EP0053413B1 - Device for the continuous control of the phase angle in electric energy transmission installations - Google Patents

Description

The present invention relates to a device for the continuous control of the phase angle in electrical energy transmission devices according to the preamble of claim 1.

When interconnecting several energy transmission lines, for example, the aim should be that the phase angles of the interconnected AC voltages match. This reduces undesirable effects on the generators. This endeavor is made more difficult because the phase angle of a voltage fed into a transmission line is rotated along this line and by the load at the end of the line, provided this is not a purely ohmic resistance.

In the case of interconnected networks, so-called transverse transformers are therefore used to adjust the phase angle of the voltage in the various network parts. The transverse transformer induces in each conductor of the line a transverse voltage superimposed on the input voltage, the phase angle of which is offset by 90 ° with respect to that of the input voltage, so that an output voltage arises whose phase angle is shifted with respect to that of the input voltage.

Furthermore, a controllable phase shifter with at least two reactive impedances connected in series is known (DE-A 2 853 358). A tap is provided between the impedances and at least one electrically controlled current switch, preferably a bidirectional thyristor, in series with this. This phase shifter enables the phase angle of the tapped voltage to be rotated in small steps in both possible directions. The rotation of the phase angle is generated by the reactive power in the reactive impedances, which is why the amount of this rotation determines the required nominal power of the impedances. The nominal power for a rotation of 60 ° reaches about a quarter of the throughput. The described phase shifter can therefore only be used for energy transmission lines to a limited extent, despite its technical advantages.

From US-PS 3 444 457 it is also known in voltage regulators to add voltages inductively via a transformer.

The invention, as characterized in claim 1, solves the problem of creating a device with which the phase angle in an electrical energy transmission device can be shifted over a large angular range. This shift should be low-loss and should not be caused by reactive power.

This results in a vectorial addition of two voltages, which can be controlled or regulated separately for each phase.

By means of the device according to the invention, energy systems can be constantly compensated even in the case of strongly changing reactive power loads.

Advantageous further developments are described in the following subclaims.

By a self-commutated inverter according to claim 2, arbitrarily chosen phase angles can be set in a simple manner.

The embodiment according to claim 3 is particularly economical.

The further development according to claim 4 allows a further reduction in the technical control effort, since the area to be continuously controlled or regulated can be chosen to be almost arbitrarily small.

• Fig. 1 das Prinzip der vektoriellen Addition einer Zusatzspannung zur Eingangsspannung in beliebiger Richtung;
• Fig. 2 eine Prinzipdarstellung einer Schaltungsanordnung zur vektoriellen Addition einer Kompensationsspannung in einer Phase eines Leitungsnetzes;
• Fig. 3 eine Variante zur Schaltungsanordnung nach Fig. 2 nach einer Gleichrichter-Brückenschaltung;
• Fig. 4 eine Schaltungsanordnung für ein Dreiphasen-System mit einer vektoriellen Addition in Querrichtung zur Eingangsspannung;
• Fig. 5 eine weitere Schaltungsanordnung mit einer nach einer Potenzreihe abgestuften Sekundärwicklung eines Erregertransformators.

Exemplary embodiments of the invention are described in more detail below with the aid of schematic drawings; show it:

• 1 shows the principle of vectorial addition of an additional voltage to the input voltage in any direction;
• 2 shows a basic illustration of a circuit arrangement for vectorial addition of a compensation voltage in one phase of a line network;
• 3 shows a variant of the circuit arrangement according to FIG. 2 after a rectifier bridge circuit;
• 4 shows a circuit arrangement for a three-phase system with a vectorial addition in the transverse direction to the input voltage;
• 5 shows a further circuit arrangement with a secondary winding of an excitation transformer graded according to a power series.

1, the input voltage of a high-voltage line is denoted by U. The phase angle of this input voltage U has a phase angle ( ^p , which can be leading (capacitive load) or lagging (inductive load) due to various loads applied to the high-voltage line. By inductive connection of an additional voltage UZ with a phase angle (p there is a phase shift of 6.1f! The resulting output voltage is designated U '.

In a circuit arrangement, FIG. 2, the high-voltage line HL is symbolized with its input voltage U and its output voltage U '. The voltages U and U 'relate to the secondary side of an additional transformer ZT. There is an additional voltage UZ on the primary winding of the additional transformer ZT, which is generated on the one hand by an excitation transformer ET and on the other hand by a voltage source 1. The voltage source 1 is formed from an additional voltage source 3, a downstream rectifier circuit 2 and a self-commutated inverter or power electronics LE. A measurement / control signal S is fed to the power electronics.

The mode of operation of this circuit arrangement is based on the fact that an additional voltage UZ is added inductively, via the additional transformer ZT, to the input voltage U, which results in the output voltage U '. In this case, a constant alternating voltage UK, shifted by a fixed phase angle with respect to the voltage U, and a variable alternating voltage UV connected in series are connected via an excitation transformer ET. The AC voltage UV is varied in its phase position and in its amplitude by the measurement / control signal S.

The advantage of such a circuit arrangement is that only the current phase angle change 6.1f! must be controlled or regulated. Reactive powers present over longer time intervals can be at least approximately compensated for by the excitation transformer ET with its constant AC voltage UK.

The circuit arrangement according to FIG. 3 in turn has an excitation transformer ET, to which an input voltage UK _o is applied on the primary side. The output voltage UK at the transformer ET is led to a bridge circuit with thyristors 4-7 'connected in anti-parallel. This bridge circuit commutates an additional current IZ formed therein, which flows through the primary winding of an additional transformer ZT. The current I of a high-voltage line HL, which has an input voltage U, flows through the secondary winding of the additional transformer ZT. The inductive addition of the additional voltage UZ sets the high-voltage line HL to a voltage U 'which is compensated for in phase and amplitude. The transformer ZT is wound in opposite directions, which, as in the following drawings, is symbolized by points on the primary and secondary windings.

The thyristors 4-7 'each have their own quenching circuit known per se and allow the additional voltage UZ to be set continuously for any phase angle between the output voltage UK of the transformer ET and the additional current IZ.

As a variant, only a single pair of thyristors 4, 4 'connected in anti-parallel can be provided with their own quenching circuit, while the other thyristors 5-7' quench at the zero crossing of the current.

As a further variant, the quenching device can be dispensed with in all thyristors; the power is transferred through natural commutation.

In a three-phase system, FIG. 4, a high-voltage line HL has the phases R, S, T. An excitation transformer ET is connected in a triangle between these phases, so that the voltage pointers can be added in the transverse direction. The compensated phases are labeled R ', S', T '.

For this purpose, the phase currents IR, IS, IT are determined by ammeters 8-10 and the voltages UST and URS are determined by voltmeters 11 and 12 connected between the phases. The resulting signals S1 (IR, IS, IT) and S2 (UST, URS) control a previously described power electronics LE with thyristor bridge circuits. On the input side, the power electronics, shown for the voltage UER, are connected to a step winding on the secondary side of the excitation transformer ET. An additional voltage UZR and an additional current IZ are set at the output of the power electronics LE, which, as described above, also achieve a compensated phase voltage here by inductive addition in the additional transformer ZT.

The remaining phases are compensated in the same way. The secondary gradation of the winding in the excitation transformer ET allows the required control or regulation stroke in the power electronics LE to be reduced by suitable interconnection.

The circuit arrangement according to FIG. 5 shows an excitation transformer ET which has a secondary winding (Vernier Winding) graded on a secondary side according to a power series (3 ").

The bridge circuits 14-16 in turn have anti-parallel connected thyristors and are fed by the voltages UK1-UK3. By suitable interconnection - with positive and negative phase position, depending on the winding direction - the required control area in the thyristor bridge circuit 13 with quenching circuits, fed by the alternating voltage UV, can be kept very small. This enables a very inexpensive solution; the additional voltage UZ or the additional current IZ can be optimally adapted to the operating conditions of energy transmission devices.

Claims (4)

1. A device for the continuous control of the phase angle in electric energy transmission installations

a) comprising a controllable rectifier switching facility for continuously controlling this phase angle, characterised in

b) that the energy transmission line (HL), the phase angle of which is to be influenced, is carried through the secondary winding of an add-transformer (ZT),

c) that the primary side of this add-transformer is effectively connected via a phase-control facility (1; 4, 4' ... 7, 7'; 13 ... 16) for continuously adjusting the phase angle between the output voltage (UK) of an exciter transformer and the current or additional current (IZ) supplied to the primary winding of the add-on transformer (ZT) to the output of this exciter transformer (EZ),

d) that the phase-control device is provided with a bridge circuit comprised of thyristors (4, 4' ... 7, 7') which are connected in antiparallel,

e) and that the thyristors are controlled by a meas- urement/control signal (S) which determines the amplitude and phase relationship of the additional voltage (UZ), supplied to the primary side of the add-on transformer (ZT).

2. A device according to Claim 1, characterised in that the phase-control device is a self-commutated inverter which is fed by an additional voltage source (3) via a rectifier circuit (2) (Figure 2.).

3. A device according to Claim 1, characterised in thatthe phase-control facility is fed by one of several secondary windings of the exciter transformer.

4. A device according to Claim 3, characterised in that the secondary winding of the exciter transformer (ET) is graduated in accordance with a power series (Figure 5.).

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