KR102566804B1 - Fault current clampling device for medium voltage direct current - Google Patents

Abstract

Disclosed is a fault current clamping device for a medium voltage direct current distribution system capable of limiting fault current in order to prevent a main converter from falling off in a radial medium voltage direct current distribution system (MVDC) distribution system. A fault current clamping device for a medium voltage DC distribution system that provides a transmission path for current applied from the converter side to the consumer side. It includes a main conducting part, a current clamping part and a switching module. The main conducting unit includes a plurality of main switches disposed in series between the main converter and the main circuit breaker or between the section converter and the local circuit breaker. The current clamping part includes a plurality of current clamping switches connected in parallel and serially connected to the main conducting part and a clamping resistor connected in series to a rear end of the last current clamping switch. The switching module turns off the operation of the main conducting part and turns on the operation of the current clamping part, when it is checked that the DC current applied to the main conducting part increases rapidly and the fault current is generated, so that the fault current is reduced by the current clamping The fault current is limited by forcibly flowing to the negative.

Description

Fault current clamping device for medium voltage DC distribution system {FAULT CURRENT CLAMPLING DEVICE FOR MEDIUM VOLTAGE DIRECT CURRENT}

The present invention relates to a fault current clamping device for medium voltage direct current (MVDC), and more particularly, to a medium voltage direct current distribution system for limiting fault current to prevent a main converter from falling out in a radial MVDC distribution system. It relates to a fault current clamping device for a system.

In general, the distribution system of a medium voltage direct current (MVDC) is in the form of radial, loop, BTB (back-to-back), multi-terminal, etc. , and can be configured in various ways according to the needs and purposes of the operator. Here, the radial distribution system is known as a form that is highly likely to be adopted in terms of constituting an MVDC distribution system because it is similar to the existing AC distribution system and is easy to analyze accidents.

1 is a diagram for explaining the configuration of a general radial MVDC distribution system.

Referring to FIG. 1, in a typical radial MVDC distribution system, a main converter (AC-DC, DC-DC) and a protection device operating in several ms are installed and operated. When an accident occurs in the branch line, the magnitude of the current flowing through the main converter may exceed the overload tolerance and the main converter may drop out. The protection function built into the main converter, that is, hardware (H/W) and software (S/W), in order to protect semiconductor devices, operates instantaneously within several ms when the parameter measured by the sensor is out of the protection range. Because.

Therefore, protection devices installed on the trunk line or branch line of the MVDC distribution line do not have enough time to perform fault section determination and protection coordination operation, and there is a possibility that the blackout section may be expanded. That is, due to the sensitive operating characteristics of the main converter, the MVDC protection coordination method is difficult to equally apply the cooperation method using the coordination time difference and the T-C curve (inverse time) employed in the existing AC distribution system.

Therefore, there is a need for a new method of protection cooperation to prevent the main converter from being rapidly disconnected from the fault current and to secure a time difference between protection devices.

2 is a diagram for explaining line fault characteristics in a radial MVDC distribution system. In FIG. 2 , the line fault at point F1 occurs on the trunk line directly below the main converter, F2 is a line fault that occurs at the end of the trunk line, and F3 and F4 indicate line faults that occur directly below and at the end of the branch line.

Referring to FIG. 2, line faults in the radial MVDC distribution system can be classified into main line faults at F1 or F2 points and branch faults at F3 or F4 points, depending on the location of the accident point. Protection coordination between section converters and protection devices must be performed.

First, when a line fault occurs at point F1, the main converter is immediately dropped or protective devices such as the 1st main circuit breaker (MVCB1) operate, resulting in a power outage in the entire MVDC system. In the case of F2, before the main converter is dropped A protection cooperation method has been proposed in which protection devices for trunk lines, for example, a second main circuit breaker (MVCB2) and a third main circuit breaker (MVCB3) operate to separate accident sections.

On the other hand, when a line fault occurs at the points F3 and F4, a protection cooperation method is required to operate the branch line protection device (LVCB1) before the main converter is dropped in order to minimize power failure in the main line section.

Korean Registered Patent No. 10-1963348 (2019. 03. 22.) (Line distributed switching system for blocking DC fault current) Republic of Korea Patent Publication No. 2016-0081067 (2016. 07. 08.) (low voltage direct current distribution system and distribution method) Republic of Korea Patent Registration No. 10-1996510 (2019. 06. 28.) (fault current limiter for DC grid and its control method)

Therefore, the technical problem of the present invention is focused on this point, and the object of the present invention is for a medium voltage DC distribution system capable of limiting the fault current in order to prevent the main converter for the trunk line from being rapidly disconnected in the event of an accident in the branch line. It is to provide a current clamping device.

According to one embodiment to realize the above object of the present invention, a fault current clamping device for a medium voltage DC distribution system that provides a transmission path for current applied from a converter side to a consumer side is between a main converter and a main circuit breaker or a section converter. a main conducting unit disposed between the circuit breaker and the local circuit breaker and including a plurality of main switches connected in series; a current clamping unit including a plurality of current clamping switches connected in parallel to the main conducting unit and connected in series, and a clamping resistor connected in series to a rear end of the last current clamping switch; and when it is checked that the DC current applied to the main conducting part rapidly increases and the fault current is generated, the operation of the main conducting part is turned off and the operation of the current clamping part is turned on so that the fault current is forced into the current clamping part. Including a switching module that limits the fault current by allowing it to flow,
The number (m) of the semiconductor switch modules connected in series is (here, : Number of semiconductor switch modules, : voltage across the fault current clamping device [kV], : IGBT breakdown voltage duty cycle, : It is calculated by the formula of IGBT's collector-emitter breakdown voltage [kV]), and the limiting current (Icc) for calculating the capacity of the clamping resistor (Rcc) is for Medium Voltage Direct Current (MVDC) It is calculated to be smaller than the value obtained by multiplying the current limiting ratio by the overload tolerance of the converter (for main line, branch line) connected to the primary side of the fault current clamping device, and the capacity of the clamping resistor is 1 It is calculated by dividing the voltage on the secondary side, and each of the limiting current (Icc) and the clamping resistance (Rcc) and (Where, I _CC : limit current [A], α: current limit ratio, Idc-oc: overload capacity of converter for main line and branch line [A], Pcon: capacity of converter for main line and branch line [MW], Vpri : It is characterized in that it satisfies the formula of the primary side voltage [kV]) of the fault current limiting device.

In one embodiment, each of the main switches may include a first insulated/isolated gate bi-polar transistor (IGBT) turned on or off in response to control of the switching module; and a second IGBT that is turned on or turned off in response to control of the switching module, wherein the first IGBT and the second IGBT have emitters connected in common to control current in both directions. .

In one embodiment, each of the current clamping switches may include a third IGBT turned on or turned off in response to control of the switching module; and a fourth IGBT that is turned on or turned off in response to control of the switching module, wherein the third IGBT and the fourth IGBT have emitters connected in common to control current in both directions. .

In one embodiment, the first to fourth IGBTs may have the same size as each other.

In one embodiment, in the fault current clamping device for the medium voltage DC distribution system, in a state where DC current in a normal state flows at a value of a first current before an accident occurs, the main switch and the current clamping switch are each turned- In the initial operation mode that maintains the on state and the turn-off state, and when an accident occurs, the DC current starts to increase rapidly and when the current flowing to the main conducting part is determined as the fault current, the current clamping switch is turned on. an auxiliary operation mode that is turned on, and a main operation mode in which, when the main switch is turned off, the fault current flowing through the main conducting part is forcibly flowed to the current clamping part to limit the fault current to a second current, and the fault current When the current starts to decrease and approaches the first current, the current clamping switch is turned off and operated in a recovery operation mode to return to a normal state.

According to the fault current clamping device for the medium voltage DC distribution system, the fault current is limited by the CCR (current clamping resistor) circuit inside the device to secure the protection cooperation time for the branch line protection device to separate the fault section, By preventing the converter from falling off, it is possible to continuously supply power to a healthy section.

1 is a diagram for explaining the configuration of a general radial MVDC distribution system.
2 is a diagram for explaining line fault characteristics in a radial MVDC distribution system.
3 is a circuit diagram illustrating a fault current clamping device for MVDC according to an embodiment of the present invention.
FIG. 4 is a graph for explaining the limitation of fault current by the fault current clamping device for MVDC shown in FIG. 3 .
FIG. 5 is a configuration diagram for explaining an installation example of the fault current clamping device 100 for MVDC shown in FIG. 3 .
6 is a graph for explaining voltage and current characteristics of the fault current clamping device for MVDC.
FIG. 7 is a circuit diagram for explaining an operation of an initial operation mode (mode-I) in FIG. 6 .
FIG. 8 is a circuit diagram for explaining the operation of the auxiliary operation mode (mode-II) in FIG. 6 .
FIG. 9 is a circuit diagram for explaining the operation of the main operation mode (mode-III) in FIG. 6 .
FIG. 10 is a circuit diagram for explaining the operation of the recovery operation mode (mode-IV) in FIG. 6 .
11 is a conceptual diagram for explaining modeling of a main converter for a main line of an MVDC distribution line.
12 is a conceptual diagram for explaining modeling of a section converter for a branch line of an MVDC distribution line.
13 is a conceptual diagram for explaining modeling of a fault current clamping device for MVDC.
14 is a graph for explaining voltage and current characteristics of a current clamping unit.
15 is a conceptual diagram for explaining entire system modeling including a fault current clamping device.
16 is a diagram for explaining the MVDC model system.
17a, 17b, 17c and 17d are graphs for explaining the characteristics of the fault current clamping device in the main converter of the primary feeder.
18a, 18b, 18c and 18d are graphs for explaining the characteristics of the fault current clamping device in the section converter of the secondary feeder.

Hereinafter, with reference to the accompanying drawings, the present invention will be described in more detail. Since the present invention may have various changes and various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Like reference numerals have been used for like elements throughout the description of each figure. In the accompanying drawings, the dimensions of the structures are shown enlarged than actual for clarity of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this application, terms such as "comprise" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

In addition, unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

3 is a circuit diagram for explaining the fault current clamping device 100 for MVDC according to an embodiment of the present invention.

Referring to FIG. 3, the fault current clamping device 100 for MVDC according to an embodiment of the present invention includes a main path 110, a current clamping path 120, and a switching module ( 130), and provides a transmission path for current applied from the converter side to the customer side.

The main conducting unit 110 includes a plurality of main switches S _M connected in series. In FIG. 3 , the number of main switches S _M is n. Each of the main switches S _M includes a first insulated/isolated gate bi-polar transistor (hereinafter referred to as an IGBT) and a second IGBT. The first IGBT and the second IGBT are semiconductor switches, which are devices that have a high breakdown voltage and operate quickly within several microseconds. To control the current in both directions, the emitter of the first IGBT and the emitter of the second IGBT are connected in common.

The current clamping unit 120 includes a plurality of current clamping switches (S _CC ) connected in series and a clamping resistor (R _CC ) connected in series to a rear end of the last current clamping switch. In FIG. 3 , the number of current clamping switches S _CC is n. Each of the current clamping switches S _CC includes a third IGBT and a fourth IGBT. The third IGBT and the fourth IGBT are semiconductor switches that are devices that operate quickly within several microseconds and have a high breakdown voltage. To control the current in both directions, the emitter of the third IGBT and the emitter of the fourth IGBT are connected in common. The current clamping switches S _CC have the same shape as the main switches S _M . In this embodiment, the size of each of the first IGBT and the second IGBT included in the main switch S _M is the same, and the size of each of the third IGBT and the fourth IGBT included in the current clamping switches S _CC may be equal to each other. Here, the sizes of the first to fourth IGBTs may be defined by a channel width versus a channel length (W/L). Also, the size of the first IGBT included in the main switch S _M and the size of the third IGBT provided in the current clamping switches S _CC may be the same.

The switching module 130 turns off the operation of the main conducting unit 110 and stops the operation of the current clamping unit 120 when it is checked that the DC current applied to the main conducting unit 110 rapidly increases and a fault current is generated. turn on Here, the change in DC current is sensed through a current transformer (CT).

FIG. 4 is a graph for explaining the limitation of fault current by the fault current clamping device 100 for MVDC shown in FIG. 3 .

Referring to FIGS. 3 and 4 , when an accident occurs in the time zone t0, the fault current clamping device 100 for MVDC operates in the time zone t1 to limit the fault current (idc) until the time zone t2 separating the fault section.

The fault current clamping device 100 for MVDC according to an embodiment of the present invention can be installed and operated in various parts of a radial MVDC line.

FIG. 5 is a configuration diagram for explaining an installation example of the fault current clamping device 100 for MVDC shown in FIG. 3 .

Referring to FIGS. 3 and 5 , the fault current clamping device 100 for MVDC installed at part A is applied directly below the main converter for the main line of the MVDC distribution line. When a fault occurs, since high voltage is applied to both ends of the fault current clamping device 100 for MVDC, the main conducting part 110 and the current clamping part 120 are composed of many switches, but limit the fault current of the entire MVDC line. has a function to

In addition, the fault current clamping device 100 for MVDC installed in part B is applied directly below the section converter installed in the branch lines (MV, LV) of the MVDC distribution line. When a fault occurs, since a relatively low voltage is applied to both ends of the fault current clamping device 100 for MVDC, the main carrying unit 110 and the current clamping unit 120 can be configured with a small number of switches, but the section converter It is necessary to install the fault current clamping device 100 for MVDC directly under each.

Therefore, the fault current clamping device 100 for MVDC according to the present invention requires an optimal design considering the size, capacity, supply voltage, and the like of trunk and branch lines of a radial MVDC distribution system.

Then, the operation mode of the fault current clamping device 100 for MVDC will be described below.

6 is a graph for explaining voltage and current characteristics of the fault current clamping device 100 for MVDC. FIG. 7 is a circuit diagram for explaining an operation of an initial operation mode (mode-I) in FIG. 6 . FIG. 8 is a circuit diagram for explaining the operation of the auxiliary operation mode (mode-II) in FIG. 6 . FIG. 9 is a circuit diagram for explaining the operation of the main operation mode (mode-III) in FIG. 6 . FIG. 10 is a circuit diagram for explaining the operation of the recovery operation mode (mode-IV) in FIG. 6 . 7 to 10, the illustration of the switching module 130 is omitted.

6 and 7, in the initial operation mode (mode-I) of the fault current clamping device, which is a state before an accident occurs in the MVDC distribution system, the DC current in the normal state flows at the value of the first current i1. . At this time, the main switch (S _M ) of the main conductive part 110 is in a turn-on state, and the current clamping switch (S _CC ) of the current clamping part 120 is in a turn-off state.

Referring to FIGS. 6 and 8 , in the auxiliary operation mode (mode-II) of the fault current clamping device, in which an accident occurs at time t0, the DC current starts to increase rapidly. Accordingly, when the fault current clamping device 100 determines that the current flowing through the main conducting part 110 is the fault current, the current clamping switch S _CC of the current clamping part 120 is turned on.

6 and 9, in the main operation mode (mode-III) of the fault current clamping device in which the main switch S _M is turned off, the fault current flowing to the main conducting part 110 is current clamped. It is forced to flow to section 120. That is, as shown in FIG. 9 , the main switch (S _M ) of the main conduction unit 110 is in a turn-off state, and the current clamping switch (S _CC ) of the current clamping unit 120 is in a turn-on state, and the fault current is limited to the second current i2 by the fault current clamping device 100. In addition, in this mode, the fault current clamping device 100 must maintain its operation until the time t2 when the fault section is separated.

6 and 10, current clamping of the current clamping unit 120 in the recovery operation mode (mode-IV) of the fault current clamping device, in which the fault current starts to decrease and approaches the first current i1. The switch (S _CC ) turns off and returns to a normal state.

Then, modeling of the fault current clamping device 100 for MVDC using power system analysis software (PSCAD/EMTDC) will be described below.

<Modeling of main converter for main line>

11 is a conceptual diagram for explaining modeling of a main converter for a main line of an MVDC distribution line. In particular, modeling of a main converter for main lines of a ±35 kV class MVDC distribution line is shown.

Referring to FIG. 11, the main converter for the main line of the MVDC distribution line is composed of a 3-winding transformer, an SCR rectifier, an L-C filter, and the like.

The rectifier transformer has three windings Yg-Y- By adopting the wiring method, the Y side and the delta ( The input of the SCR rectifier on the ) side has a phase difference of 30°. Y-side and delta ( ) side of the SCR rectifier, the content of harmonics generated on the AC side can be reduced by making the input phase of the SCR rectifier different.

The SCR rectifier includes thyristor elements of a 6-pulse bridge for converting three-phase AC power into DC power.

The L-C filter serves to reduce the ripple of the rectified DC-side output.

<Modeling of section converter for branch line>

12 is a conceptual diagram for explaining modeling of a section converter for a branch line of an MVDC distribution line. In particular, modeling of a section converter for a branch line of a ±35 kV class MVDC distribution system is shown.

Referring to FIG. 12, a section converter for a branch line that supplies power from a ±35kV class MVDC distribution system to a ±750V class low voltage direct current (LVDC) distribution system is a full-bridge type IGBT element (full- bridge IGBT), a high frequency transformer for electrical isolation and step-down, and an L-C filter.

<Modeling of fault current clamping device for MVDC>

When modeling of the power system analysis software (PSCAD/EMTDC) is performed based on the configuration diagram of the fault current clamping device 100 for MVDC of FIG. 3 , it can be represented as shown in FIG. 13 .

13 is a conceptual diagram for explaining modeling of the fault current clamping device 100 for MVDC.

Referring to FIG. 13, the number of semiconductor switch modules (m) connected in series is calculated by dividing the voltage of the fault current clamping device by the switch withstand voltage (V _CE ) and the duty cycle (k) of the switch withstand voltage, and Equation (1) can be shown together.

(One)

(here, : Number of semiconductor switch modules, : voltage across the fault current clamping device [kV], : IGBT breakdown voltage duty cycle, : Collector-emitter breakdown voltage of IGBT [kV])

On the other hand, the limiting current (I _CC ) for calculating the capacity of the clamping resistor (R _CC ) is the current limiting ratio (α ) is calculated to be smaller than the multiplied value, and can be expressed as in Equation (2). Therefore, the capacity of the clamping resistor (R _CC ) is calculated by dividing the primary side voltage of the fault current limiting device by the limiting current of the converter, and can be expressed as in Equation (3).

(2)

(3)

(Where, I _CC : limit current [A], α: current limit ratio, Idc-oc: overload capacity of converter for main line and branch line [A], Pcon: capacity of converter for main line and branch line [MW], Vpri : Primary side voltage of fault current limiter [kV])

Meanwhile, voltage and current characteristics of the current clamping unit are shown in FIG. 14 in order to calculate the energy of the clamping resistor (R _CC ).

14 is a graph for explaining voltage and current characteristics of a current clamping unit.

Referring to FIG. 14, the voltage v _ccs (t) of the clamping resistor (R _CC ) considers the line impedance, and the duration (t _FCC ) during which voltage is applied to the clamping resistor (R _CC ) is It must be greater than the protection coordination time (t _CB ) of the circuit breaker (MVCB, LVCB), and can be expressed as in Equation (4). Therefore, the energy of the clamping resistor (R _CC ) is calculated by integrating the product of the voltage and current of the clamping resistor (R _CC ) during the duration of Equation (4), and can be expressed as Equation (5).

(4)

(5)

(Where t _FCC : Time when voltage is applied to clamping resistor [ms], t _CB : Protection coordination time between circuit breakers (MVCB, LVCB) [ms], E _rccmin : Energy of clamping resistor [J], v _ccs (t ): voltage applied to the clamping part [kV], i _dc (t): steady-state DC current [A])

For example, the configuration of the fault current clamping device in the ±35kV class MVDC distribution line based on Equations (1) to (5) above can be shown in Table 1.

Table 1 shows the configuration of the fault current clamping device according to the installation conditions.

[Table 1]

As shown in Table 1, when the fault current clamping device is installed directly under the main converter for trunk line, 9 switch modules and 2.2 [MJ] of CCR (current clamping resistor) energy are calculated, and When installed, it can be confirmed that one switch module and 87.4 [kJ] of CCR energy are calculated.

Therefore, according to the operation method of the radial MVDC distribution system, an optimal design for the number of modules of the switch constituting the fault current clamping device and the capacity of the CCR is required.

Based on the modeling presented above, the entire system modeling for evaluating the performance of the fault current clamping device is shown in FIG. 15.

15 is a conceptual diagram for explaining entire system modeling including a fault current clamping device.

Referring to FIG. 15, the entire system modeling including the fault current clamping device is composed of a DC voltage source, fault current clamping device, line impedance, and resistive load. Here, the DC voltage is assumed to be 70kV (±35kV) considering the voltage of the MVDC distribution system as a bi-pole and ungrounded method.

In the following, simulation results and analysis are described.

Simulation conditions for analyzing the operating characteristics of the fault current clamping device for MVDC according to the present invention can be represented as shown in FIG. 16 and Table 2.

16 is a diagram for explaining the MVDC model system.

Referring to FIG. 16, the sections of the MVDC distribution line are assumed to be 0 to 10 [km] and 10 to 20 [km], respectively, and a section converter for branch line is installed at the midpoint of each section to provide a low voltage direct current distribution system (LVDC: Low Voltage Direct Current), and the fault current clamping device is installed at part A, which is directly under the main converter, or part B, which is directly under the section converter.

Table 2 shows the simulation conditions.

[Table 2]

As shown in Table 2, the capacity and supply voltage of the main converter for trunk line are 24[MW], 70[kV] (±35[kV]), and the capacity and voltage of section converter for branch line are 1[MW], 1.5[kV] (±750[V]), and the overload capacity of main and section converters is assumed to be 300[%].

In addition, the breakdown voltage and usage rate of IGBT used in the fault current clamping device are assumed to be 6.5 [kV] and 60 [%], and the direct current clamping resistor (CCR) of the main and section converters is 46 [Ω] and 0.56 [ Ω], and the blocking operation time of the protection device is set to 10 ms.

On the other hand, the total length of the MVDC distribution line (length of the distribution line) is 20 [km], and the type of line (type of line) is assumed to be ACSR 160mm2, which is the same as that of the AC distribution line.

<Operating Characteristics of Fault Current Clamping Device for Main Converter>

17a, 17b, 17c and 17d show the operating characteristics of the fault current clamping device for MVDC when an accident occurs directly under the trunk converter according to the simulation conditions of Table 2.

17a, 17b, 17c and 17d are graphs for explaining the characteristics of the fault current clamping device in the main converter of the primary feeder. In particular, FIG. 17A is the gate signal of the fault current clamping device, FIG. 17B is the fault current and the current of the clamping part, FIG. 17C is the voltage applied to both ends of the fault current clamping device and the consumer side, and FIG. 17D is the energy characteristic of the clamping resistor. am.

As shown in FIG. 17B, when a P-N fault occurs directly under the section converter, it can be confirmed that the fault current is limited to 673 [A] by the switching operation of the fault current clamping device. Here, the P-N accident means an accident that occurs when any one of the R phase, S phase, and T phase lines come into contact with the N phase line.

While the fault current clamping device operates as shown in FIG. 17D, the energy accumulated in the CCR (current clamping resistor) is estimated to be about 2.2 [MJ].

Therefore, if the fault current clamping device according to the present invention is installed directly under the main converter for the trunk line, it is possible to secure the time for the protection device of the corresponding branch line to operate, thereby preventing the main converter from falling off, and preventing the accident section It can be confirmed that the can be separated.

<Operating Characteristics of Fault Current Clamping Device for Section Converter>

18a, 18b, 18c and 18d show the operating characteristics of the fault current clamping device for MVDC when an accident occurs directly under the branch line converter according to the simulation conditions of Table 2.

18a, 18b, 18c and 18d are graphs for explaining the characteristics of the fault current clamping device in the section converter of the secondary feeder. In particular, FIG. 18A is the gate signal of the fault current clamping device, FIG. 18B is the fault current and the current of the clamping part, FIG. 18C is the voltage applied to both ends of the fault current clamping device and the consumer side, and FIG. 18D is the energy characteristic of the clamping resistor. is shown.

As shown in FIG. 18B, when a P-N fault occurs directly under the section converter, it can be confirmed that the fault current is limited to 1,297 [A] by the switching operation of the fault current clamping device.

As shown in FIG. 18D, while the fault current clamping device operates, the energy accumulated in the current clamping resistor (CCR) is estimated to be about 87.4 [kJ].

Therefore, it can be seen that if the fault current clamping device according to the present invention is installed directly under the branch line section converter, when an accident occurs in the branch line, the main converter can be prevented from falling off and power can be supplied to the healthy section.

As described above, as a result of analyzing the operating characteristics based on the modeling of the fault current clamping device according to the present invention, the main converter can It can be confirmed that the main converter can be prevented from falling out by quickly limiting the fault current before falling out by exceeding the overload capacity from the semiconductor switch, which is a device that operates quickly.

In addition, when the fault current clamping device according to the present invention is installed and operated directly under the main converter for trunk lines, when a P-N fault occurs directly under the section converter, the fault current is 673 [A] due to the switching operation of the fault current clamping device. , and the energy accumulated in the current clamping resistor (CCR) is estimated to be about 2.2 [MJ]. Therefore, it can be confirmed that the fault current clamping device according to the present invention can secure the operating time of the protection device in the branch line where the fault occurred, prevent the main converter from falling off, and separate the fault section. there is.

In addition, when the fault current clamping device according to the present invention is installed and operated directly under the section converter for branch lines, when a P-N fault occurs in the branch line, the fault current is limited to 1,297[A] by the switching operation of the fault current clamping device. and the accumulated energy in CCR (current clamping resistor) is estimated to be about 87.4 [kJ]. Therefore, it can be confirmed that the fault current clamping device according to the present invention can prevent the main converter from falling off and supply power to a healthy section.

Although the above has been described with reference to examples, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention described in the claims below. You will understand.

100: Fault current clamping device for medium voltage DC distribution system
110: main conducting part 120: current clamping part
S _M : Main switches S _CC : Current clamping switches
R _CC : clamping resistance

Claims (5)

In a fault current clamping device for a medium voltage DC distribution system that provides a transmission path for current applied from the converter side to the consumer side,
a main conducting unit disposed between the main converter and the main circuit breaker or between the section converter and the local circuit breaker and including a plurality of main switches connected in series;
a current clamping unit including a plurality of current clamping switches connected in parallel to the main conducting unit and connected in series, and a clamping resistor connected in series to a rear end of the last current clamping switch; and
When it is checked that the DC current applied to the main conducting part increases rapidly and a fault current is generated, the operation of the main conducting part is turned off and the operation of the current clamping part is turned on so that the fault current is forcibly flowed into the current clamping part. Including a switching module for limiting the fault current by
The number (m) of the semiconductor switch modules connected in series is

(here, : Number of semiconductor switch modules, : voltage across the fault current clamping device [kV], : IGBT breakdown voltage duty cycle, : Calculated by the formula of IGBT's collector-emitter breakdown voltage [kV]),
The limiting current (Icc) for estimating the capacity of the clamping resistor (Rcc) is the converter (for main line or branch line) connected to the primary side of the fault current clamping device for Medium Voltage Direct Current (MVDC). It is calculated to be smaller than the value obtained by multiplying the overload tolerance by the current limiting ratio,
The capacity of the clamping resistor is calculated by dividing the primary side voltage of the fault current limiting device by the limiting current,
Each of the limiting current Icc and the clamping resistor Rcc is
and (Where, I _CC : limit current [A], α: current limit ratio, Idc-oc: overload capacity of converter for main line and branch line [A], Pcon: capacity of converter for main line and branch line [MW], Vpri : A fault current clamping device for a medium voltage DC distribution system, characterized in that it satisfies the formula of the primary side voltage [kV]) of the fault current limiting device. The method of claim 1, wherein each of the main switches,
a first insulated/isolated gate bi-polar transistor (IGBT) turned on or off in response to control of the switching module; and
A second IGBT turned on or turned off in response to control of the switching module;
Wherein the first IGBT and the second IGBT have emitters commonly connected to control current in both directions. The method of claim 2, wherein each of the current clamping switches,
a third IGBT turned on or turned off in response to control of the switching module; and
A fourth IGBT turned on or turned off in response to control of the switching module;
The fault current clamping device for a medium voltage DC distribution system, characterized in that the third IGBT and the fourth IGBT have emitters commonly connected to control current in both directions. 4. The fault current clamping device according to claim 3, wherein the first to fourth IGBTs have the same size. According to claim 1,
Before an accident occurs, an initial operation mode in which the main switch and the current clamping switch maintain a turn-on state and a turn-off state, respectively, in a state in which a DC current in a normal state flows at a value of a first current;
When an accident occurs, the DC current starts to increase rapidly and when the current flowing into the main conducting part is determined as the fault current, an auxiliary operation mode for turning on the current clamping switch;
a main operation mode in which, when the main switch is turned off, the fault current flowing in the main conducting part is forcibly flowed into the current clamping part to limit the fault current to a second current;
When the fault current starts to decrease and approaches the first current, the current clamping switch is turned off and operated in a recovery operation mode to return to a normal state.