JP7006237B2 - A system with a protective device for the power supply system - Google Patents

Description

The present invention relates to a protection technique for dealing with a short-circuit accident in a power supply system, and in particular, a protection device for dealing 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 source and the like. Regarding the system equipped with.

In the power system (hereinafter, also referred to as a power supply system), the voltage supplied from the generator to the bus is supplied to various power demand devices via a plurality of distribution lines (distribution systems) connected in parallel to each other. To. When an accident (short circuit accident) occurs in a specific distribution line, the entire power supply system will be cut off unless the distribution line is cut off from the bus. Therefore, in the power system, it is detected that a large current (hereinafter referred to as an accident current) has flowed through the distribution line due to an accident, and the accident section is cut off by a protection relay to prevent a power failure of the entire power system.

The accident detection will be specifically shown with reference to FIG. In FIG. 1, the AC voltage generated by the generator 900, which is a synchronous machine, is converted into a predetermined voltage by the transformer 902 and supplied to the bus 904. Two distribution lines, distribution lines 910 and 920, are connected to the bus 904. The distribution lines 910 and 920 supply power to the loads 918 and 928 via the circuit breakers 912 and 922, respectively.

The circuit breakers 912 and 922 are switches that open and close the current of the power line and protect the equipment and facilities on the load side by cutting off the accident current (particularly the short circuit accident current) in cooperation with the protection relay. Prevent the spread of accidents to the upstream side.

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

The current transformers 914 and 924 are instrument transformers that transform the primary current into a secondary current proportional to the primary current. If the overcurrent protection relays 916 and 926 detect the fault current, they transmit a signal to operate the circuit breaker.

When a short-circuit accident 930 occurs in the distribution line 910, an accident current 932 larger than the normal current flows in the distribution line 910. The fault current 932 is detected by the current transformer 914, and the overcurrent protection relay 916 outputs a cutoff signal to the circuit breaker 912. The circuit breaker 912 to which the cutoff signal is input cuts off the 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 separated from the bus 904, and it is possible to prevent the entire power supply system from being cut off.

In remote islands, etc., a diesel generator (synchronous machine) is used to independently configure an electric power system (hereinafter, also referred to as a microgrid). Also in this case, as described above, an overcurrent protection relay is provided on each distribution line to detect an accident and prevent a power failure of the entire microgrid.

On the other hand, a technique of using interorder harmonics in a power supply system is known. For example, in Patent Document 1 below, a power supply system in which a plurality of distribution systems are connected to a bus is injected with harmonics of different orders, and the power demand status of each distribution system is estimated by the consumer. How to do it is disclosed. This method calculates the admittance of interorder harmonics for each distribution system, calculates the inductive susceptance that does not include capacitive susceptance by solving simultaneous equations, and estimates the power demand situation at each consumer based on it. ..

Further, in Patent Document 2 below, in a power supply system in which a distributed power source such as solar power generation or wind power generation is connected to a power system, in order to prevent independent operation due to reverse charging when the system power supply is lost, the order A technique for detecting isolated operation using harmonics is disclosed.

Japanese Unexamined Patent Publication No. 2012-228089 Japanese Unexamined Patent Publication No. 2017-5859

Fuel costs are a burden for diesel generators used in microgrids, and as a measure against fuel costs, a distributed power source is installed in the microgrid to supply stored electricity via a converter (inverter). Is being considered. To protect the power supply system by the converter, it is conceivable to use the overcurrent protection relay used in the power system by the synchronous machine as it is.

However, the power supply by the converter does not have a sufficient capacity to supply the accident current due to its specifications, so that there is a problem that the protection relay cannot be operated. The current supply capacity is usually 5 to 6 pu (self-capacity base) in the synchronous machine, while it is as small as 1.1 to 1.5 pu (self-capacity base) in the converter. In order to use an overcurrent protection relay in a power supply system using a converter, it is necessary to change the specifications to increase the current supply capacity of the converter, which causes a problem of high cost.

Therefore, the present invention can detect an accident (short circuit accident) in the distribution system and protect the entire power supply system in a power supply system using a converter without changing the specifications of the converter. It is an object of the present invention to provide a device and a system equipped with the device.

The protective device according to the first aspect of the present invention is a protective device for a power supply system. This protection device is a harmonic supply unit that supplies harmonics having a frequency higher than the predetermined frequency to the bus to which the AC voltage of the predetermined frequency is supplied, and a current that measures the current value of the distribution line connected to the bus. A current component extraction unit that extracts the current component, which is the Fourier coefficient of the harmonic, from the measurement unit, the voltage measurement unit that measures the voltage value of the bus or distribution line, and the time-varying waveform of the current value measured by the current measurement unit. And the voltage component extraction unit that extracts the voltage component that is the Fourier coefficient of the harmonic from the time fluctuation waveform of the voltage value measured by the voltage measurement unit, and the current component and voltage component extraction unit that extracts the current component extraction unit. It includes a calculation unit that calculates impedance or admittance as a calculated value from the voltage component extracted by the above method, and a determination unit that determines whether or not a short-circuit accident has occurred in the distribution line based on the calculated value.

This makes it possible to detect 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 in which the short-circuit accident has occurred from the bus.

Preferably, the protective device further includes an output unit that outputs a cutoff signal in the cutoff unit that cuts off the connection between the distribution line and the bus in response to the determination that the short circuit accident has occurred by the determination unit.

As a result, when a short-circuit accident occurs on the distribution line, the distribution line can be quickly disconnected from the bus, and the entire power supply system can be prevented from power failure.

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

As a result, it is possible to prevent the voltage (constant voltage) of the bus from being affected by the harmonics supplied to the bus.

More preferably, the harmonic supplied to the bus by the harmonic supply unit is an interorder harmonic having a frequency that is a non-integer multiple of a predetermined frequency.

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

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

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

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

This makes it possible to detect that a short-circuit accident has occurred on a distribution line in an existing power supply system using a converter without changing the specifications of the converter. Therefore, it is possible to take appropriate measures such as disconnecting the distribution line in which the short-circuit accident has occurred from the bus.

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

As described above, when the conversion unit converts the voltage from direct current to alternating current, the harmonics are superimposed on the alternating current voltage, so that a device for supplying the harmonics 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, it is possible to prevent the entire power supply system from being cut off by taking appropriate measures such as promptly disconnecting the distribution line in which the short-circuit accident has occurred from the bus.

In addition, since the occurrence of a short-circuit accident can be detected independently of the magnitude of the fault current, it is possible to detect a short-circuit accident even in a power supply system using a converter with a low fault current supply capacity. can. That is, a short-circuit accident can be detected in a power supply system using an existing converter without causing the converter to have an accident current supply capacity unlike a generator of a synchronous machine. Therefore, the increase in cost can be suppressed.

Further, since the injection of harmonics can be realized by incorporating it into the control of the converter by software, it is possible to suppress an increase in cost.

It is a block diagram which shows the conventional protection technique used in a power supply system. It is a block diagram which shows the structure of the protection device which concerns on embodiment of this invention. It is a block diagram which shows an example of the power supply system including the protection device of FIG. It is a flowchart which shows the operation of the protection device in the power supply system of FIG. FIG. 2 is a block diagram showing another example of a power supply system including the protection device of FIG. It is a block diagram which shows the structure of the simulation system of 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 (power supply from a generator) of the 2nd Example. It is a graph which shows the simulation result (power supply from an inverter power source) of the 2nd Example. It is a graph which shows the simulation result of the 2nd Example (the power and the 4th harmonic are supplied from the inverter power supply). It is a graph which shows the simulation result of the 2nd Example (power is supplied from an inverter power source, and the harmonics of 2.5th order are supplied).

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

(Configuration of protective device)
With reference to FIG. 2, the protection device 100 according to the embodiment of the present invention includes a harmonic generation unit 102 and a 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 protective device 100 also includes a power source and the like (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 generator 102 generates a signal S0 having a constant frequency higher than the fundamental frequency (for example, 50 Hz or 60 Hz) of the power (voltage) output by the power supply supplying power to the bus, and generates a power system. Supply to the bus. 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. Of these, a signal having a frequency that is an integral multiple of the fundamental frequency is a so-called harmonic. A signal with a frequency that is a non-integer multiple of the fundamental frequency is called an interorder harmonic because it is a signal between harmonics that are an integral multiple, and its order is represented by a positive non-integer. In the present specification, in relation to the use of the term interorder harmonic, a signal having a frequency that is an integral multiple of the fundamental frequency is referred to as an "integer harmonic", and the interorder harmonic and the integer harmonic are combined. It shall be described as "harmonic". Therefore, the signal S0 is also referred to as a harmonic S0.

The voltage measuring unit 104 measures the voltage of the bus. The voltage measuring unit 104 is, for example, a known instrument transformer. The current measuring unit 108 measures the current of the distribution line connected to the bus. The current measuring unit 108 is, for example, a known instrument transformer. The voltage transformer and the instrument transformer convert the voltage and current of the high voltage circuit into a voltage and current that can be easily handled by the instrument, a relay, or the like. The measured voltage value and current value are input to the harmonic component calculation unit 110.

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

For integer harmonics, the fundamental frequency of power can be used as the fundamental frequency of the Fourier transform, but for interorder harmonics whose order is non-integer, a frequency different from the fundamental frequency of power is used. Need 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 interorder harmonic is an integer.

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

The impedance calculation unit 112 calculates the impedance from the input data each time two data (voltage and current harmonic components) are input, and outputs the calculated value to the control unit 114. The impedance calculation unit 112 calculates the impedance by dividing the harmonic component of the voltage by the harmonic component of the current.

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 if the impedance becomes equal to or less than a predetermined threshold value, determines that a short circuit accident has occurred and outputs a cutoff signal S3. .. These functions are realized by the CPU reading and executing a program stored in advance in the storage unit. The cutoff signal S3 is input to a circuit breaker provided in the distribution system in which the current measuring unit 108 is arranged, and the circuit 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 representing the frequency or 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 calculation unit 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 the harmonics, the information S2 may be the fundamental frequency and the frequency of the harmonics calculated from the information S1. Further, the control unit 114 may acquire information on the harmonics supplied by the harmonic generation unit 102 from other than the harmonic generation unit 102. For example, the control unit 114 may be provided with an interface for inputting a numerical value, and may receive an input of the order or frequency of the harmonic to be detected via 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 may be configured by a general-purpose CPU and a storage unit as in the control unit 114. When the harmonic component calculation unit 110 and the impedance calculation unit 112 are realized by a general-purpose CPU, their functions are executed by a predetermined program.

(System including protective device)
A mode of applying the protection device 100 to the power supply system will be described with reference to FIG. Here, it is assumed that 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 source (indicated by an alternate long and short dash line) composed of a secondary battery 212 and a converter 210, and a switch 214. The generator 200 or the converter 210 is connected to the transformer 202 by the switching operation of the switch 214. The AC voltage output from the generator 200 or the converter 210 is converted into a predetermined voltage by the transformer 202 and supplied to the bus 204. The first distribution line 220 and the second distribution line 230, which are two distribution systems, are connected to the bus 204. The first distribution line 220 and the second distribution line 230 supply electric power to the first load 228 and the second load 238 via the first circuit breaker 222 and the second circuit 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 DC power (voltage), which is the output of the secondary battery 212, into alternating current. The converter 210 is provided with a control device such as a microcontroller inside, executes a known control program (for example, PWM control), and has AC power (hereinafter, also referred to as reference power) of a predetermined frequency (for example, 50 Hz or 60 Hz). ) Is generated. 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 are 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. Has been 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 measuring unit 108 in FIG. 2, and the first harmonic relay 226 and the second harmonic relay 236 correspond to the relay unit 106 in FIG. 2, respectively. Corresponds to. The current measured by the first current transformer 224 and the second current transformer 234 includes the current of the harmonics 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 voltage transformer 206 corresponds to the voltage measuring unit 104 of FIG.

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

When the first harmonic relay 226 detects a short circuit accident, the first harmonic relay 226 outputs a cutoff signal to the first circuit breaker 222. The first circuit breaker 222 receives the cutoff signal and disconnects the first distribution line 220 from the bus 204.

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

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

(Short circuit accident detection process)
Hereinafter, the process of detecting a short circuit accident in the power supply system shown in FIG. 3 will be described 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 processing executed by the first harmonic relay 226 and the second harmonic relay 236 means the processing independently executed by the CPUs included in each. Here, it will be described as a process executed by the first harmonic relay 226.

In step 300, the first harmonic relay 226 generates digital data from the voltage and current (analog) input from the voltage transformer 206 and the first current transformer 224, and 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 processing of steps 300 and 302 corresponds to the function of the harmonic component calculation unit 110 of FIG. 2 described above.

In step 304, the first harmonic relay 226 calculates the impedance by dividing the harmonic component of the voltage calculated in step 302 by the harmonic component of the current.

In step 306, the first harmonic relay 226 compares the impedance calculated in step 304 with a predetermined threshold. If it is determined that the impedance is below the threshold, control proceeds to step 308. Otherwise, control shifts to step 310.

In step 308, the first harmonic relay 226 determines that a short-circuit accident has occurred in the first distribution line 220 to be monitored, and outputs a cutoff signal to the first circuit breaker 222. As a result, 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 or not it has been instructed to end the execution of this program. The end instruction is given, 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 terminates this program. If not, control returns to step 300 and repeats the above process.

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

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 and disconnects the second distribution line 230 from the bus 204 to prevent the entire power supply system from being cut off. can do.

The first harmonic relay 226 can detect the occurrence of a short-circuit accident without depending on the magnitude of the accident current 242 flowing through the first distribution line 220 due to the short-circuit accident. Similarly, the second harmonic relay 236 can detect the occurrence of a short-circuit accident regardless of the magnitude of the accident current flowing through the second distribution line 230 due to the short-circuit accident. Therefore, the distributed power supply using the existing converter has a lower capacity to supply the fault current than the power supply of the synchronous machine, but even in that case, the short circuit fault can be detected.

The order of harmonics 216 can be any positive integer or non-integer. Since the power equipment contains reactance components (inductor and capacitance), the voltage can be measured with a certain magnitude by supplying a signal having a frequency higher than a specific frequency. Therefore, the voltage component and the 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 the interorder harmonics are usually rarely present in the power system, the short circuit accident can be detected easily and accurately by using the harmonic S0 supplied to the bus as the interorder harmonic. can. For example, the one between the second order and the third order, that is, the one having the order n of 2 <n <3 can be used.

Further, the harmonic S0 is not limited to the inter-degree harmonic, and may be an integer-order harmonic. Normally, in a power system, harmonics with frequencies that are odd multiples of the fundamental frequency (odd-order harmonics) exist in a non-negligible magnitude, but harmonics with frequencies that are even multiples of the fundamental frequency (even-order harmonics). Harmonics) are few (small amplitude). Therefore, if even-order harmonics are used, the voltage component and current component of the harmonic S0 supplied to the bus are extracted without being affected by interference with signals already existing on the bus and attenuation. It is possible to detect the occurrence of a short circuit accident. For example, 4th or 2nd harmonics can be used.

The threshold value can be clearly distinguished from the impedance in the state where no short-circuit accident has occurred and normal power is supplied according to each power system, and if it is set to an appropriate value smaller than that. Well, it's optional. That is, the threshold value of the first harmonic relay 226 and the threshold value of the second harmonic relay 236 do not necessarily have to be the same value. The threshold value may be configured to be changeable.

In the above, the case where the converter 210 has the function of the harmonic generation unit 102 has been described, but 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 a function of supplying harmonics, and the harmonics 216 are supplied to the bus 204 by the harmonic supply device 218. Therefore, the duplicate explanation is not 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 the monitoring targets, by the first harmonic relay 226 and the second harmonic relay 236, respectively. In addition, it can be detected to activate the corresponding first circuit breaker 222 and second circuit breaker 232.

In the above, the case where the voltage value measured by the instrument transformer 206 is used has been described, but the present invention is not limited thereto. 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 the harmonic component.

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

Harmonics of one order may be supplied to detect short-circuit accidents, but since harmonics are used for various purposes, harmonics are used for different purposes in the same power supply system than for short-circuit accident detection. Is conceivable to use. Therefore, it is preferable that the order or frequency of the harmonics used for detecting the short circuit accident can be set to an arbitrary value. For example, the configuration may be such that one can be selected from a plurality of harmonic candidates.

Further, the functions of measuring the voltage and current of harmonics and calculating the impedance may be built in the existing protection relay of the distribution station (substation).

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

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

In the above, the case where the harmonic relay is applied in the power supply system by the distributed power source using the converter (inverter) has been described, but the present invention is not limited to this. Harmonic relays can also be applied in place of protection relays in power supply systems that use synchronous generators.

The simulation results regarding the interorder harmonics are shown below, and the effectiveness of the present invention is shown. In order to simulate the operation in the system of FIG. 3, known software tools (open source Scilab® and Xcos) were used to arrange each component as shown in FIG.

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 the AC power supply 400 is output via the resistor R1. The resistance R1 was set to 3Ω.

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

The voltmeter 404 measures the voltage output via the resistor R1 by the AC power supply 400, and outputs the measured value. The voltage signal Vs output from the voltmeter 404 is input to the first interorder harmonic component extraction unit 408. The 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 corresponding second-order harmonic component extraction unit 410.

The first interorder harmonic component extraction unit 408 extracts a predetermined interorder harmonic component from the voltage signal Vs. The first-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, and two amplification units 422. It is composed of a complex number generation unit 424, an amplitude generation unit 426, a sine signal generation unit 430, and an amplification unit 432. The cosine signal generation unit 412 generates a cosine wave having a frequency of a predetermined interorder harmonic. 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, a 2.5th-order interorder harmonic (frequency 125 Hz) was used.

The blocks from the multiplication unit 414 to the amplification unit 422 are for calculating the Fourier coefficient. The multiplication unit 414 multiplies the 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 a cumulative value (initial value is, for example, “0”), adds the multiplication result of the input value and Δt (input sampling interval) to the current cumulative value, and adds the multiplication result to the current cumulative value. The result is overwritten as a new cumulative value and output. 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, the delay time of the delay unit 418 is set to T, and the amplification factor of the amplification unit 422 is set to 2 / in order to calculate the Fourier coefficient with the period of 25 Hz as T. It was set to T. As a result, the _Fourier coefficient an (numerical integration value) represented by the following equation is output from the amplification unit 422.

Vs (t) clearly 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 output of the multiplication unit 414 during the period (t = τ−T to τ) corresponding to the delay time T. It is an integrated value.

The reason why 25 Hz is adopted as the fundamental frequency used for calculating the Fourier coefficient is that the harmonics between orders are targeted. Any function F (t) can be expanded by orthogonal function systems cos (nω ₀ t) and sin (nω ₀ t) (n is an integer of 0 or more) with ω ₀ as the basic frequency (angular frequency). .. When the object for which the component is calculated is an interorder harmonic, the order is a non-integer, and 50 Hz cannot be used as it is as the fundamental frequency used for calculating the Fourier coefficient. Therefore, the fundamental frequency used for calculating the Fourier coefficient was set to 25 Hz so that the order is an integer. The 2.5th-order frequency component (125Hz) having a fundamental frequency of 50Hz corresponds to the 5th-order component (n = 5 in the above equation) having a fundamental frequency of 25Hz.

The complex number generation unit 424 generates and outputs a complex number having the input value at the upper input end as the real part and the input value at the lower input end as the imaginary part. The amplitude generation unit 426 calculates and outputs the amplitude (absolute value) of the input complex number. That is, the amplitude C when the complex number a + jb is expressed as Ce ^jθ = C (cosθ + jsinθ) 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 amplification unit 432, the real number part and the imaginary number part (Fourier coefficient) of the predetermined interorder harmonic component are output from the amplification unit 422. By using the cosine wave generated by the cosine signal generation unit 412 (the upper path of the first interorder harmonic component extraction unit 408), the real number part is calculated. By using the sine wave generated by the sine signal generation unit 430 (the lower path of the first interorder harmonic component extraction unit 408), the imaginary part is calculated. Then, the complex number generation unit 424 and the amplitude generation unit 426 output the amplitude (voltage) of the predetermined interorder harmonic component. The output value from the amplification unit 422 arranged in the lower path of the first interorder harmonic component extraction unit 408 is the Fourier coefficient b _n (numerical integration value) expressed by the following equation.

The second interorder harmonic component extraction unit 410 is for extracting a predetermined interorder harmonic component from the current signal (I1 or I2), and is the same as the first interorder harmonic component extraction unit 408. It is configured in. The second-order harmonic component extraction unit 410 differs from the first-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 and imaginary parts of the predetermined interorder harmonic components are output from the amplification unit 422 and the complex number generation unit is output in the same manner as described above. The amplitude of the interorder harmonic component of the current I1 is output by the 424 and the amplitude generation unit 426. Similarly, when the current signal I2 of the second feeder is input to the corresponding amplification unit 434, the corresponding amplitude generation unit 426 outputs the amplitude of the interorder harmonic component of the current I2.

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 dividing unit 436, in which the interorder harmonic component of the voltage Vs is input to the upper input end and the interorder harmonic component of the current I1 of the first feeder is input to the lower input end, is the impedance Z1 (= Vs / I1) is output. Similarly, the division unit 436 in which the interorder harmonic component of the voltage Vs is input to the upper input end and the interorder harmonic component of the current I2 of the second feeder is input to the lower input end is the 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 resistor R4 was set to 1Ω. By turning on (short-circuiting) the switch 450, a short-circuit accident can occur in the first feeder.

The signal monitor unit 452 outputs the input value as a waveform in time series. In FIG. 6, the voltage Vs in which the interorder harmonics are superimposed on the output voltage of the AC power supply 400, the current I1 of the first feeder, the current I2 of the second feeder, and the interorder harmonic components of the first feeder are shown. It is set to output each waveform of the impedance Z1 and the impedance Z2 of the interorder harmonic component of the second feeder.

While each waveform was being output by the signal monitor unit 452, the switch 450 was 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 (second). At time t = 0.5 (seconds), a short-circuit accident occurred in the first feeder. As a result, at the time when the short-circuit accident occurred (t = 0.5), Vs decreased, the current I1 increased (generation of the accident current) with respect to the first feeder in which the short-circuit accident occurred, and the impedance Z1. Rapidly decreased to approximately 0Ω. No change was observed in the current value I2 and the impedance Z2 of the second feeder before and after the time when the short circuit accident occurred.

Impedance Z1 quickly decreases to 0Ω when a short-circuit accident occurs, detects a short-circuit accident in a time shorter than the operating time of a normal overcurrent protection relay (50 ms or less), and outputs a cutoff signal to the circuit breaker. can.

Therefore, it is possible to detect that a shunt accident has occurred by monitoring the impedance of the interorder harmonic component of each feeder. That is, when the impedance value suddenly decreases to about 0Ω, it is understood that a short-circuit accident has occurred in the feeder.

In FIG. 7, the values of impedances Z1 and Z2 are 1/10 of the actual values, but they do not affect the detection of short-circuit accidents. This is because the amplification factors of the voltage signals Vs and the current signals I1 and I2, which are the targets of the Fourier transform, are different (the amplification factor of the amplification unit 432 is 1/100, whereas the amplification factor of the amplification unit 434 is different. Is 1/10).

The following shows the results of simulations performed for integer harmonics and interorder harmonics. In order to confirm the operation in the system of FIG. 3, a known software tool (MATLAB (registered trademark) and Simulink (registered trademark)) manufactured by MathWorks was used to define a component as described later, and FIG. 8 shows. The simulation was performed by arranging them as shown.

The generator (synchronizer) 500 is supposed to output a three-phase AC voltage of 210 V (frequency 50 Hz, power 200 kW). The Breaker 502 is a switch for turning on / off (cutting off) the output of the generator 500. Xg508 represents the initial transient reactance of the generator 500 and was set to j0.14pu (self-capacity basis). The reactance of the synchronous machine depends on the passage of time after startup, and is represented by the initial transient reactance, the transient reactance, the synchronous reactance, and the like. In the simulation, since the output of the generator 500 at the time of the short circuit accident is observed, only the initial transient reactance is considered.

Like the generator 500, the inverter power supply 510 is supposed to output a three-phase AC voltage of 210 V (frequency 50 Hz, power 200 kW). However, the upper limit of the current that can be supplied by the inverter power supply 510 in the event of a short circuit accident is 1.5 times the rating, and the current supply capacity in the event of a short circuit accident is limited. Further, the inverter power supply 510 can output a current (1 A) of an integer harmonic (frequency 200 Hz) or an interorder harmonic (frequency 125 Hz). With the AC voltage frequency of 50 Hz as the fundamental frequency, the frequency of 200 Hz is a fourth-order harmonic (integer-order harmonic), and the frequency of 125 Hz is a 2.5-th-order harmonic (inter-order harmonic).

The Breaker 512 is a switch for turning on / off (cutting off) the output of the inverter power supply 510. The Xi518 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 to connect the inverter power supply 510 to the generator 500, and has j0.1pu (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 resistance loads, via the distribution lines connected in parallel. The R loads 504 and 514 are both 100 kW and 1.0 pu (self-capacity basis). Waveforms (three-phase voltage, three-phase current) on each distribution line can be observed by Scoppe (A) 506 and Scoppe (B) 516.

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

With the configuration of FIG. 8, the generator 500 and the inverter power supply 510 are operated, and the Breaker 502 and the Breaker 512 are turned ON / OFF (power is supplied to the R loads 504 and 514), and the pulse is applied to the control line 520 of the Breaker 522. 9 to 12 show the results of observing (simulating) changes in voltage and current with Scopé (A) 506 and Scoppe (B) 516 by inputting a pulse signal 524 with a width of 0.1 seconds. In each of the graphs of FIGS. 9 and 10, all three-phase waveforms having 120-degree phases different from each other are displayed. The 0.1 second in the center of each graph is the period during which a short-circuit accident occurs. In FIGS. 9 to 12, the graph in the upper row (A) corresponds to the observation result in Scopé (A) 506, and the graph in the lower row (B) corresponds to the observation result in Scopé (B) 516.

FIG. 9 shows the result when the Breaker 502 is turned on and the Breaker 512 is turned off. At the time of a short-circuit accident, almost no current flows through the distribution line where the short-circuit accident has not occurred, and a large current flows through the distribution line where the short-circuit accident has occurred. Therefore, it can be seen that the short-circuit current can be cut off by the overcurrent relay for the distributed power source (generator) having a large current supply capacity in the event of a short-circuit accident.

FIG. 10 shows the result when the Breaker 502 is turned off and the Breaker 512 is turned on. However, harmonics were not supplied from the inverter power supply 510. A larger current flows through the distribution line in which the short-circuit accident has occurred than in the distribution line in which the short-circuit accident has not occurred, but it is much smaller than the current in the upper part of FIG. 9 (when power is supplied from the generator 500). Therefore, it can be seen that the overcurrent relay does not operate at the time of a short circuit and the short circuit current cannot be cut off for the distributed power supply (inverter power supply) having a small current supply capacity at the time of a short circuit accident.

11 and 12 show the results when Breaker 502 is turned off and Breaker 512 is turned on, as in FIG. 10. Unlike FIG. 10, harmonics were output from the inverter power supply 510. That is, FIG. 11 shows the results when an integer order harmonic (frequency 200 Hz) is output from the inverter power supply 510, and FIG. 12 shows a result when an interorder harmonic (frequency 125 Hz) is output from the inverter power supply 510. In the graphs of FIGS. 11 and 12, the supplied harmonic components are calculated by Fourier transform from the voltage waveforms and current waveforms observed in Scopé (A) 506 and Scoppe (B) 516, respectively, and the impedance of each distribution line is obtained. Is the result of calculation.

From FIGS. 11 and 12, the impedance of the distribution line is about 0 when no short circuit accident occurs regardless of whether the integer harmonic (frequency 200 Hz) is supplied or the interorder harmonic (frequency 125 Hz) is supplied. It is .44 (Ω), and at the time of a short-circuit accident, the impedance of the distribution wire in which the short-circuit accident occurs is about 0 (Ω). Therefore, by supplying harmonics and determining the magnitude of the impedance of the harmonic components, the distribution line where the short-circuit accident has occurred can be detected even for the distributed power supply (inverter power supply) whose current supply capacity is low in the event of a short-circuit accident. It can be seen that the distribution line can be cut off according to the detection result.

Although the present invention has been described above by explaining the embodiments, the above-described embodiments are examples, and the present invention is not limited to the above-described embodiments. The scope of the present invention is indicated by each claim of the scope of claims, taking into consideration the description of the detailed description of the invention, and all changes within the meaning and scope equivalent to the wording described therein are made. include.

100 Protective device 102 Harmonic generator 104 Voltage measuring unit 106 Relay unit 108 Current measuring 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 Converter 212 Secondary battery 214 Switch 216 Harmonic 218 Harmonic supply device 220 1st distribution wire 222 1st breaker 224 1st current changer 226 1st harmonic relay 228 1st load 230 2nd distribution Wire 232 2nd breaker 234 2nd harmonic 236 2nd harmonic relay 238 2nd load 240, 930 Short circuit accident 242, 932 Accident current 400 AC power supply 402 Interorder harmonic generator 404 Voltage meter 406 Current meter 408 1st order harmonic component extraction unit 410 2nd order harmonic component extraction unit 412 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 Harmonic generator 430 Sign signal generator 436 Divider 450 Switch 452 Signal monitor unit 500 Generator 502, 512, 522 Breaker
504, 514 R load 506 Scopy (A)
508 Xg
510 Inverter power supply 516 Scopy (B)
518 Xi
520 Control line 524 Pulse signal 910, 920 Distribution line 912, 922 Circuit breaker 914, 924 Current transformer 916, 926 Overcurrent protection relay 918, 928 Load

Claims (4)

Power supply system protection device and
It includes a conversion means for converting a DC voltage supplied from a DC power supply into an AC voltage and supplying the AC voltage to a bus to which an AC voltage of a predetermined frequency is supplied .
The protective device is
A harmonic supply means for supplying a harmonic having a frequency higher than the predetermined frequency to the generatrix.
A current measuring means for measuring the current value of the distribution line connected to the bus, and
A voltage measuring means for measuring the voltage value of the bus or the distribution line,
A current component extracting means for extracting a current component which is a Fourier coefficient of the harmonic from a time fluctuation waveform of the current value measured by the current measuring means, and a current component extracting means.
A voltage component extracting means for extracting a voltage component which is a Fourier coefficient of the harmonic from a time fluctuation waveform of the voltage value measured by the voltage measuring means, and a voltage component extracting means.
A calculation means for calculating impedance or admittance as a calculated value from the current component extracted by the current component extraction means and the voltage component extracted by the voltage component extraction means.
A determination means for determining whether or not a short-circuit accident has occurred in the distribution line based on the calculated value is included.
The harmonic supply means is realized by the conversion means.
The conversion means is a system characterized in that the harmonics are superimposed on the AC voltage converted from the DC voltage . The protective device further includes an output means for outputting a cutoff signal in the cutoff means for cutting off the connection between the distribution line and the bus in response to the determination that the short circuit accident has occurred by the determination means. The system according to claim 1, wherein the system is characterized by the above. The system according to claim 1 or 2, wherein the harmonics are supplied as a current having a constant amplitude. One of claims 1 to 3, wherein the harmonic supplied to the bus by the harmonic supply means is an interorder harmonic having a frequency that is a non-integer multiple of the predetermined frequency. The system described in.

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