US2196886A - Voltage regulation - Google Patents

Description

April 9, 1940, 5 ADAMS 2,196,886

voLuc-s nzwm'rxou Filfld July 17, 1937 2 ShOEtS-ShGGt I Invent or: Elliot Q Adams,

His Attorney.

P 1940- I v a. Q. ADAMS 2,196,886

VOLTAGE REGULATION filed July 17. 1957 2 Sheets-Sheet 2 7'0 J PHASE LUAID 7D 3 PHASE L060 Inventor: Elliot Q. Adams His Attorney.

Patented Apr. 9, 1940 UNITED STATES PATENT OFFICE VOLTAGE REGULATION Application July 1'1, 1937, Serial No. 154,294

11 Claims.

My invention relates generally to voltage regulation and more particularly to the compensation of load circuits for variations in voltage drop caused by variation in current in their supply 0 circuits.

Much trouble is experienced with flickering of incandescent lamps caused by instantaneous variations in voltage caused by starting motors, are welders, and other fluctuating power loads drawn 10 from the same feeder lines. These variations are so large, in many cases, that no practicable increase in the-wire sizes will reduce the variations to an acceptable range.

I have found that by drawing the lighting and 15 power loads, respectively, from the two sides of a 3-wire load circuit, and adjusting the impedance of the common neutral to a proper relation to the impedance of the common supply side of the circuit, that the flickering of the lamps caused by variations in the power load can be eliminated; and this adjustment remains good for all reasonable values of the lighting and power loads.

This result is explainable as follows: In a threewire circuit, current in the two sides of the cir- 6 cuit flows in opposite directions in the common neutral. Therefore, if the load current of one side causes a voltage drop in the common neutral with respect to that side, the same current will produce a voltage rise with respect to the other side. This voltage rise I utilize to cancel the voltage drop caused by the current producing it in the supply side of the circuit.

While my invention is particularly adapted for use with the three-wire transformer secondi aries of conventional single phase distribution transformers it may also be used in three-wire direct current circuits and in polyphase alternating current circuits.

An object of my invention is to improve the voltage regulation of load circuits.

Another object of my invention is to prevent lamp flicker as the result of fluctuating loads applied to a main supply circuit which also supplies current for incandescent lamps.

A further object of my invention is to improve the voltage regulation of one side of a three-wire transformer secondary by properly relating the impedance of the common neutral to the' impedance of the primary circuit of the transformer. 1

My inventionwill be better understood from the following description, taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings, Fig. 1 illustrates diagrammatically an embodiment of my invention using a single phase insulating transformer; Fig. 2 is a modification using a single phase auto-trans-' former; and Figs. 3, 4 and 5 are modifications using three-phase transformers.

Referring now to Fig. 1 of the drawings, a

transformer, having a primary winding H), has secondary winding sections II and I2 connected respectively between a. common neutral conductor l3 and the outer sides of a three-wire load circuit. To the side of this circuit supplied by secondary section I l is connected a load, the voltage of which it is desired to make independent of the load on the other side. This load is shown by way of example as a lamp load Ii, the connections of which are controlled by switches l5. To the side of the three wire circuit supplied by secondary section I2 is connected a variable power load, shown by way of example as a pair of induction motors IS, the connections of which are controlled by switches ll. The circuit of primary winding l 0 is energized by any suitable source of alternating current (not shown).

Of the letters on the drawings, V denotes voltage; Icurrent; Zlmpedance and n-number of turns. The subscripts denote respectively: Icircuit of primary I0; l--secondary section I I; IAecondary section I2; and 3-common neutral.

It can be shown, by calculation, that neglecting magnetizing current, stray flux, and such part of the iron losses as cannot be assigned to one of the circuits, the voltages available for the two secondary loads are respectively:

The last term of each equation represents the change in voltage of one side of the transformer secondary caused by the load on the other side.

By making Z3 equal to may be referred to as the equivalent primarycircuit impedance referred to the secondary.

tor or angle X (tan may contain added lumped impedance elements. These elements may be reactive or resistive or both. If reactive they may be positive (inductive) or negative (capacitive). If resistive they may also be either positive (ordinary resistor) or negative (series connected commutator type generator or self-excited induction generator). Z3 should ordinarily have the same power factor or impedance angle as Ze.

It is also important that there be a point at which the common neutral impedance Z: terminates. In Fig. 1 this is the point on neutral conductor ii at which the two load circuits branch of! and become entirely separate. Usual wiring practice will make the common neutral terminate at the panel board.

Instead of matching Z: to Z0, Z0 may be matched to Z: by making Various special cases can be derived from this by omitting (i. e., placing equal to zero) certain of the ns and Zs, e. g.: Z4=Z5=0 gives the analytic equivalent of an insulating transformer. n1=nz=0 gives the symmetrical two-coil autotransformer case. nz=m=0, Z4==0 gives the unsymmetrical two-coil auto-transformer case. This last arrangement is particularly useful where one of the circuits requires a very small part of the total power, since it permits the use of a correspondingly small transformer.

In the last factor in square brackets, the terms in Z; and Z5 may in the general case, and in the symmetrical two-coil auto-transformer case will, have a resistance component negative in sign. These negative components should not be so large as to overbalance the resistance component of the term in Zn, or no static impedance Z; can be used to make the last factor in square brackets vanish. Stated otherwise, the resistances of the coils in and us should not be too large. It is unlikely, however, that this condition will call for wire in coils m and us any larger than is required by good transformer practice.

No such difliculty arises in the case of an unsymmetrical two-coil auto-transformer.

The power consumed in an impedance in the common neutral is, of course, zero at no load, and likewise zero if the current in the neutral is zero, that is, when the currents taken by the two sides of the secondary are equal. In a balanced system this will be the case when the system is fully loaded, hence the maximum voltage drop under load will not be increased by the presence of the impedance in the neutral. It will, however, occur when the particular line is fully loaded, even if other lines are lightly loaded.

In Fig. 3 the invention is extended to a polyphase case. Motor Ii is connected as a conventional three-phase induction motor to the terminals of the delta secondary winding of a three-phase transformer. The phase windings of the secondary are extended and lamp loads ll are connected between the terminals of the extensions and the motor leads which then act as common neutrals. Most three-phase voltages are 220 and if the secondary extensions are also 220 volts, balancing transformers II can be used to obtain volts for the lamps.

To obtain proper regulation in Fig. 3, the impedance angle of Z: should be 30 different from that of Zn because unity power factor motor current flowing through Z0 will be 30' out of phase with unity power factor lighting current flowing through Z1.

The circuit of Fig. 3 does not permit grounding of one side of each of the lamp circuits.

Fig. 4, however, shows a three-phase circuit in which the neutral impedances Z; have the same phase angle as the primary or supply circuit impedance and in which a side of each of the lighting circuits may be grounded so as to conform to usual house wiring practice.

As shown in Fig. 4, the individual phase windings of a three-phase transformer winding are 45 star-connected by means of three neutral impedances Z3 connected respectively between a neutral point, shown grounded, and corresponding intermediate points on each of the phase windings. This polyphase winding may either be the secondary winding of an insulating transformer excited by any suitable primary winding, or it may be considered an auto-transformer energized by any suitable supply circuit.

Three of the winding sections whose potentials are electrical degrees apart are connected to supply any suitable balanced three-phase load, such for example as the motor I in Fig. 3. The remaining three winding sections are connected to ground through separate lamp loads I.

As similar power factor three-phase and lighting load currents are in line (phase opposition) in the neutral impedances Z3 these impedances will have the same phase angle as that of Z0, so that merely by relating Z; and Z0 as explained above in connection with Figs. 1 and 2, the lamp voltages will be independent of three-phaseload fluctuations.

In Fig. 5, the individual phase windings are mesh-connected through the neutral impedances Z3 which interconnect respectively, the intermediate or neutral points on each of the windings with the outer or free ends of the power circuit sections of these windings.

The three-phase load is connected to the outer ends of the'power circuit sections of the three windings, and lighting loads are connected between the outer ends of the lighting load sections of thewindings and the three-phase load connection points.

As-the neutral impedances Z: carry the threephase load currents instead of the three-phase load line currents, which are 30 out of phase with each other, the load and lighting currents in the neutral impedances Z: will be in line at the same power factor and Z: will have the same angle as Z0. Z3 and Z0 will, of course, be related to each other in accordance with the formulas developed above in connection with Figs. 1 and ?n The number of turns of the power and lighting sections of each three-wire transformer 'secondary may of course be any values desired and need not be equal as indicated in the first four figures. l

While I have shown and described particular embodiments of my invention it will be obvious to those skilled in the art that changes and modifications can be made, and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention. I

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a transformer, a primary winding circuit therefor, and a three-conductor secondary winding circuit therefor, said secondary winding circuit including a common neutral conductor, said primary winding circuit having an impedance which causes a voltage change on one side of said secondary winding circuit when a load is placed on the other side of said secondary winding circuit, said common neutral conductor having an impedance which produces an opposite direction change in voltage on said one side of said secondary winding circuit when said load is placed on the said other side of said secondary winding circuit, said voltage changes being substantially equal in magnitude.

2. In combination, an alternating current supply circuit, a transformer having its primary winding connected thereto, and a pair of loads connected to the secondary winding of said transformer in such a manner that the power components of the two load currents flow in opposite instantaneous directions in a common neutral conductor, the impedance of said common neutral conductor being substantially equal to the equivalent primary circuit impedance with respect to the secondary'current taken by at least one of said loads.

3. In combination, a power supply circuit, a transformer having a primary winding of no turns connected to said supply circuit, a pair of loads connected respectively between an intermediate point on the secondary winding of said transformer and two points thereon on opposite sides of said intermediate point, said two points being spaced m and 1:: turns respectively from.

said intermediate point and an impedance Z: connected between said intermediate point and said loads, the value of said impedance being so correlated to the impedance Zo of the primary winding circuit of said transformer that Z: is substantially equal to 4. In combination, a transformerhaving a three-wire secondary circuit provided with a secondary winding.

common neutral, a power load connected to one side of said circuit and a lighting load connected to the other side of said circuit, the impedance of the common neutral being substantially equal to the equivalent primary circuit impe nce of said transformer referred to said seconda y circuit.

5. In combination, an electric. circuit having a supply side and a three-wire load side, said supply' side having a given impedance, separate loads connected to each half of said three-wire load side through a predetermined neutral impedance, said supply side impedance being such as to produce a substantial change in the voltage of one of said loads in response to a given change in value of the other of said loads, said neutral impedance being such as to produce a substantial change in the voltage of said one load in response to saidgiven change of said other load, said voltage changes being substantially equal and' opposite.

6. In combination, a polyphase load circuit, a plurality of single phase transformer windings interconnected to form a polyphase transformer secondary winding for energizing said load circuit, a plurality of impedances connected to be traversed by the phase currents in said load circuit, extensions on -each of said single phase windings, single phase loads connected to be individually energized by said extensions through said impedances respectively. a polyphase primary exciting circuit for said windings having a given impedance, each of said plurality of impedances being substantially equal to the equiva lent primary circuit impedance referred to its respective secondary winding circuit.

7. In combination, a plurality of single phase three-wire transformer secondary windings, a polyphase load circuit energized by all of said windings, separate single phase loads energized by each of said windings, the neutrals of each of said windings having an impedance which is common to one of the phases of said polyphase circuit and one of said single phase loads, and an exciting circuit for said windings having a given impedance, each of said neutral impedances being substantially equal to the equivalent exciting circuit impedance referred to its respective 8. In combination, a transformer having a polyphase primary winding and a mesh-connected secondary winding, a polyphase supply circuit for said primary winding, a polyphase load circuit connected to said secondary winding,

extensions on each of the phase windings of said mesh-connected secondary, single phase load cit cuits connected to be energized by said extensions, separate impedances which are common respectively to oneof the'conductors of said polyphase load circuit and to one of said single phase load circuits, each of said plurality of impedances being substantially equal to the equivalent primary circuit impedance referred to its respective secondary winding circuit.

9. In combination, a polyphase transformer secondary comprising a plurality of windings, a plurality of impedances connected respectively between said windings and a neutral point, a polyphase load circuit connected to said windings, extensions on said windings on the opposite sides thereof to which said impedances are connected, and single phase loads connected respectively between terminals on said extensions and said neutral point, each of said plurality of impedances being substantially equal to the equivalent primary circuit impedance referred to its respective secondary winding circuit.

10. -In combination, a plurality of three-wire transformer secondary windings each having a variable load section and a second load section, a plurality of impedances connected respectively between the neutral of one winding and the outer end of the variable load section of another winding whereby a mesh connection of alternate impedances and variable load sections is formed, a polyphase load circuit connected to the outer ends of said variable load sections, and single phase load circuits connected across said second load sections and the impedances directly connected thereto, each of said plurality of impedances being substantially equal to the equivalent primary circuit impedance referred to its respective secondary winding circuit.

11. In combination, an autotransformer wind- 7 ing, a two-wire supply circuit and a three-wire load I circuit therefor, one of the load circuit wires being a common neutral for the other two,

said common neutral being connected to an intermediate point on said winding and having an impedance Z3, said supply circuit having an impedance Z0 and having its two conductors connected to said winding at points which are separated from said neutral by m and m turns of said winding respectively, said 114 and m turns having respective impedances Z4 and Z5. the other two load circuit wires being connected to said winding at points which are separated from the'points to which said supply circuit is connected by m and 11: turns respectively, the arrangement being such that the total turns between the neutral and the other two load circuit wires are (m+m) and (112+7l5) respectively, said neutral impedance Z: being equal to

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