WO2023002770A1

WO2023002770A1 - Power distribution system and malfunction detection method for power distribution system

Info

Publication number: WO2023002770A1
Application number: PCT/JP2022/023249
Authority: WO
Inventors: ハマゴヤル; 輝菊池
Original assignee: 株式会社日立製作所
Priority date: 2021-07-21
Filing date: 2022-06-09
Publication date: 2023-01-26
Also published as: JP2023016308A

Abstract

Provided are a power distribution system wherein it is possible to accurately identify a power supply line that has malfunctioned, regardless of the form of a power distribution grid and the variety of problem that has occurred, and a malfunction detection method therefor. This malfunction detection method for a power distribution system, which identifies a power supply line which has malfunctioned within a power distribution grid, is characterized by: injecting a plurality of high-frequency currents into a plurality of power supply lines from a power converter or an arbitrary active device; detecting the high-frequency impedances of the plurality of power supply lines; and identifying the power supply line which has malfunctioned on the basis of the detected high-frequency impedances.

Description

DISTRIBUTION SYSTEM AND FAILURE DETECTION METHOD FOR DISTRIBUTION SYSTEM

The present invention relates to the configuration of a power distribution system and its failure detection method, and particularly to technology applicable to identifying failed power supply lines.

In the power distribution network, transmission lines and distribution lines play an essential and important role in order to efficiently transmit power over long distances from centralized power plants. However, these power lines are often subject to faults due to storms, lightning, snow, freezing rain, insulation breakdown, or short circuits caused by birds or other external objects. After a fault occurs, a protection relay detects the fault and activates a circuit breaker to open the faulty wiring section, resulting in a power outage. Power outages are a serious problem in modern society.

If the faulty power supply line can be identified with high accuracy, it can be restored quickly. This can reduce power outages for users connected to power lines that are not directly affected by the fault. Electrical failures often lead to mechanical damage to the equipment or equipment receiving power, requiring repair. Identifying a failed power supply line enables early repair, preventing recurrence of failures and serious damage.

Therefore, a fast and reliable method to detect faults and restore power is essential for high quality service and overall cost reduction in the distribution grid.

By the way, as one of the main grounding modes, a method in which the neutral point is ungrounded or grounded with high resistance is widely used, especially in Europe and China's Medium Voltage (MV) distribution networks. Such a Neutral Ineffectively Grounded Distribution Grid (NIGDG) has the advantage that the phase-to-phase voltage remains symmetrical even after a single-phase ground fault occurs. There is The distribution system is capable of operating with sustained faults for 1-2 hours, and possibly longer. This gives the power company time to clear the outage and provide uninterrupted power.

However, an inherent drawback of NIGDG is that the magnitude of the fault current does not greatly exceed the normal operating current, and one of the challenges is that the detection and identification of faulty power lines is very difficult. .

In addition, electrical grid conductors often come into contact with poorly grounded objects such as trees, wooden fences, and vehicles. Occasionally, these energized conductors break and contact high impedance grounds such as asphalt, concrete, grass, sand, and the like. These contacts limit fault currents to only a few milliamperes to tens of amperes. Conventional protection schemes based on overcurrent relays, reclosers, and fuses have difficulty detecting such low-current High-Impedance Faults (HIFs).

Undetected HIFs do not damage distribution network components, but energized conductors on the ground can harm humans. Such faults also create a fire hazard when arcing occurs.

　According to several reports, HIFs account for about 20-25% of all failures in the distribution grid. However, in practice, this rate is higher than reported values, so it is essential to solve this HIF detection problem.

In recent years, electric power companies aiming for a sustainable society have shifted to smart grids in order to provide more renewable energy and electric vehicles (EVs). A power converter is necessary for power conversion from renewable energy and EVs. By using intelligent monitoring and control from multifunction power converters, utilities can reduce outages.

As a background technology in this technical field, there is a technology such as Patent Document 1, for example. Patent document 1 describes a method of locating fault points for determining fault types of ground faults and short-circuit faults by measuring phase-to-phase impedance and ground impedance of distribution lines using a high-frequency power source, a voltage measurement sensor, and a current measurement sensor. is disclosed.

In addition, Patent Document 2 discloses "a system that ensures that a distributed resource of a distribution system remains connected to a circuit of the distribution system when a failure occurs in a distributed resource node".

In addition, Patent Document 3 describes "exploration signal injection means for injecting two probe signals with phases different by 180° between an underground distribution line and the ground, and a magnetic field generated by the two probe signals propagating through the underground distribution line. and ground fault point detection means for detecting the ground fault point of the underground distribution line based on the magnetic field detected by the magnetic field detection means". disclosed.

JP-A-2002-122628 U.S. Pat. No. 9,459,308 Japanese Patent Application Laid-Open No. 2007-279031

Past inventions have applied the injection of a single high-frequency current from power devices at multiple locations on the transmission line for fault detection and identification. These power units not only inject high frequency currents during system failures, but also block high frequency currents injected by other adjacent power units. High Voltage (HV) voltage and current are detected by sensors installed along with power devices on multiple power lines. By evaluating and comparing the high frequency (HF) impedances of multiple power lines, faulty power lines are identified.

However, in the case of high impedance faults (HIF) and ungrounded or high resistance grounded neutral distribution networks (NIGDG), the difference between the HF impedances of the power supply lines is small and such a method works well. may not be identifiable.

Any of the technologies of Patent Documents 1 to 3 above may similarly fail to distinguish well in the case of high impedance disturbances (HIF) and power distribution networks (NIGDG) in which the neutral point is ungrounded or grounded with high resistance. have a nature.

Therefore, an object of the present invention is to provide a power distribution system and a failure detection method thereof that can accurately identify a failed power supply line regardless of the form of the power distribution network or the type of failure that occurs.

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is a method of failure detection in an electrical distribution system to identify failed power lines in an electrical grid, comprising: a power converter or any active device to multiple power lines; of high-frequency current is injected, high-frequency impedances of the plurality of power supply lines are detected, and a failed power supply line is identified based on the detected high-frequency impedances.

Further, the present invention provides a power converter or any active device for injecting a plurality of high-frequency currents into a plurality of power supply lines, a bus to which the current values of the plurality of power supply lines and the plurality of power supply lines are connected. and a sensor for detecting the bus voltage of, injecting a plurality of high-frequency currents from the power converter or the arbitrary active device into the plurality of power supply lines, and detecting the current value and the bus voltage detected by the sensor and detecting the high-frequency impedances of the plurality of power supply lines based on the above, and identifying a failed power supply line based on the detected high-frequency impedances.

According to the present invention, it is possible to realize a power distribution system capable of accurately identifying a failed power supply line and a failure detection method thereof, regardless of the type of power distribution network or the type of failure that occurs.

This will enable the construction of a highly reliable smart grid.

Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

1 is a schematic diagram of a comb-type medium voltage distribution network with power converters installed on multiple buses; FIG. 1 is a schematic diagram of a mesh medium voltage distribution network with power converters installed on multiple buses; FIG. 1 is a diagram illustrating a power supply line configuration and components when a high impedance fault (HIF) occurs on one of a plurality of power supply lines of a medium voltage distribution network; FIG. 1 illustrates a power line configuration and components in which a fault has occurred in one of a plurality of power lines of a Neutral Non-Grounded Grid (NIGDG); FIG. FIG. 4 illustrates a method for identifying a faulty power supply line according to an embodiment of the present invention; 6 is a diagram showing the detailed configuration and operation of a faulty power supply line identification (FFI) block of FIG. 5; FIG. 4 is a flow chart illustrating a method for identifying a bad power supply line according to an embodiment of the invention;

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each drawing, the same configurations are denoted by the same reference numerals, and detailed descriptions of overlapping portions are omitted.

In the following, we also refer to high-voltage (HV), medium-voltage (MV), and low-voltage (LV) distribution networks for interconnected distribution networks based on their relative voltage range relationships. Although referred to as a grid, the invention is not limited to any particular voltage range and is applicable to distribution networks of any voltage range.

First, a power distribution network to which the present invention is applied will be described with reference to FIGS. Figures 1 and 2 show two different configurations of medium voltage (MV) distribution networks. FIG. 1 is a comb type medium voltage distribution network with power converters installed in multiple buses, and FIG. 2 is a mesh type medium voltage distribution network with power converters installed in multiple buses.

A medium voltage (MV) distribution network 1 in FIG. It is configured as a comb-shaped medium voltage distribution network connected to the

A medium voltage (MV) distribution network 1 is divided into a plurality of

power supply lines

104 , 108 , 112 by a plurality of buses (buses) 102 , 106 , 110 , 114 .

Here, a fault in any power supply line can be isolated by

circuit breakers

103, 105, 107, 109, 111, 113, and restoration of the remaining normal power supply lines can be efficiently performed. . Each of the

different buses

102, 106, 110, 114 has a

power converter

116, 117, 118, 119 that performs the additional function of Faulty Feeder Identification (FFI).

The medium voltage (MV) distribution network 1 in FIG. 2 is connected at one end to the high voltage (HV) distribution network by the HV/MV transformer 201 and at the other end to the low voltage (LV) distribution network by the MV/LV transformer 207 . It is configured as a mesh-type medium-voltage distribution network connected to

Circuit components such as

buses

202, 206, 212,

power supply lines

204, 210, 215,

power converters

208, 213, 217 perform similar functions as the components described in FIG.

Circuit breakers

203, 205, 209, 211, 214, 216 are used to isolate and reconfigure each power supply line from the main grid in the event of a fault or during maintenance.

Next, a case where a failure occurs in the power supply line 204 will be described with reference to FIGS. 3 and 4. FIG. FIG. 3 is an equivalent circuit when a high impedance fault (HIF) occurs in the power supply line 204, and FIG. This is an equivalent circuit when

FIG. 3 shows each component of

power supply lines

204 and 210 connected to bus 206 . A high impedance fault is introduced through fault resistor 304 , which is the resistance between fault point 302 and ground 305 . A fault point 302 divides the faulty power supply line 204 into two sections with

respective impedances

301 and 303 . The total line impedance of normal power supply line 210 is 306 .

In FIG. 4, the total fault resistance includes fault resistance 304 and ground resistance 401 regardless of the type of fault.

Next, the configuration of the power distribution system and the failure detection method of the present invention will be described with reference to FIGS. 5 to 7. FIG. FIG. 5 is a diagram illustrating a method for identifying faulty power supply lines in the medium voltage distribution network of FIG. FIG. 6 is a diagram showing the detailed configuration and operation of the faulty power supply line identification (FFI) block 510 of FIG. FIG. 7 is a flow chart showing a method of identifying a defective power supply line according to the present invention.

In the present invention, when a fault is detected, the next step is to identify and isolate the faulty power supply line so that the normal part of the system continues to operate.

As shown in FIG. 5, power converters 208 are typically installed on a common bus 206 to which multiple

power supply lines

204, 210 are also connected.

In the present invention, two different high frequency (HF) currents 504 are injected by block 502 after fault detection signal 501 is generated. Also, after the fault detection signal 501 is generated, the converter control block 503 stops injecting the base current from the power converter 208 and injects only two different high frequency (HF) currents 504 . The two different high frequency (HF) currents 504 are, for example, high frequency (HF) currents with frequencies above 50 Hz.

The injected high frequency (HF) current 504 is split between the power supply lines as high frequency (HF) current 505 on power supply line 204 and high frequency (HF) current 506 on power supply line 210 .

Sensors

507, 508, 509 record bus voltage and power line current signals from the two

power lines

204, 210 and transmit them to a faulty power line identification (FFI) block 510 for FFI operation. do.

It should be noted that the injection of two separate high frequency (HF) currents 504 can be done simultaneously or sequentially and the resulting output of the FFI operation will be the same.

FIG. 6 shows the detailed steps performed by the power converter 208 FFI algorithm.

A faulty power line identification (FFI) block 510 requires recording of bus voltage and power line current by

sensors

507, 508, 509 to assess high frequency (HF) impedance at different frequencies.

Because this evaluation requires extracting discrete high frequency (HF) components from the sensed bus voltage and power line current, they are passed through a selected discrete high frequency (HF) tuned second order filter. Let These filters are typically

bandpass filters

601, 602, 603 and two output signals 604 corresponding to two separate high frequency (HF) signals from the input signals of bus voltage VA and power line currents IL1, IL2. , 605, 606, 607, 608 and 609, respectively. Output signals 604, 605, 606, 607, 608 and 609 are VAh1, VAh2, IL1h1, IL1h2, IL2h1 and IL2h2, respectively.

The transfer function of this filter is defined by equation (1).

where s is the Laplace operator, WHF is the selected high frequency (HF), and ξ is the damping ratio.

Output signals 604, 605, 606, 607, 608, 609 of

bandpass filters

601, 602, 603 compute high frequency (HF)

impedances

614, 615, 616, 617 by impedance evaluation blocks 610, 611, 612, 613. used for High frequency (HF)

impedances

614, 615, 616 and 617 are respectively ZL1h1, ZL1h2, ZL2h1 and ZL2h2.

For the failed power supply line 204, the high frequency (HF) impedance is calculated using equations (2) and (3).

On the other hand, for the normal power supply line 210, the high frequency (HF) impedance is calculated using equations (4) and (5).

where VAh1, VAh2 are the bus voltages at the selected high frequency (HF) h1 and h2, and IL1h1, IL1h2, IL2h1, IL2h2 are the high frequency (HF) currents flowing through the failed and normal power lines respectively. . Also, ZL1h1, ZL1h2, ZL2h1, and ZL2h2 are the line impedances of the faulty and normal power supply lines at high frequency (HF), respectively.

If the fault resistance Rf is nearly zero, the power supply line with the lowest impedance contains the fault point and only one high frequency (HF) data can be used to perform FFI.

For higher fault resistance, the difference between the impedance of the faulty power supply line and the impedance of the normal power supply line becomes smaller.

The effect of fault resistance can be eliminated by subtracting the high frequency (HF) impedances ZL1h1 and ZL2h1 at two separate high frequencies (HF) from ZL1h2 and ZL2h2 in subtraction blocks 618 and 619, respectively.

The

outputs

620, 621 of the subtraction blocks 618, 619 are then compared as the new high frequency (HF) impedance in a comparison block 622 to identify the power line with the lowest value as the failed power line. Also, three or more high frequency (HF) currents can be injected to evaluate and compare high frequency (HF) impedances to identify faulty power lines.

After identifying the failed power line, the recorded high frequency (HF) data of the failed power line, output 624 of compare block 622, is used to determine the type of fault (fault type 626) in compare block 625. judge.

The calculated impedance ZL1h has three components corresponding to the three phases of the faulted line. In comparison block 625, the type of fault (fault type 626) is determined by comparing the impedances of the three phases.

For all line-to-ground (LG) faults, the phase with the lowest impedance contains the fault point, and the remaining two phases have relatively high high frequency (HF) impedance.

If the two phases of the faulty power feed line present similar impedances and the third power feed line has a relatively high impedance, then a double line (LL) fault or double line-to-ground (LLG) to-ground) failure.

Also, when the impedance of all three phases is low compared to the typical line impedance under normal grid conditions, a triple line (LLL) fault or triple line-to-ground (LLLG) Obstacles are possible.

FIG. 7 shows a flowchart of a method for identifying a defective power supply line in the present invention.

First, in step S701, it is determined whether or not there is a failure. If it is determined that there is no obstacle (NO), the operation is continued without doing anything (step S702). If it is determined that a fault exists (YES), the process proceeds to step S703, where the power converter injects two separate high frequency (HF) currents simultaneously (or sequentially).

Next, in step S704, the sensor of the power converter detects and records the bus voltage and the current flowing through the plurality of power feeders.

Subsequently, the recorded data (bus voltage VA and power supply line currents IL1, IL2) are passed through a bandpass filter in step S705 to extract samples at selected high frequencies (HF) (steps S706, S707). ).

Based on the output signals VAh1, VAh2, IL1h1, and IL1h2 of the band-pass filters respectively extracted in steps S706 and S707, the high frequency (HF) impedance is calculated at the selected high frequency (HF) in steps S708 and S709 to They are subtracted from each other to cancel out the effects of resistance.

Here, a new parameter shown in equation (6) is used to distinguish between a failed power supply line and a normal power supply line.

However, power supply lines can be of different cable materials, line impedances and lengths connected in various grid configurations. So, to correct this, the new high frequency (HF) impedances are based on the pre-fault impedance values Z'L1 pre-fault and Z'L2 pre-fault (steps S713 and S711) in steps S712 and S710 respectively. Normalized.

After that, in step S714, the new normalized high frequency (HF) impedance is compared to identify the defective power supply line that has failed. The defective power supply line that has failed is separated from the distribution network (step S716), and the normal power supply line is restored as the distribution network to continue operation (step S715).

Finally, in step S717, the high frequency (HF) impedance of the faulty power supply line is compared between phases to identify the type of fault (failure type). Knowledge of fault type is useful in estimating fault location.

It should be noted that the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations. In addition, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Moreover, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

1...Medium-voltage distribution network, 101, 201...HV/MV transformer, 115, 207...MV/LV transformer, 102, 106, 110, 114, 202, 206, 212...Bus (bus), 103, 105, 107, 109, 111, 113, 203, 205, 209, 211, 214, 216... circuit breakers, 104, 108, 112, 204, 210, 215... power supply lines, 116, 117, 118, 119, 208, 213, 217... power converter, 301, 303, 306... impedance, 302... fault point, 304... fault resistance, 305... grounding, 401... grounding resistance, 501... fault detection signal, 502... two different high frequencies (HF) Blocks for injecting current, 503 ... converter control blocks, 504, 505, 506 ... high frequency (HF) currents, 507, 508, 509 ... sensors, 510 ... faulty power line identification (FFI) blocks, 601, 602, 603 ... Bandpass filters, 604, 605, 606, 607, 608, 609... Output signals of bandpass filters, 610, 611, 612, 613... Impedance evaluation blocks, 614, 615, 616, 617... High frequency (HF) impedances, 618 , 619...

Subtraction block

620, 621... Output of subtraction block 622... Comparison block 623... Identification and separation of faulty power supply line 624... Output of comparison block 625... Comparison block 626... Fault type

Claims

1. A method of fault detection in an electrical distribution system for identifying faulty power lines in an electrical distribution network, comprising the steps of:
injecting multiple high frequency currents into multiple power supply lines from a power converter or any active device,
detecting high-frequency impedance of the plurality of power supply lines;
A failure detection method for a power distribution system, comprising identifying a failed power supply line based on the detected high-frequency impedance.
A failure detection method for a power distribution system according to claim 1,
injecting high-frequency currents of two different frequencies into the plurality of power supply lines from the power converter or the optional active device;
detecting high-frequency impedances of the plurality of power supply lines at the two different frequencies, calculating a difference between the detected high-frequency impedances at the two different frequencies for each power supply line,
A failure detection method for a distribution system, comprising identifying a failed power supply line based on the calculated difference.
A failure detection method for a power distribution system according to claim 1,
A failure detection method for a power distribution system, wherein the power converter or the optional active device injects the plurality of high-frequency currents simultaneously or sequentially.
A failure detection method for a power distribution system according to claim 2,
A fault detection method for a power distribution system, characterized by performing a subtraction of high frequency impedances at said two different frequencies to eliminate the effect of fault resistance.
A failure detection method for a power distribution system according to claim 1,
A failure detection method for a power distribution system, wherein the power converter or any active device injects any number of two or more high-frequency currents.
A failure detection method for a power distribution system according to claim 2,
detecting a current value of the plurality of power supply lines and a bus voltage of a bus to which the plurality of power supply lines are connected;
passing the detected current value and bus voltage through a band-pass filter to extract the voltage value and current value at the two different frequencies;
A failure detection method for a power distribution system, comprising: calculating a high-frequency impedance based on the extracted voltage value and current value.
A failure detection method for a power distribution system according to claim 1,
A failure detection method for a power distribution system, comprising identifying a failed power supply line from among a plurality of power supply lines forming a medium voltage distribution network.
A failure detection method for a power distribution system according to claim 1,
A failure detection method for a power distribution system, characterized in that it is applicable to power distribution networks having any kind of grounding system.
A failure detection method for a power distribution system according to claim 2,
The failure detection method for a power distribution system, wherein the two different frequencies are frequencies of 50 Hz or higher.
A failure detection method for a power distribution system according to claim 2,
A fault detection method for a distribution system, comprising normalizing the high frequency impedance using a pre-failure impedance.
A failure detection method for a power distribution system according to claim 1,
A failure detection method for a power distribution system, comprising comparing high-frequency impedances of three phases of three-phase currents flowing through the plurality of power supply lines.
a power converter or any active device that injects multiple high frequency currents into multiple power supply lines;
a sensor that detects the current values of the plurality of power supply lines and the bus voltage of a bus to which the plurality of power supply lines are connected;
injecting a plurality of high frequency currents into the plurality of power supply lines from the power converter or the optional active device;
detecting high-frequency impedance of the plurality of power supply lines based on the current value and the bus voltage detected by the sensor;
A power distribution system, wherein a failed power supply line is identified based on the detected high-frequency impedance.
13. The power distribution system of claim 12, comprising:
injecting high-frequency currents of two different frequencies into the plurality of power supply lines from the power converter or the optional active device;
detecting high-frequency impedances of the plurality of power supply lines at the two different frequencies, calculating a difference between the detected high-frequency impedances at the two different frequencies for each power supply line,
A power distribution system, wherein a failed power supply line is identified based on the calculated difference.
A failure detection method for a power distribution system according to claim 12,
A power distribution system, wherein said power converter or said optional active device injects said plurality of high frequency currents simultaneously or sequentially.