Method and apparatus for regulating the voltage of a transformer system

Abstract

A method for controlling a value of a voltage at a conductor to which at least one secondary winding of a first steppable transformer and a secondary winding of a second steppable transformer are connected is provided. The method includes: if a voltage deviation of the voltage at the conductor from a voltage setpoint value is within a first range around the voltage setpoint value, and if an overall deviation of a sum of the voltage deviation and a reactive current deviation from the voltage setpoint value respectively for the first and the second transformer is outside of a second range, which is larger than the first, around the voltage setpoint value: setting a delay time for stepping the first transformer and/or the second transformer in such a way that stepping of the first or the second transformer that counteracts the voltage deviation is prioritized.

Claims

1. A method for controlling a value of a voltage at a conductor to which at least one secondary winding of a first steppable transformer and a secondary winding of a second steppable transformer are connected, which method comprises the steps of: if a voltage deviation of the voltage at the conductor from a voltage setpoint value is within a first range around the voltage setpoint value, and if an overall deviation of a sum of the voltage deviation and a reactive current voltage deviation from the voltage setpoint value respectively for the first and the second steppable transformer is outside of a second range, which is larger than the first range, around the voltage setpoint value: setting a delay time for stepping the first steppable transformer and/or the second steppable transformer in such a way that stepping of the first or the second steppable transformer that counteracts the voltage deviation is prioritized.

2. The method according to claim 1, wherein the delay time of the first or the second steppable transformer for which the overall deviation has a different sign to the voltage deviation is set to be greater than another delay time for the other of the first or the second steppable transformer.

3. The method according to claim 2, wherein: if the overall deviation and/or the reactive current voltage deviation for at least the delay time that is set to be greater is outside of the second range, the first or second steppable transformer is stepped up if the overall deviation is negative and is stepped down if the overall deviation is positive, and wherein the stepping is left if the overall deviation is outside of the second range for a shorter time than the delay time that is set to be greater.

4. The method according to claim 2, wherein the delay time that is set to be greater is between 1.5 and 2.5 times the another delay time.

5. The method according to claim 2, wherein when the voltage deviation is negative, the delay time for a voltage regulator or regulators, which exceed the second range, that is to say step down, is set to be greater if the following holds true:
DV<=0,
BCC_DV<DV<BCC_DV,
DCC,D>B wherein the first range is given by the band [BCC_DV, BCC_DV], the second range is given by the band [B, B], DV is the voltage deviation, DCC is the reactive current voltage deviation, D is the overall deviation, wherein the delay time that is set to be greater is between 1.5 and 2.5 times the other delay time.

6. The method according to claim 5, wherein when the voltage deviation is positive, the delay time for the voltage regulator or the regulators, which undershoot the second range, that is to say step up, is set to be greater if the following holds true:
Dv>0
BCC_DV<Dv<BCC_DV
D.sub.CC,D<B.

7. The method according to claim 6, wherein the first range BCC_DV, BCC_DV is between 0.3 and 0.7 times the second range B, B.

8. The method according to claim 6, wherein the first range BCC_DV, BCC_DV is 0.5 times the second range B, B.

9. The method according to claim 5, which further comprises optimizing a calculation of the reactive current voltage deviation D.sub.CC resulting from a circulating reactive current in accordance with:
DCC=(k*ICC*(X+Term A)*root(3)*100%)/UN, wherein
Term A=X/(X*BP1), k is a settable circulating reactive current control factor, ICC is the circulating reactive current, X is a transformer series reactance calculated from short-circuit voltage, BP is the overall reactive conductance or overall susceptance of all of the parallel transformers, and UN is a rated transformer voltage.

10. The method according to claim 2, wherein the delay time that is set to be greater is 2 times the another delay time.

11. The method according to claim 1, wherein: when stepping up one of the first and second steppable transformers, a higher voltage and, when stepping down one of the first and second steppable transformers, a lower voltage is present at an output of the secondary winding of a respective steppable transformer, wherein the stepping up and/or the stepping down takes place by appropriate tapping at a respective primary winding, an input of which is connected to a further conductor, at which, the high voltage between 70 kV and 300 kV is present; and the voltage setpoint value is between 5 kV and 20 kV.

12. The method according to claim 1, wherein the overall deviation for the other of the first or the second steppable transformer has an identical sign to the voltage deviation.

13. An apparatus for controlling a value of a voltage at a conductor to which at least one secondary winding of a first steppable transformer and a secondary winding of a second steppable transformer are connected, the apparatus comprising: a logic unit configured such that: if a voltage deviation of the voltage at the conductor from a voltage setpoint value is within a first range around the voltage setpoint value; and if an overall deviation of a sum of the voltage deviation and a reactive current voltage deviation from the voltage setpoint value respectively for the first and the second steppable transformer is outside of a second range, which is larger than the first range, around the voltage setpoint value; to set a delay time for stepping the first steppable transformer and/or the second steppable transformer in such a way that stepping of the first or the second steppable transformer that counteracts the voltage deviation is prioritized.

14. The apparatus according to claim 13, further comprising a measuring apparatus for measuring the value of the voltage and values of a reactive current of the first steppable transformer and of the second steppable transformer.

15. A transformer system, comprising: a first steppable transformer; a second steppable transformer connected in parallel with said first steppable transformer; and an apparatus for controlling a value of a voltage, said apparatus having a logic unit configured such that: if a voltage deviation of the voltage at a conductor from a voltage setpoint value is within a first range around the voltage setpoint value; and if an overall deviation of a sum of the voltage deviation and a reactive current voltage deviation from the voltage setpoint value respectively for said first and said second steppable transformer is outside of a second range, which is larger than the first range, around the voltage setpoint value; to set a delay time for stepping said first steppable transformer and/or said second steppable transformer in such a way that stepping of said first or said second steppable transformer that counteracts the voltage deviation is prioritized.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a block diagram schematically illustrating a transformer system having an apparatus for controlling a value of a voltage at a conductor in accordance with one embodiment of the present invention; and

(2) FIGS. 2 and 3 are bar charts illustrating deviations that are observed in embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown schematically a transformer system 1 for controlling a value of a voltage at a conductor 3 to which at least one secondary winding 5A of a first steppable transformer 7A and a secondary winding 5B of a second steppable transformer 7B are connected, in accordance with one embodiment of the present invention. The transformer system 1 schematically illustrated in FIG. 1 has the first steppable transformer 7A and the second steppable transformer 7B connected in parallel therewith, and an apparatus 13 for controlling a value of a voltage at the conductor 3.

(4) The apparatus 13 has a logic unit 15, which is formed in the illustrated exemplary embodiment by a first voltage regulator 17A and a second voltage regulator 17B, which voltage regulators are connected to one another by a communication line 21. The logic unit 15 is configured, if a voltage deviation D.sub.V of the voltage at the conductor from a voltage setpoint value is within a first range [B.sub.CC_DV, B.sub.CC_DV] around the voltage setpoint value, and if an overall deviation D of a sum of the voltage deviation D.sub.V and a reactive current deviation D.sub.CC from the voltage setpoint value respectively for the first and the second transformer is outside of a second range [B, B], which is larger than the first, around the voltage setpoint value, to set a delay time T1 for stepping the first transformer 7A and/or the second transformer 7B in such a way that stepping of the first or the second transformer that counteracts the voltage deviation is prioritized.

(5) In particular, the logic unit 15 is configured to execute a method for controlling a value of a voltage in the conductor 3 to which the at least one secondary winding 5A of the first steppable transformer 7A and the secondary winding 5B of the second steppable transformer 7B are connected, in accordance with one embodiment of the present invention.

(6) The first transformer 7A has the first primary winding 9A and the second transformer 7B has the second primary winding 9B. Furthermore, switches 37 are provided between a high-voltage rail 27 and the busbar or conductor 3 in order to selectively isolate the first and/or the second transformer 7A, 7B from the high-voltage rail 27 and/or from the busbar 3.

(7) In the illustrated embodiment, the apparatus 13 also contains a measuring apparatus, which is formed by partial measuring apparatuses 23A and 23B, wherein the measuring apparatus 23A is available communicatively with the first voltage regulator 17A in order to measure a first (reactive) current I.sub.A and a first open-circuit voltage or load voltage U.sub.A at the outputs of the secondary winding 5 of the first transformer 7A. The partial measuring apparatus 23B is communicatively connected to the second voltage regulator 17B and is configured to measure the reactive current I.sub.B or generally the current I.sub.B and the output voltage U.sub.B at the output connection of the second secondary winding 5B of the second transformer 7B and to feed the measurements to the second voltage regulator 17B.

(8) To step the first transformer 7A, a tap changer 25A is provided, which receives control signals 26A from the first voltage regulator 17A, whereupon corresponding stepping (tapping at the primary winding 9A or at the secondary winding 5A of the first transformer 7A) is carried out. To step the second transformer 7B, a further tap changer 25B is provided, which receives control signals 26B from the second voltage regulator 17B, whereupon it performs desired stepping at the second transformer 7B.

(9) The two transformers 7A and 7B are electrically connected in parallel with one another between a high-voltage rail 27 and the conductor 3 (also referred to as busbar). If the two transformers 7A and 7B have different open-circuit voltages (or else voltages under load), this can lead to a circulating reactive current 29 (I.sub.KBS), which is undesired and is eliminated according to an embodiment of the present invention.

(10) Embodiments of the present invention achieve stabilization of the regulation to a voltage setpoint value on the busbar 3, in particular, in the case in which the output voltages of the two transformers 7A and 7B are slightly different but are close to the voltage setpoint value.

(11) In the following text, a prioritization range B.sub.CC_DV is established as B.sub.CC_DV=factor.Math.B, wherein the factor can be, for example, 0.5 and B is a conventionally used range. In the two transformers 7A and 7B having approximately the same transformer reactance and D.sub.V=0, a step difference produces exactly the opposite circulating reactive current voltage deviation D.sub.CC and hence an overall deviation D. The voltage deviation D.sub.V is then in A close to 0 and hence within the prioritization range (also referred to as the first range). In the case of D.sub.V0, the stepping up is temporally prioritized. That is to say that in the regulator in the transformer A (transformer 7A), where a positive circulating reactive current is measured, the doubled delay time is applied (criterion D>B). In the case of D.sub.V0, the stepping down is accordingly prioritized.

(12) FIG. 2 schematically illustrates a bar chart, wherein the voltage deviation D.sub.V, the overall deviation D.sub.A for the first transformer 7A, the reactive current deviation D.sub.CCA for the first transformer 7A, the overall deviation D.sub.B for the second transformer 7B and the reactive current deviation D.sub.CCB for the second transformer 7B are plotted. The deviations are in this case plotted relative to the setpoint voltage 31 plotted as a proportion. As can be seen from FIG. 2, the voltage deviation D.sub.V is within the first range 33 and is negative. Furthermore, D.sub.A and also D.sub.CCA are outside of the second range 35 and, in particular, are greater than B. Furthermore, D.sub.B and D.sub.CCB are outside of the second range 35 and are, in particular, >B.

(13) In this case, the first delay time (the delay time of the regulation for the first transformer 7A) is increased, in particular is set to double the value of the value of the delay time that is used for the second transformer 7B. Stepping up of the second transformer 7B is thus prioritized. VACT illustrates the voltage actually measured at the busbar, wherein the difference D.sub.V exists from the voltage setpoint value.

(14) FIG. 3 illustrates, in a similar bar chart to in FIG. 2, a situation during a regulation method, wherein other values of the different deviations are present. In particular, the voltage deviation D.sub.V is within the first range 33 and at the same time is greater than 0 (>0). Furthermore, the overall deviation and the reactive current deviation of the first transformer and of the second transformer are also outside of the second range 35. In this case, the delay time for the control of the second transformer 7B is increased, in particular is set to double the value compared to the value T1 of the delay time that is used for the first transformer 7A. Stepping down of the first transformer 7A is thus prioritized.

(15) Embodiments of the present invention can ensure regulation stability for the user, in the case of reliable dimensioning of the circulating reactive current or elimination of the circulating reactive current. The set value introduced from the prior art is therefore insufficient and can be managed poorly by the user. Owing to the low conventional regulating quality and circulating reactive current associated therewith, the power loss of the transformers is increased and hence the efficiency is decreased.

(16) The stability achieved by embodiments of the invention simultaneously prevents unnecessary stepping and hence the lifetime of the on-load tap changers (OLTC) is increased. Costs for the network operator can thus be reduced.

(17) The delay time T1 can be prescribed by the network operator and can relate to the elimination of voltage fluctuations in the network. The doubling of the delay time relates to the elimination of the circulating reactive current and therefore has no effect on the coordination of voltage regulation processes in radial networks.