EP0482361B1 - Method for the parallel regulation of step transformers - Google Patents

Abstract

The invention relates to a method for the parallel regulation of step transformers which act in arbitrary switching combinations on a two-rail bus system. <??>In this arrangement, each step transformer is associated with a separate controller which acts on the associated motor drive which, in turn, actuates the associated step switch. <??>In the method according to the invention, the current transformer configuration is first sensed in a parallel control device, then the current amplitude and phase values of voltage and current of all step transformers are transferred to this device, from which the part-load current and reactive circuit current are determined for each step transformer and from this an influencing quantity is formed for the respective voltage controllers. <IMAGE>

Description

The invention relates to a method for parallel operation control of step transformers equipped with tap changers according to the preamble of the claim.

Methods for regulating the parallel operation of step transformers are already known in numerous forms.

If the step transformers to be connected in parallel are identical with regard to their voltage steps and number of steps, the control process is relatively simple; all that is important is that all tap changers are at the same voltage level at all times, otherwise there will be a compensating current between the secondary windings. This is already known from DE 11 39 918. From AT 126 517 it is also known to provide auxiliary changeover switches that have the same number of contacts as the tap changer.

On the other hand, there are more complicated control procedures if the parallel step transformers to be controlled are those with different voltage steps and number of steps; in these cases a regulation in the narrower sense is required.

The known control methods can essentially be divided into two groups:

On the one hand, for example from DE 11 56 880, the so-called "master-slave" methods are known, ie a synchronous control is implemented in which a step transformer is used as "Master" is selected, which the other step transformers "follow".

The second option is real parallel control, with all step transformers working in equal operation.

A corresponding control device is known from the SIEMENS magazine 1956, volume 2, pages 100 ff .: "The parallel control of transformers with tap changers", in which a control device is assigned to each tap changer; a similar device is disclosed in DE 30 32 874.

Finally, from the operating instructions 63/82 (BA 63/62 de / en-1088/1000), as of October 1988, the Maschinenfabrik Reinhausen GmbH has become aware of a device for automatic parallel control according to the balancing current method, which provides that each step transformer has its own Voltage regulator and an associated parallel control unit is equipped.

In the method on which this device is based, the voltage regulators measure the respective voltage by means of a voltage converter; the downstream parallel control units are required to ensure that a different step position of the step transformers connected in parallel leads to regulation even if the sum of the voltages corresponds to the nominal voltage of the system.

With this method, the parallel control units generate a control variable that is proportional to the circulating reactive current component of their own step transformer and acts on the voltage regulator.

This circuit and the underlying method are practicable for control on a busbar. However, if any connection to step transformers that work on a second busbar is to be possible, the corresponding circuit for carrying out the method becomes very much complicated and contains numerous possibilities for errors.

This is due to the fact that there are numerous cross-connections between the parallel control devices and associated auxiliary or signal contacts required for the detection of the system configuration. This expenditure increases correspondingly to the rapidly increasing number of possible circuit arrangements of these step transformers with an increasing number of existing step transformers and makes universal and expandable circuits practically impossible.

The object of the invention is to use a new method for parallel control without cross connections between the control and regulating devices assigned to each step transformer and thus to create the possibility of enabling a universal connection of the system to any number of step transformers and busbars, which can also be added subsequently is expandable with little effort. In addition, the circuit complexity is to be further reduced by the fact that the novel method should allow only one parallel control unit to be used.

This object is achieved by the method according to the patent claim.

When implementing the circuitry, the new method requires a, preferably microprocessor-controlled, parallel control device which is connected in series to the individual voltage regulators, which, as is known from the prior art, are each associated with each step transformer. The serial data lines reduce the likelihood of wiring and other errors.

The previously necessary connection to the motor drive for step position detection is also eliminated.

Fig. 1

zeigt eine schematische Darstellung der ablaufenden Verfahrensschritte

Fig. 2

zeigt ein Prinzipschaltbild von beispielsweise 6 Stufentransformatoren in einem Zweisammelschienensystem

Fig. 3

zeigt die prinzipielle serielle Zusammenschaltung der 6 Stufentransformatoren mit einem einzigen Parallelsteuergerät zur Durchführung des Verfahrens.

The method according to the invention will be explained in more detail below using an exemplary embodiment:

Fig. 1

shows a schematic representation of the process steps taking place

Fig. 2

shows a basic circuit diagram of, for example, 6 step transformers in a double busbar system

Fig. 3

shows the basic serial interconnection of the 6 step transformers with a single parallel control device for performing the method.

By means of the signaling contacts S1 ... S16 of the corresponding isolators and circuit breakers, a parallel control unit P is informed of the current step transformer configuration, i.e. the information about which step transformers work on which busbars connected in parallel.

It can be seen that the step transformers T1 ... T6 can be linked to the two busbars in all conceivable switching combinations.

Each step transformer T1 ... T6 is assigned a voltage regulator R1 ... R6, which measures the amplitudes of voltage and current and the phase angle on each step transformer in a manner known per se and successively transmits these values to a parallel control device P via serial data lines.

Subsequently, partial load current and circulating reactive current are determined separately for each voltage regulator R1 ... R6 and the disturbance variable for each voltage regulator R1 ... R6 is calculated.

Subsequently, the disturbance variable and the partial load current are in turn transmitted to the individual voltage regulators R1 ... R6 via the serial data lines.

Then, in each voltage regulator R1 ... R6, a disturbance variable is generated in a manner known per se according to the line drop compensation (LDC) method for compensating for the voltage drop (cf. DE-A-2 504 278).

The line voltage drop can thus be compensated for in a manner known per se.

This can be done by a circuit arrangement, for example according to DE 26 16 798 or DE 26 30 933, or by a suitable program part.

Finally, for each voltage regulator R1 ... R6, the measurement voltage, the disturbance variable transmitted from the parallel control device and the disturbance variable from the compensation of the line voltage drop are added and the result is switched to the corresponding voltage regulator as a new value.

In a further embodiment of the invention, the serial data line can also be designed as a ring line (e.g. RS485) instead of as a point-to-point connection as described.

Claims (2)

1. Method for the regulation of parallel operation of tapped transformers (T1...T6) operating in parallel in any switching combination in a double bus bar system and equipped with tap switches for switching different voltage taps under load, wherein the respective setting of the isolating and power switches of the system is detected by signalling contacts (S1...S16) and wherein moreover each tapped transformer (T1...T6) is associated with a separate voltage regulator (R1...R6), which acts on the respective motor drive which in turn actuates the associated tap switch, characterised thereby that in a parallel control apparatus (P) it is detected through the setting of the signalling contacts (S1...S16) which tapped transformers (T1...T6) operate in which configuration in the parallel operation that subsequently in the voltage regulators (R1...R6) the actual values of the amplitude and the phase angle of voltage and current of the respective tapped transformer (T1...T6) are measured and communicated to the parallel control apparatus (P) by way of serial data lines, that following thereon the partial load current and the circuit reactive current are determined for each tapped transformer (T1...T6) from those individual values and thereafter a first interference magnitude is generated as an influencing magnitude for the individual voltage regulators (R1...R6), that the values of the partial load current and the first interference magnitude are transmitted respectively by way of the serial data lines from the parallel control apparatus (P) to the corresponding voltage regulators (R1...R6), that subsequently a second interference magnitude for compensation for the line voltage drop is generated in the corresponding voltage regulator from the respective partial load current and that finally the values of measured voltage, first interference magnitude and second interference magnitude are summated in each voltage regulator (R1...R6) and the regulating magnitudes are imposed.
2. Method according to claim 1, characterised thereby that the serial data line is constructed as a ring main.

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