Method for regulating the voltage of a transformer

The invention relates to a method for regulating the voltage of a transformer (1) having different winding taps (3). The problem addressed by the invention is that of providing a method with which different load flow directions can be regulated with conventional transformers (1) and voltage regulators (7) in order to ensure a safe and reliable supply of voltage. The general inventive concept consists in determining, using a method in which a quadrant system (11) is used, the phase angle of the conduction current (I) and thus the load flow direction, thereby preventing deviation from the voltage range as a result of power input that is too high, by controlling the load tap changer (4).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US-national stage of PCT application PCT/EP2013/069446 filed 19 Sep. 2013 and claiming the priority of German patent application 102012109639.2 itself filed 10 Oct. 2012.

The invention relates to a method for voltage regulation of a transformer with different winding taps and a voltage regulator.

An arrangement for voltage regulation of a transformer is known from DE 25 04 278, which is in a position of providing compensation for voltage drops by way of vector addition with the help of a resistive impedance, a capacitor and a plurality of potentiometers.

Moreover, a voltage regulator for compensation for power-voltage drop for tapped transformers is known from DE 26 16 798 [GB 1,535,622]. The voltage regulator consists of, inter alia, a current converter connected with the secondary side of the transformer. A resistive impedance and a capacitance that are used for influencing an inductive or capacitive voltage drop, are connected with this current converter. Not only the tap for the resistive voltage drop, but also the tap for the inductive voltage drop can be repoled independently of one another by changeover switches.

A voltage regulator and a method for voltage regulation of a transformer with a tap changer are known from DE 197 28 220. The described voltage regulator, which is for automatic control of transformers by tap changers actuated by a motor drive, is the ‘microprocessor-controlled voltage regulator MK30’ of the applicant known from the company publication. This voltage regulator activates the motor drive that operates according to the principle of step switching; this produces a voltage change of the transformer winding by one step. A setting command ‘higher’ or ‘lower’ is delivered by the voltage regulator to the motor drive if the voltage actual value deviates within predetermined limits from the voltage target value. This known voltage regulator has numerous function buttons and setting elements by which parameterizing of the voltage regulator is undertaken, i.e. specific criteria for the regulation to be undertaken are manually set by the operator.

As can be inferred from the prior art documents, the starting point is always that the load flow direction, namely from the high voltage side to the low voltage side, is always the same. It is assumed that the load flows from the energy generators such as, for example, power stations to the end users such as, for example, industry or private households. Due to this assumption, the known voltage regulators were mounted on the secondary side, thus on the low voltage side. These measure the voltage fluctuations and thus control the voltages of each phase of each leg by on-load tap changers on the primary side of the tapped transformer, thus on the high voltage side. The energy supply has thus always reacted to the user and seeks, via the high voltage side, to selectively regulate the supply voltage delivered at the low voltage side.

Having regard to dwindling fossil fuels for coal power stations as well as the risk emanating from atomic energy there is increasing resort to energy sources from environmentally friendly resources such as, for example, wind, sun, etc. Some of these new energy sources are present with consumers, in the form of solar installations on roofs and the like. These new starting-point situations impose new demands on the infrastructure of energy supply mains, particularly on transformer plants as well as on the methods for control thereof.

The object of the present invention is to indicate a method that is in a position of regulating different load flow directions with conventional transformer plants and voltage regulators so as to ensure a secure and reliable voltage supply.

This object is fulfilled by a method comprising the features of claim1. The subclaims in that case relate to particularly advantageous developments of the method.

The idea according to the invention consists of using, in the method for voltage regulation, a generator/consumer quadrant system and to reproduce the conduction current therein. As soon as the conduction current is in a consumer quadrant the target value of the voltage regulator is increased. In the case of positioning of the conduction current in a generator quadrant the target value of the voltage regulator is lowered. The fundamental difference between consumer and generator makes it possible to determine the load flow direction and thus prevent harm to the voltage band through a too-high feed power.

According to a further form of embodiment of the method, windings of the winding on the primary side of the transformer are switched off after increase of the voltage value.

According yet a further form of embodiment of the method, windings of the winding on the primary side of the transformer are switched on after lowering of the target value.

A transformer1with a tap winding2and different winding taps3is depicted inFIG. 1. This has a primary side P and a secondary side S. The winding taps3are switched on or switched off by an on-load tap changer4. The switching-off and switching-on can, however, be realized by any means such as, for example, load selectors, tap changers, etc. The actuation of the on-load tap changer4takes place by way of a motor drive5. This motor drive5is controlled by a control6and a voltage regulator7integrated therein. The voltage regulator7detects, at an input point8, a conduction current I in a line9connecting the transformer1with a consumer/generator10. In that case there can obviously also be a plurality of consumers/generators. In addition, the voltage regulator7detects a voltage U present between the transformer1and the consumers/generators10.

The quadrant system11depicted inFIG. 2consists of an X-axis X and a Y-axis Y that delimit a first quadrant12, a second quadrant13, a third quadrant14and a fourth quadrant15. The actual part of the conduction current I, which is determined by the load of the consumer/generator and the lines, is recorded on the X-axis. The Y-axis represents the imaginary part of the conduction current I. The angle φ between the vector, which represents the conduction current I, and the X-axis reflects the phase displacement. If the angle φ adopts a value between 0° and +180° the conduction current I trails the voltage U, i.e. an inductive generator/consumer is connected. If the angle φ adopts a value between 0° and −180°, the conduction current I leads the voltage U, i.e. a capacitive generator/consumer is connected.

In the prior art it was always assumed that the conduction current I, starting from a consumer directional arrow system, was to be found in the third quadrant14or fourth quadrant15, i.e. different inductive consumers were connected with capacitive or resistive components on the low voltage side.

As can be seen inFIG. 3, a voltage drop can move within a target value range16, which is bounded by an upper voltage limit value G1and a lower voltage limit value G2, without intervention by the voltage regulator7being required. The voltage continuously drops over the length of a line L to the consumers. If the upper voltage limit value G1or the lower voltage limit value G2is exceeded intervention by the voltage regulator7is required. Otherwise, the voltage drop can be kept within the upper voltage limit value G1and the lower voltage limit value G2by switching-on one or more windings of a tapped winding4by the on-load tap changer2on the primary side P of the transformer1. The voltage drop lies within the target value range16(voltage band).

Since, now, not only consumers, but also generators can be connected on the secondary side S of the transformer1it is necessary to be able to reproduce this. These generators are similarly reproduced by the conduction current I. According to the invention it was recognized for the first time that the generators that are similarly represented by the phase positions φ of the conduction current I, are—by contrast to the consumers—reproduced in the first and second quadrants12,13. These can similarly comprise inductive or capacitive components.

The regulating method is illustrated inFIG. 4as a flow chart. An input of the power parameters of the plant is carried out in the first step20. By plant there is to be understood, in accordance with the invention, the transformer1, the on-load tap changer4and the lines associated therewith. Also belonging thereto are technical characteristic variables of the transformer1, the on-load tap changer4and the line lengths to the consumers/generators. This method step is usually used in all is regulating methods known from the prior art.

In operation, the second step then takes place, namely the measurement30and40of, respectively, the conduction current I and the voltage U at the transformer1. These data are ultimately evaluated by the voltage regulator7and used for the purpose of carrying out determination50of the position of the conduction current I with the associated phase position in the quadrant system explained inFIG. 2.

If the vector of the conduction current I is now in one of the consumer quadrants, thus in the third or fourth quadrant14or15, an increase60in the voltage value Usof the voltage regulator takes place. This has the consequence that windings, which are on the primary voltage side, of the tap winding of the transformer1are switched off; the translation ratio between primary windings and secondary windings is lower. A leveling70of the voltage drop as a consequence of a high consumption thus takes place.

If the conduction current is in the generator quadrants, thus in the first or second quadrant12or13, a reduction80in the target value of the voltage regulator takes place. Windings of the tapped winding are switched on the primary voltage side; the translation ratio between primary windings and secondary windings is higher. As a result, a leveling90of the voltage increase as a consequence of a high power feed is produced. The procedure is filed as an algorithm in a fixed value memory in the voltage regulator.

An advantage of this method is the fundamental difference between consumer and generator on the secondary side of a transformer1. Ascertaining whether power is fed in or consumed on the secondary side prevents, by adaptation of the transforming ratio of the transformer, a voltage excess, i.e. an exceeding of the limit values of the voltage band16, from being caused by a high feed power.

A further advantage of this method is that no additional apparatus has to be installed in order to detect and appropriately level the changing load flow. It is possible by the method to use the existing components, for example transformer, voltage regulator, etc.

REFERENCE NUMERAL LIST

16target value range of the voltage

20input of the power parameters

30measurement of the conduction current at the transformer

40measurement of the voltage at the transformer

50determination of the phase position of the flow indicator (conduction current) in the quadrant system

60increase in the target value of the voltage regulator

70leveling of the voltage drop as a consequence of high consumption

80lowering of the voltage value of the voltage regulator

90leveling of the excess voltage as a consequence of high feed power

G1upper voltage limit value

G2lower voltage limit value

I conduction current

P primary side

S secondary side

U voltage