JP2018183034A - POWER SUPPLY SYSTEM PROTECTION DEVICE AND SYSTEM PROVIDED WITH THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protection device capable of detecting a short circuit accident in a distribution line and protecting the entire system in a power supply system using a converter, and a system including the protection device. A protection device (100) includes a harmonic supply unit (102) that supplies harmonics (integer harmonics or interharmonics) to a bus, a voltage measuring unit (104) that measures the voltage of the bus, and a power distribution line. A current measuring unit 108 that measures a current, a harmonic component calculating unit 110 that calculates a harmonic component from each of the voltage and current measurement waveforms, an impedance calculating unit 112 that calculates an impedance from the voltage and current harmonic components, And a control unit 114 that determines whether or not a short-circuit accident has occurred in the distribution line based on the calculated impedance. As a result, it is possible to detect a short-circuit accident that has occurred in the distribution line, disconnect the distribution line from the busbar, and prevent the power failure of the entire system. [Selection diagram] Figure 2

Description

  The present invention relates to a protection technique for coping with a short circuit accident in a power supply system, and in particular, a protection device for coping with a short circuit accident in a power system such as a remote island or a community using a converter (inverter) as a main power A system with

  In an electric power system (hereinafter, also referred to as an electric power supply system), voltages supplied from a generator to a bus are supplied to various electric power demand devices via a plurality of distribution lines (distribution systems) connected in parallel to one another. Ru. If an accident (short circuit accident) occurs on a specific distribution line, the entire power supply system will fail if the distribution line is not disconnected from the bus. Therefore, in the power system, it is detected that a large current (hereinafter referred to as an accident current) flows to the distribution line due to an accident, and the accident section is interrupted by the protective relay to prevent a power failure of the entire electric power system.

  Referring specifically to FIG. 1, specific description will be given regarding accident detection. In FIG. 1, an alternating voltage generated by a generator 900 which is a synchronous machine is converted into a predetermined voltage by a transformer 902 and supplied to a bus 904. Two main distribution lines, distribution lines 910 and 920, are connected to the bus 904. Distribution lines 910 and 920 provide power to loads 918 and 928 via breakers 912 and 922, respectively.

  The circuit breakers 912 and 922 are switches, and protect the equipment and equipment on the load side by switching the current of the power line and interrupting the accident current (especially short circuit accident current) in cooperation with the protection relay, Prevent the spread of accidents upstream.

  A current transformer 914 and an overcurrent protection relay 916 are disposed in the distribution line 910, and a current transformer 924 and an overcurrent protection relay 926 are provided in the distribution line 920. The current value flowing through the distribution line 910 is measured by the current transformer 914 and input to the overcurrent protection relay 916. Similarly, the current value flowing through the distribution line 920 is measured by the current transformer 924 and input to the overcurrent protection relay 926.

  Current transformers 914 and 924 are instrument transformers that transform the primary current into a secondary current proportional thereto. The over-current protection relays 916 and 926 transmit a signal to operate the circuit breaker when the fault current is detected.

  In the distribution line 910, when a short circuit accident 930 occurs, an accident current 932 larger than the normal current flows through the distribution line 910. The fault current 932 is detected by the current transformer 914, and the overcurrent protection relay 916 outputs a shutoff signal to the circuit breaker 912. The breaker 912 to which the interrupting signal is input disconnects the power distribution line 910 so as not to be energized. As a result, the distribution line 910 in which the short circuit accident has occurred can be disconnected from the bus 904, and a power failure of the entire power supply system can be prevented.

  In remote islands and the like, a diesel generator (synchronous machine) uniquely configures an electric power system (hereinafter also referred to as a micro grid). Also in this case, as described above, the overcurrent protection relays are provided on the respective distribution lines to detect an accident and prevent a power failure of the entire micro grid.

  On the other hand, techniques using inter-order harmonics in a power supply system are known. For example, in Patent Document 1 below, a plurality of inter-order harmonics of different orders are injected into a power supply system in which a plurality of distribution systems are connected to a bus bar, and the power demand situation at the customers of each distribution system is estimated Methods are disclosed. This method calculates the admittance of interharmonics for each distribution system, calculates inductive susceptance that does not include capacitive susceptance by solving simultaneous equations, and estimates the power demand situation at each customer based on it. .

  In addition, in the power supply system in which distributed power sources such as solar power generation and wind power generation are connected to the power system in Patent Document 2 below, in order to prevent isolated operation due to reverse charging at the time of system power loss, A technique for detecting islanding using harmonics is disclosed.

JP, 2012-228089, A JP, 2017-5859, A

  The fuel cost is a burden in the diesel generator used in the micro grid, and as a countermeasure for the fuel cost, the micro grid is provided with a distributed power supply, and the stored electricity is supplied via a converter (inverter) Is being considered. In order to protect the power supply system by the converter, it is conceivable to use the over-current protection relay used in the power system by the synchronous machine as it is.

  However, the power supply by the converter has a problem that it can not operate the protection relay because it does not have sufficient capability to supply an accident current in its specification. The current supply capacity is as small as 1.1 to 1.5 pu (self-capacitance base) in the converter, whereas the synchronous machine normally has 5 to 6 pu (self-capacitance base). In the converter power supply system, in order to use the over-current protection relay, it is necessary to change the specifications thereof to increase the current supply capability of the converter, resulting in an increase in cost.

  Therefore, in the power supply system using the converter, the present invention can protect the entire power supply system by detecting an accident (short circuit accident) in the distribution system without changing the converter specifications. It aims at providing an apparatus and a system provided with the same.

  A protection device according to a first aspect of the present invention is a protection device of a power supply system. The protection device includes a harmonic supply unit for supplying a harmonic having a frequency higher than a predetermined frequency to a bus to which an AC voltage of a predetermined frequency is supplied, and a current for measuring a current value of a distribution line connected to the bus. A current component extraction unit that extracts a current component, which is a Fourier coefficient of a harmonic, from a measurement unit, a voltage measurement unit that measures a voltage value of a bus or a distribution line, and a time variation waveform of the current value measured by the current measurement unit And a voltage component extraction unit for extracting a voltage component that is a Fourier coefficient of a harmonic from a time variation waveform of voltage values measured by the voltage measurement unit, a current component and a voltage component extraction unit extracted by the current component extraction unit Calculation unit that calculates impedance or admittance as a calculated value from the voltage component extracted by the control unit, and a determination unit that determines whether a short circuit accident has occurred in the distribution line based on the calculated value Including.

  Thereby, it can be detected that a short circuit accident has occurred on the distribution line. Therefore, it is possible to take appropriate measures such as disconnecting the distribution line where the short circuit accident has occurred from the bus bar.

  Preferably, the protection device further includes an output unit that outputs a shutoff signal to the shutoff unit that shuts off the connection between the distribution line and the bus in response to the judgment that the shorting accident has occurred by the judgment unit.

  Thereby, when a short circuit accident occurs on the distribution line, the distribution line can be immediately separated from the bus bar, and a power failure of the entire power supply system can be prevented.

  More preferably, the harmonics are supplied as a current of constant amplitude.

  Thereby, the influence of the voltage (constant voltage) of the bus can be suppressed by the harmonics supplied to the bus.

  More preferably, the harmonics supplied to the bus bar by the harmonics supply unit are interorder harmonics having frequencies that are non-integer multiples of the predetermined frequency.

  Thus, voltage components and current components of inter-order harmonics supplied to the bus can be extracted easily and accurately without being affected by attenuation due to interference with existing signals.

  Preferably, the harmonics supplied to the bus by the harmonic supply unit are harmonics having a frequency twice or four times the predetermined frequency.

  As a result, the voltage component and the current component of the harmonics supplied to the bus can be extracted easily and accurately without being affected by attenuation due to interference with the existing signal.

  A system according to a second aspect of the present invention includes the above-described protection device, and a conversion unit that converts a DC voltage supplied from a DC power supply into an AC voltage and supplies the AC voltage to a bus.

  Thereby, in the existing power supply system using the converter, it is possible to detect that a short circuit accident has occurred on the distribution line without changing the converter specification. Therefore, it is possible to take appropriate measures such as disconnecting the distribution line where the short circuit accident has occurred from the bus bar.

  Preferably, the function by the harmonic supply unit is realized by the conversion unit. The converter superimposes a harmonic on the AC voltage converted from the DC voltage.

  As described above, when the conversion unit converts a voltage from direct current to alternating current, by superimposing the harmonic on the alternating voltage, a device for supplying the harmonic becomes unnecessary, and the cost can be reduced.

  According to the present invention, it is possible to detect that a short circuit accident has occurred on a distribution line. Therefore, appropriate measures can be taken such as quickly disconnecting the distribution line in which the short circuit accident has occurred from the bus bar, etc. to prevent a power failure of the entire power supply system.

  In addition, since the occurrence of a short circuit accident can be detected without depending on the magnitude of the accident current, the short circuit accident can be detected even in a power supply system using a converter having a low capability of supplying the accident current. it can. That is, a short circuit fault can be detected in the power supply system using the existing converter without providing the converter with the fault current supply capability as in the generator of the synchronous machine. Therefore, the increase in cost can be suppressed.

  In addition, since the injection of harmonics can be realized by software integration into the control of the converter, the increase in cost can be suppressed.

FIG. 1 is a block diagram illustrating a conventional protection technique used in a power supply system. It is a block diagram showing composition of a protection device concerning an embodiment of the invention. It is a block diagram which shows an example of a power supply system containing the protection apparatus of FIG. It is a flowchart which shows operation | movement of the protection apparatus in the electric power supply system of FIG. FIG. 5 is a block diagram illustrating another example of a power supply system including the protection device of FIG. 2; It is a block diagram showing composition of a simulation system of the 1st example. It is a graph which shows the simulation result of 1st Example. It is a block diagram which shows the structure of the simulation system of 2nd Example. It is a graph which shows the simulation result (electric power supply from a generator) of 2nd Example. It is a graph which shows the simulation result (power supply from inverter power supply) of 2nd Example. It is a graph which shows the simulation result (The electric power and the 4th harmonic are supplied from an inverter power supply) of 2nd Example. It is a graph which shows the simulation result (The power and 2.5th-order harmonics are supplied from an inverter power supply) of 2nd Example.

  In the following embodiments, the same parts are given the same reference numerals. Their names and functions are also identical. Therefore, detailed description about them will not be repeated.

(Configuration of protection device)
Referring to FIG. 2, protection device 100 according to the embodiment of the present invention includes harmonic generation unit 102 and relay unit 106. The relay unit 106 includes a harmonic component calculation unit 110, an impedance calculation unit 112, and a control unit 114. The protection device 100 also includes a power supply (not shown) for operating each part. FIG. 2 shows the minimum configuration, and the protection device 100 may include a plurality of relay units 106 as described later.

  The harmonic generation unit 102 generates a signal S0 having a constant frequency higher than the basic frequency (for example, 50 Hz or 60 Hz) of the power (voltage) output from the power supply supplying power to the bus, thereby Supply to the bus of The harmonic generation unit 102 superimposes the harmonic S0 on the voltage supplied from the power supply to the bus.

  The frequency of the signal S0 can be classified into a frequency that is an integral multiple of the fundamental frequency and a frequency that is a non-integer multiple. Among these, the signal of the frequency of integral multiples of the fundamental frequency is a so-called harmonic. A signal at a frequency that is a non-integer multiple of the fundamental frequency is a signal between harmonics of an integer multiple, and is thus called an inter-order harmonic, and the order is represented by a positive non-integer. In the present specification, a signal at a frequency that is an integral multiple of the fundamental frequency is referred to as "integer harmonic" because the term interharmonic is used, and the interharmonic and the integer harmonic are combined. It shall be described as "harmonic". Therefore, signal S0 is also described as harmonic S0.

  The voltage measurement unit 104 measures the voltage of the bus. The voltage measurement unit 104 is, for example, a known instrument transformer. The current measurement unit 108 measures the current of the distribution line connected to the bus. The current measuring unit 108 is, for example, a known instrument current transformer. Instrument transformers and instrument current transformers convert the voltage and current of high voltage circuits into voltages and currents that are easy to handle with instruments, relays, and the like. The measured voltage value and current value are input to the harmonic component calculation unit 110.

  The harmonic component calculation unit 110 samples, at predetermined time intervals, voltage values and current values that are analog signals input from the voltage measurement unit 104 and the current measurement unit 108, and acquires digital voltage data and current data. And temporarily store data for a predetermined time in an internal buffer or the like. The harmonic component calculation unit 110 calculates a component of a predetermined frequency included in time series data (hereinafter also referred to as waveform data) of the stored voltage and current. The frequency for which the component is to be calculated is the frequency of the harmonic S0 supplied by the harmonic generation unit 102. A known Fourier transform may be used to calculate the predetermined frequency component.

  Note that for integer harmonics, the fundamental frequency of power can be used as the fundamental frequency of the Fourier transform, but for interharmonics whose order is non-integer, a frequency different from the fundamental frequency of power can be used It is necessary to use. Specifically, as will be described later, the fundamental frequency of the Fourier transform is determined so that the order (non-integer) of the inter-order harmonics becomes an integer.

  The harmonic component calculation unit 110 outputs a calculated value to the impedance calculation unit 112 each time it calculates frequency components of predetermined harmonics (hereinafter referred to as harmonic components) included in each of the voltage and the current.

  The impedance calculating unit 112 calculates an impedance from input data each time two pieces of data (a harmonic component of a voltage and a current) are input, and outputs a calculated value to the control unit 114. The impedance calculation unit 112 divides the harmonic component of the voltage by the harmonic component of the current to calculate the impedance.

  The control unit 114 includes a CPU (Central Processing Unit) and a storage unit. The control unit 114 stores the input impedance in the storage unit, observes the change, and determines that a short circuit accident has occurred if the impedance becomes equal to or less than a predetermined threshold value, and outputs the cutoff signal S3. . These functions are realized by the CPU reading and executing a program stored in advance in the storage unit. The shutoff signal S3 is input to a breaker provided in the distribution system in which the current measurement unit 108 is disposed, and the breaker operates.

  As described above, the harmonic component to be calculated by the harmonic component calculation unit 110 is the harmonic S0 supplied by the harmonic generation unit 102. Therefore, the harmonic component calculation unit 110 needs information on the target harmonic. In FIG. 2, the information S1 indicating the frequency or the order of the harmonic S0 output from the harmonic generation unit 102 is input from the harmonic generation unit 102 to the control unit 114, and the control unit 114 corresponds to the information S1. The information S2 is output to the harmonic component calculator 110. The information S2 may be the same information as the information S1 or may be different information. For example, if the information S1 is information representing the order of harmonics, the information S2 may be the fundamental frequency and the frequency of the harmonics calculated from the information S1. In addition, the control unit 114 may acquire information on harmonics supplied by the harmonic generation unit 102 from other than the harmonic generation unit 102. For example, the control unit 114 may include an interface for inputting a numerical value, and may receive an input of the order or frequency of a harmonic to be detected through the interface.

  The harmonic component calculation unit 110 and the impedance calculation unit 112 may each be configured as a dedicated semiconductor device such as an ASIC or the like, or may be configured by a general-purpose CPU and a storage unit as in the control unit 114. When the harmonic component calculating unit 110 and the impedance calculating unit 112 are realized by a general purpose CPU, their functions are executed by a predetermined program.

(System including protective device)
With reference to FIG. 3, the form which applies the protection apparatus 100 to an electric power supply system is demonstrated. Here, the protection device 100 includes two relay units corresponding to the relay unit 106 in FIG.

  The power supply system includes a generator 200 which is a synchronous machine, a distributed power supply (shown by a dashed dotted line) composed of a secondary battery 212 and a converter 210, and a switch 214. By the switching operation of the switch 214, the generator 200 or the converter 210 is connected to the transformer 202. The alternating voltage output from the generator 200 or the converter 210 is converted to a predetermined voltage by the transformer 202 and supplied to the bus 204. The bus 204 is connected to a first distribution line 220 and a second distribution line 230 which are two distribution systems. The first distribution line 220 and the second distribution line 230 supply power to the first load 228 and the second load 238 via the first breaker 222 and the second breaker 232, respectively.

  The converter 210 provides the function of the harmonic generation unit 102 of FIG. 2 in addition to the normal AC power. The converter 210 is a known inverter that converts direct current power (voltage), which is the output of the secondary battery 212, into alternating current. For example, the converter 210 internally includes a control device such as a microcontroller, executes a known control program (for example, PWM control), and performs AC power of a predetermined frequency (for example, 50 Hz or 60 Hz) Say). Therefore, by changing the control program of the inverter, the converter 210 can generate a harmonic signal having a predetermined amplitude and a predetermined frequency, superimpose it on the basic power, and output it.

  Since the basic power supplied by the converter 210 is usually supplied in the voltage source mode (constant voltage), it is preferable that the harmonics be supplied in the current source mode (constant current).

  The first distribution line 220 is provided with a first current transformer 224 and a first harmonic relay 226, and the second distribution line 230 is provided with a second current transformer 234 and a second harmonic relay 236. It is done. The current value flowing through the first distribution line 220 is measured by the first current transformer 224 and input to the first harmonic relay 226. Similarly, the current value flowing through the second distribution line 230 is measured by the second current transformer 234 and input to the second harmonic relay 236.

  The first current transformer 224 and the second current transformer 234 correspond to the current measurement unit 108 of FIG. 2, and the first harmonic relay 226 and the second harmonic relay 236 are respectively the relay unit 106 of FIG. 2. Corresponds to The currents measured by the first current transformer 224 and the second current transformer 234 include the harmonic current supplied from the converter 210.

  The instrument transformer 206 measures the voltage of the bus 204 and outputs the measured value to the first harmonic relay 226 and the second harmonic relay 236. The instrument transformer 206 corresponds to the voltage measurement unit 104 in FIG.

  The first harmonic relay 226 calculates harmonic components included in the current (waveform data) input from the first current transformer 224 and the voltage (waveform data) input from the instrument transformer 206. Calculate the impedance from them. The first harmonic relay 226 observes the change in the calculated impedance. When the short circuit accident 240 occurs and the accident current 242 flows, the impedance is lowered, so that the first harmonic relay 226 can detect the short circuit accident.

  When the first harmonic relay 226 detects a short circuit fault, it outputs a shutoff signal to the first breaker 222. The first circuit breaker 222 disconnects the first distribution line 220 from the bus 204 in response to the shutoff signal.

  The second harmonic relay 236 and the second breaker 232 operate in the same manner as the first harmonic relay 226 and the first breaker 222, respectively.

  Although two distribution lines are shown in FIG. 3, three or more distribution lines may be connected to the bus 204. Each distribution line is provided with a breaker and a harmonic relay.

(Short-circuit accident detection processing)
A process of detecting a short circuit fault in the power supply system shown in FIG. 3 will be described below with reference to FIG. The program of FIG. 4 is executed by each of the first harmonic relay 226 and the second harmonic relay 236. As described above, each of the first harmonic relay 226 and the second harmonic relay 236 corresponds to the control unit 114 of FIG. 2 and includes a CPU and a storage unit inside. Therefore, the processes executed by the first harmonic relay 226 and the second harmonic relay 236 mean processes executed independently by the CPUs included therein. Here, the process performed by the first harmonic relay 226 will be described.

  In step 300, the first harmonic relay 226 generates digital data from the voltage and current (analog) input from the instrument transformer 206 and the first current transformer 224, and generates time-series data (waveform data). Remember as.

  In step 302, the first harmonic relay 226 calculates the frequency component (harmonic component) of the harmonic supplied from the converter 210 from each of the voltage and current of the time series data stored in step 300. . The processes of steps 300 and 302 correspond to the function of the harmonic component calculation unit 110 of FIG. 2 described above.

  In step 304, the first harmonic relay 226 divides the harmonic component of the voltage calculated in step 302 by the harmonic component of the current to calculate the impedance.

  At step 306, the first harmonic relay 226 compares the impedance calculated at step 304 with a predetermined threshold. If it is determined that the impedance is less than or equal to the threshold, control transfers to step 308. Otherwise, control passes to step 310.

  In step 308, the first harmonic relay 226 determines that a short circuit accident has occurred in the monitored first distribution line 220, and outputs a shutoff signal to the first breaker 222. Thereby, the first circuit breaker 222 operates to disconnect the first distribution line 220 from the bus 204.

  In step 310, the first harmonic relay 226 determines whether an instruction to end the execution of the program has been received. The termination instruction is made, for example, by turning off the power of the first harmonic relay 226. If it is determined that the end instruction has been received, the first harmonic relay 226 ends the program. Otherwise, control returns to step 300 to repeat the process described above.

  As described above, when the first harmonic relay 226 detects a short circuit accident 240 in the first distribution line 220, the first harmonic relay 226 detects it and disconnects the first distribution line 220 from the bus 204, and the entire power supply system loses power. Can be prevented.

  The second harmonic relay 236 also executes the program of FIG. The second harmonic relay 236 detects a short circuit accident in the second distribution line 230, detects it, disconnects the second distribution line 230 from the bus 204, and prevents a power failure of the entire power supply system. can do.

  The first harmonic relay 226 can detect the occurrence of a short circuit fault independently of the magnitude of the fault current 242 flowing to the first distribution line 220 due to the short circuit fault. Similarly, the second harmonic relay 236 can detect the occurrence of a short circuit accident independently of the magnitude of the accident current flowing to the second distribution line 230 due to the short circuit accident. Therefore, although the distributed power supply using the existing converter has a lower ability to supply an accident current than the synchronous machine's power supply, it can still detect a short circuit accident.

  The order of the harmonics 216 can be any positive integer or non-integer. Since the power equipment includes reactance components (inductor and capacitance), the voltage can be measured to some extent by supplying a signal having a frequency higher than a specific frequency. Therefore, the voltage component and current component of the harmonic S0 supplied to the bus can be extracted, and the occurrence of a short circuit accident can be detected.

  Since inter-order harmonics are usually scarcely present in the power system, it is possible to easily and accurately detect a short circuit accident by setting the above-mentioned harmonic S0 supplied to the bus as inter-order harmonics. it can. For example, it is possible to use one between the second to third orders, that is, one in which the order n is 2 <n <3.

  Further, the harmonics S0 are not limited to the inter-order harmonics, and may be integer-order harmonics. Normally, in a power system, harmonics of odd-numbered multiples of the fundamental frequency (odd-order harmonics) exist with a non-negligible magnitude, but harmonics of even-multiples of the fundamental frequency (even-order) Harmonics) is small (amplitude is small). Therefore, if even-order harmonics are used, the voltage component and current component of harmonic S0 supplied to the bus can be extracted without being affected by attenuation due to interference with a signal already present in the bus. And can detect the occurrence of a short circuit accident. For example, fourth or second harmonics can be used.

  According to each power system, the threshold can be clearly distinguished from the impedance in the state where the short circuit accident does not occur and the normal power is supplied, and it is set to an appropriate value smaller than that. Well, it's optional. That is, the threshold of the first harmonic relay 226 and the threshold of the second harmonic relay 236 may not necessarily be the same value. The threshold may be configured to be changeable.

  Although the case where the converter 210 has the function of the harmonic generation unit 102 has been described above, the present invention is not limited to this. For example, as shown in FIG. 5, the harmonic generation unit may be realized as a harmonic supply device 218 which is a dedicated device.

  FIG. 5 differs from FIG. 3 only in that the converter 210 does not have the function of supplying harmonics, and the harmonics 216 are supplied to the bus 204 by the harmonic supply device 218. Therefore, repeated description will not be repeated. The harmonic supply device 218 is realized by, for example, an inverter. Also in the power supply system of FIG. 5, when a short circuit accident occurs in the first distribution line 220 and the second distribution line 230 which are targets of monitoring by the first harmonic relay 226 and the second harmonic relay 236. Can be detected to activate the corresponding first breaker 222 and second breaker 232.

  Although the case where the voltage value measured by instrument transformer 206 was used was described above, it is not limited to this. The voltage of each distribution line may be measured, the harmonic component included in the voltage value may be calculated, and the impedance may be calculated using it.

  Although the case of calculating the impedance has been described above, the present invention is not limited to this. It is a physical quantity obtained from harmonic signal components of voltage and current, and may be changed as a result of a short circuit accident. For example, the short circuit fault may be detected by comparing the admittance calculated from the voltage and current harmonic signal components with a predetermined threshold.

  Although it is sufficient to supply one order of harmonics to detect a short circuit fault, since the harmonics are used for various purposes, in the same power supply system, the harmonics are used for purposes other than short circuit fault detection. It is conceivable to use Therefore, it is preferable to be able to set the order or frequency of the harmonics used to detect a short circuit accident to any value. For example, one of the plurality of harmonic candidates may be selected.

  Also, the function of measuring the voltage and current of the harmonics and calculating the impedance may be incorporated in the existing protective relay of the distribution site (substation).

  In addition, the above-mentioned harmonic relay for detecting a short circuit fault may be added to the existing trip sequence. For example, in an existing trip sequence consisting of series connected relays and trip coils, harmonic relays can be connected in parallel to existing relays to detect short circuit faults.

  The supplied power of the power system may be either two-phase power or three-phase power.

  Although the case where a harmonic relay is applied in the electric power supply system by the distributed power supply using a converter (inverter) was explained above, it is not limited to this. In a power supply system using a synchronous generator, a harmonic relay can be applied instead of the protection relay.

  Below, the simulation result regarding an interorder harmonic is shown, and the effectiveness of this invention is shown. In order to simulate the operation in the system of FIG. 3, each component was arranged as shown in FIG. 6 using known software tools (open source Scilab (registered trademark) and X cos).

  The AC power supply 400 outputs an AC voltage having an effective value of 100 V and a fundamental frequency of 50 Hz. The output voltage of AC power supply 400 is output via resistor R1. The resistance R1 was 3 Ω.

  The inter-order harmonics generation unit 402 outputs an inter-order harmonic current having an amplitude of 0.1 A and a 2.5th order (frequency of 125 Hz). The output (current) of the inter-harmonic generator 402 is supplied to the output line of the AC power supply 400. The voltage output from AC power supply 400 is supplied to two paths (hereinafter referred to as a feeder). The feeder to which the resistor R2 is connected and through which the current I1 flows is referred to as a "first feeder", and the feeder to which the resistor R3 is connected and through which the current I2 flows is referred to as a "second feeder". Here, the resistances R2 and R3 are both 100 Ω.

  The voltmeter 404 measures a voltage output from the AC power supply 400 via the resistor R1 and outputs a measured value. The voltage signal Vs output from the voltmeter 404 is input to the first inter-harmonic component extraction unit 408. An ammeter 406 is connected to each feeder, and measures and outputs the current (I1, I2) flowing through each feeder. The current signals (I1 and I2) output from the ammeter 406 are input to the second inter-order harmonic component extraction unit 410 corresponding to each.

  The first inter-order harmonic component extraction unit 408 extracts a predetermined inter-order harmonic component from the voltage signal Vs. The first inter-order harmonic component extraction unit 408 includes a cosine signal generation unit 412, two multiplication units 414, two time integration units 416, two delay units 418, two subtraction units 420, two amplification units 422, A complex number generation unit 424, an amplitude generation unit 426, a sine signal generation unit 430, and an amplification unit 432 are included. The cosine signal generation unit 412 generates a cosine wave of the frequency of the predetermined interharmonic. The sine signal generation unit 430 generates a sine wave having the same frequency as the cosine wave generated by the cosine signal generation unit 412. Here, as described above, the 2.5th-order interharmonics (frequency 125 Hz) are used.

  The blocks from the multiplication unit 414 to the amplification unit 422 are for calculating Fourier coefficients. The multiplication unit 414 multiplies two input values and outputs the result. The time integration unit 416 integrates the input from the start time to the current time as a function of time. For example, the time integration unit 416 stores an accumulated value (initial value is, for example, “0”), adds the multiplication result of the input value and Δt (sampling interval of input) to the present accumulated value, and The result is overwritten and output as a new cumulative value. The delay unit 418 holds the input value for a predetermined delay time from the input time, and outputs the held value after the delay time has elapsed. The subtraction unit 420 subtracts the input value at the negative (-) input end from the input value at the positive (+) input end, and outputs the result. The amplification unit 422 amplifies the input value and outputs the result.

Here, 25 Hz is adopted as the fundamental frequency of the Fourier transform, and the period of 25 Hz is T, and in order to calculate the Fourier coefficient, the delay time of the delay unit 418 is set to T, and the amplification factor of the amplifier 422 is 2 / It was set to T. Thus, from the amplifier 422, the Fourier coefficient is expressed by the following equation a _{n (numerical} integration value) is outputted.

  Vs (t) explicitly indicates that the voltage signal Vs changes with time. τ represents an arbitrary time. Since the time integration unit 416 outputs the time integration of the input, the value output from the subtraction unit 420 at time τ is the value of the output of the multiplication unit 414 in a period (t = τ−T to τ) corresponding to the delay time T. It is an integral value.

The reason why 25 Hz is adopted as the fundamental frequency used for calculating the Fourier coefficient is because harmonics between orders are considered. Arbitrary function F (t) can be expanded by orthogonal function system cos (nω ₀ t), sin (nω ₀ t) (n is an integer greater than or equal to 0) where ω ₀ is a fundamental frequency (angular frequency) . When the target for calculating the component is an interharmonic, the order is non-integer, and 50 Hz can not be used as it is as the fundamental frequency used for calculating the Fourier coefficient. Therefore, the fundamental frequency used to calculate the Fourier coefficient is 25 Hz so that the order is an integer. The 2.5th-order frequency component (125 Hz) of the fundamental frequency 50 Hz corresponds to the fifth-order component (n = 5 in the above equation) of the fundamental frequency 25 Hz.

The complex number generation unit 424 generates and outputs a complex number in which the input value at the upper input end is a real part and the input value at the lower input end is an imaginary part. The amplitude generation unit 426 calculates and outputs the amplitude (absolute value) of the input complex number. That is, the amplitude C in the case of expressing the complex number a + jb as Ce ^jθ = C (cos θ + j sin θ) is obtained by C = (a ² + b ² ) ^1/2 . The amplification unit 432 amplifies the input value and outputs the result. The amplification factor of the amplification unit 432 was set to 1/100.

When the voltage signal Vs is input to the amplifier 432, the real part and the imaginary part (Fourier coefficient) of the predetermined interharmonic component are output from the amplifier 422. By using the cosine wave generated by the cosine signal generation unit 412 (the upper path of the first inter-order harmonic component extraction unit 408), the real part is calculated. The imaginary part is calculated by using the sine wave generated by the sine signal generation unit 430 (the lower path of the first inter-order harmonic component extraction unit 408). Then, the complex number generation unit 424 and the amplitude generation unit 426 output the amplitude (voltage) of the predetermined interharmonic component. The output value from the amplification unit 422 disposed in the lower path of the first inter-order harmonic component extraction unit 408 is a Fourier coefficient b _n (numerical integration value) represented by the following equation.

  The second inter-order harmonic component extraction unit 410 is for extracting a predetermined inter-order harmonic component from the current signal (I1 or I2), and is similar to the first inter-order harmonic component extraction unit 408. Is configured. The second inter-order harmonic component extraction unit 410 is different from the first inter-order harmonic component extraction unit 408 only in that the amplification unit 432 is replaced by the amplification unit 434. The amplification factor of the amplification unit 434 was set to 1/10.

  When the current signal I1 of the first feeder is input to the corresponding amplification unit 434, the real part and imaginary part of the predetermined interharmonic component are output from the amplification unit 422 in the same manner as described above, and the complex number generation unit The amplitude generation unit 426 outputs the amplitude of the inter-order harmonic component of the current I1. Similarly, when the current signal I2 of the second feeder is input to the corresponding amplification unit 434, the amplitude of the inter-order harmonic component of the current I2 is output from the corresponding amplitude generation unit 426.

  The division unit 436 outputs a value obtained by dividing the input value to the upper input end (indicated by “x”) by the input value to the lower input end (indicated by “÷”). The division unit 436 receives an inter-order harmonic component of the voltage Vs at the upper input end and an inter-order harmonic component of the current I1 of the first feeder at the lower input end. Output I1). Similarly, the division unit 436 into which the inter-order harmonic component of the voltage Vs is input to the upper input terminal and the inter-order harmonic component of the current I2 of the second feeder is input to the lower input terminal has an impedance Z2 ( = Vs / I2) is output.

  One end of the switch 450 is connected to the first feeder, and the other end is grounded via the resistor R4. The resistance R4 was set to 1 Ω. By turning on the switch 450 (short circuit), a short circuit fault can be generated in the first feeder.

  The signal monitor unit 452 outputs an input value as a waveform in time series. In FIG. 6, a voltage Vs in which an inter-order harmonic is superimposed on an output voltage of AC power supply 400, a current I1 of the first feeder, a current I2 of the second feeder, and an inter-order harmonic component of the first feeder Each waveform of the impedance Z1 and the impedance Z2 of the inter-order harmonic component of the second feeder is set to be output.

  In the state where each waveform is output by the signal monitoring unit 452, the switch 450 is turned on at a predetermined timing to cause a short circuit accident in the first feeder. The results are shown in FIG.

  In the five graphs of FIG. 7, the horizontal axis represents a common time (seconds). At time t = 0.5 (seconds), a short circuit accident occurred in the first feeder. As a result, Vs decreases at the time (t = 0.5) at which the short circuit accident occurred, and the current I1 increases (occurrence of the accident current) for the first feeder in which the short circuit accident occurs, impedance Z1 Rapidly decreased to about 0 Ω. No change was seen in the current value I2 and the impedance Z2 of the second feeder before and after the time when the short circuit accident occurred.

  The impedance Z1 decreases rapidly when a short circuit accident occurs and is 0Ω, and detects a short circuit accident in a time shorter than the operation time (50 ms or less) of a normal overcurrent protection relay, and outputs a shutoff signal to the circuit breaker it can.

  Therefore, it is possible to detect that a short circuit accident has occurred by monitoring the impedance of the inter-order harmonic component of each feeder. That is, if the value of the impedance sharply decreases to approximately 0 Ω, it can be understood that a short circuit accident has occurred in the feeder.

  In addition, in FIG. 7, although the value of impedance Z1 and Z2 is 1/10 of an actual value, it does not affect detection of a short circuit accident. This is because the amplification factors of the voltage signal Vs and the current signals I1 and I2 to be subjected to the Fourier transform are different (the amplification factor of the amplification part 434 is 1/100 while the amplification factor of the amplification part 434 is Is 1/10).

  The following is a simulation result performed for integer harmonics and interharmonics. In order to confirm the operation in the system of FIG. 3, the components are defined as will be described later using known software tools (MATLAB (registered trademark) and Simulink (registered trademark)) manufactured by Mathworks, Inc., as shown in FIG. The simulation was performed by arranging as shown.

  The generator (synchronous machine) 500 outputs three-phase AC voltage 210 V (frequency 50 Hz, power 200 kW). Breaker 502 is a switch for turning on / off the output of the generator 500. Xg 508 represents the initial transient reactance of the generator 500 and is j0.14 pu (self-capacitance base). The reactance of the synchronous machine depends on the passage of time after startup and is represented by an initial transient reactance, a transient reactance, a synchronous reactance, and the like. In the simulation, since the output of the generator 500 at the time of a short circuit accident is observed, only the initial transient reactance is considered.

  Similar to the generator 500, the inverter power supply 510 outputs three-phase AC voltage 210 V (frequency 50 Hz, power 200 kW). However, the upper limit value of the current that can be supplied by the inverter power supply 510 at the time of a short circuit accident is 1.5 times the rating, and the current supply capability at the time of a short circuit accident is limited. Furthermore, the inverter power supply 510 can output current (1 A) of integer harmonics (frequency 200 Hz) or inter-order harmonics (frequency 125 Hz). The frequency 200 Hz is the fourth harmonic (integer harmonic) with the frequency 50 Hz of the AC voltage as the basic frequency, and the frequency 125 Hz is the harmonic of the 2.5 harmonic (interharmonics).

  Breaker 512 is a switch for turning on (passing) / off (breaking) the output of inverter power supply 510. The Xi 518 is an interconnection reactor for connecting the output of the inverter power supply 510 to the distribution line of the output of the generator 500 and interconnecting the inverter power supply 510 with the generator 500, with j0.1 pu (self capacity base) did.

  The outputs of the generator 500 and the inverter power supply 510 are supplied to the R loads 504 and 514 which are resistive loads via distribution lines connected in parallel. The R loads 504 and 514 are both 100 kW and 1.0 pu (self capacity basis). The waveforms (three-phase voltage, three-phase current) on the respective distribution lines can be observed by Scope (A) 506 and Scope (B) 516.

  The Breaker 522 is controlled ON / OFF by an external control line 520. The outputs of the generator 500 and the inverter power supply 510 are input to one of three terminals of the Breaker 522, and the other three terminals are mutually connected. Therefore, when Breaker 522 is turned ON, it can be simulated that a short circuit accident has occurred in the three-phase distribution line.

  In the configuration of FIG. 8, the generator 500 and the inverter power supply 510 are operated, and the Breaker 502 and Breaker 512 are turned ON / OFF (the power is supplied to the R loads 504 and 514). FIGS. 9 to 12 show results of observation (simulation) of changes in voltage and current with Scope (A) 506 and Scope (B) 516 by inputting a pulse signal 524 having a width of 0.1 second. In each of the graphs of FIG. 9 and FIG. 10, all three-phase waveforms that are 120 degrees out of phase with each other are displayed. The center 0.1 seconds of each graph is a period in which a short circuit accident has occurred. In FIG. 9 to FIG. 12, the upper graph (A) corresponds to the observation result of Scope (A) 506, and the lower graph (B) corresponds to the observation result of Scope (B) 516.

  FIG. 9 shows the result when Breaker 502 is turned ON and Breaker 512 is turned OFF. At the time of a short circuit accident, almost no current flows through the distribution line where no short circuit accident has occurred, and a large current flows through the distribution line where the short circuit accident has occurred. Therefore, it is understood that the short circuit current can be cut off by the overcurrent relay with respect to the distributed power supply (generator) having a large current supply capacity at the time of the short circuit accident.

  FIG. 10 shows the result when Breaker 502 is turned OFF and Breaker 512 is turned ON. However, harmonics were not supplied from the inverter power supply 510. Although a larger current flows through the distribution line in which the short circuit accident has occurred than the distribution line in which the short circuit accident has not occurred, it is much smaller than the current in the upper stage of FIG. 9 (during the power supply from the generator 500). Therefore, with respect to the distributed power supply (inverter power supply) having a small current supply capacity at the time of a short circuit accident, it is understood that the overcurrent relay does not operate at the time of the short circuit and the short circuit current can not be cut off.

  11 and 12 show the results when Breaker 502 is turned off and Breaker 512 is turned on, as in FIG. Unlike FIG. 10, harmonics were output from the inverter power supply 510. That is, FIG. 11 shows the result in the case where the inverter power supply 510 outputs the integral harmonics (frequency 200 Hz), and FIG. 12 shows the result in the case where the inverter power supply 510 outputs the inter-order harmonics (frequency 125 Hz). In the graphs of FIGS. 11 and 12, the supplied harmonic components are calculated by Fourier transform from the voltage waveform and current waveform respectively observed by Scope (A) 506 and Scope (B) 516, and the impedance of each of the distribution lines is calculated. Is the result of calculating

  From FIG. 11 and FIG. 12, the impedance of the distribution line is about 0 when the short circuit accident does not occur, either when supplying the integral harmonic (frequency 200 Hz) or when supplying the inter-harmonic (frequency 125 Hz). In the case of a short circuit accident, the impedance of the distribution line where the short circuit accident occurred is approximately 0 (Ω). Therefore, by supplying harmonics and determining the magnitude of the impedance of the harmonic component, a distribution line in which a short circuit accident has occurred is detected even for a distributed power supply (inverter power supply) having a low current supply capacity at the time of a short circuit accident. It can be understood that the distribution line can be cut off according to the detection result.

  Although the present invention has been described above by describing the embodiment, the above-described embodiment is an exemplification, and the present invention is not limited to the above-described embodiment. The scope of the present invention is defined by each claim of the claims in consideration of the description of the detailed description of the invention, and all the changes within the meaning and range equivalent to the words and phrases described therein Including.

100 protection device 102 harmonic generation unit 104 voltage measurement unit 106 relay unit 108 current measurement unit 110 harmonic component calculation unit 112 impedance calculation unit 114 control unit 200, 900 generator 202, 902 transformer 204, 904 bus 206, 906 for instruments Transformer 210 Transformer 212 Secondary battery 214 Switch 216 Harmonic 218 Harmonic feeder 220 First distribution line 222 First breaker 224 First current transformer 226 First harmonic relay 228 First load 230 Second distribution Electric wire 232 Second circuit breaker 234 Second current transformer 236 Second harmonic relay 238 Second load 240, 930 Short circuit accident 242, 932 Accident current 400 AC power supply 402 Interharmonic generation unit 404 Voltmeter 406 Ammeter 408 First inter-order harmonic component extraction unit 410 Second inter-order harmonic component extraction unit 12 cosine signal generation unit 414 multiplication unit 416 time integration unit 418 delay unit 420 subtraction unit 422, 432, 434 amplification unit 424 complex number generation unit 426 amplitude generation unit 430 sine signal generation unit 436 division unit 450 switch 452 signal monitor unit 500 generator 502, 512, 522 Breaker
504, 514 R load 506 Scope (A)
508 Xg
510 Inverter power supply 516 Scope (B)
518 Xi
520 control line 524 pulse signal 910, 920 distribution line 912, 922 breaker 914, 924 current transformer 916, 926 overcurrent protection relay 918, 928 load

Claims (6)

A protection device of the power supply system,
Harmonic supply means for supplying a harmonic having a frequency higher than the predetermined frequency to a bus to which an AC voltage of the predetermined frequency is supplied;
Current measurement means for measuring the current value of the distribution line connected to the bus;
Voltage measuring means for measuring a voltage value of the bus or the distribution line;
Current component extraction means for extracting a current component which is a Fourier coefficient of the harmonic from the time variation waveform of the current value measured by the current measurement means;
Voltage component extraction means for extracting a voltage component which is a Fourier coefficient of the harmonic from the time variation waveform of the voltage value measured by the voltage measurement means;
Calculation means for calculating impedance or admittance as a calculation value from the current component extracted by the current component extraction means and the voltage component extracted by the voltage component extraction means;
And a judging means for judging whether or not a short circuit accident has occurred in the distribution line based on the calculated value.   According to the determination that the short circuit accident has occurred by the determination means, the cutoff means for disconnecting the connection between the distribution line and the bus bar further includes an output means for outputting a cutoff signal. The protection device according to claim 1.   The protection device according to claim 1, wherein the harmonic is supplied as a current having a constant amplitude.   The said harmonics supplied to the said bus-line by the said harmonics supply means are the interharmonics which have the frequency of the non-integer multiple of the said predetermined frequency, It is characterized by the above-mentioned. Protection device according to. The protection device according to any one of claims 1 to 4.
And D. conversion means for converting a DC voltage supplied from a DC power supply into an AC voltage and supplying the AC voltage to the bus bar. The harmonic supply means is realized by the conversion means,
The system according to claim 5, wherein the conversion means superimposes the harmonics on the alternating voltage converted from the direct current voltage.

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