461,004

PATENT SPECIFICATION

Application Date: July 4, 1935. No. 19170/35.

Complete Specification Left: July 6, 1936.

Complete Specification Accepted: Feb. 4, 1937.

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PROVISIONAL SPECIFICATION

Improvements in and relating to Apparatus for the Supply of Electrical Energy to Varying Loads

I, ALAN DOWER BLUMLEIN, a British Subject, of 32, Audley Road, Ealing, London, E.5, do hereby declare the nature of this invention to be as follows:-

The present invention relates to apparatus for the supply of electrical energy to varying loads.

When two or more loads are fed from the same source of alternating current power, trouble may be experienced due to a variation of one load causing a variation of voltage on another load. Such variation of voltage is due to the effective impedance of the source not being zero. For example, the effective reactance and sometimes the resistance of an alternator will cause the variations of one load connected across it to affect the voltage applied to other loads. A typical example of this occurs in a large radio transmitting or modulating amplifier fed from an alternator. In such a case the various stages of amplification are fed from separate rectifiers all fed from the same source. With variations of average signal strength (e.g. variations of average picture brightness in a television transmission) the current taken by the final valve and so the load taken by the rectifier for the final valve will vary, causing a voltage variation at the generator terminals which voltage variation reacts on earlier valves. This difficulty could be overcome by providing separate machines for each stage or group of stages, but this would add to the cost.

Another similar case occurs when two or more loads are fed from a single long power line. The inductance of the line (apart from any regulation at the generating station) will cause variations of one load to effect the voltage on other load or loads, which variations might be very undesirable if one of the loads is itself a long power line subject to serious surges.

It is the object of the present invention to provide a circuit by which two or more loads may be fed from a common source, the circuit being designed to remove some or all of the internal impedance of the source as regards its effect in causing interaction of one load on another load.

According to the present invention there is provided apparatus for the supply of electrical energy to two loads from a common alternating current source having appreciable internal impedance, so that the regulation of the source tends to cause the variation of one of the loads to interact with the voltage across the other load, the apparatus being characterised by the provision of a tightly coupled impedance of the same nature as the said internal impedance, connections whereby the two loads may be connected to two different points on said impedance and a connection whereby the source may be connected to a point on said impedance intermediate the said two different points.

By a tightly coupled impedance is meant the electrical equivalent of an auto-transformer having an impedance bridged across part or all of it or the electrical equivalent of such a circuit arrangement. Such an electrical equivalent might for example be a choke having a central or non-central intermediate tapping, the two parts of the choke being tightly coupled.

According to a feature of the present invention apparatus for feeding two loads from a common polyphase source of power (with n phases) comprises n tightly coupled impedances each of which is connected at one end to the corresponding phase of one of the loads, at the other end to the same phase of the other load and at a point intermediate its ends to the source.

According to yet another feature of the present invention, apparatus for feeding two loads from a common alternating current source comprises a choke having its ends connected to the two loads and a point intermediate said ends connected to the source, the arrangement being such that there is partial or complete neutralisation of the reactance of said source as regards its effect in causing said loads to influence each other.

The invention is illustrated by way of example in the accompanying diagrammatic drawings in which

Fig. 1 shows one circuit arrangement according to the invention,

Fig. 2 indicates the effect of the circuit of Fig. 1 and

Figs. 3 to 6 show further circuits according to the invention,

Referring to Fig. 1, this shows a typical example of the invention in which two loads L1 and L2 are fed from a source A through a conventionalised tight coupled impedance represented by an impedance z bridged across an auto-transformer T, which is assumed to be perfect. The source A is connected to an intermediate point on the auto-transformer T, the impedance Z including the impedance of the source. The loads L1 and L2 which may comprise rectifiers supplying direct current to load circuits, are connected to points on the auto-transformer separated respectively by S1 and S2 turns from the point of connection of the source. The impedance z is bridged across S0 turns of the auto-transformer T.

It can be shown that if

EQUAT. HERE

 

then the circuit of Figure 1 is equivalent to that shown in Figure 2 where the loads are fed through separate impedances equal to

EQUAT. HERE

The interaction of the loads produced by impedance Z has now been removed, and if the source has no internal impedance (other than that included in the original Z) the variations of one of the loads will not affect the other. It will be noted that when the currents in L1 and L2 are in the ratio of S2 to S1, then the regulation of the voltage has not been effected by the introduction of the bridging impedance Z; this follows from the fact that such a current ratio will produce no magnetisation of the auto-transformer (it being assumed that the currents are in phase). In general the ratio S2 to S1 may be fixed to represent the normal or full load ratio of the currents in L1 and L2 (assuming the same power factors) so that under these conditions the voltage drop at L1 and L2 due to Z will be no greater than without the bridge impedance Z. if however a short circuit occurs in either of the loads, the current taken from the source will be less than without the bridging circuit, since each load is in effect connected through a separate impedance, each of which is greater than Z. this latter feature is of use when the loads are fed through long transmission lines, especially when one of the loads is small compared with the other. In this case it can be arranged that a fault on the smaller load produces such a small line current that the line and source can carry it without any damage, and furthermore, the voltage at the large load will be unaffected.

Fig. 3 shows a circuit for neutralising the effect of a reactance X (which represents the internal impedance of the source A together with any other inductive impedance which may be effectively in series with the source) as regards its effect on interaction of three loads. In this case instead of an auto-transformer and impedance, chokes D and E are used with intermediate tappings. The two parts of the chokes should be tightly coupled, any leakage inductance between ab and bc is in effect an addition to X, this additional inductance being that which would be measured between b and ac short-circuited. For the purpose of designing the first choke, D, L2 and L3 are treated as one load. Then, the point C being taken as the source, the choke E is designed. Similarly, L1, L2 or L3 can be replaced by two smaller loads and so on. When feeding a large number of small loads in this manner, it can be arranged that whereas the voltage when all the loads are at full load is that obtained without any added chokes, a short circuit of one load will not produce dangerous currents in the source, and furthermore, the other loads will be unaffected. The reactance X may represent some or all of the reactance of a generator (including or excluding the effect of armature reaction) or other source such as a generating station and power line.

Fig. 4 shows a circuit for neutralising the effect of both resistance and reactance of a source A. the resistance R and reactance X of the generator A may be replaced by a resistance R1 and a reactance X1 (of the same kind as X) arranged in parallel, the latter circuit being equivalent to the circuit X, R for the frequency of the generator. The choke D and shunt resistance R2 then operates as an auto-transformer shunted by a suitable multiple of X1 and R1.

All the circuits so far shown may represent one phase of a polyphase system, the earth connections being replaced by the neutral point, or effective neutral point of the loads or generators are in ring connection.

Figures 5 and 6 show two further arrangements illustrating the many types of connection possible. In Fig. 5, which shows only one phase of a polyphase system, one phase of the primary of a transformer P feeds energy from the source to two load secondaries F and G feeding lines l1 and l2 not necessarily at the same voltage. The transformer t couples the neutralising bridging impedance z. leads m1, and m2 are connected to the star points of l1 and l2. The ratio of turns on the two primaries of t are fixed with reference to the normal or full load currents of l1 and l2.

Fig. 6 shows one phase of a tapping of a power line H passing on at K to the main load. The line l1 carries the tapped load. The centre tapped choke N neutralises the reactance of the line to the left. The transformer t avoids the necessity of putting the choke N in the high voltage circuit and fixes the ratio of the normal currents to K and l1. W is the star point of the line l1. A more complex impedance than the simple choke N shown may be used in order to allow the complex impedance of the line.

Dated this 4th day of July, 1935.

REDDIE & GROSE,

Agents for the Applicant,

6, Breamís Buildings, London, E.C.4.

COMPLETE SPECIFICATION

Improvements in or relating to Apparatus for the Supply of Electrical Energy to Varying Loads

I, ALAN DOWER BLUMLEIN, a British subject, of 32, Audley Road, Ealing, London, W.5, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in any be the following statement:-

The present invention relates to apparatus for the supply of electrical energy to varying loads.

When two or more load are fed from the same source of alternating current power, it may be found that a variation of current in one load causes a variation of the voltage on another load, this variation of voltage being due to the effective impedance of the source. Thus, for example, the effective reactance (and sometimes also the resistance) of an alternator causes variations of the current in one load connected across it to affect the voltage applied to other loads, and in the case of a radio transmitting or modulating amplifier in which the various stages of amplification are supplied with direct current from separate rectifiers all fed from the same alternator, each rectifier constituting a separate load, variations of average signal strength (e.g. variations of average picture brightness in a television transmission system) may cause interaction between the various amplifier valves. This difficulty can be overcome by providing separate alternators for each amplifier stage or group of stages, but this solution adds considerably to the cost.

Similarly, when two or more loads are fed from a single long power line, the inductance of the line (apart from any impedance at the generating station) causes variations of the current in one load to affect the voltage on another load or other loads; the resulting voltage variations might be very undesirable, particularly, for example, if one of the loads is itself a long power line subject to serious surges.

It is the object of the present invention to provide novel or improved means which enable two or more loads to be fed with alternating current power from a common source, the arrangement being such that reaction between one load and another is substantially reduced or eliminated.

According to the invention there is provided apparatus for the supply of electrical energy to two loads from a common alternating current source, the effective internal impedance of the source being such that variations of the current in one of the loads tend to affect substantially the voltage across the other load, wherein there are provided two impedance elements, one connected between each of said loads and the source, said apparatus being characterised in that said impedance elements are of such natures, and are coupled together in such a manner, that the mutual impedance between them is substantially equal to the effective internal impedance of the source, and in that the ratio of the impedances of the said two impedance elements is such that, under normal mean or full load operating conditions, the voltage applied to either of said loads is not substantially less than the voltage which would be applied thereto in the absence of said impedance elements.

In practical cases, a ratio of impedances which is such that the voltage at the loads is not reduced by more than about 20% due to the presence of said impedance elements may be found satisfactory, but although in such circumstances the invention may provide a considerable advantage, the ratio of impedances is preferably so chose that the loss of voltage is less than 20%.

The effective internal impedance of the source is the impedance to which the regulation of the source can be attributed, wholly or in large part, in practice; that is to say, it is the effective impedance to which interaction of the load is chiefly due: the effective impedance of the source may include the impedance of power lines, or other apparatus, arranged between the source and the point of connection of the loads. In some cases, as will be made clear hereinafter, the impedance elements referred to may take the form of impedance networks.

The two elements referred to above are preferably tightly coupled to one another; that is to say, the mutual impedance between them is preferably greater than 70% (or form optimum working, greater than 95%) of the square root of the product of their impedances.

The coupled impedance elements conveniently comprise the two parts of a tapped choke, or the two windings of a transformer, having an impedance bridged across the whole or a part thereof. If the auto-transformer effectively constituted by the tapped choke or transformer windings is practically perfect, the mutual impedance between the two parts of the winding, or between the two windings, can be made any desired multiple of the impedance bridged across the auto-transformer; similarly the impedances across either of the two parts of the auto-transformer can be also made a desired multiple of the bridging impedance. The bridging impedance may if desired by connected to a further winding coupled to the auto-transformer.

The invention is applicable to single phase and to polyphase systems.

The invention will be further described by way of example with reference to the diagrammatic drawings filed with the Provision Specification; in these drawings,

Fig. 1 shows one circuit arrangement according to the invention,

Fig. 2 illustrates the operation of the circuit of Fig. 1, and

Figs. 3 to 6 show further circuits to which the present invention is applicable.

Reference will also be made to the accompanying drawing, in which

Figs. 7 and 8 illustrate the application of the invention to polyphase systems.

Referring to Fig. 1, two loads L1 and L2 are fed from a source A of alternating current power through a tightly-coupled impedance represented by an impedance z bridged across part of an auto-transformer T; the auto-transformer T is assumed to be theoretically perfect, so that the tight coupling is theoretically absolute. The source A is connected to an intermediate point on the auto-transformer T, and the impedance Z includes the impedance of the source. The loads L1 and L2, which may comprise rectifiers supplying direct current to load circuits, not shown, are connected to points on the auto-transformer separated respectively by S1 and S2 turns from the point of connection of the source. The impedance z is bridged across S0 turns of the auto-transformer T. it is known that the mutual impedance between the two parts of such a shunted auto-transformer is EQUAT. HERE. Hence, if EQUAT. HERE then the circuit of Fig. 1 is equivalent to that shown in Fig. 2, where the loads L1 and L2 are fed through separate impedances equal to

EQUAT. HERE

 

The interaction of the loads produced by impedance Z has now been removed, and if the source A has no internal impedance other than that included in Z, variations of the current in one of the loads will not affect the other load.

Now it will be noted that when the currents in L1 and L2 are in the ratio of S2 to S1, then the regulation of the voltage is unaffected by the presence of the tightly-coupled impedance T, z; this follows from the fact that such a current ratio will produce no magnetisation of the auto-transformer T (it being assumed that the currents are in phase). According to this invention, therefore, the ratio S2 to S1 is made substantially equal to the ratio of the normal or full-load currents in L1 and L2 respectively under these conditions, assuming the power factors of the currents to be substantially the same, the voltage drop at L1 and L2 due to Z is no greater than without the bridged impedance T, z. It is to be noted that, since the inductance of a coil is proportional to the square of the number of turns it comprises, when the normal mean or full load currents in L1 and L2 are in the ratio of S2 to S1, the ratio of the impedances through which loads L1 an L2 are connected to source A is substantially the inverse of the square of the currents in L1 and L2. Power-factor correcting means may be associated with either or both of the two loads if desired in order to achieve the desired substantial identity of power factor.

It is to be understood, however, that the invention is not limited in application to cases in which the separate load currents are in phase with one another. If the currents are out of phase with one another the ratio of the turns S1:S2 may still be adjusted to give a minimum magnetisation of the choke under normal mean or full load working conditions, so that the loss of voltage due to the choke will be a minimum. It will usually be possible in practical cases to find a turns ratio such that the voltage applied to the load is not less than about 80% of that applied thereto in the absence of the choke.

It will be noted that if a short circuit occurs in either of the loads, the current taken from the source will be less than without the bridging circuit, since each load is in effect connected through a separate impedance, each of which is greater than Z. This latter feature is of great use, for example, when the loads are fed through long transmission lines, especially when one of the loads is small compared with the other. In this case it can be arranged that a fault on the smaller load produces such a small line current that the line and source can carry it without any damage, and furthermore, the voltage at the larger load will be substantially unaffected.

It should be borne in mind that alternating current machines of most usual kinds may have, in effect ,two possible values of internal impedance. One value which may be described as the surge impedance, represents the reactance of the armature inductance, and the other, which may be called the regulation impedance, includes the effect of magnetism of the field system. The regulation impedance is slow in operation. In practice, in the circuit arrangements described in this specification, it will be found satisfactory in many cases to base the design of the tightly-coupled impedance on the armature inductance only; the armature inductance is the chief cause of regulation, especially with loads having low power-factors, and controls the surge conditions resulting from a short circuit.

Fig. 3 shows, therefore, a circuit for neutralising the effect of a reactance X (which represents the impedance of the armature inductance of the source A together with any other inductive impedance which may be effectively in series with the source) in producing interaction between three loads. In this case, the auto-transformer T and impedance z of Fig. 1 are replaced by choke D; choke E is similar to choke D and is arranged between loads L2 and L3 and the end C of choke D. the two parts of each of the chokes should be coupled as tightly as possible; any leakage inductance between parts ab and bc of the choke D is in effect an addition to X, this additional inductance being that which would be measured between tapping b and the ends ac short-circuited. The mutual reactance between ab and bc is made equal to reactance X of source A which is to be neutralised. For the purpose of designing the first choke D, L2 and L3 are treated as one load. The product of the number of turns in one part of the winding of the choke D and the normal load current in this part is made equal to the corresponding product for the other part. Then, the point c being taken as the source, the choke E is designed. Similarly, L1, L2 or L3 can be replaced by two smaller loads and so on. When a large number of small loads is to be fed in this manner, it can be arranged by suitable choice of the turns ratios for the several chokes that the voltage when all the loads are at full load is not substantially less than that obtained without the interposition of the chokes; the arrangement is, however, such that a short circuit of one load does not produce dangerous currents in the source, and, furthermore, does not substantially affect the other loads.

The chokes D and E are conveniently wound on iron cores, suitable air gaps being provided if necessary to permit the required inductance to be obtained. The magnitude of the coupling between the two parts of each choke is preferably made such that the mutual inductance between the two parts is greater than about 95% of the square root of the product of the impedances of the two parts, although satisfactory results may be obtained with smaller rations down to about 70%. The air gap provided in the core of each choke is preferably arranged in that limb of the core which carries the choke winding.

With a relatively weak coupling, interaction between the loads can be substantially avoided provide that the mutual impedance between the parts of each choke is equal to the effective impedance of the source; in such cases, however, the loss of voltage due to the insertion of the more loosely-coupled impedance tends to become appreciable; in other words, the effective impedance of the source is increased.

Fig. 4 shows a circuit of neutralising the effect of both resistance and reactance of a source A. Now the resistance R and reactance X of the source A, which may be a generator for example, may be replaced by an equivalent circuit comprising resistance of value R1 and a reactance of the same kind as reactance X and of value X1, arranged in parallel, the circuit R1, X1 being equivalent to the circuit X, R for the frequency of the generator. The choke D is shunted by a resistance R2, and the choke D and resistance R2 may be regarded as a perfect auto-transformer, that is, one of infinite inductance, shunted by a circuit comprising an inductance which is equal to that of choke D, and will be referred to as X2, and resistance R2 in parallel. It is arranged that the inductance X2 of choke D and resistance R2 are in the same numerical ratio as the reactance X1 and resistance R1 referred to above. The reactance X and resistance R together constituted the impedance Z referred to in Fig. 1, and X2 and R2 correspond to impedance z. The source A is tapped into choke D at such a point that z = EQUAT. HERE where S0, S1 and S2 have the same meanings as in Fig. 1; preferably also it is arranged that the turns ratio in the two parts of the choke to the right and left of the intermediate tap is substantially equal to the ratio of the full-load currents in loads L1 and L2.

All the circuits so far shown may represent one phase of a polyphase system, the earth connections being replaced by connections to the neutral point, or to the effective neutral point if a ring connection is employed.

Figs. 5 and 6 show two further arrangements which illustrate the application of the invention. In Fig. 5, which shows only one phase of a polyphase system, one phase of the primary of a transformer P feed energy from a source of power (not shown) to two load secondaries F and G which in turn feed lines l1 and l2; the lines need not necessarily operate at the same voltage. The transformer t has an iron core (not shown) and serves to coupled a neutralising bridging impedance z to the windings F, G, the value of the impedance z being dependent upon the regulation of the source to which the primary winding P is connected.

In practice, the impedance z includes the inductance of the transformer t, and the nature of impedance z depends upon the nature of the regulation impedance of the source to which primary winding P is connected. If the regulation impedance has a resistive component, the nature and magnitude which impedance z should have can be determined in the manner described with reference to the arrangement of Fig. 4.

Leads s1 and s2 are connected to the star points of the lines l1 and l2. The ratio of turns on the two primaries of transformer t are so chosen with reference to the normal or full load currents in lines l1 and l2 that impedance z does not affect the voltage regulation on the lines l1 and l2.

If it is desired to neutralise reactance only with an arrangement of the kind shown in Fig. 5, the secondary winding of transformer t and the impedance z are omitted and the mutual inductance between the two primary windings of transformer t is given a desired suitable value by introducing an air gap in the transformer core.

Fig. 6 shows one phase of a tapping of a power line H which passes on at K to a main load, the tapping being effected by transformer t1. The lines l1 passes to the tapped load. The centre-tapped choke N neutralises the reactance of the line H to the left of the tapping. The transformer t is provided to avoid putting the choke N in the high voltage circuit of line H and fixes the ratio of the normal or full load currents to K and l1. This ratio is so chose that choke N has substantially no effect on the regulation of the current in line l1. W is the star point of the line l1, an also of the outgoing feeder K. a more complex impedance than the simple choke N shown may be used if desired in order to allow for the complex impedance of the line H.

In a modification of the arrangement of Fig. 6, the tightly coupled choke N is omitted. The neutral point of the out-going feeder K is connected t one end of the secondary winding of the transformer t, and the end of the secondary winding of the main transformer t1 (shown connected to one end of the choke N in Fig. 6) is connected to the other end of the secondary winding of the transformer t. the mutual inductance between the windings of transformer t is adjusted by introducing an air gap to produce the necessary reactive coupling between the two circuits l1 and K, due allowance being made for the transformation ratio of transformer t. For such an arrangement, if the step-down ratio of transformer t1 is equal to n, then the mutual impedance (in this case the mutual reactance) between the two windings of transformer t should be equal to EQUAT. HERE times the reactance of the source from which feeders K and l1 are fed, and which is effective in coupling these two loads.

Fig. 7 of the accompanying drawings illustrate an arrangement according to this invention comprising three tapped chokes and a 3-hase machine which functions as a generator. Two outgoing feeders 1 and 2 are connected as shown to the ends of three tapped chokes 4, 5 and 6. The machine, together with any transformers and other equipment which may be connected between the machine and the chokes, is indicated by 3. Any symmetrical arrangement of a machine and transformers, or other equipment, whether connected in delta or star, can be represented as an equivalent star as shown, the three star-connected reactances representing the equivalent reactances of the machine or other equipment.

The mutual impedance between the two parts of each of chokes 4, 5 and 6 is made approximately equal to the reactance of the 3-phase limb connected to it. Where the impedances of the three limbs are not equal, the mutual reactances of the parts of each choke are not the same for all three chokes, but the mutual reactance for each choke is made equal to the reactance limb connected to it. A further division to more than two three-phase feeders can be made by treating the three outgoing lines of a feeder in a similar manner, representing their reactances by a group of three reactances, such as 3 in the Fig. 7; a branched structure can be built up in this way for as many feeders as are required.

Fig. 8 illustrates the use of tightly coupled impedances in a delta-connected arrangement. The machine 3 is represented by 3 windings in delta, into which any 3-phase group of reactances can be resolved. If the resultant is to be kept symmetrical and balanced, it is necessary to introduce six tightly coupled impedances, which take the form of tapped chokes 4, 41, 5, 51 and 6, 61. Considering by way of example chokes 5 and 51, the mutual impedance between the two parts of choke 51, is made approximately equal to the impedance of the winding to which they are connected. In practice, the reactors or transformer windings associated with 5 and 51 may conveniently be wound on the same core, as they operate in the same phase, the resultant arrangement then requiring the same total amount of copper and iron for its construction as the arrangement shown in Fig. 7, provided negligible space is involved in insulating the turns of the windings.

The invention is not limited to the arrangements described, and may modifications within the scope of the appended claims will occur to those versed in the art.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:-

  1. Apparatus for the supply of electrical energy to two loads from a common alternating current source, the effective internal impedance of the source being such that variations of the current in one of the loads tend to affect substantially the voltage across the other load, wherein there are provided two impedance elements, one connected between each of said loads and the source, characterised in that said impedance elements are of such natures, and are coupled together in such a manner that the mutual impedance between them is substantially equal to the effective internal impedance of the source, and in that the ratio of the impedances of said tow impedance elements is such that, under normal mean or full load operating conditions, the voltage applied to either of said loads is not substantially less than the voltage which would be applied thereto in the absence of said impedance elements.
  2. Apparatus according to claim 1, in which said impedance elements are constituted by or comprise inductances, wherein the ratio of the impedances of said impedance elements is substantially equal to the inverse of the square of the normal mean or full load currents in the corresponding loads.
  3. Apparatus according to claim 1 or 2, in which there is provided a choke having between its ends a tapping which divides it into two coupled portions, and in which said impedance elements therefor having a resistive component and an inductive component, and wherein the magnitude of said resistance is such that the mutual impedance between said impedance elements is substantially equal to the resultant of the inductive and resistive components of the effective impedance of the source.
  4. Apparatus according to any of the preceding claims, in which said common alternating current source comprises a polyphase system an in which there are provided a plurality of pairs of coupled impedance elements one pair associated with each phase, wherein the separate windings of a star-connected load system are connected respectively to the junction between the coupled impedance elements of each pair.
  5. Apparatus according to any of claims 1 to 3, in which said common alternating current source comprises a three-phase system, wherein the three windings of a delta-connected load system are each associated with separate coupled impedance elements.
  6. Apparatus for the supply of electrical energy to a plurality of loads from a common alternating current source substantially as described with reference to the drawings filed with the Provisional Specification, and to the accompanying drawing.

Dated this 4th day of July, 1936.

REDDIE & GROSE,

Agents for the Applicant,

6, Breamís Buildings, London, E.C.4

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Leamington Spa: Printed for His Majestyís Stationery Office, by the Courier Press. Ė 1937.