JP6769564B2 - Power system and relay - Google Patents

Description

The present invention relates to power systems and relays.

Conventionally, as described in, for example, Japanese Patent Application Laid-Open No. 2015-065719, a grid interconnection device for a photovoltaic power generation facility including a photovoltaic power generation unit, a power conditioner, and an interconnection protection device has been known. There is. In this grid interconnection device, an linkage protection device is provided between the power conditioner and the distribution system. The linkage protection device includes a switch, which can separate the power conditioner and the photovoltaic unit from the distribution system. Paragraph 0060 of this publication slightly mentions that the switch may be provided with a protective relay necessary to perform a protective operation.

Japanese Patent Application Laid-Open No. 2015-06571

There are fossil energy and non-fossil energy as energy sources, and non-fossil energy is classified into nuclear power and renewable energy. In recent years, electric power systems using renewable energy have become more and more popular. A so-called grid interconnection system, in which a renewable energy power system and other power systems such as fossil energy are operated in parallel, is widespread. In addition, a so-called independent power supply system, which is composed only of a renewable energy power system and does not perform grid interconnection, has also been put into practical use.

Renewable energy power systems include power conditioners. The power conditioner converts DC power into desired AC power by driving a built-in inverter circuit.

The power of the renewable energy power system is also supplied to the consumers through the transmission lines of the transmission network, like the existing power system. Generally, the grid is equipped with protective relays in case of an accident on the transmission line. Many protective relays for power transmission line protection detect accidents based on the electrical physical quantity on the power transmission line. In such a protective relay, it is considered that an accident has occurred in the transmission line when the electrical physical quantity on the transmission line shows a predetermined behavior. For example, when a ground fault occurs in a transmission line, an excessive ground fault current should normally flow, so that the accident can be detected based on the increase in such current.

The power conditioner has a function of limiting the output current according to the voltage on the output side of the power conditioner. When the power conditioner suppresses the output current by this output current limitation, it is possible to prevent an excessive ground fault current from flowing in the transmission line. However, this output current suppression is different from the current behavior when a short-circuit accident occurs in a conventional power system that does not include a power conditioner. Suppression of the output current of the power conditioner causes unplanned current behavior for conventional relays. In a power system including a power conditioner, there is a problem that the accident detection accuracy of the relay may be lowered due to the current control peculiar to the power conditioner.

This application has been made to solve the above-mentioned problems, and an object of the present invention is to provide a relay and a power system capable of accurately detecting an accident even in a power system including a power conditioner.

The electric power system according to the first invention of the present application is
The output current of the inverter circuit that converts the DC power from the DC power supply into AC power and supplies the AC power to the transmission line, and the output current of the inverter circuit when the voltage on the output side of the inverter circuit meets predetermined conditions. A power conditioner having a control circuit constructed to enable current limit control to suppress or stop the inverter.
A relay that detects the occurrence of an accident on the transmission line based on whether or not the current limit control is executed, and
To be equipped.

The relay according to the second invention of the present application is
The first input section for receiving a signal indicating the control content of the power conditioner, and
A second input unit for receiving signals according to the magnitude of the voltage of the transmission line,
When a specific signal indicating that the power conditioner has executed a predetermined current limit control is received from the first input unit and the voltage of the transmission line becomes equal to or lower than the predetermined voltage, the transmission line of the transmission line Judgment unit that detects the occurrence of an accident and
To be equipped.

According to the power system or the relay, whether or not the current limit control of the power conditioner is performed can be included in the accident detection condition. As a result, even if the electrical physical quantity on the transmission line is affected by the control of the power conditioner, the occurrence of an accident can be accurately detected.

It is a circuit diagram which shows the electric power system and a relay which concerns on Embodiment 1. FIG. It is a circuit diagram which shows the power conditioner of the electric power system which concerns on Embodiment 1. FIG. It is a graph for demonstrating the operation of the power conditioner which concerns on Embodiment 1. FIG. It is a graph for demonstrating the operation of the relay which concerns on Embodiment 1. FIG. It is a graph for demonstrating the operation of the relay which concerns on Embodiment 1. FIG. It is a circuit diagram which shows the electric power system and a relay which concerns on the modification of Embodiment 1. It is a circuit diagram which shows the electric power system and a relay which concerns on the modification of Embodiment 1. It is a circuit diagram which shows the electric power system and a relay which concerns on Embodiment 2. FIG.

FIG. 1 is a circuit diagram showing a power system 1 and a relay 73 according to the first embodiment. The electric power system 1 transmits electric power via the grid interconnection power generation unit 2, the first bus 6 that receives the power generated by the grid interconnection power generation unit 2, the transmission network 7 connected to the first bus 6, and the transmission network 7. It includes a second bus 9 for receiving and a load 8 connected to the second bus 9.

The grid interconnection power generation unit 2 includes a rotary generator 4, a first circuit breaker 5, a solar cell array 3, and a power conditioner system 12 which is a power conversion device. The "power conditioner system" is also abbreviated as "PCS".

The rotary generator 4 is connected to the first bus 6 via the first circuit breaker 5. The rotary generator 4 supplies electric power to the transmission line 70 through the first bus 6. The rotary generator 4 is a rotary generator mounted on a fossil energy generator or a nuclear power generator. The rotary generator 4 operates in grid interconnection together with a photovoltaic power generation system composed of a solar cell array 3 and a PCS 12.

As shown in FIG. 2, the PCS 12 includes an inverter circuit 22 and a power conversion control device 40. The PCS 12 is a power conversion device that converts DC power into AC power. The inverter circuit 22 converts the DC power from the solar cell array 3 into AC power. The AC power output from the inverter circuit 22 is supplied to the transmission line 70 via the first bus 6. The power conversion control device 40 controls the operation of the inverter circuit 22, and specifically controls the switching of the switching elements included in the inverter circuit 22. The power conversion control device 40 is constructed so that "current limit control" can be executed separately from the steady control. The "current limit control" according to the first embodiment suppresses or stops the output current of the inverter circuit when the voltage on the output side of the inverter circuit meets a predetermined condition. The detailed structure of the PCS 12 will be described later with reference to FIG.

The electric power system 1 includes an instrument transformer 69, a second circuit breaker 71, a relay 73, and an instrument transformer 75. The power grid 7 includes a power transmission line 70. One end of the transmission line 70 is connected to the first bus line 6, and the other end of the power transmission line 70 is connected to the second bus line 9. An instrument transformer 69 and an instrument transformer 75 are provided near the connection portion between the transmission line 70 and the first bus line 6. The current I measured by the instrument transformer 69 and the voltage V measured by the instrument transformer 75 are input to the relay 73. Reference numeral 76 is a schematic representation of a situation in which a ground fault 76 has occurred on the transmission line 70.

The relay 73 is a distance relay. The relay 73 can detect an accident on the transmission line 70 based on whether or not the impedance of the transmission line 70 meets a predetermined impedance condition. The relay 73 detects that an accident has occurred in the transmission line 70 in at least one of the cases where the impedance of the transmission line 70 meets the predetermined impedance condition and the case where the above-mentioned current limit control is executed.

In general, protective relays are usually installed in power plants or substations. Many protective relays for protecting the transmission line 70 detect accidents based on the electrical physical quantity on the transmission line 70. In such a protective relay, it is considered that an accident has occurred in the transmission line 70 when the electrical physical quantity on the transmission line 70 shows a predetermined behavior. For example, when a ground fault occurs in the transmission line 70, an excessive ground fault current should normally flow, so that the accident can be detected based on the increase in such current. An example of such a protective relay is a "distance relay". The relay 73 according to the first embodiment also has the same structure as the distance relay. The relay 73 detects whether or not an accident has occurred by monitoring the impedance of the transmission line 70. Impedance is an electrical measure that determines the distance of the transmission line 70. The relay 73 can also know the distance to the accident point based on the impedance of the transmission line 70.

The rotary generator 4, the power transmission line 70 of the power grid 7, and the PCS 12 are connected to the first bus 6. The rotary generator 4 and the PCS 12 are connected in parallel to the first bus 6, and the transmission line 70 receives the output power of these power generation facilities. The first bus 6 is the bus of the substation.

FIG. 2 is a circuit diagram showing PCS12 of the power system 1 according to the first embodiment. The PCS 12 includes an inverter circuit 22 which is a power conversion unit, an interconnection transformer 23, a capacitor 24, a DC reactor 25, a DC voltage detector 26, a DC current detector 27, an AC voltage detector 28, and an AC. It includes a current detector 29 and a power conversion control device 40.

The main circuit 21 is a circuit that supplies the electric power generated by the solar cell array 3 to the first bus 6. The main circuit 21 is provided with an inverter circuit 22, an interconnection transformer 23, a capacitor 24, and a DC reactor 25.

The inverter circuit 22 converts the DC power supplied from the solar cell array 3 into AC power synchronized with the AC power supply of the first bus 6. The inverter circuit 22 outputs the converted AC power to supply the first bus 6.

The interconnection transformer 23 is provided on the output side (AC side) of the inverter circuit 22. The interconnection transformer 23 transforms the AC voltage output from the inverter circuit 22 into a voltage for supplying the first bus 6.

The capacitor 24 and the DC reactor 25 form an AC filter. The AC filter is provided on the AC side of the interconnection transformer 23. The AC filter suppresses the harmonic current flowing out from the inverter circuit 22 to the first bus 6.

The DC voltage detector 26 is provided on the input side (DC side) of the inverter circuit 22. The DC voltage detector 26 detects the DC voltage input from the solar cell array 3. The DC voltage detector 26 outputs the detected DC voltage to the power conversion control device 40.

The DC current detector 27 is provided on the input side of the inverter circuit 22. The direct current detector 27 detects the direct current input from the solar cell array 3. The direct current detector 27 outputs the detected direct current to the power conversion control device 40.

The AC voltage detector 28 is provided on the output side (AC side) of the DC reactor 25. The AC voltage detector 28 detects the AC voltage output from the inverter circuit 22. The AC voltage detector 28 outputs the detected AC voltage to the power conversion control device 40.

The AC current detector 29 is provided on the output side of the DC reactor 25. The alternating current detector 29 detects the alternating current output from the inverter circuit 22. The AC current detector 29 outputs the detected AC current to the power conversion control device 40.

The power conversion control device 40 is a control device that controls the inverter circuit 22. The power conversion control device 40 includes a DC voltage measuring unit 41, a DC current measuring unit 42, an AC voltage measuring unit 43, an AC current measuring unit 44, a power control unit 45, and a PWM (Pulse Width Modulation) control unit 46. It has.

The DC voltage measuring unit 41 measures the DC voltage input from the solar cell array 3 by the DC voltage detected by the DC voltage detector 26. The DC voltage measuring unit 41 outputs the measured DC voltage to the power control unit 45.

The DC current measuring unit 42 measures the DC current input from the solar cell array 3 by the DC current detected by the DC current detector 27. The direct current measuring unit 42 outputs the measured direct current to the power control unit 45.

The AC voltage measuring unit 43 measures the system voltage of the first bus 6 (output voltage of the inverter circuit 22) by the AC voltage detected by the AC voltage detector 28. The AC voltage measuring unit 43 outputs the measured AC voltage to the power control unit 45.

The AC current measuring unit 44 measures the AC current output from the inverter circuit 22 by the AC current detected by the AC current detector 29. The AC current measuring unit 44 outputs the measured AC current to the power control unit 45.

The power control unit 45 measures the DC voltage measured by the DC voltage measuring unit 41, the DC current measured by the DC current measuring unit 42, the AC voltage measured by the AC voltage measuring unit 43, and the AC current measuring unit 44. Based on the generated alternating current, arithmetic processing is performed to control the amount of electricity (current, voltage, power, etc.) output from the inverter circuit 22. The power control unit 45 outputs the calculated amount of electricity to the PWM control unit 46 as an output command value for the inverter circuit 22.

The PWM control unit 46 generates a gate signal for PWM control of the inverter circuit 22 based on the output command value input from the power control unit 45. The PWM control unit 46 drives and controls the inverter circuit 22 by the generated gate signal. As a result, AC power having a desired frequency can be output from the inverter circuit 22.

The PCS 12 has a function of limiting the output current of the inverter circuit 22 according to the voltage on the output side of the inverter circuit 22. One of the current limiting functions of the PCS 12 is called FRT (Fault Ride Through). According to the FRT, even if the voltage on the load 8 side, that is, the voltage on the output side of the PCS 12 drops, the PCS 12 controls the current so that the output current continues to flow while being throttled for a certain period of time. Another of the current limiting functions of the PCS 12 is a function in which the PCS 12 shuts down the output current when the voltage on the output side of the PCS 12 becomes equal to or lower than a predetermined voltage. The predetermined voltage may be set to, for example, about 20% of the steady-state voltage of the transmission line 70. The PCS 12 is constructed to transmit the current control flag signal UCC to the relay 73 in response to the execution of the current limit control. As a result, the information of the current control performed by the PCS 12 can be transmitted to the relay 73.

FIG. 3 is a graph for explaining the operation of the PCS 12 according to the first embodiment. FIG. 3 is an example of the verification waveform of the FRT function, and shows the verification waveform by the mini model. In the region of the section 100 ms indicated by the arrow Q0, the magnitude of the AC voltage output by the PCS 12 suddenly and extremely decreases. When such a voltage drop occurs, the FRT operates. The portion of the PCS output current waveform indicated by the arrow Q1 indicates that the current output from the PCS 12 is continued by the FRT. The portion of the DC voltage input to the PCS 12 indicated by the arrow Q2 indicates that the DC voltage is increasing due to the decrease in the output power indicated by the arrow Q0. The DC voltage rise applied to the arrow Q2 is due to the characteristics of the solar cell.

The relay 73 receives the control information from the PCS 12 and detects the accident of the transmission line 70 based on whether or not the current limit control is executed. The relay 73 includes a plurality of input units, a determination logic circuit 74 that outputs a trip command signal Str2, an impedance determination unit 77, and a fail-safe relay unit 78. In FIG. 1, for convenience, the impedance determination unit is also referred to as a “Z determination unit”, and the fail-safe relay unit is referred to as an “FS relay unit”. The plurality of input units included in the relay 73 include the current value input unit that acquires the current value signal I measured by the instrument transformer 69 and the magnitude of the voltage of the transmission line 70 measured by the instrument transformer 75. The voltage value input unit for receiving the voltage value signal V according to the above, the communication input unit for receiving the current control flag signal UCC by communicating with the PCS 12, and the trip indicating the trip state of the first breaker 5. Includes a trip state input unit for acquiring the state signal Str1. The determination logic circuit 74 includes a plurality of signals input to the current value input unit, the voltage value input unit, the communication input unit, and the trip state input unit, the impedance flag signal UZ output by the impedance determination unit 77, and a fail-safe relay. The trip command signal Str2 is output to the second breaker 71 based on the fail-safe flag signal UFS output by unit 78.

The specific internal circuit structure of the relay 73 can be based on various known distance relays. In the first embodiment, the relay 73 includes a determination logic circuit 74. The determination logic circuit 74 includes a first AND gate 74a, a OR gate 74b, and a second AND gate 74c. The determination logic circuit 74 is constructed so as to perform the following first calculation step to third calculation step. As the first calculation step, the first AND gate 74a outputs the logical product of the current control flag signal UCC and the trip state signal Str1. Let the output of the first AND gate 74a be the output signal U0. The impedance flag signal UZ is determined by the impedance determination unit 77 executing the operation of FIG. 3 described later. As the second calculation step, the OR gate 74b outputs the OR of the impedance flag signal UZ and the output signal U0 of the first AND gate 74a. The OR output of the OR gate 74b is the flag signal U1. As the third operation step, the second logical product gate 74c outputs the logical product of the flag signal U1 and the fail-safe flag signal UFS.

When the PCS 12 executes the current limit control, the current control flag signal UCC is given to the relay 73 from the PCS 12. Since the relay 73 incorporates the contents of the current control flag signal UCC into the first to third calculation steps described above, the control information of the PCS 12 can be used as information for detecting an accident on the transmission line 70. it can.

Hereinafter, the operation of the relay 73 will be described with reference to FIGS. 4 to 5 in addition to FIG.

FIG. 4 is a graph for explaining the operation of the relay 73 according to the first embodiment. FIG. 4 shows a case where an accident occurs in the transmission line 70 while the rotary generator generator 4 is in operation. Hereinafter, “impedance seen by the relay” will be described with reference to FIG. However, the items to be explained individually are the contents already implemented by the known distance relay, and are not new items. Therefore, the explanation will be simplified by focusing on the necessary items. FIG. 4 shows an impedance straight line 81 of the transmission line 70, an operating range 80 of the relay 73, an offset 82 and an offset 83 of the operating range 80, and a load impedance 85 on a complex plane representing impedance. There is. The origin O of the RX Cartesian coordinates corresponds to the vicinity of the installation of the relay 73 in FIG. In FIG. 1, for convenience, the mounting position of the instrument transformer 69 on the transmission line 70 is associated with the origin O. Further, in RX Cartesian coordinates, the intersection P of the impedance straight line 81 and the operating range 80 represents the end of the protection range of the relay 73. In FIG. 1, for convenience, the connection point between the transmission line 70 and the second bus line 9 is associated with the intersection P.

The relay 73 measures the magnitude of the impedance of the transmission line 70 based on the current flowing through the transmission line 70 and the voltage of the first bus 6. In normal operation without an accident, the load impedance 85 located far from the origin O is dominant. In normal operation, the load impedance 85 exists at a considerable distance from the relay 73. On the other hand, if the impedance seen by the relay 73 is only the line impedance of the transmission line 70 due to an accident occurring in the protected section, the impedance becomes an extremely small value. The impedance seen by the relay 73 moves from a distance into the operating range 80 of the relay 73, as shown by the arrow 84 in FIG. As a result, it is detected that the transmission line 70 has an accident. By executing the above contents, the impedance determination unit 77 determines whether or not an accident has occurred in the protection section based on the fact that the impedance becomes small enough to be within the operating range 80. Accident detection based on impedance is made, and the second circuit breaker 71 is quickly tripped.

Generally, an instrument transformer 69, a relay 73, and an instrument transformer 75 are installed in a substation. The relay 73 captures the voltage value of the transmission line 70 via the voltage transformer 75, and captures the current value of the transmission line 70 via the current transformer 69 for the instrument. In FIG. 1, an instrument transformer 69 is installed between the first bus 6 and the second circuit breaker 71.

The protection of the transmission line 70 is preferably performed by a so-called OR operation that detects an accident based on the logical sum of a plurality of relays. This is to emphasize the certainty of protection. The plurality of relays include, for example, a short-circuit differential relay and a short-circuit impedance relay. For the short-circuit operation relay, for example, the 87S relay is selected for main protection. For the short-circuit impedance relay, for example, a 44S relay is selected for protection of the rear equipment. As an example, the range of about 80% of the total length of the first stage 44SX of the 44S relay or the transmission line 70 is treated as a protection range. Further, the voltage detected by the 44S relay becomes zero for an accident near the installation point of the relay 73. If the operating range 80 is set only on the positive side of the R axis and the positive side of the X axis, normal operation may not be possible when the voltage detected by the 44S relay becomes zero. Therefore, it is preferable that the offset 82 and the offset 83 are set in the operating range 80. Note that "87S" and "44S" represent the device type defined by the JIS standard or the JEM standard and the type of short circuit / ground fault, and since they belong to known technology, detailed description thereof will be omitted. In addition, the correspondence between device types and numbers is partially different between the JIS standard and the IEC standard, which is an overseas standard, and the JIS standard No. 44 corresponds to the IEC standard No. 21.

FIG. 5 is a graph for explaining the operation of the relay 73 according to the first embodiment. FIG. 5 shows a case where an accident occurs in the transmission line 70 when the rotary generator 4 is inactive and power is generated only by the solar cell array 3. When the voltage of the first bus 6 drops, the FRT operates and the PCS 12 limits the magnitude of the output current. If the PCS 12 limits the current, the relay 73 may not be able to perform accurate impedance ranging. This is because the FRT of the PCS 12 operates earlier than the impedance ranging of the relay 73 is performed. In this case, although the voltage is lowered, the impedance cannot reach the inside of the operating range 80 as shown by the arrow 86 in FIG. 5, so that the short-circuit accident determination does not work. As a result, the relay 73 erroneously measures the accident point.

If the impedance ranging function of the relay 73 is operating normally as shown in FIG. 4, there is no problem. However, as shown in FIG. 5, the impedance ranging function may be hindered. Therefore, in the first embodiment, the current output limiting state of the PCS 12 is input to the relay 73. The relay 73 takes in the current output limiting state of the PCS 12 as accident determination information, and outputs an open command, that is, a trip command to the second circuit breaker 71 of the transmission line 70 when an accident occurrence is detected. By tripping the second circuit breaker 71, it is possible to promptly take measures against the accident of the transmission line 70.

Actually, it is preferable that the relay 73 is constructed so as to detect the occurrence of an accident when a plurality of accident detection conditions are satisfied. As an example of the first accident detection condition, it is preferable that the rotary generator 4 is not operating and the FRT function of the PCS 12 is working. In addition to this first accident detection condition, it is preferable that a second accident detection condition for fail-safe is also imposed. As an example of the second accident detection condition, a condition that the occurrence of an accident may be detected when the voltage of the transmission line 70 is equal to or lower than a predetermined voltage may be added by incorporating the fail-safe relay unit in the relay 73. .. As the fail-safe relay unit, for example, a 27S undervoltage relay may be used. Note that "27S" represents the device type defined by the JIS standard or the JEM standard and the type of short circuit / ground fault, and since it is information belonging to a known technique, detailed description thereof will be omitted.

The specific operation of the determination logic circuit 74 will be described in more detail with reference to FIG. When the current control flag signal UCC becomes high according to the operation of the FRT and the trip state signal Str1 becomes high because the first circuit breaker 5 is in the cutoff state, the output signal U0 of the first AND gate 74a becomes high. Become high. When the impedance seen by the relay 73 falls within the operating range 80 as described with reference to FIG. 4, the impedance determination unit 77 sets the impedance flag signal UZ to high. When at least one of the output signal U0 and the impedance flag signal UZ becomes high, the flag signal U1 becomes high. In the first embodiment, the fail-safe flag signal UFS becomes high when the voltage of the transmission line 70 measured by the voltage transformer 75 becomes equal to or lower than a predetermined voltage. When the impedance flag signal UZ or the current control flag signal UCC becomes high and the fail-safe flag signal UFS becomes high, the first AND gate 74a sets the trip command signal Str2 as a high output. When both the current control flag signal UCC and the impedance flag signal UZ are low, the first AND gate 74a holds the trip command signal Str2 low. If the fail-safe flag signal UFS is low, the first AND gate 74a holds the trip command signal Str2 low. According to the above operation, it is possible to accurately detect that an accident has occurred in the transmission line 70, thereby accurately operating the second circuit breaker 71. According to the relay 73, whether or not the current limit control is performed can be included in the accident detection condition, so that even if the electrical physical quantity on the transmission line 70 is affected by the control of the PCS 12, it is accurate. Accident detection can be performed. A notification signal may be output to the outside of the relay 73 when the output of the trip command signal Str2 becomes high. As a result, it may be notified to the outside that an accident has been detected on the transmission line 70.

The relay 73 may be modified as follows. In the first embodiment, the relay 73 detects an accident by a logic circuit as an example, but as a modification, a determination program may be executed on a microcomputer instead of the logic circuit. Digital protective relays are widely used as protective relays for distance relays and the like. The digital protected relay includes a CPU, an analog filter, an A / D converter, a digital filter, and a memory. The function of the relay is exhibited by the CPU executing the accident detection program and the protection operation program stored in the memory. The first calculation step to the third calculation step performed by the determination logic circuit 74 may be constructed on the software.

In the electric power system 1 according to the first embodiment, when the rotary generator 4 is operated, the rotary generator 4 does not stop suddenly for a certain period of time even if an accident occurs in the transmission line 70. Continues to generate electricity. The relay 73 can perform fault point distance measurement based on impedance by utilizing the current generated by the power generation for a certain period of time. On the other hand, when the power generation by the rotary generator 4 is stopped, only the renewable energy generated power obtained through the solar cell array 3 and the PCS 12 is supplied to the transmission line 70. Also in this case, the relay 73 according to the first embodiment can perform accident detection using the current control flag signal UCC instead of the accident detection based on impedance. Therefore, according to the first embodiment, the impedance fault point distance measurement by the distance relay and the fault detection using the current control flag signal UCC can be properly used depending on the situation.

In the first embodiment, since the current limit control includes the FRT, the PCS 12 transmits the current control flag signal UCC to the relay 73 according to the execution of the FRT. The relay 73 detects an accident based on the current control flag signal UCC. On the other hand, as a modification, if the current limit control does not include the FRT and only the shutdown control is performed, the PCS 12 may transmit the current control flag signal UCC to the relay 73 in response to the execution of the shutdown control.

FIG. 6 is a circuit diagram showing a power system 1 and a relay 73 according to a modified example of the first embodiment. In FIG. 6, the storage battery 13 is connected to the PCS 12 instead of the solar cell array 3. As shown in FIG. 7, the wind power generation system 14 may be connected to the PCS 12 instead of the storage battery 13. The wind power generation system 14 includes a wind power generator 15 and a power conversion device 16. The AC power generated by the wind power generator 15 depends on the strength of the wind. Since the strength of the wind changes from moment to moment, the AC power generated by the wind power generator 15 is difficult to stabilize. Therefore, it is preferable that the power conversion device 16 converts the AC power from the wind power generator 15 into a constant DC voltage, and the PCS 12 further converts this DC voltage into a stable AC power. As another variant, two or more DC power systems may be selected from the DC power system group consisting of the solar cell array 3, the storage battery 13, and the wind power generation system 14, and the selected DC may be selected via a plurality of PCS 12. Each power supply system may be connected to the first bus 6. As a result, a plurality of DC power supply systems may be operated in parallel.

Embodiment 2.
FIG. 8 is a circuit diagram showing the power system 101 and the relay 173 according to the second embodiment. The power system 101 of the second embodiment differs from the first embodiment in the following two points. The first difference is that the rotary generator 4 is not connected to the first bus 6, and only the series circuit of the PCS 12 and the solar cell array 3 is connected to the first bus 6. The second difference is that in the second embodiment, the relay 73 is replaced with the relay 173. The relay 173 includes a determination logic circuit 174 instead of the determination logic circuit 74. Except for these points, the power system 101 of the second embodiment has the same configuration as that of the first embodiment.

The determination logic circuit 174 includes a fourth AND gate 174a. Since the impedance flag signal UZ is not used, the relay 173 does not have to take in the current using the instrument transformer 69. The fourth logical product gate 174a calculates the logical product of the current control flag signal UCC and the fail-safe flag signal UFS. As a result, the fourth AND gate 174a trips when the current control flag signal UCC becomes high in response to the operation of the FRT and the fail-safe flag signal UFS becomes high in response to the voltage drop of the transmission line 70. The command signal Str2 can be set to high. Therefore, as in the first embodiment, whether or not the current limit control is performed can be included in the accident detection condition, so that the electrical physical quantity on the transmission line 70 is affected by the control of the PCS 12. However, accurate accident detection can be performed. Since the impedance flag signal Z is not required unlike the first embodiment, the structure of the relay 173 may be made based on the internal configuration of various protective relays other than the distance relay.

The same modifications as in the first embodiment may be applied. The determination logic circuit 174 may be realized by software as in the first embodiment. The storage battery 13 or the wind power generation system 14 may be connected to the first bus 6 as shown in FIGS. 6 and 7. Two or more DC power supply systems selected from the DC power supply system group consisting of the solar cell array 3, the storage battery 13, and the wind power generation system 14 may be connected to the first bus 6.

1,101 Power system, 2 grid interconnection power generation unit, 3 solar cell array, 4 rotary generator, 5 1st breaker, 6 1st bus, 7 transmission network, 8 load, 9 2nd bus, 12 power condition System (PCS), 13 storage battery, 14 wind power generation system, 15 wind power generator, 16 power converter, 21 main circuit, 22 inverter circuit, 23 interconnection transformer, 24 capacitors, 25 direct current reactor, 26 direct current voltage detector, 27 DC current detector, 28 AC voltage detector, 29 AC current detector, 40 power conversion controller, 41 DC voltage measurement unit, 42 DC current measurement unit, 43 AC voltage measurement unit, 44 AC current measurement unit, 45 power Control unit, 46 PWM control unit, 69 instrument transformer, 70 transmission line, 71 second breaker, 73, 173 relay, 74, 174 judgment logic circuit, 74a first logic product gate, 74b logic sum gate, 74c Second logical product gate, 75 instrument transformer, 76 ground fault, 77 impedance judgment unit, 78 fail-safe AC unit, 80 operating range, 81 impedance straight line, 82, 83 offset, 85 load impedance, 173 AC relay, 174a Four logic product gate, Str1 trip state signal, Str2 trip command signal, U0 output signal, U1 flag signal, UCC current control flag signal, UFS fail-safe flag signal, UZ impedance flag signal

Claims (3)

The output current of the inverter circuit that converts the DC power from the DC power supply into AC power and supplies the AC power to the transmission line, and the output current of the inverter circuit when the voltage on the output side of the inverter circuit meets predetermined conditions. A power conditioner having a control circuit constructed to enable current limit control to suppress or stop the inverter.
A relay that detects the occurrence of an accident on the transmission line based on whether or not the current limit control is executed, and
Power system with. Further equipped with a rotary generator that supplies electric power to the transmission line,
The relay is a distance relay that detects an accident on the transmission line based on whether or not the impedance of the transmission line meets a predetermined impedance condition.
According to claim 1, the distance relay detects that an accident has occurred in the transmission line when the impedance meets the predetermined impedance condition and at least one of the cases where the current limit control is executed. The power system described. The first input section for receiving a signal indicating the control content of the power conditioner, and
A second input unit for receiving signals according to the magnitude of the voltage of the transmission line,
When a specific signal indicating that the power conditioner has executed a predetermined current limit control is received from the first input unit and the voltage of the transmission line becomes equal to or lower than the predetermined voltage, the transmission line of the transmission line Judgment unit that detects the occurrence of an accident and
A relay equipped with.

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