US3162799A

US3162799A - Variable ratio transformer

Info

Publication number: US3162799A
Application number: US85744A
Authority: US
Inventors: Marion L Roberts
Original assignee: Osborne Electronic Corp
Current assignee: Osborne Electronic Corp
Priority date: 1961-01-30
Filing date: 1961-01-30
Publication date: 1964-12-22
Anticipated expiration: 1981-12-22

Description

Dec. 22, 1964 M. L. ROBERTS 3,162,799

VARIABLE RATIO TRANSFORMER Filed Jan. 30, 1961 L-O OUT 4 Fig. I

V I R 2 C F lg. 3 I R s T TT P I! INVENTOR. Q IF 4 Marion L. Roberfs Buck/70m, Chearham 3 Blore ATTORNEYS United States Patent 3,162,1 9? VAlltliAlilLE litraTilU TRANSFGRMER Marion L. Roberts, Portland, Greg, assignor to Gshorne Electronic Corporation, Portland, Greg, a corporation of Oregon Filed .lan. 3d, 1961, Ser. No. 85,744 8 Claims. (Cl. 323-45) This invention relates to electrical transformers in genoral, and to variable ratio transformers in particular in which the output voltage is at least in part obtained from secondary windings and in which the input to output voltage ratio can be adjusted to any of a large number of values in order to provide a selected ratio whose value will be precisely known. These precision transformers are useful in performing many types of electrical test measurements and the like.

It is well known to provide transformers of the general type above referrend to in which the ratio of input voltage to output voltage can be selected from a number of different values. When these types of transformers are used for very precise measuring or controlling functions under no load conditions, their transformation ratios must be known with an accuracy that is much greater than that of the ordinary transformer. While the precision ratio transformers of the prior art have been carefully constructed so that their primary windings and secondary windings are evenly distributed and have the exact number of turns required for a turns ratio which should result in the desired transformation ratio of input voltage to output voltage, this has not been the case because the resultant output voltage is not in phase with the applied input voltage and is not equal in magnitude to the applied voltage multiplied by the turns ratio 'of thetransformer. The major cause of this inaccuracy is due to the fact that even under no load condition the exciting current flowing in primary windings causes an internal voltage drop due to the winding resistance and leakage reactance of the primary windings. The result is that the. voltage appearing across the secondary windings consists merely of the voltage induced therein due to the mutual flux in the magnetic core of the transformer so that it is les than the applied primary voltage multiplied by the turns ratio and is also somewhat out of phase with the applied primary voltage. This presents a problem when it is desired to employ the secondary voltage, in whole or in part, to provide a plurality of output voltages which are accurately related to the applied primary voltage as fractions or multiples thereof.

In order to overcome this problem, the present inven tion makes use of a compensation impedance connected in series with the primary windings of the precision ratio transformer to add a compensating voltage, developed across this compensation impedance by primary current flowing therethrough, to the voltage induced in the secondary windings so that the output voltage of the transformer is more nearly in phase with its input voltage and the output voltage is more closely equal to the input voltage multiplied by the turns ratio of the transformer.

In one form, this compensation impedance is divided into a plurality of impedance steps corresponding in numher to a plurality of voltage steps in the secondary windings of a transformer forming part of a precision ratio transformer apparatus. Selected portions of this compensation impedance can be connected in series with selected portions of the secondary windings of the. transformer so that a compensation voltage in phase with the voltage drop due to the impedance of the primary windings is added to the induced voltage in such portions of the secondary windings. For example, the impedance steps of the compensation impedance can be selectively connected in series with the voltage steps of the secondamass "ice o (in! ary windings by means of a switch ganged with the voltage selection switch for the secondary windings. This enables the proper amount of compensating voltage having a correct phase angle to be added to each step of the induced secondary voltage. The vector sum of such voltage is an output voltage which is more nearly in phase with the applied input voltage of the transformer and more nearly equal to the applied voltage multiplied by the turns ratio.

In another form, a compensation impedance is connected in series with the primary windings of a transformer forming a part of the variable ratio transformer apparatus and the compensating voltage developed acr'oss such compensation impedance is added to the voltage developed in the secondary windings of such transformer by means of another transformer having a proper turns ratio and having its primary windings connected across the compensation impedance and secondary windings connected in series with the secondary windings of the transformer to which the compensation is being applied.

Therefore, one object of the present invention is to provide a compensation circuit which provides compensation to the secondary windin s for the impedance voltage drop in the primary windings of a precision transformer.

Another object of the invention is to provide a variable ratio transformer having a compensation impedance to correct the improper voltage transformation, in the form of inaccurate magnitude ratios and phase shift of output voltage to input voltage, in the transformer due to the internal voltage drop in the primary windings thereof.

A further object of this invention is to provide a precision transformer of the variable ratio type having a compensation impedance to correct for the voltage drop in the primary windings of the transformer when such transformer is under a no load condition.

Still another object of the present invention is to provide a test circuit for measuring the characteristics of transformers, or other electrical devices, by variable ratio transformers having compensation circuits to correct for the voltage drop in the primary windings thereof so that they may be used as accurately calibrated standards in such test circuit.

()ther objects and advantages of the present invention will be apparent when referring to the following detailed description of preferred embodiments of the invention, given by way of example and described in connection with the attached drawings, of which:

FIG. 1 is a schematic diagram of the electrical circuit of a variable ratio transformer in accordance with the present invention;

PEG. 2 is a vector diagram illustrating the relative magnitudes and phase relationships of various voltages and currents and the mutual flux related to the primary windings of the variable ratio transformer of FIG. 1;

FIG. 3 is a vector diagram of part of the output voltage from one portion of the variable ratio transformer in PEG. 1; and

PEG. 4 is the schematic diagram of a test circuit in accordance with the present invention using the variable ratio transformer of HG. l.

The schematic diagram illustrated in FIG. 1 shows the electrical circuit used in the variable ratio transformer apparatus of the present invention and the voltage compensation circuit used therein. This apparatus includes five separate transformers, T T T T and T each having a separate core of ferromagnetic material. Such transformers are arranged so that their output windings may be connected in series so the voltage developed across each of these windings can be added thereby. This arrangement gives a final output voltage which is the sum of the series added voltages. Step down transformer T, has primary windings A which are connected across a source of AC. voltage, shown as an A.C. line including conductors indicated by terms HIGH and LOW. Primary windings A of transformer T are shown as being divided into ten equal voltage steps which can be selectively connected by switch S in series between the line conductor marked LOW and the lower end of secondary windings B positioned on a common magnetic core with primary windings A It should be noted here that while each of the windings on step down transformers T T and T have been shown to be divided into ten equal steps each, that it is possible to divide these windings into any number of equal or unequal voltage steps. It should be understood that the only reason for using a decade arrangement of ten equal steps is to enable the utilization of the decimal system in computing the voltage transformation ratio. Secondary windings B of step down transformer T also have a decade arrangement so that they are divided into ten equal voltage steps which are in turn selectively connectabie by switch S in series between the switch S and lower end of secondary windings C Secondary windings C are similarly divided into a decade arrangement of ten equal steps which are selectively connectable by switch S in series between the switch S and the lower end of primary windings A of transformer T Primary windings A of step down transformer T are connected across secondary windings D of transformer T so that the voltage across secondary windings D is used as the input voltage of transformer T Primary windings A and secondary windings B C and D along with their associated switches, S S and S can be identical to the similar parts of transformer T Any number of step down transformers similar to T may be connected in series therewith in order to obtain the degree of precision desired. The final step down transformer T is connected with its primary winding A across secondary windings D of transformer T so that the volt-age across secondary windings D serves as the input voltage of transformer T Primary windings A also have a decade arrangement whose equal voltage steps are connectable by switch S7 in series between switch S and the lower end of secondary windings B on transformer T Secondary windings B are likewise provided with a decade arrangement of equal voltage steps connectable by means of switch S in series between the switch S and the lower end of secondary windings B of transformer T It will be apparent that the transformers T and T will be by-passed if the switch S is in its lowermost position 1X.

In this arrangement each step of primary windings A has one-tenth of the input voltage V across its terminals while each step of secondary windings B has induced therein somewhat less than one-tenth of the vdltage across each step of primary windings A or somewhat less than one-hundredth of the input voltage V since there is a ten-to-one turns ratio between windings A and B Secondary windings C have one-tenth of the voltage developed across each step of secondary B induced in each of its individual steps, or somewhat less than one-thousandth of the input voltage V since there is a similar ten-to-one turns ratio between windings B and C The voltage developed across secondary windings D is equal to the voltage induced in one step of secondary windings C due to a ten-to-one turns ratio between windings C and D Each step of primary windings A has induced therein one-tenth of the voltage across secondary windings D or approximately one ten-thousandth of input voltage V; of step down transformer T In a similar manner secondary windings B have induced in each step thereof a voltage of approximately 10* V secondary windings C have induced in each of its steps approximately 10* V each step of primary windings A has about 10* V induced therein, and finally, secondary windings B have induced in each of its steps about 10- V This is continued until the desired degree of precision is obtained in the final output voltage measured between switch S on transformer B and the LOW side of the line. The positions of the various switches associated with transformers T T and T in PEG. 1 result in an output voltage of approximately 036453564 times the input voltage V between switch S and the LOW side of the line.

As shown in FIG. 2 the A.C. input voltage V applied to the primary windings A of transformer T causes an A.C. current 1 to flow in the primary windings which lags applied voltage V by phase angle 0. Under no load conditions the primary winding current I equals the exciting current for the magnetic core of the transformer. This exciting current I may be resolved into two components, a magnetizing current 1 and a core loss current 1 in quadrature therewith. Magnetizing current 1 produces a mutual flux which links with the primary windings A and secondary windings B of the transformer. This mutual flux at induces a voltage E in primary winding A which lags the mutual flux by degrees. The core loss current I supplies the energy for the hysteresis and eddy-current losses in the magnetic core of the transformer T When exciting current I flows through primary A the winding resistance of this primary causes a voltage drop I R which is in phase with the exciting current I Since the leakage flux and its associated leakage reactance can be neglected in a well-designed toroidal transformer, the applied voltage V can be considered to be the vector sum of the induced voltage E and the winding resistance voltage drop I R The voltage developed across the secondary windings B when no load is applied to such secondary windings consists only of the voltage E which is induced in secondary windings B by mutual flux as shown in FIG. 3. This induced voltage E is in phase with the induced voltage E; of primary windings A since primary windings A and secondary windings B are on the same magnetic core and are linked by the same mutual flux. Since no current flows in the secondary windings B due to its no load condition, no voltage drop due to the internal resistance or leakage reactance of the windings B is produced. Therefore, the voltage developed across secondary windings B is merely the induced voltage E which is out of phase with the voltage V applied to primary windings A by the phase angle a and is not equal to such voltage multiplied by the turns ratio of windings A and B the magnitudes of such phase angle on and the voltage R being exaggerated in FIG. 2. That is to say, increments of the induced secondary voltage E do not provide output voltage steps which are in phase with or which have a magnitude equal to the applied voltage V multiplied by the turns ratio so that an inaccuracy occurs.

In order to compensate for the inaccuracy discussed above selected portions of a compensation impedance, which may be suitable tapped resistor R are connectable in series with primary A by means of a switch S ganged with the switch S for secondary windings B Compensation resistor R is divided into a plurality of resistance steps corresponding in number to the voltage steps of secondaries B put voltage of each selected step of secondary windings B and the corresponding step of compensating resistor R consists of a fraction E of the induced voltage E of secondary windings B and a voltage l R which very closely approaches the fraction of 1 R required to produce a resulting output voltage step in phase with the input voltage V and of the desired magnitude. value of each resistance step of compensating resistor R is selected so that it is proportional by the turns ratio to the winding resistance of each voltage step in primary A primary current 1 flowing through this compensation resistance produces a voltage drop in phase with and proportional to the resistance voltage drop in the windings As a result the combined out- Since the.

of primary A When the total compensating resistance voltage l R is added to the total induced voltage E of the secondary winding 13;, the resultant voltage V; is obtained as shown in FIG. 3 which is in phase with the primary voltage V applied to the primary A and more nearly equal. to the applied voltage nultiplied by the turns ratio. The same relation holds for each step of the windings B and compensating resistance R as indicated by the voltages E and f R of FIG. 3. It should be noted that the resistance of compensation resistor R is small compared to the impedance of primary A so that its effect upon the magnitude and phase angle of applied voltage V can be neglected.

Since step down transformers T T and T are connected with their output windings in series, the voltages developed across each of their windings are added. it is apparent that voltage compensation similar to that discussed above could be applied to each of the remaining windings of these transformers to obtain an even more accurate transformation. This is not done in practice because the voltages developed across the remaining windings are very small with respect to the voltage developed across primary A so that such compensation is, in general, not necessary.

it is often desirable, however, to add a step up transformer T to the variable ratio transformer apparatus in order to add a multiple of the line voltage tothe output voltage of the transformer apparatus. When this is done a compensating impedance in the form of a resistor R is connected in series with the primary windings A of thestep up transformer T since the secondary windings B and C are operated under no load condition and the volt-ages induced therein are less than the applied voltage times the turns ratio because of the resistance voltage drop in primary windings A Unlike compensating resistor R the compensating resistor R is not divided into a plurality of resistance steps, but the voltage drop across this compensating resistance is stepped up and added to the voltage induced in secondary windings B and C by means of a compensating transformer T A step up compensating transformer is required since it is necessary to add a voltage to the output voltage of each of the secondary windings B and (1, which is equal to the IR drop in primary windings A and compensating resistor R This transformer T has its primary windings A connected across the compensating resistor R and has its secondary windings B and C connected in series with secondary windings C and B respectively of step up transformer T When switch S has its movable contact in the lower position IX in FlG. l transformers T and T a e bypassed and no multiple of the line voltage is added to the output of the variable ratio transformer apparatus. Also the switch S is ganged with the switch S to disconnect transformer T,; from the line when such switches are in the position lX. However, wh n switches S and S are in the position 2X, as shown in FIG. 1, the step up transformer T4- is connected to the line audits secondary windings C are connected-in series withthe secondary windings E through secondary windings B of the transformer T so that a compensated voltage, which is a multiple of the linevoltage is added to the output voltage from windings B If there is a one-tonne turns ratio between primary winding A and each of the secondary windings B and C this added voltage will be equal to the line voltage. When switches S and S are in the position 3X, both secondary windings B and C are connected in series with the output from secondary windings B; through secondary windings B and C of transformer T resulting in a compensated, voltage equal to two times the line voltage being added to the output from secondary windings B The turns ratio of compensating transformer T between primary windings A and each of the secondary windings B and C is selected so that the compensating voltage developed across compensating resistor R is properly transformed in order that the magnitude and phase angle of the compensating voltage so transformed corresponds to that of the resistance voltage drop in primary windings A and R This variable ratio transformer with its compensation means may be used to test any electrical device in any test circuit where the transformer is used under no load condition. One such test circuit is shown in FIG. 4 by which other transformers may be tested for their accuracy of voltage transformation. The primary windings of the transformer T T being tested are connected across an AC. voltage source E. A variable ratio percentage transformer T is connected with its primary windings in parallel with the primary windings of test transformer T The compensated variable ratio transformer T of FIG. 1, shown as an auto transformer in FIG. 4 for simplicity, is used as a comparison standard by having one end of its windings connected directly to the low side LO of the line, and a selected tap of the primary windings connected in series with the secondary windings of the percentage transformer T through switch S to the high side HI of the line. The secondary windings of test transformer T have one end connected directly to the low side of the line, and the other end by switch S to a selected voltage output tap on the windings of the standard transformer T through an electrical meter M. The secondary windings of the test transformer T and the windings of standard transformer T are connected to have their voltages oppose or buck each other so that the standard transformer T is operated under no load conditions.

When testing for the turns ratio or the accuracy of the voltage transformation ratio of the transformer T being tested, the meter M connected in series with the secondary windings of test transformer and the standard transformer is a voltage indicator. The desired voltage transformation ratio may then be set on the compensated variable ratio transformer T which is used as a standard because of its precision and accuracy. The contact switch S on percentage transformer T is then moved until a minimum reading is obtained on the voltage indicator M. Since the secondary windings of percentage transformer T are divided into a plurality of percentage steps, the setting of switch S on such secondary windings is then read to determine how accurate the transformer under test is compared to the standard transformer T The reading on the percentage transformer T given by the setting of switch S can be terms of the percentage deviation of the transformer under test T from the desired turns ratio set on variable ratio transformer T It is also possible to determine the actual transformation ratio of the test transformer T directly from the reading given by switch S on standard transformer T In order to obtain this actual ratio directly switch S is set at zero on percentagetransformer T p and the switch S oil-standard transformer T is moved until a minimum voltage reading appears on voltage indicator M.

It is also possible to accurately determine the phase shift between the input and output voltages of the transformer T under test by using the test circuit shown in FIG. 4 when a phase angle meter is substituted for the voltage indicator and connected in the circuit to show the phase angle between the voltage across the test transformer T and that across the terminals connected to the meter M in FIG. 4. The output voltage of percentage transformer T is set to zero voltage by switch S and the standard transformer T is adjusted to produce a phase angle reading of the phase meter. This indicates that the voltage across the terminals shown connected to the meter M in FIG. 4- is 90 out of phase with the voltage developed across the output of standard transformer T which voltage is very nearly in phase with the input voltage of transformer T with its compensation means. Since at this time the same input voltage is across the primary of both transformers T and T the output voltage of transformer T is very nearly in phase with the input voltage of transformer T Next the switch S on percentage transformer T is moved from its zero position until the reading of the phase meter is 45. It can then be shown that the output voltage of transformer T divided by the output voltage of transformer T s is the tangent of the angle of phase difference between the output voltages of transformers T and T Since the phase shift of standard transformer T is very small or zero with its compensation, this angle is also the phase angle between the input and output voltages of the transformer under test T It should be noted that the frequency of AC. voltage source B should be near that of the rated frequency of the transformers used in the test circuit of FIG. 4 and that the percentage transformer T may have a compensation means similar to that used in standard transformer T While the present invention has been described above in connection with certain specific embodiments thereof, it should be understood that various modifications as to detail will occur to those skilled in the art and that such modifications which would be obvious to one having ordinary skill are encompassed by the concept of the present invention. Therefore, the scope of the present invention is not limited to the embodiments illustrated, but is defined only in the following claims.

I claim:

l. A precision electrical transformer comprising:

a magnetic core,

primary and secondary windings on said core,

compensation means connected to said secondary winding to produce under no load conditions an output voltage on said secondary winding which is substantially in phase with the input voltage applied to said primary winding and equal to the product of said input voltage multiplied by the turns ratio between said primary and secondary windings,

said compensation means including means to produce a compensating voltage in phase with and equal to the product of the impedance voltage drop in said primary windings multiplied by the turns ratio between said primary and secondary winding and to add said compensating voltage to the voltage induced in said secondary winding under no load conditions.

2. A precision electrical transformer comprising:

a magnetic core,

primary and secondary windings on said core,

a compensation impedance connected in series with said primary winding to provide under no load conditions a compensation impedance voltage drop across said compensation impedance in phase with and proportional to the impedance voltage drop in said primary winding due to current flowing in said pr-imray winding, and

means for connecting said compensation impedance to the secondary winding to add to the voltage induced in said secondary winding under no load condition a compensating voltage derived from said compensation impedance voltage drop which is in phase with the impedance voltage drop in said primary winding and equal to the product of said impedance voltage drop in said primary winding multiplied by the turns ratio between said primary and secondary windings.

3. A precision electrical transformer comprising:

a core of magnetic material,

primary windings on said core,

secondary windings on said core divided to provide a plurality of first voltage steps,

a compensation impedance connected in series wit said primary windings and divided to provide a plurality of second voltage steps,

a switch to connect a selected number of said first voltage steps in series with the output of said transformer, and

Cit

a second switch to connect a corresponding number of said second voltage steps in series with said secondary winding and the output of said transformer so that the effective open circuit output voltage of said econdary windings is equal to the sum of the voltage across said selected steps of said secondary windings and the voltage across said selected steps of said compensation impedance.

4. A precision electrical transformer comprising:

a core of magnetic material,

primary windings on said core,

secondary windings on said core,

compensation resistance connected in series with said primary windings,

first switch means connected between said primary and said secondary windings to divide said primary windings into a plurality of equal voltage steps,

a second switch means connected between said secondary windings and its output to divide said secondary windings into a plurality of equal voltage steps,

third switch means connected between said primary windings and said compensation resistance to divide said compensation resistance into a plurality of resistance steps and to connect it in series with said secondary windings so that the effective open-circuit output voltage of each step of said secondary windings is equal to the sum of the voltage induced in the last mentioned step of said secondary winding by the varying magnetic flux in said core due to the AC. current flowing in said primary windings plus the voltage drop developed across the corresponding step of said compensation resistance by said primary winding current.

5. A precision electrical transformer comprising:

a core of magnetic material,

primary windings on said core,

secondary windings on said core,

compensation impedance means connected in series with said primary windings,

a first switch connected between said primary windings and said secondary windings to divide said primary windings into a plurality of equal voltage steps,

a second switch connected between said secondary windings and the output of said transformer to divide said secondary windings into a plurality of equal voltage steps,

a third switch connected between said primary windings and said compensation impedance to divide said compensation impedance into a plurality of impedance steps and to connect it in series with said secondary windings so that the effective open-circuit output voltage of each step of said secondary windings is equal tothe sum of the voltage induced in eachstep of said secondary windings by the varying magnetic flux in said core due to the AC. current flowing in said primary and the voltage drop developed across each step in said compensation impedance by said primary current, said second and third switches being mechanically ganged so that each voltage step of said secondary windings is coupled with a separate impedance step of said compensation impedance in order to compensate for the imedance voltage drop in said primary windings.

6. A precision electrical transformer apparatus com:

a plurality of transformers each having a core of magnetic material, primary windings on said core and a plurality of secondary windings on said core,

compensation impedance connected in series with the primary windings of the first of said transformers,

a first switch connected between the primary windings and the first secondary windings of said first transformer to divide said primary windings into a plurality of equal voltage steps,

a second switch connected between said first secondary a compensation transformer connected with its primary the secondary windings of said step up transformer in order to correct for the impedance voltage drop in the primary windings of said step up transformer.

into a plurality of equal voltage steps, 8. A precision electrical transformer apparatus coma third switch connected between said primary windprising:

ings and said compensation impedance to divide said a plurality of voltage step down transformers each compensation impedance into a plurality of steps having a core of magnetic material, primary windand to connect it in series with said first secondary ings on said core and a plurality of secondary windwindings so that the effective open-circuit output ings on said core, voltage of each step of said first secondary windings 9 a first compensation impedance connected in series is equal to the sum of the voltage induced in each with the primary windings of the first of said step step of said first secondary windings plus the voltage down transformers, drop developed across each step of said compensaa first switch connected between said primary windings tion impedance by the electrical current flowing in and first secondary windings ofsaid first transformer said primary, each of the remaining windings of to divide said primary windings into a plurality of said first transformer and the remaining transformers equal voltage steps, being connected in series by switches which divide a second switch connected between said first secondary each of them into a plurality of equal voltage steps windings and other secondary windings on said first in order to add the output voltages of said windings transformer to divide said first secondary windings and obtain a final output voltage having a high de into a plurality of equal voltage steps, gree of precision. a third switch connected between said primary wind- 7. A precision electrical transformer apparatus comh1g8 and Said first pe ti impe ance to divid prising: said first compensation impedance into a plurality of a plurality of voltage step down transformers each hav- Steps and t0 Connect it in 56165 With Said first ing a core of magnetic material, primary windings (mdfiry ndings So that the effective open-circuit on said core and a plurality of secondary windings Output Voltage of each p of Said first Secondary on said core, windings is equal to the sum of the voltage induced first compensation impedance connected in series in each p of Said first secondary windings by the with the primary windings of the first of said step Varying magnetic flux in Said Core P the Voltage down tran former drop developed across each step of said first coma first switch connected between the primary windings Phhsahoh impcdahcfi y U16 electrical Current and first secondary windings of said first transihg in Said P y windings, each of the Ifimainiflg former to divide said primary windings into a pluwindings 0f Said first transformer and the remaining rality f equal Voltage steps, step down transformers being connected in series by a second switch connected between said first secondary Switches which divide each of them into a plurality windings and other secondary windings on said first of equal Voltage Steps in Order to add the Output transformer to divide said first secondary windings Voltages of said remaining windings and Obtain an into a plurality of equal voltage steps, Output Voltage having a high degrfie of Precision, third switch connected between said primary wind- 21 Vohagfi p p transformer With its p y windings ings and said first compensation impedance to divide COhheCthd in Parallel With the p 'y windings and said first compensation impedance into a plurality of first Compensation impedance of Said first p down steps and to connect it in series with said first sectransformer, and having its Secondary windings C011- ondary windings so that the effective open-circuit hected in Series with the output of the p down output voltage of each step of said first secondary transformers so their Output Voltages are addhd windings is equal to the sum of the voltage induced thereby, i h t f id fi t Secondary i d by the a second compensation impedance connected in series varying magnetic flux in said core plus the voltage With the Primary windings of Said P P transdrop developed across each step of said first comformeh and pensation impedance by the electrical current flowing a co'mphhsatioh trahsfhrmel Cohhhcted With its P in said primary windings, each of the remaining merywindinssin Parallelwithsaidsewnd compensawindings of said first transformer and the remaintioh impedance and its Secondary windings in Series ing step down transformers being connected in series With the Secondary windings of said p P tra11$- b i h hi h divide each f them into a former in order to correct for the impedance voltage rality of equal voltage steps in order to add the drop in the Primary windings of Said Step P trans output voltages of said remaining windings and obfohheh and wi an Output voltage having a high degree of mg a sw tch means connected to the secondary winding of i i said step up transformer to change the ratio of the a step up voltage transformer with its primary windings voltage Output to the Voltage input of Said Step P connected in parallel with the primary windings and tmhsfcmlerfirst compensation impedance of said first ste down transformer and having its secondary windings con- References Cited by the Exammer nected in series with the output of the last step down UNITED STATES PATENTS gansformer so their output voltages are added there- 2,667,617 1/54 Boyajian Y, i 2,891,214 6/59 Rogers 323-44 a Second compensatlon im pedance connected in series 2,396,156 7/59 Perrins 324 55 with the primary windings of said step up trans- 2 911 91 11 59 Pritchgtt 324 55 f and 3,040,240 6/62 Gotal et a1 323-4 09 X LLOYD MCCOLLUM, Primary Examiner.

MILTON O. HIRSHFIELD, Examiner.

Claims

8. A PRECISION ELECTRICAL TRANSFORMER APPARATUS COMPRISING: A PLURALITY OF VOLTAGE STEP DOWN TRANSFORMERS EACH HAVING A CORE OF MAGNETIC MATERIAL, PRIMARY WINDINGS ON SAID CORE AND A PLURALITY OF SECONDARY WINDINGS ON SAID CORE, A FIRST COMPENSATION IMPEDANCE CONNECTED IN SERIES WITH THE PRIMARY WINDINGS OF THE FIRST OF SAID STEP DOWN TRANSFORMERS, A FIRST SWITCH CONNECTED BETWEEN SAID PRIMARY WINDINGS AND FIRST SECONDARY WINDINGS OF SAID FIRST TRANSFORMER TO DIVIDE SAID PRIMARY WINDINGS INTO A PLURALITY OF EQUAL VOLTAGE STEPS, A SECOND SWITCH CONNECTED BETWEEN SAID FIRST SECONDARY WINDINGS AND OTHER SECONDARY WINDINGS ON SAID FIRST TRANSFORMER TO DIVIDE SAID FIRST SECONDARY WINDINGS INTO A PLURALITY OF EQUAL VOLTAGE STEPS, A THIRD SWITCH CONNECTED BETWEEN SAID PRIMARY WINDINGS AND SAID FIRST COMPENSATION IMPEDANCE TO DIVIDE SAID FIRST COMPENSATION IMPEDANCE TO DIVIDE STEPS AND TO CONNECT IT IN SERIES WITH SAID FIRST SECONDARY WINDINGS SO THAT THE EFFECTIVE OPEN-CIRCUIT OUTPUT VOLTAGE OF EACH STEP OF SAID FIRST SECONDARY WINDINGS IS EQUAL TO THE SUM OF THE VOLTAGE INDUCED IN EACH STEP OF SAID FIRST SECONDARY WINDINGS BY THE VARYING MAGNETIC FLUX IN SAID CORE PLUS THE VOLTAGE DROP DEVELOPED ACROSS EACH STEP OF SAID FIRST COMPENSATION IMPEDANCE BY THE ELECTRICAL CURRENT FLOWING IN SAID PRIMARY WINDINGS, EACH OF THE REMAINING WINDINGS OF SAID FIRST TRANSFORMER AND THE REMAINING STEP DOWN TRANSFORMERS BEING CONNECTED IN SERIES BY SWITCHES WHICH DIVIDE EACH OF THEM INTO A PLURALITY OF EQUAL VOLTAGE STEPS IN ORDER TO ADD THE OUTPUT VOLTAGES OF SAID REMAINING WINDINGS AND OBTAIN AN OUTPUT VOLTAGE HAVING A HIGH DEGREE OF PRECISION, A VOLTAGE STEP UP TRANSFORMER WITH ITS PRIMARY WINDINGS CONNECTED IN PARALLEL WITH THE PRIMARY WINDINGS AND FIRST COMPENSATION IMPEDANCE OF SAID FIRST STEP DOWN TRANSFORMER, AND HAVING ITS SECONDARY WINDINGS CONNECTED IN SERIES WITH THE OUTPUT OF THE STEP DOWN TRANSFORMERS SO THEIR OUTPUT VOLTAGES ARE ADDED THEREBY, A SECOND COMPENSATION IMPEDANCE CONNECTED IN SERIES WITH THE PRIMARY WINDINGS OF SAID STEP UP TRANSFORMER, AND A COMPENSATION TRANSFORMER CONNECTED WITH ITS PRIMARY WINDINGS IN PARALLEL WITH SAID SECOND COMPENSATION IMPEDANCE AND ITS SECONDARY WINDINGS IN SERIES WITH THE SECONDARY WINDINGS OF SAID STEP UP TRANSFORMER IN ORDER TO CORRECT FOR THE IMPEDANCE VOLTAGE DROP IN THE PRIMARY WINDINGS OF SAID STEP UP TRANSFORMER, AND A SWITCH MEANS CONNECTED TO THE SECONDARY WINDING OF SAID STEP UP TRANSFORMER TO CHANGE THE RATIO OF THE VOLTAGE OUTPUT TO THE VOLTAGE INPUT OF SAID STEP UP TRANSFORMER.