and decrease current thereof;
(2) a full wave rectifier means adapted to receive an AC signal from said step-up transformer means for rectifying thereof, said full wave rectifier means adapted to generate said TR output signal; and d) a current limiting reactor positioned electrically in series between said silicon controlled rectifier stack and said transformer rectifier set, said current limiting reactor being electrically variable, current limiting reactor including a CLR control means for varying inductance of said current limiting reactor, said current limiting reactor being operative to achieve maximum inductance responsive to deactivation of said CLR control means, said current limiting reactor including:
(1) an inductor winding means electrically in series between said silicon controlled rectifier stack and said transformer rectifier set, said inductor winding means comprising:
(a) a first inductor winding;

(b) a second inductor winding electrically connected in parallel with respect to said first inductor wlnding;
(c) a first core extending through said first inductor winding, said first core defining a plurality of first gaps therein of varied sizes, said first inductor winding being positioned extending about said first core and said first gaps defined therein;
(d) a second core extending through said second inductor winding, said second core defining a plurality of second gaps therein of varied sizes, said second inductor winding being positioned extending about said second core and said second gaps defined therein; and (2) a control winding means extending about said first core and said second core to be electrically operatively coupled with respect to said inductor winding means to control the inductance thereof responsive to current flow through said control winding means, said first core and said second core also being positioned extending through said control winding means in opposite directions to eliminate induced voltage and instantaneous flux therein.

11. An electrically variable power supply means having a control means with low distortion characteristics for use with an electrostatic precipitator comprising:
a) a silicon controlled rectifier stack electrically connected to an AC input voltage line;
b) a SCR voltage control means operatively connected with respect to said silicon controlled rectifier stack to control voltage output therefrom;
c) a transformer rectifier set in series with respect to the output of said silicon controlled rectifier stack, said transformer rectifier set including a TR input signal and a TR output signal, said transformer rectifier set including:
(1) a step-up transformer means adapted to receive said TR input signal and increase voltage and decrease current thereof;
(2) a full wave rectifier means adapted to receive an AC signal from said step-up transformer means for rectifying thereof, said full wave rectifier means adapted to generate said TR output signal; and d) a current limiting reactor positioned electrically in series between the output of said silicon controlled rectifier stack and said transformer rectifier set, said current limiting reactor being electrically variable, said current limiting reactor including an automatic CLR control means operatively responsive to the current of said TR input signal to vary the inductance of said current limiting reactor, said automatic CLR control means including:
(1) a CLR current transformer comprising:
(a) a CLR primary placed in series between said silicon controlled rectifier stack and said transformer rectifier set;
(b) a CLR secondary winding electrically coupled with respect to said CLR
primary winding;
(2) a CLR full wave rectifier electrically connected with respect to the output of said CLR secondary winding;

(3) a CLR inductor winding means in series between said silicon controlled rectifier stack and said CLR current transformer; and (4) a CLR control winding electrically connected to the output of said CLR full wave rectifier, said CLR control winding being electrically operatively coupled with respect to said CLR inductor winding means to control the inductance thereof responsive to the output of said CLR full wave rectifier.

12. An electrically variable power supply means having a control means with low distortion characteristics for use with an electrostatic precipitator as defined in Claim 11 wherein said CLR full wave rectifier is a CLR full wave bridge rectifier.

13. An electrically variable power supply means having a control means with low distortion characteristics for use with an electrostatic precipitator as defined in Claim 11 wherein the inductance of said CLR inductor winding means is inversely proportional to the current flow through said CLR primary winding.

14. An electrically variable power supply means having a control means with low distortion characteristics for use with an electrostatic precipitator comprising:
a) a silicon controlled rectifier stack electrically connected to an AC input voltage line, said silicon controlled rectifier stack comprising two silicon controlled rectifiers electrically connected in an inverse-parallel relationship with respect to one another and being in series with respect to the AC input voltage line;
b) a SCR voltage control means operatively connected with respect to said silicon controlled rectifier stack to control voltage output therefrom;
c) a transformer rectifier set in series with respect to the output of said silicon controlled rectifier stack, said transformer rectifier set including a TR input signal and a TR output signal, said transformer rectifier set including:
(1) a step-up transformer means adapted to receive said TR input signal and increase voltage and decrease current thereof;
(2) a full wave rectifier means adapted to receive an AC signal from said step-up transformer means for rectifying thereof, said full wave rectifier means adapted to generate said TR output signal; and d) a current limiting reactor positioned electrically in series between the output of said silicon controlled rectifier stack and said transformer rectifier set, said current limiting reactor being electrically variable, said current limiting reactor including an automatic CLR control means operatively responsive to the current of said TR input signal to vary the inductance of said current limiting reactor, said automatic CLR control means including:
(1) a CLR current transformer comprising:
(a) a CLR primary winding placed in series between said silicon controlled rectifier stack and said transformer rectifier set;
(b) a CLR secondary winding electrically coupled with respect to said CLR
primary winding;
(2) a CLR full wave bridge rectifier electrically connected with respect to the output of said CLR secondary winding;
(3) a CLR inductor winding means in series between said silicon controlled rectifier stack and said CLR current transformer; and (4) a CLR control winding electrically connected to the output of said CLR full wave bridge rectifier, said CLR control winding being electrically operatively coupled with respect to said CLR inductor winding means to control the inductance thereof responsive to the output of said CLR full wave bridge rectifier, the inductance value of said CLR inductor winding means being inversely proportional to the current flow through said CLR
primary winding, said CLR inductor winding means being operative to maximize inductance thereof responsive to deactivation of said CLR control means.

15. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator power supply including a silicon controlled rectifier stack electrically connected to an AC
input voltage line, a SCR voltage control means connected with respect to the silicon controlled rectifier stack to control voltage output therefrom, a transformer rectifier set in series with respect to the output of the silicon controlled rectifier stack and having a step-up transformer means adapted to receive a TR input signal and a full wave rectifier means adapted to receive an AC signal from the step-up transformer means for rectifying thereof and generation of a TR output signal, wherein the improvement comprises a variable current limiting reactor positioned electrically in series between the silicon controlled rectifier stack and the transformer rectifier set, said variable current limiting reactor including a CLR control means for varying the inductance of said current limiting reactor, said current limiting reactor further including:
a) a core means defining at least one gap means therein to enhance linearity of said current limiting reactor, said gap means comprising a plurality of individual gaps within said core means, said individual gaps being of at least two different sizes;
b) an inductor winding means extending around said core means and around said individual gaps defined therein to reduce distortion of said current limiting reactor, said inductor winding means being electrically in series between the silicon controlled rectifier stack and the transformer rectifier set;
c) a control winding means extending around said core means to be electrically operatively coupled with respect to said inductor winding means to control the inductance thereof responsive to current flow through said control winding means.

16. A variable inductance current limiting reactor having low distortion characteristics as defined in Claim 15 wherein said current limiting reactor achieves maximum inductance responsive to deactivation of the CLR control means.

17. A variable inductance current limiting reactor having low distortion characteristics as defined in Claim 15 wherein said inductor winding means comprises a first inductor winding and a second inductor winding electrically connected in parallel with respect to one another and being identical with respect to one another.

18. A variable inductance current limiting reactor having low distortion characteristics as defined in Claim 17 further comprising:
a) a first core extending within said first inductor winding mounted thereon, said first core defining at least one first gap means therein within said first inductor winding; and b) a second core extending within second inductor winding mounted thereon, said second core defining at least second one gap means therein within said second inductor winding, said first core and said second core also extending through said control winding means in opposite directions to eliminate induced voltage and instantaneous flux in said control winding means.

, 36

19. An improved electrically variable current limiting reactor for use with an electrostatic precipitator power supply including a silicon controlled rectifier stack electrically connected to an AC input voltage line, a SCR
voltage control means operatively connected with respect to the silicon controlled rectifier stack to control voltage output therefrom, a transformer rectifier set in series with respect to the output of step-up transformer means adapted to receive a TR input signal and a full wave rectifier means adapted to receive an AC signal from the step-up transformer means for rectifying thereof and generation of a TR output signal, wherein the improvement comprises a variable current limiting reactor positioned electrically in series between the silicon controlled rectifier stack and the transformer rectifier set, said variable current limiting reactor including an automatic CLR control means operatively responsive to the TR input signal to vary the inductance of said current limiting reactor, said automatic CLR control means including:
a) a CLR current transformer comprising:
(1) a CLR primary winding placed in series between the silicon controlled rectifier stack and the transformer rectifier set;
(2 ) a CLR secondary winding electrically coupled with respect to said CLR primary winding;
b) a CLR full wave rectifier electrically connected with respect to the output of said CLR secondary winding;
c) a CLR inductor winding means in series between the silicon controlled rectifier stack and said CLR current transformer; and d) a CLR control winding electrically connected to the output of said CLR full wave rectifier, said CLR control winding being electrically operatively coupled with respect to said CLR
inductor winding means to control the inductance thereof responsive to the output of said CLR
full wave rectifier.

20. An improved electrically variable current limiting reactor as defined in Claim 19 wherein said CLR full wave rectifier is a CLR full wave bridge rectifier.

21. An improved electrically variable current limiting reactor as defined in Claim 19 wherein the inductance of said CLR inductor winding means is inversely proportional to the current flow through said CLR primary winding.

22. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator as defined in Claim 1 wherein said gap means comprising a plurality of gaps individually defined within said core means under said inductor winding means.

23. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator as defined in Claim 22 wherein said individual gaps are all of different sizes.

24. A variable inductance current limiting reactor being adapted to induce an electrical current having low distortion comprising:
a) a core means defining a gap means therein to enhance linearity of the electrical current induced;
b) an inductor winding means extending around said core means and around said gap means defined therein to reduce distortion of electrical current induced by said reactor;
c) a control winding means extending around said core means to be electrically operatively coupled with respect to said inductor winding means to control the inductance thereof responsive to current flow through said control winding means.

25. A variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 24 wherein said inductor winding means achieves maximum inductance responsive to deactivation of said control winding means.

26. A variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 24 wherein said inductor winding means comprises:
a) a first inductor winding extending about said core means; and b) a second inductor winding extending about said core means to be electrically connected in parallel with respect to said first inductor winding.

27. A variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 26 wherein said core means comprises:
a) a first core with said first inductor winding mounted thereon, said first core defining a first gap means therein with said first inductor winding extending therearound; and b) a second core with said second inductor winding mounted thereon, said second core defining a second gap means therein with said second inductor winding extending therearound.

28. A variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 27 wherein said first core and said second core are positioned extending through said control winding means in opposite directions to eliminate induced voltage and instantaneous flux in said control winding means.

29. A variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 27 wherein said first gap means comprises a plurality of first gaps individually of different sizes with respect to one another.

30. A variable inductance current limiting reactor being adapted. to induce an electrical current having low distortion as defined in Claim 27 wherein said second gap means comprises a plurality of second gaps individually of different sizes with respect to one another.

31. A variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 24 further including a means for supplying a DC current to said control winding means to induce an electrical current with minimal distortion within said inductor winding.

32. A variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 24 further including a means for electrically controlling said control winding means to induce an electrical current within said inductor winding of minimal distortion.

33. A system for generating electrical power having a variable inductance current limiting reactor being adapted to induce an electrical current having low distortion comprising:
a) means for generating power with a desired waveform including:
(1) a core means defining a gap means therein to enhance linearity of the electrical current induced;
(2) an inductor winding means extending around said core means and around said gap means defined therein to reduce distortion of electrical current induced by said reactor;
b) means for modifying desired waveform of the generated power including; and (1) a control winding means extending around said core means to be electrically operatively coupled with respect to said inductor winding means to control the inductance thereof responsive to current flow through said control winding means.

34. A system for generating electrical power having a variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 33 wherein said core means comprises:
a) a first core with said first inductor winding mounted thereon, said first core defining a first gap means therein with said first inductor winding extending therearound; and b) a second core with said second inductor winding mounted thereon, said second core defining a second gap means therein with said second inductor winding extending therearound.

35. A system for generating electrical power having a variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 34 wherein said first core and said second core are positioned extending through said control winding means in opposite directions to eliminate induced voltage and instantaneous flux in said control winding means.

36. A system for generating electrical power having a variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 34 wherein said first gap means comprises a plurality of first gaps individually of different sizes with respect to one another.

37. A system for generating electrical power having a variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 34 wherein said second gap means comprises a plurality of second gaps individually of different sizes with respect to one another.

38. A system for generating electrical power having a variable inductance current limiting reactor being adapted to induce an electrical current having low distortion as defined in Claim 33 further including a means for supplying a DC current to said control winding means to induce an electrical current with minimal distortion within said inductor winding.

39. A variable inductance current limiting reactor having low distortion characteristics for use with an electrostatic precipitator as defined in Claim 1 wherein said individual gaps are all of different sizes.