Capacitor-compensated thyristor-controlled braking resistor.

Abstract

A system (100) for stabilizing an electrical grid (102) includes a generator (104) configured to provide electrical power to the electrical grid (102), the electrical power having an active power component and a reactive power component, and a power line (106) configured to transmit the electrical power from the generator (104) to the electrical grid (102). The system (100) includes a thyristor controlled braking resistor (TCBR) (108) disposed on the power line (106) and a capacitor (110) electrically connected in series with the TCBR (108). The TCBR (108) absorbs at least a portion of the reactive power component from the generator (104) during a fault on the power line (106), and the capacitor (110) is configured to compensate for at least a portion of the reactive power component absorbed by the TCBR (108).

Description

[Technical field]

[0001] Technical Field The present disclosure relates to fault tolerance in electrical grids. More particularly, the present disclosure relates to a thyristor controlled braking resistor for use during a fault in an electrical grid. [Background technology]

[0002] background The grid comprises generators that supply power to loads. The generators are usually connected to the grid by power lines, i.e., electrical cables that transmit power from the generators to the loads in the grid. For example, in a radial network, a single generator supplies the loads via a single power line.

[0003] Although power lines are often constructed for resiliency, if a power line fault occurs, generator loads can be quickly lost. In such situations, generators may trip, be damaged, and / or need to be shut down.

[0004] Braking resistors may be used as temporary loads on the generator in the event of a fault to avoid tripping the generator until the power lines can be repaired and / or reconnected. When it is time to shut down the generator, this can be done in a controlled manner by ramping down the power using a thyristor controlled braking resistor (TCBR).

[0005] TCBRs consume reactive power when operating due to the internal inductance of resistors, reactive power consumption of thyristors when operating with firing delay, and also reactive power consumption of transformers, if used. This reactive power consumption can cause the voltage on the grid to drop, which can cause the generator to trip on undervoltage. An example of such a TCBR is disclosed in U.S. Pat. No. 5,198,745.

[0006] The reactive power absorbed by the TCBR can be compensated by mechanically switched or thyristor switched shunt capacitor banks, thus reducing the risk of generator tripping. Summary of the Invention [Means for solving the problem]

[0007] Summary of the Invention Aspects of the present disclosure are provided to improve the stability of power grids that use TCBR.

[0008] According to one aspect of the disclosure, a system for stabilizing an electrical grid is provided, the system comprising: a generator configured to provide electrical power to the electrical grid; and a power line configured to transmit the electrical power from the generator to the electrical grid.

[0009] The grid may be, for example, a radial grid having a single generator each feeding a grid load over a single power line. Alternatively, the grid may be a ring or mesh network. The grid provides power to loads that may consist of a combination of loads, such as a city's power network, commercial properties, or some other load or combination thereof.

[0010] The generator may be any generator suitable for providing power to the loads to meet the demands of the loads, which may vary widely over the course of a day or year. The generator may be driven by a renewable source, such as a wind turbine or a hydroelectric system, or some other power source. The power line is configured to deliver the power generated by the generators to the grid, and more specifically to the loads of the grid.

[0011] According to this aspect of the disclosure, the system further comprises a thyristor controlled braking resistor (TCBR) disposed on the power line and configured to absorb power from the generator during a power line fault. The TCBR may comprise a braking resistor configured to draw an electrical load from the generator and a thyristor electrically connected in series with the resistor and configured to control the electrical load drawn by the braking resistor. In general, the TCBR advantageously provides controllability of the current and power drawn from the generator, which can be controlled (e.g., via connection to a control unit or some other means) to a desired set point.

[0012] The power generated by the generator has an active and reactive component, and the TCBR is configured in its operation to absorb at least a portion of the reactive power component due to the internal inductance of the resistors and / or the reactive power consumption of the thyristors when operating with delayed firing.

[0013] Therefore, to compensate for this reactive power absorption by the TCBR, it is proposed as part of this aspect of the disclosure to provide a capacitor electrically connected in series with the TCBR, the capacitor being configured to compensate for at least a portion of the reactive power component absorbed by the TCBR. The reactive power can be compensated to a required extent depending on the current in the TCBR.

[0014]

number

[0015] Providing a series capacitor in this manner improves upon previous solutions such as, for example, shunt resistors because a disadvantage of shunt resistors is that the reactive power is compensated in discrete steps, causing undesirable steps in the grid voltage. The use of a capacitor does not cause such steps in the grid voltage because the compensation is scaled according to the current in the TCBR.

[0016] In some examples, the system may further include a transformer connected on the power line between the generator and the power grid.

[0017] In such an example, the capacitor may be placed between the transformer and the grid, i.e., on the primary side of the transformer. When the capacitor is placed on the primary side of the transformer, the voltage of the transformer may increase with the current, and the rated voltage of the transformer may also increase. The series capacitor may preferably be insulated against the high voltage levels of the grid.

[0018] Alternatively, the capacitor may be placed between the transformer and the TCBR, i.e. on the secondary side of the transformer. If the capacitor is placed on the secondary side of the transformer, this advantageously gives lower insulation requirements for the series capacitor and the transformer, but the voltage on the thyristor valve may increase with current. Optimization of the thyristor valve and resistors may become more complicated.

[0019] The particular placement of the capacitor relative to the transformer may depend on the system. Reactive power compensation may also be provided by a series capacitor with a TCBR system that does not include a transformer.

[0020] According to some exemplary embodiments, the system may further comprise a bypass switch configured to bypass the capacitor and / or the varistor electrically connected in parallel with the capacitor for further reliability of the system.

[0021] While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings which are described in detail herein. It should be understood, however, that the detailed description and the drawings accompanying this specification are not intended to limit the invention to the particular forms disclosed. Rather, the intent is to cover all modifications, equivalents, and alternatives falling within the scope of the appended claims.

[0022] Any reference in this specification to prior art documents or comparative examples should not be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the art.

[0023] As used herein, the words "comprise," "comprising," and similar words should not be construed in an exclusive or exhaustive sense. In other words, they are intended to mean "including but not limited to."

[0024] BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments will now be described, by way of example only, with reference to the following figures. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram of a system for stabilizing an electrical grid, according to one embodiment. [Diagram 2] 2 is a schematic diagram of an exemplary configuration of a capacitor for use in the system of FIG. 1. [Diagram 3] FIG. 2 is a schematic diagram of an exemplary configuration of a thyristor-controlled braking resistor for use in the system of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Detailed Description The present invention will be described below by some illustrative examples. It will be understood that these examples are provided for illustration and explanation only, and are not intended to limit the scope of the present invention. Instead, the scope of the present invention should be defined by the appended claims. Furthermore, although the examples may be presented in the form of individual embodiments, it will be recognized that the present invention also encompasses combinations of the embodiments described herein.

[0027] FIG. 1 illustrates an example system 100 for stabilizing an electrical grid 102, according to an embodiment.

[0028] The illustrated systems 100 are similar at least in that they include a generator 104 configured to provide electrical power to an electrical grid 102, the electrical power having active and reactive power components. The generator 104 is connected to the electrical grid 102 via a power line 106, which may be one or more power lines, depending on the particular implementation.

[0029] A thyristor controlled braking resistor (TCBR) 108 is disposed on the power line 106 in series with the generator 104. An exemplary configuration of the TCBR 108 is described below in connection with FIG.

[0030] The TCBR 108 acts as a temporary load for the generator 104, for example in the event of a fault in the power line 106 leading to a disconnection from the grid 102. The TCBR 108 is controllable (e.g., via a control unit connected to the thyristors of the TCBR 108) to control the power drawn from the generator 104, for example to a desired maximum or minimum set point, according to the particular requirements of the system 100.

[0031] As will be appreciated, the power from the generator 104 has a real power component and a reactive power component, and the braking resistors included in the TCBR 108 are configured to consume primarily the real power component. If much of the reactive power component is consumed (or stored rather than returned) by the components of the TCBR 108 or other components in the system 100, the voltage of the grid 102 may undesirably drop. This may cause the generator 104 to trip on an undervoltage.

[0032] The system 100 further includes a capacitor 110 electrically connected in series with the TCBR 108. This series arrangement of the capacitor 110 allows the capacitor 110 to compensate for reactive power consumption by the components of the TCBR 108. Thus, the voltage of the grid 102 does not drop undesirably and the generator 104 is at less risk of tripping due to under-voltage. As a result, the system 100 is more robust and reliable.

[0033] The construction of capacitor 110 is described in more detail below in conjunction with FIG. In some examples, the system may include a transformer 112 connected on the power line 106 between the generator 104 and the grid 102. The two systems 100 shown differ in the potential placement of the capacitor 110 relative to the transformer 112. The transformer 112 may have a high voltage (HV) primary side and a medium voltage (MV) secondary side, where the voltage is stepped up from the MV secondary side to the HV primary side before being distributed to the grid 102.

[0034] The capacitor 110 may be placed in series with the primary HV side of the transformer 112 or may be placed in series with the secondary MV side of the transformer 112. In other words, the capacitor 110 may be placed between the transformer 112 and the grid 102 or between the transformer 112 and the TCBR 108.

[0035] If the capacitor 110 is placed in series with the primary side of the transformer 112, the voltage of the transformer 112 may increase with current, and the voltage rating of the transformer 112 may be increased accordingly.

[0036] Preferably, the series capacitor 110 may be isolated with respect to the HV level of the grid 102 to accommodate placing the capacitor 110 on the HV side of the transformer 112 .

[0037] If the capacitor 110 is placed in series with the secondary side of the transformer 112, the voltage of the thyristor valve in the TCBR 108 will increase with current. Therefore, optimization of the thyristor valve and resistors in the TCBR 108 may be more complicated. However, advantageously, since the series capacitor 110 is placed on the MV side of the transformer 112, the insulation requirements may be lower.

[0038] Whether the capacitor 110 is located on the HV or MV side of the transformer 112 may depend on the system. Additionally, as shown by the dotted line in FIG. 1, the transformer 112 may not be included in the system 100. Even without the transformer 112, the capacitor 110 may still provide reactive power compensation for the system 100 with a TCBR. However, if the transformer 112 is included, the transformer 112 may contribute to reactive power consumption (or storage without return).

[0039] FIG. 2 illustrates generally an exemplary configuration 200 of a capacitor 110 for use in the system of FIG.

[0040] In the illustrated configuration 200, the capacitor 110 may have a bypass switch 114 arranged to bypass the capacitor 110, for example, arranged across the terminals of the capacitor 110 on the power line 106. This allows reactive power compensation of the capacitor 110 to be added and removed by control (e.g., remote control) of the bypass switch 114.

[0041] The bypass switch 114 may take any form suitable for allowing electrical bypass of the capacitor 110 upon closure of the bypass switch 114 while allowing electrical flow through the capacitor 110 while the bypass switch 114 is open. The provision of the bypass switch 114 may further improve the safety of the system 100 and / or the controllability of the system 100.

[0042] Additionally or alternatively, configuration 200 may further include a varistor 116 disposed in parallel with capacitor 110. Varistor 116 may advantageously provide additional protection for capacitor 110 and thus further improve the safety and reliability of system 100.

[0043] The configuration 200 may include one or both of the bypass switch 114 and the varistor 116 according to the required specifications of the system 100, for example with regard to safety, ratings, etc.

[0044] FIG. 3 illustrates generally an exemplary configuration of a TCBR 108 for use in the system 100 of FIG.

[0045] According to the illustrated example, the TCBR 108 may include a braking resistor 118 configured to draw an electrical load from the generator 104 and a thyristor 120 electrically connected in series with the resistor 118 and configured to control the electrical load drawn by the braking resistor 118.

[0046] The thyristor 120 may be one or more thyristors depending on the required specifications of the TCBR 108. For example, the thyristor 120 may comprise multiple thyristors 120 arranged in series to increase voltage capability.

[0047] As mentioned above, the primary purpose of the braking resistor 118 when drawing an electrical load is to consume real power from the generator 104 (e.g., when the TCBR 108 is acting as a temporary load for the generator 104), but the TCBR 108 can also store or consume reactive power.

[0048] The TCBR 108 may consume a relatively large amount of reactive power during its operation (e.g., relative to an ideal reactive power consumption of zero). This may be due to the internal inductance of the braking resistor 118 and / or the reactive power consumption of the thyristor 120 if there is a delay in firing the TCBR 108.

[0049] The amount of reactive power consumed by the TCBR 108 is compensated proportionally as a result of the provision of the series capacitor 110. Thus, the reactive power compensation by the capacitor 110 is proportional to the reactive power consumption by the TCBR 108. As a result, the generator 104 can be prevented from tripping and the voltage of the grid 102 does not vary erratically.

[0050] In some examples, the damping resistor 118 may include an additional resistor 118a, such that the damping resistor 118 consists of a pair of resistors 118, 118a. In such examples, the thyristor 120 may be disposed between and electrically connected to the pair of damping resistors 118, 118a.

[0051] By providing an additional resistor 118 a on the other side of the thyristor 120 it is possible to split the resistance into a portion, ie into two portions, which advantageously limits the short circuit current in the valve of the thyristor 120 .

[0052] In some further examples, a reactor (not shown) may be included in series with the thyristor 120 and thus provide additional reactance to limit the current draw through the valve of the thyristor 120 .

[0053] Resistors 118 and / or 118a may be advantageously selected for lower internal inductance (thus, e.g., reducing reactive power consumption), small temperature dependence (thus, e.g., preventing overheating during operation), and high overload capability (e.g., for better resilience).

[0054] Although only one additional resistor 118a is shown, it will be understood that more additional resistors may be provided, for example, on either side of the thyristor 120. Furthermore, as shown by the dotted lines in FIG. 3, the additional resistor 118a may not be provided.

[0055] The relationship between the resistance of resistors 118, 118a and the capacitance of capacitor 110 may be determined based on the selected voltage to which the TCBR is connected (i.e., the secondary voltage of transformer 112) and / or the reactive power that may be tolerated in system 100 during operation.

[0056] In some examples, the TCBR 108 may further include a control unit 122 configured to control the thyristors 120. The control units 122 may be provided, for example, one for each thyristor 120.

[0057] The control unit 122, which may itself be locally or remotely controlled, may locally or remotely control the thyristor 120, allowing the TCBR 108 to control the amount of power drawn from the generator 104 when the TCBR 108 is acting as a temporary load on the generator 104. For example, the TCBR 108 may be controlled to a desired set point of the drawn electrical load via control of the thyristor 120 by the control unit 122. This set point may be predetermined by some computational means or dynamically determined according to the particular requirements of the system 100.

[0058] It will be understood that the various components and features disclosed in the foregoing description may be implemented separately or in combination, unless otherwise specified. Moreover, it will be understood that the foregoing disclosed embodiments are not exhaustive and that there may be additional exemplary embodiments within the scope of the appended claims.

Claims

1. A system for stabilizing an electricity transmission and distribution grid, comprising: a generator configured to provide electrical power to the grid, the electrical power having a real power component and a reactive power component; a power line configured to transmit power from the generator to the power grid; a thyristor controlled braking resistor (TCBR) disposed on the power line and configured to control power drawn from the generator; a capacitor electrically connected in series with the TCBR; The capacitor is configured to compensate for at least a portion of a reactive power component absorbed by the TCBR.

2. a transformer connected on the power line between the generator and the power grid; The system of claim 1 , wherein the capacitor is disposed between the transformer and the TCBR or between the transformer and the grid.

3. The system of claim 1 or claim 2, further comprising a bypass switch configured to bypass the capacitor.

4. The system of any one of claims 1 to 3, further comprising a varistor electrically connected in parallel with the capacitor.

5. The TCBR is a braking resistor configured to draw an electrical load from the generator; A thyristor electrically connected in series with the braking resistor and configured to control the electrical load drawn by the braking resistor.

6. The system of claim 5 , wherein the thyristor is configured to be controlled by a control unit.

7. The braking resistor comprises at least two resistors, The system of claim 5 or claim 6, wherein the thyristor is disposed between the at least two resistors.

8. A power transmission and distribution network comprising a system according to any one of claims 1 to 7.

Images