US1816676A - Device responsive to unbalanced electric currents or voltages - Google Patents

Description

July 28; 1931. E. GRASSOT 1,816,676

DEVICE RESPONSIVE TO UNBALANCED ELECTRIC CURRENTS 0R VOLTAGES Filed Aug. 13, 1926 4 Sheets-Sheet 1 July 28, 1931. E. GRASSOT 1,816,676

DEVICE RESPONSIVE TO UNBALANCED ELECTRIC CURRENTS OR VOLTAGES ile g- 1926 4 Sheets-Sheet 2 Q NR July 28, 1931. E. GRASSOT 1,816,676

DEVICE RESPONSIVE TO UNBALANCED ELECTRIC CURRENTS OR VOLTAGES Fil ed Aug. 13, 1926 4 Sheets-Sheet 3 Fllgtlz Z07 $6.3. MW 7- July 28, 1931. E; GRASSOT 1,816,676

DEVICE RESPONSIVE T0 UNBALANCED ELECTRIC CURRENTS 0R VOLTAGES Filed Aug. 15, 1926 4 Sheets-Sheet 4 jnlrejzlar: Emil e 62195505,

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Q Patented July 28, 1931 UNITED STATES PATENT OFFICE EMILE GRASSOT, OF llIEUDON, FRANCE, ASSIGIN'OR, BY MESNE ASSIGNMENTS, TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK DEVICE BESPONSIVE 'IO UNBALANCED ELECTRIC CURRENTS OR VOLTAGES Application filed August 18, 1926, Serial No.

In measuring apparatus, in relays and in devices for line protection which take into account unbalanced voltage or current, the

equivalence between a system of any g vectors which are concurrent and situated in one plane and 9 systems each made up of g. symmetrical vectors (systems of balanced vec tors) is made use of. These vectors represent components of electric quantities, such as polyphase alternating voltages, currents, ampere-turns, fluxes or magnetic fields etc.- according to the case in point.

In one of these systems, termed positive phase sequence system, two vectors bearing consecutive numbers form between them an angle in the positive direction; in another termed negative phase sequence system, two vectors bearing consecutive numbers make betwee them an angle of in the opposite direction to the preceding one.

In order to obtain the positive or negative phase sequence components of the currents, voltages, powers, etc. or of the functions of these measures, circuit arrangements are generally utilised. The system from which the symmetrical components are thus obtained has the same number'of phases as the basic .system.

. Thus, for example, inthe case of a system of three-phase currents the positive or negative phase sequence components of ampereturns forming part of a three-phase system etc. can be obtained.

It may be of interest to obtain the posi the or negative phase'sequence components (or functions of these components) pertaining to a system with a number of phases differing from-that of the given system, for example, for protecting or measuring threephase system, the'positiye or negati e phase sequence components (or functions of these 129,032,,and ,in France December 23, 1925.

anced to the same extent as the three-phase system under considera- ,components) in a two-phase system unbaltion (D being the length of one of the vectors of the positive system and I the length of a vector of the negative system).

In this connection, the given system ofvoltages or currents (generally taken to be 9- phase) will be converted into a system of curj rents, voltages, ampere turns, fields or magnetic fluxes, etc. with a number of phases 9 differing from g, unbalanced to the same extent as the given system, that isthe ratio of the positive and negative phase sequence components of each system is the same, and then suitable circuit arrangements will be applied to this latter enabling its positive or negative phase sequence components or functions of these components to be obtained; or else circuit arrangements will be used starting from a %-phase system of voltages or currents enab ing the positive or,negat1ve phase sequence components (orfunctions of these components) to be obtained directly from a g'- phase system unbalanced to the same degree as the first. I

The present invention comprises linepror.

tecting devices, relays, and meas ring apparatus and devices, in whlch th want of balance of the circuits or lines .characterized by the application of the principles indicated above, i. e. by the use of devices,certain of which are known (the Scott system rotating field phase transformers, etc.) plays a part enabling the positive or negative phase se tion readily understandable, a few examples of its application will be given hereunder.

In these examples it will be assumed that measurements are to be made on a three-phase system or that a three-phase circuit is to be protected, and that the three-phase system of currents and voltages is transformed into a two-phase system of currents, voltages, ampere-turns, fluxes or magnetic fields, etc., or that the positive or negative phase sequence components of these values or of the active, reactive or complex power in the latter system are obtained.

Thistransformation enables the essential roperties of two-phase systems to be uti-" ized; viz: to have only two vectors which, in balanced systems, are 90 out of phase with each other.

In the accompanying drawings:

Fig. 1 shows the wiring diagram of a current responsive device of the induction type.

Fig. 2 shows the wiring diagram of a current responsive device used in conjunction with a current transformer.

Fig. 3 showsthe wiring diagram of a current responsive device similar to that shown in Fig. 1 using two transformers.

Fig. 1 shows the wiring diagram of a current responsive device using three transformers.

Figs. 5 and 6,show the wiring diagram for voltage responsive devices.

Fig. 7 shows the wiring diagram of another current responsive device.

Figs. 8, 9 and 10 are vector diagrams of current, voltage ampere-turns etc. components.

Figs. 11, 12 and 13 show wiring diagrams for wattmetric responsive devices.

Fig. 14 illustrates diagrammatically a modification of my invention.

Fig. 1 shows the wiring diagram of a relay or current responsive apparatus, of the in.- duction type in which a torque proportional to 1. +I is obtained, I being the positive phase sequence component, I the negative phase sequence component of the three-phase system of currents (i i i Now, in a three-phase circuit:

I I I being the virtual or effective values of the three currents, 2' i- 73 In order to obtain I +L it would thus be necessary to 55 use three identical electro-magnets acting on the same metallic disc D and giving torques proportional to the squares of the currents, viz; I I I through the coils of which the three currents would thus flow. With the wiring arrangement shown in -=Fig. 1 the current '5 flows through the coil a ,of an electro magnet, whilst a second electromagnet has two windings b I) through which I the currents'z' and 2' flow, the windings bee5 ing so arranged that the ampere-turns oppose each other. The net ampere-turns are thus proportional to. (d -2' If the three-phase circuit is balanced, the ampere-turns of the two electro-magnets are in quadrature. If n be the number of turns of one of the coils of the coils b or b and 11 /3 the number of turns of the coil a, the ampere-turns mi /3 and n(z' i are equal in virtual value and are in quadrature, when the currents i i i make up a balanced system.

In this case a two-phase system of ampereturns is obtained which is balanced at the same time as the three-phase system of currents and the torque given by the two suitably arranged electro-magnets will be proportioned to: If If.

The transformation into two-phase has thus enabled the apparatus to be simplified by replacing three electro-magnets by two only; the transformation from three-phase to two-phase is brought about within the apparatus.

Fig. 2 shows a wiring arrangement in which the transformation occurs outside the electro-magnets. 'Two electro-magnets a and b act on the disc D, and through the winding of a the current 2' flows, while through the winding of Z) there flows the current supplied by the secondary of a current transformer T comprising two identical primaries p and 37, through which the currents i and i flow respectively in opposite directions.

If the transformer T is designed so that for a balanced system of three phase-currents the current 2" in the secondary S has the same virtual value as the current i the current system 2' and i will constitute a two-phase system, and it will be possible for the electromagnets a and b to be identical.

Fig. 3 shows a wiring diagram similarto Fig. 1, using two current transformers T and T. D is the disc, at an electro-magnet, and b b the double winding of a second electro- Ina et.

he currents of the secondaries S S of the transformers T T flow in opposite directions through the coils b b, and the sum of these currents flows through the winding (1.

Fig. 4 shows a wiring diagram with three current transformers T T T Through the coil of the electro-magnet a a current proportional to 71 flows and through the coil of the electro-magnet ba current proportional to (2' i If the coil 6 has 71. turns and if the coil a hasn /3,the ampere-turns of the two windings form a balanced two-phase system, when the three-phase system of the currents 2' i i is balanced. 1

In this figure there has been represented a circuit-breaker actuating device which may be likewise used in connection with the other relays about to be described, when it is desired to protect a circuit instead of effecting measurements of one or other of its electrical quantities. Such device is constituted by a trip-coil P excited by an auxiliary source of current Q and mounted in a circuit adapted to be closed and opened by a switch comprising two metallic strips C which can be connected together to close the trip-coil circuit', by a finger R connected to the rotating disc D which moves said finger'into and out of contact with the metallic strips CC. The trip-coil P actuates a solenoid which in its turn is adapted to operate a circuit-breaker Z mounted in the main circuit.

Figs. 5 and 6 show wiring diagrams for voltage responsive apparatus. In Fig. 5 the three-phase voltage systems of the circuits 1, 2 and 3 is converted into a two-phase system by means of a Scott device, the. primaries of which are A B and C D, and the secondaries a ,8 and y 8. The disc D is subjected to the influence of the electro-magnets a and b, which may be identical if the correct transformation ratios of the Scott system have been suitably chosen, and 1, 2, 3 are the three wires of the three-phase circuit. L

In Fig. 6 two voltages in quadrature are? obtained when the three-phase voltages are balanced. These are the voltages between the points A B and between the points C D; The latter is used directly for the winding 6 but the first is transformed by means of the transformer A B, a ,8 to feed the winding a.

The transformers can also be completely suppressed; further the device can be combined with single or three-phase voltage transformers.

Fig. 7 shows the wiring diagram of a current relay or measuring apparatus, of in-' duction type, having a torque which is a function of (I I, I and I, beingthe positive and negative phase sequence components of the three-phase system of currents (i 2' i A single electro-magnetis provided, which acts on the disc D.; This electro-magnet may be of the wattmetric'type and, as shown, comprises a coil (1 through which the current '5 flows and a coil with two windings b b through which currents i and i flow in op posite directions, the net ampere-turns of which are proportional to (d -5 Arrangements are made so that each coil a and (b b I acts on the currents which the other induces in the disc D. For a system of balanced three-phase currents (2' 2' i the ampereturns of the coils a and (b b) are in quadrature. By suitably choosing the number of turns a two-phase system will be obtained.

If I and I are the virtual valuesof the currents of the two-phase system, and a the angle between their representative vectors, it is easily shown that the torque of the apparatus is proportional to 1' 1' sin a and that this value is proportional to (I' (I,) 2 in which expression I' and I, are the positive and negative phase sequence comonents of the two-phase system. This diference is also proportional to I E-I In order to obtain the two-phase system, the same methods can be made use of as in the cases studied .above. Following the same principles voltage measuring apparatus can be designed for example, according to the wiring diagrams of Figs. 5 and 6, but by ar-' ranging the windings a and b on an electromagnet like that in Fig. 7.

As shown in Fig. 14, a group of electromagnets a, b can be caused to act on the same movable equipment, shown as induction discs D, D", to give a torque equal to k (I +L and an electro-magnet a" b" to give a torque equal to la (L -If). I

If la= 1:70, a resultant torque proportional to L or to I is obtained, according to whether the component torques add up or substract. v

If 10 the resultant torque will be zero for a certain relation between L; and I and an apparatus will be obtained the operation of which will depend on the degree of out of balance QX FX HX where and the negative phase sequence component: 1 2X1.- =X X2.

For vector X the positivephase sequence similarly the negative phase sequence component will be:

to X and leading g in order to obtain QX and by adding to X a vector equal to Fig. 9). In order to obtaint'he negative phase sequence components vectors are added X and lagging in order to 313mm 2X11 to X and X respectively equal to and directly opposite to those used for the positive phase sequence components (Fig. 9).

In certain cases, for example when X and X represent currents, it is not handyto obtain the values represented by the vectors jX jX or y'r y'X. But it can be noticed (Fig. 9) that the positive and negative phase sequence components of X are obtained by adding geometrically to a vector equal to X a vector of length X making with it an respectively in a suitable direction; similarly, in order to obtain the positive and negative phase sequence components of X a vector of length X is added geometrically to X and making with X angles of respectively in a suitable direction. Often the length of X or Xgd only is re quired, or of X or X in this case, to obtaln for instance the positive phase sequence component a vector X can be taken instead of X of length lcX equal to or proportional to the length of X and out of phase with respect to it by an angle ,8 (Fig. 10) lagging for example; if a vector X is added to it of length X equal or proportional to .X with the same coefficient of proportion, but leadlng by g with respect to X hence by ,8) with respect to X the resultant of the two 'vectors thus obtained (Fig. 10) will give a vector X of length lcX equal or proportional to K and lagging it by angle ,8.

Similar remarks can be made concerning the other components of X and X From these remarks it follows that values can be obtained equal to or proportional to the 'positive and negative phase sequence components of the given out of phase values by producing suitable phase-displacements, leading or lagging, of angles difiering from net flows a current proportional to the posi- I suitably regulating the resistances and reactances, a value for the resulting. ampere-turns negative phase sequence component of one of the currents and the phases can be regulated so that the torque is proportional to the active, reactive or complex power or the positive or negative phase sequence components of power.

The reactance coils and resistances in series can be completed by resistances and reactances shunted across the voltage coil or both across this latter and part of the reactances or again by other devices allowing the necessary phase displacements to be obtained.

Matters can also be arranged so that the balanced three-phase system is converted into a two-phase system unbalanced to a certain extent, which can facilitate obtaining the positive or negative phase sequence component.

One of the systems of values can be transformed into two-phase for example the voltages, and the other}, for example the currents, left in three-phase form.

On the contrary, the voltages and currents can be transformed from three-phase to two phase and the two negative (or positive) 105 phase sequence components of the voltages can be acted upon by the two-phase currents themselves or vice-versa. It can be shown that, is these cases torques are likewise obtained depending on only the positive or negative phase sequence component of the power. Fig. 12 shows thewiring diagranrof a relay or wattmeter measuring the negative (or positive) phase sequence components of power: a and aare two voltage windings; b, b the current windings on the corresponding electro-magnets D a disc: S a Scott trans; former: T T T three current transformers which feed I) with current proportional to the current i of phase 3 and the coil 1) with 1 current proportional to (11-5 the differ- .ence between the currents i and i of phases 1 and-2: 1', 1, r r r r 8 8' 8 8 8, 8 are resistances and rcactances which produce the necessary phase displacements in order to obtain the negative (or positive) phase sequence components of the two-phase voltages given by the secondaries 1 and 2 of the Scott syste r Fig. 13 is a wiring diagram for a wattmeter or wattmeter relay measuring the negative phase sequence component of power in which two negative phase sequence components of ampere-turns are obtained 90 out of phase with each other, that is to say the two negative phase sequence components of a two-phase system of values proportional to voltage winding of an electro-magnet, of

which I) is the current coil; a, a b are the respective windings of a second electro-magnet; 1', r' 1" 2 are resistances, s, ,s 8' are reactances, allowing resultant ampere-turns to be produced in a, a proportional to the negative phase sequence component of the voltage u and in a", (1' a component equal to respect to it. In practice the current in a can be in phase with u that in a 60 lagging u the current in a will lag u i-- and that in a' will lead um 30. T T ,T represent three current transformers enabling ampere-turns, in quadrature to be obtained the preceding one an d out of phase with in the current coils b and b.

The desired phase displacements can be effected by windings short-cineuited through variable resistances, said windings being associated with the voltage and current circuits I figure, without departing from the limits of the invention.

' Iclaim:

1. Electroresponsive apparatus fora threephase circuit including in combination two electro-magnets, three current transformers and a movable member on which said electro-magnets act, the primaries of said transformers being respectively connected to the 5 phases of said three-phase circuit, one electromagnet having a winding connected across the secondary of one of said transformers, and the secondaries 'of the remaining transformers being connected in opposition across a winding of the other electro-magnet.

2. Electroresponsive apparatus for a three-phase circuit including in combination two electro-magnets, three current transformers and a movable member on which said electro-magnets act, the primaries of nected to the phases of said three-phase circuit, said electro-magnets being connected to said transformers to form part of a twophase system which is balanced when said three-phase circuit is balanced.

3. Electroresponsive apparatus for athr phase circuit including incombination an electro-magnet and a rotatable disc on which said electro-ma'gnet acts, said electro-magnet having two cooperating windings respectively arranged on opposite sides of said disc, said windings being respectively connected to be energized in accordance with the currents in one phase conductor of the cir- 'cuit and the difference between the currents in the other two phase conductors, the ampere-turns of said electro-magnet windings forming part of a two-phase system.

4. In combination with a three-phase circuit, electroresponsive apparatus including polyphase transforming means connected to e energized from the circuit, a movable member and actuating means therefor including two independent electro-magnets each arranged to exert a force on the memher, the windings of said electro-magnets being connected to said transforming means to be energized respectively in accordance with the components of an electric quantity of a two-phase system having efl'ective values dependent on the components of the corre-' sponding electric quantity of the three-phase circuit. Y

5. Incombinationwith a three-phase circuit, electroresponsive apparatus including polyphase transforming means connected to be energized from the circuit, a disc of electric current conducting material and actuating means therefor including two independent electro-magnets respectively arranged to exert additive torques on the disc, the windings of said electro-magnets being connected to said transforming means to be energized nents of the current of a two-phase system having efiective Values proportional to the components of the current of the three-phase circuit.

6. In combination with a three-phase circuit, electroresponsive apparatus including movable disc means and controlling means therefor including two elect-ro-magnets in ductively associated with said disc means and connected and arranged to exert thereon a torque proportional to I +L and electromagnetic means inductively associated with said disc means and connected and arranged to exert thereon a torque proportional to I -L I and L being respectively the positive and negative phase sequence components of the current of said circuit.

7. In combination with a three-phase circuit, electroresponsive apparatus including a movable disc of electric current conducting material and actuating means therefor iiirespectively in accordance with the compoeluding two electro-magnetic elements inductively associated with said disc and connected to be energized from said circuit respectively in accordance with two components of an electric quantity displaced 90 in phase relation under balanced circuit conditions and having effective values dependent on the components of the same electric quantity of the circuit.

8. In electroresponsive apparatus for a three-phase circuit, electro-magnetic means for exerting forces respectively dependent on the sum of and the difference between the squares of the positive and negative phase sequence components of the currents of a twophase system derived from and unbalanced to the same extent as the three-phase circuit, and movable means arranged to be controlled in accordance with a resultant of said forces.

9. In electroresponsive apparatus for a polyphase circuit, electro-magnetic means for exerting forces respectively dependent on two different predetermined functions of the phase sequence components of a system derived from and unbalanced to the same extent as the polyphase circuit and having a different number of phases, and a movable member controlled in accordance with a. resultant of said forces.

10. In combination with a three-phase circuit, electroresponsive apparatus including a movable disc of electric current conducting material and means for exerting thereon a torque proportional to the difference between the squares of the positive and negative phase sequence components of the circuit current including two cooperating electro-magnetic elements inductively associated with the disc on opposite sides thereof, the winding of one element being connected to be energized in accordance with the current in one phase conductor of the circuit and the winding of the other element being connected to be energized in accordance with the difference between the currents in the other two phase conductors.

11. In combination with a. three-phase circuit, electroresponsive apparatus including a v movable disc of electric current conducting material and actuating means therefor including two electro-magnetic elements inductively associated with said disc and connected to be energized from the currents of said circuit by two currents respectively displaced 90 in phase relation under balanced circuit conditions and having effective values dependent on the currents of said circuit.

12. In combination, a three-phase circuit, clectroresponsive apparatus including a movable disc of electric current conducting material and means for exerting thereon a torque proportional to the sum of the squares of the positive and negative phase sequence components including twe independent electro-magnets inductively fiSSOClatBdlVlth the (1150, one electro-magnet bemg connected to be energized in accordance with the current in one phase conductor of the circuit and the other electromagnet being connected to be energized in accordance with the difference between the currents in the other two phase conductors of the circuit. a

13. In electroresponsive apparatus for a three-phase circuit, electro-magnetic means for exerting two forces respectively dependent on two different predetermined-functions of the phase sequence components of a two-phase system derived from and unbalanced to the same extent as the three-phase circuit and a movable member inductively associated with said means and controlled in accordance with the difierence between said forces.

14. In combination, a three-phase circuit, electroresponsive apparatus including a. movable member of electric current conducting material, electro-magnetic means inductively associated with said member and arranged to exert thereon a torque dependent on a predetermined function of two of the phase sequence components of the current of said three-phase circuit and means for diminishing theefiect of one of said components on said torque including electromagnetic means inductively associated with said member and cuit for exerting on said member a force dependent on a predetermined sum function of the. phase sequence components ofa system derived from and unbalanced to the same extent as the polyphase circuit and having a different number of phases.

ELHLE GRASSOT.

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