JP6672115B2 - Apparatus and method for preventing harmonic resonance - Google Patents

Description

  Embodiments of the present invention relate to a harmonic resonance prevention apparatus and method for preventing harmonic resonance in a system.

  Regarding the allowable limit of the harmonic voltage generated in the power transmission and distribution system, the electric technology guideline JEAG-9702-2013 "Guidelines for Measures for Harmonic Suppression" states that the limit value of the total distortion factor is "3% in the special high-voltage system". Also, a harmonic environmental target level of "5% in the distribution system" is described. Normally, a harmonic voltage of 0.1% to 3% or less exists in the system, but when resonance occurs, the harmonic voltage is increased from several times to about 20 times.

  Problems that occur when a harmonic overvoltage occurs include overheating of the cable, overheating of the phase adjustment capacitor, and damage to the insulation of various devices depending on the overvoltage value. Generally, as the harmonics generated in the AC power transmission system, there are odd harmonics such as third, fifth and seventh harmonics, and there are no even harmonics. Therefore, in the AC transmission system, it is necessary to avoid resonance with odd-order harmonics.

  In a long-distance cable transmission system extending over several tens of kilometers, there is a high possibility that harmonic resonance will occur. For example, power transmission to an island several tens km away from Honshu (hereinafter referred to as a remote island) cannot be realized by an overhead power transmission line, and therefore, a power cable laid on the sea floor is used. That is, a long-distance submarine cable of several tens km is used.

  A characteristic of such a long-distance cable system is that the inductance and the capacitance are very large. For this reason, the resonance frequency of the system is several kHz in a normal overhead transmission line system, but considerably lower in a long-distance cable system. For example, in a long-haul cable system of 60 Hz, resonance tends to occur at the third to ninth (180 Hz to 540 Hz) harmonics.

Bunan Anan, 6 others, "Overview and Systematization of Special Phenomena in Long-distance Cable Systems," IEEJ National Convention, 2006, 7-127, p. 189-p. 190 Kazuhiko Iiyama and six others, "Harmonic Resonance in Japan's Longest AC Long-Distance Cable System and Its Countermeasures," IEEJ National Convention 2006, 7-128, p. 191-p. 192

JP 2013-74691 A

  Transmission systems using long-haul submarine cables to remote islands have already been realized. In such a system, a technique for preventing resonance due to harmonics by making the leakage inductance of the transformer larger than a standard is known. A method of preventing resonance by installing a series reactor is also known.

  As described above, in the related art, the magnitude of the inductance of the main transformer or the series reactor is increased so that resonance can be prevented. However, in this case, since the inductance is increased, the voltage fluctuation in the system is increased, and it is necessary to employ a voltage regulator which requires a large cost. Alternatively, the voltage fluctuation becomes large until power transmission becomes impossible. The voltage fluctuation (voltage distortion rate) allowed from the viewpoint of power quality is ± 3% or less. If the magnitude of the voltage distortion rate exceeds 3%, various failures occur, so that it may be necessary to stop the power transmission, that is, to stop the power supply.

  A harmonic resonance prevention device and a method therefor according to the present embodiment have been made in order to solve the above problems, and a harmonic resonance prevention device capable of automatically avoiding harmonic resonance in a system. And a method thereof.

In order to achieve the above object, the harmonic resonance prevention device of the present embodiment is provided in a system including a transformer, a cable, and a harmonic voltage detection relay, and has the following configuration.
(1) A transformer operating number determination unit that determines the number of operating transformers.
(2) A cable operation line number determination unit that determines the number of operation lines of the cable.
(3) A circuit configuration determining unit that determines the circuit configuration of the system from the determination results of the transformer operating number determining unit and the cable operating line number determining unit.
(4) When the harmonic voltage in the system is equal to or higher than the set value of the harmonic voltage detection relay provided in the system, the resonance frequency of the system is in a resonance frequency range in which odd harmonics resonate. A circuit configuration change unit that changes the circuit configuration out of the range.
(5) The system is provided with a circuit breaker that disconnects the transformer or the cable from the system.
(6) The circuit configuration changing unit includes a disconnection determining unit that determines the transformer or the cable to be disconnected from the system, and a circuit breaker for the transformer or the cable to be disconnected determined by the disconnection determining unit. And a shutoff command generating unit that generates a shutoff command to shut off the power supply and outputs the shutoff command to the circuit breaker.
(7) The cutoff determining unit compares the number of the operating transformers with the number of lines of the cable, and sets a larger one as a cutoff target.

  In addition, the present embodiment can be regarded as a method for preventing system harmonic resonance.

FIG. 2 is a single-line diagram of a system to which the harmonic resonance prevention device according to the first embodiment is applied. FIG. 2 is a functional block diagram of the harmonic resonance prevention device according to the first embodiment. It is a figure showing the circuit composition pattern of a system. FIG. 4 is a diagram for explaining a resonance frequency region. FIG. 2 is an equivalent circuit diagram of the system of FIG. 1. (A) is a simplified equivalent circuit diagram of the system of FIG. 1. (B) is an equivalent circuit diagram obtained by further simplifying (a). It is a figure which shows the resonance frequency in the case of 70 km of cables with respect to each circuit configuration. It is a figure for explaining a prior art, and is a single-line connection diagram at the time of providing a serial reactor by a prior art. FIG. 5 is a single-line diagram of a system of a first modification to which the harmonic resonance prevention device according to the first embodiment is applied. FIG. 10 is a diagram illustrating a resonance frequency for each circuit configuration in the system of FIG. 9 (cable 50 km). FIG. 3 is a diagram illustrating resonance frequencies for respective circuit configurations when the cable length is 50 km in the system according to the first embodiment. It is a figure which shows the resonance frequency with respect to each circuit structure in the case where it does not resonate at the 3rd harmonic or the 5th harmonic in all of the circuit configurations (A) to (D). It is a single-line connection diagram of the system of the modification 2 to which the harmonic resonance prevention device concerning a 1st embodiment was applied. It is a single-line connection diagram of a system of a modification 3 to which the harmonic resonance prevention device according to the first embodiment is applied. It is a single-line connection diagram of the system of the modification 4 to which the harmonic resonance prevention device concerning a 1st embodiment was applied.

[1. First Embodiment]
Hereinafter, the harmonic resonance prevention device of the present embodiment will be described with reference to FIGS.

[1-1. Constitution]
FIG. 1 is a single-line diagram of a system to which the harmonic resonance prevention device according to the present embodiment is applied. The system according to the present embodiment is a long-distance cable system, and includes a power supply 1, a first substation 3, a power cable 11, and a second substation 12.

  The power supply 1 is, for example, a three-phase AC power supply. The power of the power supply 1 is transmitted to the first substation 3 via the power transmission line 2. The first substation 3 steps down the received power and transmits it to the second substation 12 via the power cable 11. The second substation 12 is connected to the distribution system 16, and steps down the received power and transmits it to the distribution system 16. Hereinafter, each configuration will be described in detail.

  The first substation 3 includes a high-side bus 4a, a low-side bus 4b, a high-side breaker 5a, a low-side breaker 5b, and a first transformer 6. The high voltage side bus 4 a is a bus connected to the power transmission line 2, and the low voltage side bus 4 b is a bus connected to the power cable 11. Here, two first transformers 6 are provided in parallel between the buses 4a and 4b, and step down the received power. The high voltage side circuit breaker 5a is provided between the bus 4a, which is the high voltage side of each first transformer 6, and the first transformer 6, and the low voltage side circuit breaker 5b is connected to the low voltage side of each first transformer 6. The first transformer 6 is provided between the bus bar 4 b, which is the side, and the first transformer 6. The circuit breakers 5a and 5b switch the first transformer 6 from being disconnected or connected to the system.

  The power cable 11 is a long-distance cable of several tens km, and is, for example, a long-distance submarine cable or a land cable for transmitting power to a remote island. The power cable 11 has two lines here, and is provided in parallel between the low-voltage side bus 4b and a bus 13 of a second substation 12 described later. A cable circuit breaker 10a is provided between the low-voltage side bus 4b and the power transmitting end of the power cable 11, and a cable circuit breaker 10b is provided between the power receiving end of the power cable 11 and the bus 13. I have. The circuit breakers 10a and 10b switch the power cable 11 from the system to disconnect or connect.

  The second substation 12 includes a bus 13, a distribution system bus 15, and a second transformer 14. The bus 13 is connected to the power receiving end of the power cable 11, and the power distribution system bus 15 is connected to the power distribution system 16. For this reason, the bus 13 is installed on the high voltage side in the second substation 12, and the distribution system bus 15 is installed on the low voltage side. A plurality of second transformers 14 are provided in parallel between the buses 13 and 15, and step down received power. The electric power via the distribution system bus 15 is sent to the distribution system 16 and transmitted to a load (not shown) connected to the distribution system 16.

  In FIG. 1, a part of the switching equipment, that is, a disconnecting switch connected in series with the circuit breaker, a grounding switch for maintenance, a transformer for measuring the transmission line voltage, and a current flowing in the circuit are detected. Although a current transformer and the like are omitted, they may be provided separately.

  In the present embodiment, a harmonic voltage detection relay 8 is connected to the low-voltage side bus 4 b via an instrument transformer 7, and the harmonic voltage detection relay 8 is provided with a harmonic resonance prevention device 9. . The instrument transformer 7 transforms the bus voltage of the low voltage side bus 4 b to such an extent that the harmonic voltage detection relay 8 can detect the harmonic voltage.

  The harmonic voltage detection relay 8 detects whether the harmonic voltage is equal to or more than a set value for a predetermined time. If the odd harmonic voltage is equal to or higher than the set value for a predetermined time, an operation signal is output to the harmonic resonance prevention device 9. On the other hand, when the odd-order harmonic voltage is lower than the set value for a predetermined time, a return signal is output to the harmonic resonance prevention device 9. The term “return” as used herein means that the harmonic detection relay 8 returns to a state in which it is possible to detect whether the harmonic voltage is equal to or higher than the set value for a predetermined time. The set value and the predetermined time can be appropriately changed in design. The set value may be, for example, 3% when the system is a special high-voltage system, and 5% when the system is a distribution system, and may be a value obtained by multiplying or dividing a necessary coefficient such as a safety factor or a margin. Here, the set value is 3%. The predetermined time is, for example, one second.

  FIG. 2 is a functional block diagram of the harmonic resonance prevention device 9 according to the present embodiment. The harmonic resonance prevention device 9 is a device for changing a circuit configuration of a system triggered by input of an operation signal from the harmonic detection relay 8. Specifically, the harmonic resonance prevention device 9 includes a transformer operating number determination unit 91 that determines the number of operating first transformers 6 and a cable operating line number determining unit 92 that determines the number of operating lines of the power cable 11. And a circuit configuration determining unit 93 that determines the circuit configuration of the system from the determination results of the two determining units 91 and 92, a circuit configuration changing unit 94 that changes the circuit configuration, and detects a return signal of the harmonic voltage detection relay 8. It has a return detection unit 95 and an alarm unit 96 that issues an alarm.

  The determinations of the determination units 91 and 92 can be easily performed by acquiring information indicating the connection or disconnection state of each circuit breaker using the pallet switches of the circuit breakers 5a, 5b, 10a, and 10b. For example, the transformer operating number determination unit 91 acquires a pallet switch operation signal from the circuit breakers 5a and 5b, and the cable operation line number determination unit 92 acquires a pallet switch operation signal from the circuit breakers 10a and 10b. The current number of operating first transformers 6 and the number of operating lines of power cable 11 can be determined. In order to make the determinations 91 and 92 more reliable, a pallet switch of a disconnector (not shown) connected in series with the circuit breakers 5a, 5b, 10a, and 10b may be obtained.

  The circuit configuration determination unit 93 receives the determination result of each of the determination units 91 and 92, triggered by the input of the operation signal of the harmonic voltage detection relay 8, and determines the circuit configuration of the current system. In the present embodiment, two first transformers 6 and two power cables 11 are provided in the system, and there are four types of circuit configurations capable of transmitting power as shown below and FIG. The circuit configuration determining unit 93 determines which of the current circuit configurations is (A) to (D).

Circuit configuration (A): state in which all facilities of first transformer 6 and power cable 11 are operating [2B + 2C]
Line configuration (B): state in which the first transformer 6 is stopped by one bank [1B + 2C]
Line configuration (C): state in which one line of power cable 11 is stopped [2B + 1C]
Line configuration (D): state in which the first transformer 6 is in one bank and the power cable 11 is in one line stopped [1B + 1C]

  The circuit configuration determination unit 93 stores the number of first transformers 6 provided in the system and the number of lines of the power cable 11 in a storage device in advance, for example, so that the determination results of the determination units 91 and 92 are determined. Accordingly, the circuit configuration of the current system can be determined.

  The circuit configuration changing unit 94 changes the current circuit configuration when the harmonic voltage becomes equal to or higher than the set value set by the harmonic voltage detection relay 8, that is, when the operation signal of the harmonic voltage detection relay 8 is input. Then, the circuit configuration is changed to a circuit configuration in which the resonance frequency of the system is out of the resonance frequency region where the odd-order harmonics resonate. Resonance refers to a phenomenon in which an odd-order harmonic voltage included in a system voltage is expanded several times to several tens times. As shown in FIG. 4, the resonance frequency region is a frequency region having a predetermined width around the resonance frequency of the odd-order harmonic. The resonance frequency region can be, for example, the resonance frequency of the odd-order harmonic ± 15 Hz. This predetermined width can be appropriately changed in design. The reason why the region is defined as such is that the harmonic resonance occurs in a certain range around it even if it does not completely match the resonance frequency.

  The circuit configuration in which the resonance frequency of the system deviates from the resonance frequency region where the odd-order harmonics resonate can be known in advance as follows. That is, it is the first transformer 6 and the power cable 11 that affect the harmonic resonance, and once the number of operating units and the number of operating lines are determined, the resonance frequency in the system can be obtained. By overlapping this resonance frequency with a preset resonance frequency region as shown in FIG. 7 described later, it is possible to determine a circuit configuration in which the resonance frequency is out of the resonance frequency region. Therefore, the storage device provided in the harmonic resonance prevention device 9 can store in advance information on whether each circuit configuration and the circuit configuration whose circuit configuration is out of the resonance frequency region is applicable or not. The information can be used for changing the circuit configuration.

  The circuit configuration change unit 94 outputs an alarm signal to the alarm unit 96 when the circuit configuration of the system is changed, here, when the first transformer 6 or the power cable 11 is cut off. Here, a later-described interruption determination unit 94a outputs an alarm signal.

  The circuit configuration changing unit 94 includes a cutoff determining unit 94a that determines the first transformer 6 or the power cable 11 to be cut off from the system, and the first transformer 6 or the power to be cutoff determined by the cutoff determining unit 94a. And a cutoff command generation unit 94b that generates a cutoff command for cutting off the circuit breakers 5a and 5b or the circuit breakers 10a and 10b with respect to the cable 11.

  When there are a plurality of circuit configurations that are out of the resonance frequency region where the resonance frequency of the system causes the resonance of the odd-order harmonic, as the candidate circuit configurations, the cutoff determination unit 94a determines the priority order. The cut-off determining unit 94a determines the first transformer 6 or the power cable 11 to be cut off according to the priority order. That is, even if the first transformer 6 or the power cable 11 determined based on the highest priority is cut off, if resonance continues for some reason, the power is cut off based on the next priority. Determine the first transformer 6 or power cable 11. This operation can be repeated until resonance is prevented, that is, until the return detection unit 95 detects a return signal of the harmonic voltage detection relay 8.

  As a method of determining the priority, for example, the cutoff determining unit 94a compares the number of the first transformers 6 in operation with the number of lines of the power cable 11 and determines that the one with the larger number in operation is the target to be cutoff. I do. However, the method of determining the priority is not limited to this, and the design can be changed as appropriate.

  When the circuit configuration determination unit 93 determines that the first transformer 6 in operation is one and the power cable 11 connected to the system is one line, the cutoff determination unit 94a causes resonance. In such a case, it may be determined that both the first transformer 6 and the power cable 11 or both of them are cut off.

  The shutoff command generation unit 94b outputs the generated shutoff command to the target circuit breakers 5a and 5b or the circuit breakers 10a and 10b. The cutoff command generation unit 94b can be configured by a cutoff circuit for the first transformer 6 and a cutoff circuit for the power cable 11.

  The return detection unit 95 receives the return signal of the harmonic voltage detection relay 8 and detects the return of the detection unit 8. The return detection unit 95 can confirm that the return of the harmonic voltage detection unit 8, that is, that the harmonic resonance has been eliminated, by detecting the return signal. If the return signal is not received for a predetermined time after the shutoff command generation unit 94b outputs the shutoff command, the return detection unit 95 determines that the harmonic resonance has not been resolved, and requests that the target to be shut off again be determined. The signal is output to cutoff determining section 94a.

  The alarm unit 96 issues an alarm to the outside when the circuit configuration changing unit 94 changes the circuit configuration of the system, here, when the first transformer 6 or the power cable 11 is cut off. The target of the warning may be notified by sound or a warning may be displayed on the display screen.

[1-2. Action]
The operation of the harmonic resonance prevention device 9 will be described with reference to FIGS. As preparatory steps, a description will be given of the resonance frequency of the system and the fact that the resonance frequency of the system changes depending on the circuit configuration of the system.

(1) Resonance Frequency of System FIG. 5 is an equivalent circuit of the system shown in FIG. 1, and shows main electric elements related to harmonic resonance in the power transmission system of FIG. As shown in FIG. 5, the power transmission system includes an inductance 2L of the power supply 1 to the power supply system, an inductance 6L of the first transformer 6, an inductance 11L of the power cable 11, an electrostatic capacitance 11C of the power cable 11 to the ground, and a second And the inductance 14L of the second transformer 14 of the substation 12 of FIG. Actually, the overhead power transmission line also has a ground capacitance and a resistance, but is not shown because the influence on the resonance phenomenon is small.

  FIG. 6A shows a simplified equivalent circuit of a system having the above elements. What plays an important role in the resonance phenomenon is the number of first transformers 6 and the number of lines of the power cable 11. In FIG. 6A, the number of the first transformers 6 is two, and the number of lines of the power cable 11 is two.

The capacitance C _G of the power supply system, the capacitance C _TR of the first transformer 6, and the capacitance C _D of the second transformer 14 in FIG. It is sufficiently smaller than _CC and can be ignored. Therefore, FIG. 6A can be further simplified as shown in FIG. 6B. Note that L ₀ is the combined inductance of the entire circuit, and C ₀ is the combined capacitance of the entire circuit.

The resonance frequency _{f r} of the circuit of FIG. 6 (b), represented by the formula (1).

(2) Dependence of circuit configuration on system resonance frequency The resonance frequency of a long-distance cable system changes depending on the system circuit configuration. As described above, in the present embodiment, the first transformer 6 is composed of two units, and the power cable 11 is composed of two lines. Therefore, the circuit configuration is the same as that of the circuit configurations (A) to (D) shown in FIG. There are types. Accordingly, as described below, there are also four types of resonance frequencies of this system. That is, the resonance frequencies of the circuit configurations (A) to (D) are obtained by substituting L ₀ · C ₀ of the respective circuit configurations into L ₀ · C ₀ of the equation (1).

Ｌ_０ ：回路全体の合成したインダクタンス
Ｌ_Ｇ ：電源系統のインダクタンス
Ｌ_ＴＲ：第１の変圧器６の漏れインダクタンス
Ｌ_Ｃ ：電力ケーブル１１のインダクタンス
Ｃ_０ ：回路全体の合成した静電容量
Ｃ_Ｃ ：電力ケーブル１１の対地静電容量 Circuit configuration (A):

L _0: Inductance and the entire circuit synthesis L _G: inductance L _TR Power System: leakage inductance L _C of the first transformer 6: inductance C ₀ of the power cable 11: capacitance synthesized the entire circuit C _C: Ground capacitance of power cable 11

Circuit configuration (B):

Circuit configuration (C):

Circuit configuration (D):

  FIG. 7 shows an analysis result of the resonance frequency of the system under the following analysis condition 1 for these circuit configurations. In FIG. 7, the horizontal axis indicates the circuit configurations (A) to (D), and the vertical axis indicates the resonance frequency. The resonance frequency of each circuit configuration of the system may be obtained by Expressions (1) to (9), or may be obtained by an electronic computer using an electromagnetic transient analysis program (Electro-Magnetic Transients Program, hereinafter abbreviated as EMTP). Is also good. Here, it is assumed that the resonance frequency of each circuit configuration of the system is calculated in advance by a computer other than the harmonic resonance prevention device 9, and the result is used in the harmonic resonance prevention device 9.

(Analysis conditions 1)
(1) Power system voltage: 220 kV
(2) Rated frequency: 60 Hz
(3) Short-circuit capacity of the power supply system: 9500 MVA. The short-circuit current is 25 kA, and the inductance LG seen from the 66 kV side is 1.21 mH.
(4) Low-voltage bus voltage: 66 kV
(5) Rated capacity of the first transformer: 100 MVA
(6) Number of banks of the first transformer: 2 banks (7) Primary / secondary rated voltage of the first transformer: 220/66 kV
(8) The short-circuit impedance of the first transformer: 15%. Therefore, the inductance LTR as viewed from the 66 kV side is 17.33 mH.
(9) Voltage and length of long distance cable: 66 kV, 70 km
(10) Number of long distance cable lines: 2 lines (11) Long distance cable type: Crosslinked polyethylene cable, 325 mm ² , 3 cores, submarine cable The ground capacitance is 0.201 μF / km, and is 14.07 μF at 70 km. The inductance is 0.330 mH / km, and 23.10 mH at 70 km.
(12) Combination of the number of first transformers and the number of cable lines: 4 types as shown in FIG.

  By the way, various errors occur between the equipment at the planning stage and the actual equipment. Specifically, there is a laying error in the length of a cable or an overhead transmission line, and there is an error in inductance or capacitance due to a manufacturing error. Main transformers installed in substations also have manufacturing errors and changes in inductance due to tap switching. Further, there is a calculation error when obtaining a constant or the like for each facility. It is necessary to consider these errors when taking measures to prevent resonance due to harmonics. Therefore, a range of ± 10% is considered in the calculation result. Therefore, in FIG. 7, the resonance frequency of each case has a range of ± 10%. Further, even though the harmonic resonance does not completely match the resonance frequency, it occurs in a certain range around the resonance frequency. Therefore, as shown in FIG. 7, the odd-order harmonic ± 15 Hz is set as the resonance region.

  FIG. 7 illustrates the following. That is, the circuit configuration (A) [2B + 2C] is in a normal operation mode, and its resonance frequency is around 240 Hz, and neither the third harmonic nor the fifth harmonic resonates. The circuit configuration (B) [1B + 2C] is in the form of one transformer and two cables, and resonates at the third harmonic of 180 Hz. The circuit configuration (C) [2B + 1C] has a form of two transformers and one cable, and resonates at the fifth harmonic of 300 Hz. The circuit configuration (D) [1B + 1C] is in the form of one transformer and one cable, and its resonance frequency is around 240 Hz, and does not resonate with odd-order harmonics. Therefore, the circuit configurations (B) and (C) require measures to prevent resonance.

(3) Operation of the Harmonic Resonance Prevention Device 9 Here, the operation of the harmonic resonance prevention device 9 will be described. Hereinafter, the operation flow of the harmonic resonance prevention device 9 will be described, but the operation order is not limited to the order.

  First, when the harmonic voltage detection relay 8 detects that the odd-order harmonic has exceeded the set value for a predetermined time, the harmonic voltage detection relay 8 outputs an operation signal to the harmonic resonance prevention device 9.

  In the harmonic resonance prevention device 9, the input of the operation signal triggers the transformer operation number determination unit 91 and the cable operation line number determination unit 92 to acquire information on the pallet switches of the circuit breakers 5a, 5b, 10a, and 10b. Then, the current number of operating first transformers 6 and the number of operating lines of power cable 11 are determined. Then, upon receiving the determination result, the circuit configuration determination unit 93 determines the current circuit configuration of the system. That is, it is determined which of the circuit configurations (A) to (D) in FIG. Hereinafter, as an example, a case will be described in which it is determined that the current circuit configuration is the circuit configuration (B) and that the current circuit configuration is the circuit configuration (C).

(Pattern 1): When the current circuit configuration is the circuit configuration (B) Here, as an example, the description will be given assuming that the circuit configuration determination unit 93 has determined that the current circuit configuration is the circuit configuration (B). . As shown in FIG. 7, the resonance frequency of the circuit configuration (B) is included in the resonance region of the third harmonic, and it is necessary to change the circuit configuration in order to prevent resonance. The circuit configuration determining unit 93 notifies the circuit configuration changing unit 94 that the current circuit configuration is the circuit configuration (B).

  Here, the circuit configuration changing unit 94 changes the circuit configuration to a circuit configuration in which the resonance frequency of the system is out of the resonance frequency region where the odd harmonics resonate, triggered by the input of the operation signal of the harmonic voltage detection relay 8. As shown in FIG. 7, the circuit configurations outside the region are (A) and (D), but here, the circuit configuration change unit 94 changes the circuit configuration (B) to the circuit configuration (D). .

  That is, the cutoff determining unit 94a determines that the line to be cutoff is one line of the power cable 11, and outputs a signal to that effect to the cutoff command generation unit 94b. The shutoff command generation unit 94b generates a shutoff command for shutting off the circuit breakers 10a and 10b corresponding to the power cable 11. Then, the cutoff command generation unit 94b outputs a cutoff command to the circuit breakers 10a and 10b, operates the circuit breakers 10a and 10b, disconnects the power cable 11 from the system, and changes to the circuit configuration (D). .

  As shown in FIG. 7, the resonance frequency of the circuit configuration (D) is around 240 Hz, and the third harmonic resonance can be prevented. The return detection unit 95 confirms that the harmonic resonance has been eliminated by receiving the return signal of the harmonic voltage detection relay 8, and terminates the operation of the harmonic resonance prevention device 9.

  At this time, the third harmonic resonance occurs once, and an abnormal state occurs in which one cable is interrupted. Therefore, the circuit configuration changing unit 94 outputs an alarm signal to the alarm unit 96, and the alarm unit 96 Raise an external alarm.

(Pattern 2): When the current circuit configuration is the circuit configuration (C) Since the basic operation is the same as that of the above-described pattern 1, only different portions will be described. When the current circuit configuration is the circuit configuration (C), the circuit configuration determining unit 93 notifies the circuit configuration changing unit 94 that the current circuit configuration is the circuit configuration (B).

  Here, the circuit configuration changing unit 94 changes the circuit configuration (A) or (D) out of the resonance frequency region to the circuit configuration (D). That is, the cut-off determining unit 94a determines the cut-off target to be one of the first transformers 6, and outputs a signal to that effect to the cut-off command generation unit 94b. The shutoff command generation unit 94b generates a shutoff command for shutting off the circuit breakers 5a and 5b corresponding to the first transformer 6. Then, the cutoff command generation unit 94b outputs a cutoff command to the circuit breakers 5a, 5b, operates the circuit breakers 5a, 5b, disconnects the first transformer 6 from the system, and configures the circuit (D). Change to Thereby, as shown in FIG. 7, the resonance frequency becomes close to 240 Hz, so that the fifth harmonic resonance can be prevented.

  By the way, in the above patterns 1 and 2, if the return detection unit 95 does not receive the return signal of the harmonic voltage detection relay 8 for a predetermined time even after changing to the circuit configuration (D), resonance continues. Judge that there is. In this case, when the circuit configuration change unit 94 determines that the circuit configuration determination unit 93 determines that the number of operating first transformers 6 is one and that the number of lines of the power cable 11 is one, resonance occurs. Therefore, both the first transformer 6 and / or the power cable 11 are cut off. This is for stopping power transmission and avoiding continuation of resonance. Also in this case, the cutoff determining unit 94a outputs a warning signal to the warning unit 96, and the warning unit 96 issues a warning. Originally, in the case of a circuit configuration with one transformer and one line of cable, resonance is prevented from occurring by using the impedance value of the transformer and the series reactor. This is a backup process when resonance occurs due to the above.

  As described above, in the present embodiment, when the circuit configuration is changed to (B) or (C), the circuit configuration is not changed immediately to the circuit configuration (D) but is changed after waiting for the operation of the harmonic voltage detection relay 8. ing. The reason is that even if the resonance state or a state close to the resonance state is reached, the voltage distortion rate does not always exceed the set value of 3% or more. That is, as described above, the resonance region is a region of the odd-order harmonic resonance frequency ± 15 Hz. For example, even if the resonance region is expanded by 10 times due to resonance, if the residual harmonic voltage of the system is 0.1%, the harmonic voltage becomes Only 1%. When the load is heavy or the resistance value of the circuit is large, the magnification is reduced. In these states, there is no need to change the circuit configuration. For this reason, the harmonic voltage detection relay 8 is caused to detect that the harmonic has become equal to or higher than the set value, and the circuit configuration is changed in response to this.

  Further, the circuit configuration (B) is changed to the circuit configuration (D), and the circuit configuration (C) is changed to the circuit configuration (D). The circuit configuration (A) is not used although resonance can be prevented. . The reason for this is that in the circuit configuration (B) or (C), one of the transformers or one cable is stopped due to an accident, a failure, or an inspection. ) Is usually a difficult situation. With the circuit configuration (D), one of the two operating cables or one of the two transformers is continuously used, and no trouble occurs. When the first transformer 6 and the power cable 11 that have been stopped can be operated, the circuit configuration (A), that is, the entire facility operation state may be set.

(4) Difference between the Operation of the Harmonic Resonance Prevention Apparatus 9 of the Present Embodiment and the Operation of the Related Art FIG. 8 is a single-line diagram in the case where a series reactor according to the related art is provided. As shown in FIG. 8, in all of the circuit configurations (A) to (D), a series reactor for preventing the third and fifth harmonic resonances from being generated is provided with a cable circuit breaker 10a. It is inserted as a serial reactor 17 between the power cable 11 and the power transmission end.

  That is, as shown in FIG. 7, since the circuit configuration that provides the highest resonance frequency is (C), the resonance frequency is set to less than 165 Hz, which is 15 Hz lower than the third harmonic 180 Hz, that is, 164 Hz or less. . As a result, in other circuit configurations, as shown in FIG. 9, the resonance frequency can be reduced to a lower frequency, and resonance can be prevented.

  However, the magnitude of the inductance is 59 mH, and the impedance of the first transformer 6 is 15%, that is, while the impedance of the first transformer 6 is 15.33 mH. It is 3.4 times as large as the first transformer 6. Since the voltage fluctuation is proportional to the inductance, a large voltage fluctuation occurs. On the other hand, in the present embodiment, the series reactor is unnecessary, so that the inductance of the circuit can be suppressed small and the voltage fluctuation can be suppressed small.

[1-3. effect]
(1) The harmonic resonance prevention device 9 of the present embodiment is provided in a system including the first transformer 6, the power cable 11, and the harmonic voltage detection relay 8, and controls the number of operating first transformers 6. The number of transformer operating number determination unit 91 to be determined, the number of cable operation line determination unit 92 to determine the number of operating lines of the power cable 11, and the system based on the determination results of the number of transformer operation number determination unit 91 and the number of cable operation line determination unit 92. And a circuit configuration determining unit 93 that determines the circuit configuration of the above. When the harmonic voltage in the system becomes equal to or higher than the set value of the harmonic voltage detection relay 8 provided in the system, the resonance frequency of the system becomes an odd harmonic. And a circuit configuration changing unit 94 configured to change to a circuit configuration outside a resonance frequency region where wave resonance occurs.

  As a result, harmonic resonance in the system can be automatically avoided. In particular, since the circuit configuration is changed in response to the operation of the harmonic voltage detection relay, unnecessary changes can be prevented. Further, even if voltage distortion due to resonance occurs, the circuit is automatically changed, so that resonance under unexpected conditions can be prevented.

  Further, since it is not necessary to increase the leakage inductance of the transformer or install a series reactor as in the prior art, it is possible to reduce the voltage fluctuation and to increase the voltage which requires a large cost. It is also economical, space and time-consuming, with only small adjustments required.

(2) The system is provided with circuit breakers 5a, 5b, 10a, and 10b that disconnect the first transformer 6 or the power cable 11 from the system, and the circuit configuration changing unit 94 disconnects the first transformer 6 from the system. 6 or the power cable 11, and a cut-off that cuts off the circuit breakers 5 a, 5 b, 10 a, and 10 b for the first transformer 6 or the power cable 11 to be cut off determined by the cut-off determining unit 94 a. And a shutoff command generation unit 94b that generates a command and outputs a shutoff command to the circuit breakers 5a, 5b, 10a, and 10b.

  Thereby, the circuit configuration of the system can be changed by interrupting the first transformer 6 or the power cable 11, and the resonance frequency of the changed circuit configuration deviates from the resonance frequency region where odd-order harmonic resonance occurs. With such a circuit configuration, it is possible to prevent harmonic resonance that would cause a power failure. In particular, since the interrupted first transformer 6 or power cable 11 is presumed to be in an accident, failure, inspection, or the like, the first transformer 6 or power cable 11 is connected to the system. When used, it is necessary to confirm that the device can be used normally, but this is not necessary because the circuit configuration is changed by cutting off the other first transformer 6 or the power cable 11. . Furthermore, since the resonance can be automatically prevented by cutting off some of the first transformers 6 or the power cable 11, power transmission or power distribution can be continued without power failure due to resonance.

(3) When there are a plurality of candidate circuit configurations, the cutoff determining unit 94a determines the priority order. Thus, even if the resonance cannot be avoided for some reason even after the priority is changed to the highest-level circuit configuration, it is possible to quickly change to the next-highest circuit configuration.

(4) The cutoff determining unit 94a compares the number of the first transformers 6 in operation with the number of lines of the power cable 11, and sets the one with the larger number as a target to be cutoff. Thereby, at least one pair of the first transformer 6 and the power cable 11 during operation can be secured, and power transmission or power distribution can be continued. For example, it is possible to avoid a situation in which the two power cables 11 are operable but two first transformers 6 are stopped.

(5) A return detection unit 95 that detects a return signal from the harmonic voltage detection relay 8 is provided, and after the cutoff command generation unit 94b outputs a cutoff command, the return detection unit 95 does not receive the return signal for a predetermined time. In this case, the cutoff determining unit 94a determines the first transformer 6 or the power cable 11 to be cutoff according to the priority order, and the cutoff command generation unit 94b determines the first transformer 6 or the power cable 11 for the determined first transformer 6 or power cable 11. An interruption command is output to the circuit breakers 5a, 5b, 10a, and 10b. As a result, even if the resonance has not been avoided for some reason even after the change of the circuit configuration, the situation can be escaped, and the power failure due to the resonance can be avoided.

(6) The circuit configuration changing unit 94 generates resonance when the circuit configuration determination unit 93 determines that the operating transformer is one and the cable connected to the system is one line. If so, the transformer and / or the cable were cut off.

  Normally, when the circuit configuration is such that the first transformer 6 is one and the power cable 11 is one line, resonance is prevented from occurring by using the impedance value of the first transformer 6 and the series reactor. Incidentally, when resonance occurs due to an unexpected cause in such a circuit configuration, power transmission is stopped by shutting off the first transformer 6 and / or the power cable 11 as a backup measure. And prevent accidents.

(7) When the circuit configuration changing section 94a changes the circuit configuration of the system, an alarm section 96 for issuing an alarm is provided. When the circuit configuration is changed, the harmonic voltage is equal to or higher than the set value of the harmonic voltage detection relay 8, and the first transformer 6 or the power cable 11 must be cut off to eliminate the harmonic voltage. Since this is an abnormal state that the user must be alerted, the watchman can be alerted by issuing an alarm.

(8) The alarm unit 96 issues an alarm when there is no power cable 11 connected to the first transformer 6 or the system during operation. Thus, in this case, too, since the state is abnormal, it is possible to call attention to the observer and urge the user to take measures.

[2. Modification of First Embodiment]
Modifications 1 to 5 of the first embodiment will be described. Each modification is the same as the basic configuration of the first embodiment. Hereinafter, only different points from the first embodiment will be described, and the same parts as those in the first embodiment will be denoted by the same reference numerals and detailed description thereof will be omitted.

(1) Modification 1
[Constitution]
In the above, the difference in operation between the harmonic resonance prevention device according to the first embodiment and the conventional technology has been described, but it does not prevent the provision of the series reactor in the first embodiment. That is, the series reactor 17 may be provided between the power transmission end of at least any one of the power cables 11 and the circuit breaker 10a. The series reactor 17 has an inductance that does not cause resonance in a plurality of circuit configurations including the circuit configuration (A) in which the first transformer 6 and the power cable 11 of the system all operate.

  FIG. 9 is a single-line diagram in the case where the series reactor 17 is provided in the system of the first embodiment. In the first modification, the cable length of the power cable 11 is set to 50 km, which is different from the cable length 70 km of the power cable 11 of the first embodiment, according to the following analysis condition 2.

FIG. 10 is a diagram illustrating the resonance frequency for each circuit configuration in the system of FIG. 9 (cable 50 km) when analyzed under the following analysis condition 2.
(Analysis condition 2)
The analysis condition 2 differs from the analysis condition 1 in the cable length, and is otherwise the same.
(9) Length of long distance cable: 50km

  As shown in FIG. 10, the resonance frequencies of the circuit configurations (A) and (D) are out of the resonance region, and it can be seen that the series reactor 17 has an inductance that does not cause resonance in a plurality of circuit configurations.

[Action / Effect]
The operation and effect of the first modification will be described. As a pre-stage, first, the fact that the resonance frequency changes due to the change in the cable length of the power cable 11 will be described, and the disadvantages of applying the conventional series reactor to all circuit configurations will be described.

  FIG. 11 is a diagram illustrating the resonance frequency for each circuit configuration when the cable length is 50 km in the first embodiment in which the series reactor 17 is not provided. As described above, the resonance frequency of each circuit configuration can be obtained by EMTP or Equations (1) to (9).

  As shown in FIG. 11, the fifth harmonic resonance occurs in the circuit configurations (A) and (D). On the other hand, as is apparent from comparison with FIG. 7 in which the cable length is 70 km, in the first embodiment, the resonance frequencies are out of the resonance region in the circuit configurations (A) and (D). From this, it can be confirmed that the resonance frequency changes when the cable length changes.

  By the way, in the circuit configurations (A) and (D), the fifth harmonic resonance occurs, and power cannot be transmitted. In particular, the circuit configuration (A) is in a state where all facilities are in operation, and it is indispensable in system design to make the circuit configuration (A) transmit power. Therefore, it is necessary to make the circuit configuration (A) capable of transmitting power.

  Here, as shown in FIG. 9, it is considered that the series reactors 17 are respectively provided in series between the circuit breaker 10 a and the power transmission end of the power cable 11. This is because the resonance frequency can be changed by inserting a series reactor.

  FIG. 12 is a diagram illustrating the resonance frequency for each circuit configuration in a case where neither the third harmonic nor the fifth harmonic resonates in all of the circuit configurations (A) to (D). In this case, as shown in FIG. 11, the resonance frequency of the circuit configuration (C) having the highest resonance frequency needs to be less than 165 Hz, which is 15 Hz lower than 180 Hz of the third harmonic, and at least 164 Hz. The inductance of the series reactor 17 required for that is 190 mH. When the leakage inductance is calculated from the short-circuit impedance of 15% of the first transformer 6 to be 17.3 mH, 190 mH reaches 165%, which is 11 times that. This means that if 100 MVA, which is the rated capacity of the transformer, is temporarily transmitted, a voltage drop of 165% occurs, and power cannot be actually transmitted. That is, although the resonance disappears, the voltage drop becomes large and power cannot be transmitted.

  Therefore, in the first modification, in the system, a series reactor 17 is provided in series at least at one end of the power cables 11 among the plurality of power cables 11, and the series reactor 17 is connected to the first transformer. A plurality of circuit configurations (A) and (D), including a circuit configuration (A) in which all the power cables 6 and the power cable 11 operate, have an inductance that does not cause resonance.

  Specifically, a series reactor 17 having an inductance that does not generate resonance in the circuit configurations (A) and (D) is provided. When the system is the circuit configuration (B) or (C) and the voltage distortion rate increases, the circuit configuration can be changed to the circuit configuration (D) as in the first embodiment to prevent resonance.

  The required inductance of the series reactor 17 is large enough to make the resonance frequency of the circuit configuration (D) less than 285 Hz, which is 15 Hz lower than the fifth harmonic 300 Hz, that is, at least 284 Hz. 8) It is 16 mH from (9). This is smaller than 17.3 mH, the leakage inductance of the first transformer 6, and about 1/12 compared to 190 mH in the case of FIG. Therefore, the voltage drop is small and 100 MVA power transmission becomes possible.

  Therefore, according to the first modification, it is possible to secure power transmission or power distribution in a circuit configuration in which all facilities are in operation, and even if resonance occurs, can avoid resonance and can transmit power. Circuit configuration.

(2) Modification 2
FIG. 13 is a single-line diagram of a system of Modification 2 to which the harmonic resonance prevention device according to the first embodiment is applied. As shown in FIG. 13, a power cable 18 is connected to the bus 13 of the second substation 12 via a cable circuit breaker 10b. An example of the second modification is a case where the second substation 12 is provided on a remote island, a power cable 18 extends from the remote island, and power is transmitted and distributed to another remote island. That is, the number of remote islands is not limited to one, and a case where the remote islands are connected by a power cable 18 laid on the sea floor may be mentioned.

  Since the power cable 18 is provided, the inductance and the capacitance in Expression (1) become larger than those in the first embodiment, so that the resonance frequency becomes smaller. Therefore, the resonance frequency becomes lower than the resonance frequency shown in FIGS. 7 and 10, and the circuit configurations (A) and (D) may resonate with the third harmonic.

  When such resonance occurs, similarly to the first embodiment, the harmonic voltage detection relay 8 operates, and the circuit configuration is changed by the circuit configuration changing unit 94 so that the resonance does not occur. . In this case, the circuit configuration may be changed to (B) or (C), or the power cable 18 may be disconnected. From the viewpoint of continuing the power transmission to the remote island, the cutoff determining unit 94a determines the priority such that the priority of the power cable 18 to be cut off is lower than that of the circuit configuration (B) or (C). good.

(3) Modification 3
The scope of application of the first embodiment is not limited to island power transmission. FIG. 14 is a single-line diagram in a case where the harmonic resonance prevention device 9 is applied to a long-distance cable system from an offshore wind farm. The second substation 12 is an offshore substation 21. That is, as shown in FIG. 14, the electric power from the offshore power station 19 is sent to the bus 22 of the offshore substation 21 via the transmission line 20 and the first substation is connected to the power cable 11 via the transformer 23. Transmit power to 3.

  Further, a solar power station may be used instead of the offshore power station 19.

(4) Modification 4
FIG. 15 is a single-line diagram of a system of Modification 4 to which the harmonic resonance prevention device according to the first embodiment is applied. As a possible example of Modification 4, a first substation 3 is installed on the mainland, a second substation 12 is installed on a remote island, and power is transmitted from the mainland to the remote island. As shown in FIG. 15, not only the low-voltage side bus 4b of the first substation 3 but also the distribution system bus 15 of the second substation 12 via the instrument transformer 7 for the harmonic voltage detection relay. 8 (hereinafter, referred to as a second relay 8, and a harmonic voltage detection relay 8 provided in the first substation 3 is referred to as a first relay 8), and a harmonic voltage on the mainland side and on the remote island side is provided. To monitor.

  The setting value of the first relay 8 is 3% or more in the case of the special high-voltage system, and the setting value of the second relay 8 is 5% or more in the case of the distribution system.

  The harmonic resonance prevention device 9 is one unit similarly to the first embodiment, and is connected to the second relay 8. That is, the operation signal and the return signal of the second relay 8 are output to the harmonic resonance prevention device 9 of the first substation 3.

  The harmonic resonance prevention device 9 can receive an operation signal from both the first relay 8 and the second relay 8, but the circuit configuration change unit 94 may operate upon any of the operation signals. .

  As described above, by providing the relay 8 at each substation, the harmonic voltage at each substation can be monitored, so that resonance can be more reliably prevented. For example, even if the harmonic voltage is less than the set value of the first relay 8 in the special high-voltage system, the voltage distortion rate tends to be added in the distribution system, so that the harmonic voltage in the distribution system is equal to the second voltage. In some cases, the setting value of the relay 8 may be exceeded. In such a case, the circuit configuration can be changed and resonance can be prevented.

(5) Modification 5
In the first embodiment, the number of the first transformers 6 and the number of lines of the power cable 11 are each two sets, but the number and the number of lines are arbitrary. In that case, it is only necessary to design one or more circuit configurations so that resonance does not occur.

[3. Other Embodiments]
In the present specification, a plurality of embodiments according to the present invention have been described. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. The embodiments described above can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

  For example, an alarm signal for causing the alarm unit 96 to issue an alarm may be generated by the circuit configuration changing unit 94, and may be generated by any of the cutoff determination unit 94a and the cutoff command generation unit 94b.

  Further, the form of each unit can be understood as a harmonic resonance prevention program that causes a computer to execute the processing of each unit.

DESCRIPTION OF SYMBOLS 1 ... Power supply 2 ... Power transmission line 3 ... 1st substation 4a ... High voltage side bus 4b ... Low voltage side bus 5a ... High voltage side circuit breaker 5b ... Low voltage side circuit breaker 6 ... 1st transformer 7 ... Instrument transformer 8 Harmonic Voltage Detection Relay 9 Harmonic Resonance Prevention Device 10a, 10b Cable Circuit Breaker 11 Power Cable 12 Second Substation 13 Bus 14 Second Transformer 15 Distribution System Bus DESCRIPTION OF SYMBOLS 16 ... Distribution system 17 ... Series reactor 18 ... Power cable 19 ... Offshore power station 20 ... Transmission line 21 ... Offshore substation 22 ... Bus 23 ... Transformer 91 ... Transformer operation number determination unit 92 ... Cable operation line number determination unit 93 ... Circuit configuration determining unit 94 ... Circuit configuration changing unit 94a ... Interruption determining unit 94b ... Interruption command generation unit 95 ... Return detection unit 96 ... Alarm unit

Claims (7)

Provided in the system with transformer, cable and harmonic voltage detection relay,
A transformer operating number determining unit for determining the operating number of the transformer,
A cable operation line number determination unit that determines the number of operation lines of the cable,
A circuit configuration determination unit that determines the circuit configuration of the system from the determination results of the transformer operating number determination unit and the cable operation line number determination unit,
When the harmonic voltage in the system is equal to or higher than the set value of the harmonic voltage detection relay provided in the system, the resonance frequency of the system deviates from a resonance frequency region in which odd-order harmonic resonance occurs. A circuit configuration change unit that changes to a circuit configuration;
Equipped with a,
The system is provided with a circuit breaker that disconnects the transformer or the cable from the system,
The circuit configuration changing unit,
A disconnection determining unit that determines the transformer or the cable to be disconnected from the system,
A shutoff command generation unit that generates a shutoff command to shut off the breaker for the transformer or the cable to be interrupted determined by the shutoff determination unit, and outputs a shutoff command to the breaker.
With
The harmonic resonance preventing device , wherein the cutoff determining unit compares the number of the operating transformers with the number of lines of the cable, and sets a larger one as a cutoff target . The blocking determination unit, when the circuit structure in which candidate is more than one harmonic resonance prevention device according to claim 1, wherein the determining the priority. Provided in the system with transformer, cable and harmonic voltage detection relay,
A transformer operating number determining unit for determining the operating number of the transformer,
A cable operation line number determination unit that determines the number of operation lines of the cable,
A circuit configuration determination unit that determines the circuit configuration of the system from the determination results of the transformer operating number determination unit and the cable operation line number determination unit,
When the harmonic voltage in the system is equal to or higher than the set value of the harmonic voltage detection relay provided in the system, the resonance frequency of the system deviates from a resonance frequency region in which odd-order harmonic resonance occurs. A circuit configuration change unit that changes to a circuit configuration;
Equipped with a,
The system is provided with a circuit breaker that disconnects the transformer or the cable from the system,
The circuit configuration changing unit,
A disconnection determining unit that determines the transformer or the cable to be disconnected from the system,
A shutoff command generation unit that generates a shutoff command to shut off the breaker for the transformer or the cable to be interrupted determined by the shutoff determination unit, and outputs a shutoff command to the breaker.
With
When there are a plurality of candidate circuit configurations, the cutoff determining unit determines the priority order,
A return detection unit that detects a return signal from the harmonic voltage detection relay,
After the shutoff command generation unit outputs the shutoff command, if the return detection unit does not receive the return signal for a predetermined time, the shutoff determination unit sets the transformer or the cable to be shutoff according to the priority order. Decide,
The cutoff command generation unit outputs a cutoff command to the determined transformer or a breaker for the cable,
A harmonic resonance prevention device. When the circuit configuration change unit changes the circuit configuration of the system, including an alarm unit that issues an alarm,
The harmonic resonance preventing device according to any one of claims 1 to 3 , wherein The alarm unit issues an alarm when the operating transformer or the cable connected to the system is absent.
The harmonic resonance preventing device according to claim 4, wherein: In the system, a series reactor is provided in series with at least one end of the cable among the plurality of cables,
The series reactor has an inductance that does not cause resonance in a plurality of circuit configurations including a circuit configuration in which the transformer and the cable all operate,
The harmonic resonance preventing device according to any one of claims 1 to 5 , wherein A harmonic resonance prevention method for preventing harmonic resonance of a system including a transformer, a cable, and a harmonic voltage detection relay,
Transformer operating number determining step of determining the operating number of the transformer,
Cable operation line number determination step of determining the number of operation lines of the cable,
A circuit configuration determining step of determining a circuit configuration of the system from the determination results of the transformer operating number determination step and the cable operation line number determination step,
When the harmonic voltage in the system is equal to or higher than the set value of the harmonic voltage detection relay provided in the system, the resonance frequency of the system deviates from a resonance frequency region in which odd-order harmonic resonance occurs. A circuit configuration change step of changing to a circuit configuration;
Equipped with a,
The system is provided with a circuit breaker that disconnects the transformer or the cable from the system,
The circuit configuration changing step includes:
Disconnection determining step of determining the transformer or the cable to be disconnected from the system,
A shutoff command generation step of generating a shutoff command to shut off the breaker for the transformer or the cable to be interrupted determined in the shutoff determination step, and outputting a shutoff command to the breaker,
With
The harmonic resonance prevention method according to claim 1, wherein the shutoff determining step compares the number of the transformers in operation with the number of lines of the cable, and sets a larger one as a shutoff target .

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