PHASE SHIFTING TRANSFORMERS COMPRISING A SINGLE COIL FOR TWO EXCITING WINDINGS FOR VOLTAGE REGULATION AND FOR PHASE SHIFT ANGLE REGULATION

Abstract

The present disclosure relates to a phase shifting transformer. The phase shifting transformer includes two exciting windings sharing the same three double taped coils, a first excited winding having three connected coils, for a phase shift regulation, a second excited winding comprising three connected coils, for a voltage regulation, each of the two exciting windings regulating the voltage of one coil of the second excited winding, and regulating the voltage level of one coil of the first excited winding.

Claims

1.-12. (canceled)

13. A phase shifting transformer, comprising: two exciting windings sharing the same three double taped coils; a first excited winding comprising three connected coils, for a phase shift regulation; and a second excited winding comprising three connected coils, for a voltage regulation; each of the two exciting windings regulating the voltage of one coil of the second excited winding, and regulating the voltage level of one coil of the first excited winding.

14. The phase shifting transformer according to claim 13, the two exciting windings sharing the same three double taped coils being star, resp. delta, connected.

15. The phase shifting transformer according to claim 13, the three connected coil windings, for a phase shift regulation, being delta, resp. star, connected.

16. The phase shifting transformer according to claim 13, the three connected coil windings, for a voltage regulation, being star, resp. delta, connected.

17. The phase shifting transformer according to claim 13, further comprising means to add a further constant dephasing angle.

18. The phase shifting transformer according to claim 17, the means to add a further constant dephasing angle comprising at least three coils, each one of the three coils being connected in series with one of the three connected coils of the first excited winding.

19. A transformer comprising an autotransformer and a phase shifting transformer according to claim 13.

20. The transformer according to claim 19, the autotransformer being of the step-down type.

21. The transformer according to claim 19, the autotransformer being of the step-up type.

22. The transformer according to claim 19, the autotransformer being a quadbooster.

23. The transformer according to claim 19, the two double tapped coil windings being in a first tank, the three coils windings, in view of a phase shift regulation, and the three coils windings in view of a voltage regulation, being in a second tank.

24. A method for regulating the voltage of a transformer according to claim 19, wherein: the level of the voltage provided by the autotransformer is regulated by a three coil excited winding of the phase shifting transformer; and the phase provided by the autotransformer is regulated by the other three coil excited winding of the phase shifting transformer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 shows an embodiment of the main parts (exciting windings and excited windings) of a phase shifting transformer according to the invention;

[0040] FIG. 2 shows the connection diagram of the combination of a step-down autotransformer of constant voltage ratio with the excitation transformer of an asymmetric three core phase shifting transformer according to the invention;

[0041] FIG. 3A is an electric equivalent scheme of a single phase of the device according to FIG. 2;

[0042] FIGS. 3B and 3C are voltage and current diagrams of a single phase of the device according to FIG. 2;

[0043] FIG. 4 shows the connection diagram of the combination of a step-up autotransformer of constant voltage ratio with the excitation transformer of an asymmetric three core phase shifting transformer;

[0044] FIG. 5 shows a variant of FIG. 2, further comprising means for a further phase shift;

[0045] FIG. 6 shows a variant of FIG. 2 for a quadrature booster.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

[0046] The present invention is described in the context of a three-phase network. In particular, without it being necessary to specify it and unless otherwise indicated, the mention of a winding will refer to any phase, the explanation given for one phase applying to the other phases.

[0047] FIG. 1 shows an embodiment of the main parts (exciting winding and excited windings) of a phase shifting transformer 2 according to the invention.

[0048] On this figure (and on FIG. 2), in order to facilitate understanding, the exciting coils 4, 6, 8 of a phase shifting transformer according to the invention are shown separated in 2 parts although these two parts form a same coil for 2 exciting windings: for example, a single coil 4, which has two tap changers 40, 40′, is implemented for both voltage adaptation coil 41v and phase shifting adaptation coil 43p. The same applies to coil 6, resp. and to coil 8, with respect to voltage adaptation coil 42v and phase shifting adaptation coil 41p, resp. to voltage adaptation coil 43v and phase shifting adaptation coil 42p.

[0049] In other words, for each exciting coil 4, resp. 6, 8: [0050] one tap changer 40′, resp.60′, 80′, regulates the voltage provided to the series active coil 41v, resp. 42v, 43v for voltage level regulation, [0051] the other tap changer 40, resp.60, 80, regulates the voltage provided to the series active coil 43p, resp. 41p, 42p for phase shift angle control.

[0052] Exciting coils 4, 6, 8 are star connected. Alternatively, they could be delta connected; however, a star connection offers some advantages: when the currents needed are becoming too large for the OLTCs, either the voltages have to be increased or the winding connection changed from star to delta to decrease the current values. But, with the delta connection the neutral point is lost and cannot be earthed that is why the delta connection is not the preferred connection mode.

[0053] The windings excited by said exciting coils 4, resp. 6, 8 comprise: [0054] delta connected winding 43p, 41p, 42p (which is connected between X1, X2 and X3), in view of a phase shift regulation; it has to be noted that additional constant phase shift angles may be allowed through introduction of additional coils and special connection of these coils, for example a delta (or extended delta) connection; other types of connections (zig-zag or polygon for example) of additional coils are available; [0055] star connected winding 41v, 42v, 43v (which is connected between n and Z1, Z2, Z3) in view of a voltage regulation.

[0056] Alternatively, exciting coils 4, 6, 8 can be delta connected, winding 43p, 41p, 42p being star connected and winding 41v, 42v, 43v being delta connected.

[0057] FIG. 2 shows the connection diagram of the combination of a step-down autotransformer 20 of constant voltage ratio with an asymmetric three core PST according to the invention. In a variant, the invention can also be applied to a step-up transformer.

[0058] For each phase, the autotransformer has 2 windings, the high voltage winding (the primary or excitation winding) comprising, or made of, two coils, 51s (resp.52s, 53s, also named “series” coils) and 51c (resp.52c, 53c, also named “common” coils) and the medium voltage winding (the secondary winding or load) comprising, or made of, common coil 51c (resp.52c, 53c).

[0059] The autotransformer may also comprise stabilizing and/or test windings, as indicated on FIG. 2 (and also on FIGS. 4, 5 and 6).

[0060] Series coil 51s (resp. 52s, 53s) is connected between medium voltage line line Y1 (resp.Y2, Y3) and high voltage (HV) line S1 (resp.S2, S3).

[0061] Medium voltage coil 51c (resp. 52c, 53c) is connected between neutral N and medium voltage (MV) line Y1 (resp.Y2, Y3).

[0062] Line Y1 (resp.Y2, Y3) is connected to coil 71v (resp. 72v, 73v), which is itself connected in series with coil 71p (resp. 72p, 73p).

[0063] The level of the output voltage (to L1, resp. L2, L3) is mainly regulated by coil 71v (resp. 72v, 73v) (although it must be noted that there is no complete separation between voltage regulation and phase shift angle control).

[0064] The phase angle α.sub.p of the output voltage (to L1, resp. L2, L3) is mainly regulated by coil 71p (resp. 72p, 73p) (here again, it is noted that there is no complete separation between voltage regulation and phase shift angle control).

[0065] Each coil 4, resp.6, 8 of both connected exciting windings is located in a first tank I, where it belongs to a first core together with the corresponding coils 51s, 51c, resp.52s, 52c, 53s, 53c, of the autotransformer (see FIG. 2). More precisely, coil 4, resp.6, 8, and coils 51s, 51c, resp.52s, 52c, 53s, 53c, are mounted on a same leg (or column) of the core (one leg (or column) per phase), not represented on FIG. 2.

[0066] Each coil 41p, resp. 42p, 43p of the delta connected winding (41p, 42p, 43p) and each coil 41v, resp. 42v, 43v of the star connected winding (41v, 42v, 43v) is preferably located in a second tank II, where it belongs to a second and third core together with one of the series L windings 71p-73p, 71v-73v (see FIG. 2), the dashed line 11 showing the separation between both tanks I and II. More precisely, both coils 41p and 71p are mounted on a same magnetic core, not represented on FIG. 2; the same applies to coils 42p and 72p, resp. 43p and 73p, 41v, and 71v, 42v and 72v, one magnetic core being provided for each phase.

[0067] Thus, the PST transformer according to the invention, in combination with an autotransformer, has 7 windings: [0068] the excitation winding 51s, 52s, 53s (which is common to both the autotransformer and the tapped exciting windings); [0069] both tapped exciting windings, sharing the same double tapped coils 4, 6, 8 (which belong to the same cores as the autotransformer); [0070] and two excited windings 41v, 42v, 43v resp. 41p, 42p, 43p, which belong to the same cores as the series windings 71v, 72v, 73v, resp.71p, 72p, 73p; [0071] and the two series windings 71v, 72v, 73v, and.71p, 72p, 73p.

[0072] FIG. 3A shows a single phase equivalent electrical scheme of a single phase of the device according to FIG. 2. It has to be noted that this scheme is valid for any of the 3 phases.

[0073] For clarity's sake, some currents are not indicated on FIG. 3A: current I.sub.s flows in coil 51s, I.sub.c flows in coil 51c, I.sub.ev flows in coil 41p, I.sub.l flows in coil 71v, I.sub.xp and I.sub.xv flow in coil 4.

[0074] Medium voltage on line Y1 is reduced compared to the input voltage V.sub.s1, according to the number of winding turns N.sub.ss1, resp. N.sub.c1, of the coils 51s, resp.51c.

[0075] The PST comprises both exciting windings sharing that same tap coil 4 which, as explained above interacts with the autotransformer 20. Said windings excite both voltage regulation coil 41v, interacting with coil 71v, and phase regulation coil 41p, interacting with coil 71p. Each tap of tap coil 4 regulates a number N.sub.xv, resp. N.sub.xp, of coil turns, which regulates a current j, resp. i, flowing to coil 41v, resp. 41p, thereby exciting voltage regulation coil 41v, resp. phase regulation coil 41p.

[0076] The level of input voltage of coil 71v is regulated by its interaction with coil 41v of the PST. In this example, as can be seen on FIG. 3A, the voltage level is increased from {right arrow over (e.sub.C1)} to {right arrow over (e.sub.C1)}+{right arrow over (e.sub.slv)}.

[0077] The phase of this regulated voltage is then regulated by the interaction of coil 71p with coil 41p of the PST. In this example, as can be seen on FIG. 3A, a voltage {right arrow over (e.sub.slp)} is added to voltage {right arrow over (e.sub.slv)}, with respect to which it is shifted by 90°.

[0078] The final output voltage {right arrow over (V.sub.l)} is given by:

V.sub.l={right arrow over (e.sub.c1)}+{right arrow over (e.sub.slv)}+{right arrow over (e.sub.slp)}

[0079] The level and the phase of this output voltage V.sub.l are thus both regulated, the level of V.sub.l being given by the ratio N.sub.ev/N.sub.sv=V.sub.l/V.sub.s.

[0080] By regulating both the voltage level (e.sub.slv on FIG. 3A) and the intensity of the phase shifted voltage (e.sub.slp on FIG. 3A), the modulus of V.sub.l is regulated on a no-load defined range of voltage and the phase of V.sub.l is controlled on a defined no-load range. For example, a dephasing angle of between +8° up to +250 can be obtained by the PST according to the invention). The phase-angle on load depends on the load current modulus and on the total impedance of the autotransformer and of the phase-shifting transformer as shown in Annex E of IEC/IEEE 60076-57-1202 standard. For example a no-load phase-shift range of +/−25°, may become +20°/−30° on load. In other words, a further constant dephasing angle may be added due to the load.

[0081] FIGS. 3B, resp. 3C, shows the corresponding voltage, resp. current, diagrams. The output voltage {right arrow over (V.sub.l)} results from the input voltage {right arrow over (V.sub.s)}, the intensity level of which is reduced down to e.sub.c+e.sub.slv which, in turn, is phase shifted by ep. The resulting phase angle is α.sub.p, which depends on the relative sizes of {right arrow over (e.sub.c)}, {right arrow over (e.sub.slv)} and {right arrow over (e.sub.slp)}. In a method according to the invention it is possible to control the modulus of {right arrow over (V.sub.l)} by (through {right arrow over (e.sub.slv)}) and/or to control the phase angle value (through {right arrow over (e.sub.slp)}).

[0082] Concerning FIG. 3C: [0083] currents I.sub.xv and I.sub.xp flow in coils 4, 6, 8; [0084] current I.sub.ev flows in coil 41v and current i.sub.ep in coil 41 p; both currents have the same direction as current I.sub.l that flows in coils 71v and 71 p. [0085] coils 41v, 42v, 43v and 4, 6, 8 are both connected; then I.sub.xv and I.sub.ev have the same direction; [0086] coils 41p, 42p, 43p are delta connected and coils 4, 6, 8 are star connected; [0087] hence currents I.sub.ep and I.sub.xp are in quadrature, and I.sub.ev and I.sub.ep are also in quadrature.

[0088] The modulus of the resulting current I.sub.xp+I.sub.xv flowing through the coils common to the two exciting windings (one exciting winding being the set of coils (4, 6, 8) connected to n and (X1, X2, X3) through the set of OLTCs for phase control, the other one being the set of coils (4, 6, 8) connected to n and (Z1, Z2, Z3) through the set of OLTCs for voltage regulation) is much lower than the sum of the moduli of the currents I.sub.xp and I.sub.xv in quadrature.

[0089] The invention was explained in combination with a step-down transformer, but can be applied as well to a step-up transformer. The connection diagram of the combination of a step-up autotransformer with an asymmetric three core PST according to the invention is obtained from FIG. 2 by inverting the source and load sides, (S1,S2,S3) and the corresponding references becoming (L1,L2,L32) and vice-versa. FIG. 4 shows a connection diagram of the combination of a step-up autotransformer 20 of constant voltage ratio with an asymmetric three core PST according to the invention: the numerical references are the same as on FIG. 2, only the currents I.sub.L1, I.sub.L2, I.sub.L3 (at the output of 51s, 52s, 53s on FIG. 4) and I.sub.S1, I.sub.S2 and I.sub.S3 (at the input of 71p, 72p, 73p on FIG. 4) being inverted.

[0090] FIG. 5 shows a variant of the invention, in which a constant dephasing is introduced by connecting further coils 41′p, resp. 42′p, 43′p, to coils 41p, resp. 42p, 43p of the excited windings 41p, 42p, 43p. A further constant phase shift is thus added. The phase-angle on load depends on the load current modulus and on the total impedance of the autotransformer and of the phase-shifting transformer (as shown in Annex E of IEC/IEEE 60076-57-1202 standard). The load angle drop has a constant sign. For example, a no-load phase-shift range of +/−25°, may become +20° (+25°−5°)/−30° (−25°−5°) on load. The constant additional phase-shift of 5° allows the range to be +25° (+25°−5°+5°)/−25° (−25°−5°+5°) on rated load, rated voltage.

[0091] FIG. 6 shows an application of a PST according to the invention to a transformer of the “quad booster” type (or “quadrature booster”, an autotransformer of ratio 1), comprising 3 coils 51c, 52c, 53c in which the voltage of each HV line S1 (resp.S2, S3) is directly applied to line Y1 (resp.Y2, Y3). Common coil 51c (resp. 52c, 53c) is connected between neutral N and HV line S1 (resp.S2, S3). A single phase equivalent electrical scheme of a single phase of device according to FIG. 6, including a quadbooster, is derived from FIG. 3A by deleting coil 51s.

[0092] All circuits described in this application can further comprise cabinets with mechanical axes (to control the tap changers) mounted on the transformer tank, with control possibilities from the cabinet and remotely from a control room.