Monitoring of a high-voltage DC transmission

Abstract

In a method for monitoring a high-voltage DC transmission the following are predefined: an amperage threshold value for an amperage of the high-voltage DC transmission, at least one interval length for time intervals and, for each predefined interval length, a change threshold value for a change in the amperage averaged over time intervals of the interval length. The amperage for each terminal of the high-voltage DC transmission is determined, and a change in the amperage averaged over time intervals of the interval length is determined for each predefined interval length. A DC error is determined if the magnitude of the amperage of at least one terminal is greater than the amperage threshold value or if, for an interval length, the magnitude of the averaged change in the amperage of at least one terminal is greater than the change threshold value predefined for the interval length.

Claims

1. A method for monitoring HVDC transmission between two power converter stations, the method comprising: presetting a current intensity threshold value for a current intensity of the HVDC transmission; presetting at least one interval length for time intervals, and setting for each preset interval length a change threshold value for a current intensity change in the current intensity of the HVDC transmission, averaged over time intervals of the interval length; for each pole of the HVDC transmission, determining the current intensity, and for each preset interval length, determining a current intensity change in the current intensity, averaged over time intervals of the interval length; for each pole of the HVDC transmission, comparing an absolute value of the current intensity with the preset current intensity threshold value, and for each preset interval length, comparing an absolute value of the averaged current intensity change with the change threshold value preset for the interval length; concluding a DC fault when the absolute value of the current intensity of at least one pole is greater than the current intensity threshold value or, for an interval length, the absolute value of the averaged current intensity change in the current intensity of at least one pole is greater than the change threshold value preset for the interval length; in the event of an identified DC fault, regulating a current of each pole to zero by activating a power converter, assigned to the respective pole, of a power converter station; and after the regulation of the currents of the poles to zero, discharging the respective pole charged by the DC fault.

2. The method according to claim 1, which comprises presetting a regulation time period for regulating the currents of the poles to zero, and discharging the pole charged by the DC fault once the regulation time period has expired.

3. The method according to claim 2, which comprises setting the regulation time period to between 100 ms and 500 ms.

4. A method for monitoring an HVDC transmission between two power converter stations, the method comprising: presetting a current intensity threshold value for a current intensity of the HVDC transmission; presetting two different interval lengths for time intervals, and setting for each preset interval length a change threshold value for a current intensity change in the current intensity of the HVDC transmission, averaged over time intervals of the interval length; for each pole of the HVDC transmission, determining the current intensity, and for each preset interval length, determining a current intensity change in the current intensity, averaged over time intervals of the interval length; for each pole of the HVDC transmission, comparing an absolute value of the current intensity with the preset current intensity threshold value, and for each preset interval length, comparing an absolute value of the averaged current intensity change with the change threshold value preset for the interval length; and concluding a DC fault when the absolute value of the current intensity of at least one pole is greater than the current intensity threshold value or, for an interval length, the absolute value of the averaged current intensity change in the current intensity of at least one pole is greater than the change threshold value preset for the interval length.

5. The method according to claim 4, wherein a first interval length lies between 100 μs and 500 μs, and a second interval length lies between 500 μs and 2 ms.

6. A power converter station for an HVDC transmission, the power converter station comprising: a measuring device configured to repeatedly record, for each pole of the HVDC transmission, a current intensity and a current intensity change in the current intensity; and a control unit configured to compare, for each pole, an absolute value of the current intensity with a preset current intensity threshold value, and to form, for at least one preset interval length, a current intensity change averaged over time intervals of the interval length from the current intensity change in the current intensity of the pole, and to compare the absolute value of said averaged current intensity change with a change threshold value preset for the interval length, and to conclude that there is a DC fault when the absolute value of the current intensity of at least one pole is greater than the current intensity threshold value or, for an interval length, the absolute value of the averaged current intensity change in the current intensity of at least one pole is greater than the change threshold value preset for the interval length; wherein each power converter of the power converter station is configured to build up a counter-voltage for counteracting a charging of a pole to which the power converter is assigned; said control unit is configured to regulate the current of each pole to zero in the event of an identified DC fault by activating a power converter, assigned to the pole, of the power converter station; and said control unit is configured to initiate discharge of a pole charged by the DC fault after the regulation of the currents of the poles to zero.

7. The power converter station according to claim 6, wherein said control unit is configured to regulate the currents of the poles to zero during a preset regulation time period, and to initiate the discharge of the pole charged by the DC fault once the regulation time period has expired.

8. The power converter station according to claim 7, wherein each power converter of the power converter station is a self-commutated power converter.

9. The power converter station according to claim 7, wherein each power converter of the power converter station is a modular multilevel power converter.

10. The power converter station according to claim 6, wherein each power converter of the power converter station is a self-commutated power converter.

11. The power converter station according to claim 6, wherein each power converter of the power converter station is a modular multilevel power converter.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 shows a schematic illustration of two power converter stations and an HVDC transmission path of an HVDC transmission between two AC power supply systems,

(2) FIG. 2 shows a flowchart of a method for monitoring an HVDC transmission,

(3) FIG. 3 shows a block diagram for the evaluation of a current intensity and a current intensity change of a pole of an HVDC transmission,

(4) FIG. 4 show characteristics of a current intensity of an HVDC transmission at the location of a first power converter station and of a trigger signal of the first power converter station in the event of a DC fault,

(5) FIG. 5 shows characteristics of a current intensity of an HVDC transmission at the location of a second power converter station and of a trigger signal of the second power converter station in the event of a DC fault.

DETAILED DESCRIPTION OF THE INVENTION

(6) Mutually corresponding parts are provided with the same reference symbols in the figures.

(7) FIG. 1 shows a schematic illustration of two power converter stations 1, 2 of an HVDC transmission, which are connected to one another on the DC side via an HVDC transmission path 3. A first power converter station 1 is connected on the AC side to a first AC power supply system 5. The second power converter station 2 is connected on the AC side to a second AC power supply system 6.

(8) The HVDC transmission is designed to be symmetrically monopolar with a first pole 7 and a second pole 8. The HVDC transmission path 3 has a first transmission line 9 for the first pole 7 and a second transmission line 10 for the second pole 8.

(9) Each power converter station 1, 2 has a power converter unit 11, a measuring device 13 and a control unit 15.

(10) Each power converter unit 11 has, for each pole 7, 8, a self-commutated power converter, which, depending on the energy transmission direction, can be used as a rectifier for converting an alternating current and an AC voltage of the respective AC power supply system 5, 6 into a direct current and a DC voltage of the HVDC transmission or as an inverter for converting a direct current and a DC voltage of the HVDC transmission into an alternating current and an AC voltage of the respective AC power supply system 5, 6 and is in the form of, for example, a modular multilevel power converter.

(11) The measuring device 13 of each power converter station 1, 2 is designed to record, for a first pole 7 of the HVDC transmission, a first current intensity I.sub.1 and a first current intensity change İ.sub.1 in the first current intensity I.sub.1 and, for the second pole 8 of the HVDC transmission, a second current intensity I.sub.2 and a second current intensity change İ.sub.2 in the second current intensity I.sub.2 at the location of the respective power converter station 1, 2.

(12) Each control unit 15 is designed to implement the method steps S3 to S6 of the method described with reference to FIG. 2.

(13) FIG. 2 shows a flowchart of an exemplary embodiment of the method according to the invention for monitoring the HVDC transmission between the two power converter stations 1, 2 comprising method steps S1 to S6. The method is implemented by each power converter station 1, 2 independently of the other power converter station 1, 2, i.e. the method steps S1 to S6 described below relate in each case to one power converter station 1, 2 and the power converter unit 11, measuring device 13 and control unit 15 thereof.

(14) In a first method step S1, a current intensity threshold value L1 for the current intensities I.sub.1, I.sub.2 of the poles 7, 8, two different interval lengths T.sub.1, T.sub.2 for time intervals and, for each preset interval length T.sub.1, T.sub.2, a change threshold value L2, L3 for a current intensity change in each current intensity I.sub.1, I.sub.2, averaged over time intervals of the interval length T.sub.1, T.sub.2, are preset. For example, a first interval length T.sub.1 is between 100 μs and 500 μs, and the second interval length T.sub.2 is between 500 μs and 2 ms.

(15) In a second method step S2, for each pole 7, 8 of the HVDC transmission, the current intensity I.sub.1, I.sub.2 and the current intensity change İ.sub.1, İ.sub.2 in the current intensity I.sub.1, I.sub.2 are recorded by the measuring device 13.

(16) In a third method step S3, for each preset interval length T.sub.1, T.sub.2, a current intensity change averaged over time intervals of the interval length T.sub.1, T.sub.2 is formed by the control unit 15 from the current intensity change İ.sub.1, İ.sub.2 in the current intensity I.sub.1, I.sub.2 of each pole 7, 8, which change was recorded by the measuring device 13 in the second method step S2.

(17) In a fourth method step S4, for each pole 7, 8, the absolute value of the current intensity I.sub.1, I.sub.2 recorded by the measuring device 13 in the second method step S2 is compared by the control unit 15 with the current intensity threshold value L1 preset in the first method step S1. In addition, in the fourth method step S4, for each pole 7, 8 and for each preset interval length T.sub.1, T.sub.2, the absolute value of the averaged current intensity change formed in the third method step S3 is compared by the control unit 15 with the change threshold value L2, L3 preset for the interval length T.sub.1, I.sub.2 in the first method step S1. When the absolute value of the current intensity I.sub.1, I.sub.2 of at least one pole 7, 8 is greater than the current intensity threshold value L1 or, for an interval length T.sub.1, T.sub.2, the absolute value of the averaged current intensity change in the current intensity I.sub.1, I.sub.2 of at least one pole 7, 8 is greater than the change threshold value L2, L3 preset for the interval length T.sub.1, T.sub.2, it is concluded that there is a DC fault, and the method is continued with a fifth method step S5. Otherwise, the method is continued with the second method step S2.

(18) FIG. 3 shows a schematic illustration of a block diagram for implementing the method steps S3 and S4 for the first pole 7. The first current intensity I.sub.1 recorded in the second method step S2 is passed to an absolute value generator 20, which generates the absolute value of the first current intensity I.sub.1. The absolute value of the first current intensity I.sub.1 is compared with the current intensity threshold value L1 by a comparator 22. When the absolute value of the first current intensity I.sub.1 is greater than the current intensity threshold value L1, the comparator 22 outputs a one as output signal to a first OR element 24; otherwise the comparator 22 outputs a zero as output signal to the first OR element 24.

(19) The first current intensity change İ.sub.1 recorded in the second method step S2 is in each case passed to a first evaluator 26 and a second evaluator 28. The first evaluator 26 averages the first current intensity change İ.sub.1 over a time interval of the first interval length T.sub.1 and compares the absolute value of the averaged first current intensity change with a first change threshold value L2. When the absolute value of the averaged first current intensity change is greater than the first change threshold value L2, the first evaluator 26 outputs a one as output signal to a second OR element 30; otherwise the first evaluator 26 outputs a zero as output signal to the second OR element 30.

(20) Correspondingly, the second evaluator 28 averages the first current intensity change İ.sub.1 over a time interval of the second interval length T.sub.2 and compares the absolute value of the averaged first current intensity change with the second change threshold value L3. When the absolute value of the averaged first current intensity change is greater than the second change threshold value L3, the second evaluator 28 outputs a one as output signal to the second OR element 30; otherwise the second evaluator 28 outputs a zero as output signal to the second OR element 30.

(21) The output signal of the second OR element 30 is passed to the first OR element 24. The first OR element 24 therefore outputs a one as a trigger signal S when the absolute value of the first current intensity I.sub.1 is greater than the current intensity threshold value L1 or the absolute value of the first current intensity change, averaged over a time interval of the first interval length T.sub.1, is greater than the first change threshold value L2 or the absolute value of the first current intensity change, averaged over a time interval of the second interval length T.sub.2, is greater than the second change threshold value L3. Otherwise, the first OR element 24 outputs a zero as trigger signal S.

(22) The absolute value generator 20, the comparator 22, the OR elements 24, 30 and the evaluators 26, 28 can be embodied as hardware components of the control unit 15 or as program steps in a software run by the control unit 15.

(23) In the fifth method step S5, the current of each pole 7, 8 is regulated to zero by the control unit 15 by activation of the power converter, assigned to the pole 7, 8, of the power converter station 1, 2. The regulation is triggered when the trigger signal S of the control unit 15 assumes the value one.

(24) FIGS. 4 and 5 show, by way of example, characteristics of the first current intensity I.sub.1 at the locations of the power converter stations 1, 2 and of the trigger signals S of the power converter stations 1, 2 in the event of a ground fault at the first pole 7. In this case, it has been assumed that the power converters of the power converter unit 11 of the first power converter station 1 are operated as rectifiers, the power converters of the power converter unit 11 of the second power converter station 2 are operated as inverters, and the ground fault occurs in the vicinity of the second power converter station 2.

(25) FIG. 4 shows the characteristic of the first current intensity I.sub.1 at the location of the first power converter station 1 and the characteristic of the trigger signal S of the first power converter station 1. The ground fault brings about an increase in the first current intensity I.sub.1 at the location of the first power converter station 1 from a first time t.sub.1. The first power converter station 1 records this increase and responds to it in accordance with the method steps S2 to S5. The regulation of the first current intensity I.sub.1 to zero by the first power converter station 1 in accordance with the fifth method step S5 starts at a second time t.sub.2, at which the trigger signal S of the first power converter station 1 assumes the value one. A response time of, for example, 500 μs is between the first time t.sub.1 and the second time t.sub.2. After the second time t.sub.2, the first current intensity I.sub.1 first decreases owing to the regulation, wherein its mathematical sign changes, and then increases again slowly and approaches the value zero.

(26) FIG. 5 shows the characteristic of the first current intensity I.sub.1 at the location of the second power converter station 2 and the characteristic of the trigger signal S of the second power converter station 2. The ground fault brings about a drop in the first current intensity I.sub.1 at the location of the second power converter station 2 from a third time t.sub.3, which is before the first time t.sub.1, since the ground fault occurs in the vicinity of the second power converter station 2 and therefore has more effect at this location than at the location of the first power converter station 1. Correspondingly, the second power converter station 2 responds to the ground fault at a fourth time t.sub.4, which is before the second time t.sub.2 and, for example, 500 μs after the third time t.sub.3.

(27) If, owing to the DC fault, one of the poles 1, 2 has been charged, the control unit 15 initiates, in a sixth method step S6, the discharge of the charged pole 1, 2. For example, for this purpose a regulation time period for the regulation of the currents of the poles 7, 8 in the fifth method step S5 is preset, and the sixth method step S6 is implemented once the regulation time period has expired. The regulation time period is, for example, between 100 ms and 500 ms.

(28) Although the invention has been illustrated and described in more detail using preferred exemplary embodiments, the invention is not restricted by the disclosed examples, and other variations can be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention.

LIST OF REFERENCE SYMBOLS

(29) 1, 2 power converter station 3 HVDC transmission path 5, 6 AC power supply system 7, 8 pole 9, 10 transmission line 11 power converter unit 13 measuring device 15 control unit 20 absolute value generator 22 comparator 24, 30 OR element 26, 28 evaluator I.sub.1, I.sub.2 current intensity İ.sub.1, İ.sub.2 current intensity change L1 current intensity threshold value L2, L3 change threshold value S trigger signal S1 to S6 method step t time t.sub.1 to t.sub.4 time T.sub.1, T.sub.2 interval length