JP7720284B2 - Distributed power supply distribution system and method for controlling the distributed power supply distribution system - Google Patents

Description

The present invention relates to a distributed power supply distribution system and a control method for a distributed power supply distribution system for estimating the point of a fault when a power outage occurs in a power distribution system to which a distributed power supply site is connected.

A conventional method for detecting fault points in power distribution systems is time-delayed sequential transmission. When a fault occurs on a distribution line, the distribution substation's sending circuit breaker is tripped, temporarily cutting off the power to the distribution line. All automatic circuit breakers for the distribution line are then opened. Next, the distribution substation's sending circuit breaker is closed, and then the automatic circuit breakers that separate the distribution lines are closed, starting with those closest to the distribution substation.

When the automatic switch is closed and the fault section is energized, a fault current flows through the distribution line. This fault current is detected at the distribution substation and the sending circuit breaker is tripped. The automatic switch for the distribution line is then opened. At this time, the automatic switch immediately preceding the fault section is locked open to prevent it from being closed again.

Next, the distribution line's sending circuit breaker is closed again, followed by the automatic circuit breakers, starting with those closest to the distribution substation. The automatic circuit breaker just before the fault section is locked open and will not be closed. Through this procedure, the fault section is detected and power is restored from the distribution substation to the section just before the fault section.

The above-mentioned timed sequential transmission method was able to detect that there were no faults between the distribution substation and the nearest fault section, but it was unable to detect faults in the section beyond the fault section (the section with normal power outage), and it was not possible to restore power to the section with normal power outage because it was blocked by the fault section.

One example of a distributed power distribution system that aims to improve this is described in Patent Document 1. In this system, power is restored to the healthy power outage section by reverse-flowing power from the power source at the distributed power source site to the healthy power outage section.

JP 2009-148098 A

The distributed power supply distribution system described in Patent Document 1 detects a power distribution system fault and performs fault recovery taking into account the reserve capacity of the distributed power supply, but does not take into account cooperative operation with an islanding prevention device to prevent reverse power flow from the distributed power supply.

Furthermore, no consideration has been given to suppressing potential changes and overvoltages at the neutral point of the distribution line when multiple ground faults occur during reverse power flow from a distributed power source.

The present invention therefore aims to provide a distributed power distribution system and a control method for a distributed power distribution system that cooperates with an islanding prevention device and can suppress overvoltages when multiple ground faults occur during reverse power flow from a distributed power source.

To achieve the above objectives, the present invention is configured as follows:

A distributed power distribution system includes a distribution system that supplies power to a power demand unit via an automatic switch, a power source, an islanding prevention device, a parallel-off circuit breaker connected to the high-voltage distribution line and opened/closed based on the output signal of the islanding prevention device, a suppression switch of the islanding prevention device, a second grounding type potential transformer, and a distributed power site that is connected to the distribution system via the high-voltage distribution line and supplies power to a load. In the event of a ground fault, when reverse power flow is caused to flow from the power source at the distributed power site to the distribution system, the second grounding type potential transformer is used to temporarily ground the neutral point of the distributed power site via the high-resistance grounding switch.

In addition, in a control method for a distributed power system that includes a power distribution system that supplies power to a power demand unit via an automatic switch and a distributed power site that is connected to the power distribution system by a high-voltage distribution line and supplies power to a load, when a ground fault occurs and reverse power flow is caused to flow from the power source at the distributed power site to the distribution system, the neutral point of the distributed power site is temporarily grounded via a high-resistance grounding switch using a second grounding-type instrument transformer.

The present invention provides a distributed power distribution system and a control method for a distributed power distribution system that cooperates with an islanding prevention device and can suppress overvoltages when multiple ground faults occur during reverse power flow from a distributed power source.

1 is a schematic configuration diagram of a distributed power supply distribution system according to a first embodiment; 1 shows a voltage waveform of a high-voltage distribution line in Example 1. 10 is a diagram showing an example of a voltage waveform of a high-voltage distribution line different from that of the present invention. FIG. 10 is a schematic configuration diagram of a main part of a distributed power supply distribution system according to a second embodiment. FIG. 10 is a schematic configuration diagram of a distributed power supply distribution system according to a third embodiment. FIG. 10 is a schematic configuration diagram of a distributed power supply distribution system according to a fourth embodiment.

The following describes preferred embodiments of the present invention with reference to the accompanying drawings. Please note that the following description is merely an example, and the invention is not limited to the specific embodiments described below. The present invention can, of course, be modified in various ways, including the embodiments described below.

Example 1
The first embodiment will be described with reference to FIGS. 1, 2A and 2B.

Figure 1 is a diagram showing the general configuration of a distributed power supply distribution system 100 according to the first embodiment.

In FIG. 1, the distributed power supply distribution system 100 includes a power distribution system 200, a distributed power supply site 21, and a high-voltage distribution line 5. The power distribution system 200 includes a distribution substation 1 and automatic switchgears 9a to 9h.

High-voltage distribution line 5 connects distribution substation 1, high-voltage consumers 10a, 10b, and 10c, and distributed power generation site 21.

Under normal circumstances, high-voltage consumer 10a receives power via automatic switches 9a to 9g, and high-voltage consumer 10b receives power via automatic switches 9a to 9e and 9h. Furthermore, under normal circumstances, high-voltage consumer 10c receives power via automatic switches 9a, 9b, and 9c.

The distribution substation 1 is equipped with a first grounded potential transformer 3a, a sending circuit breaker 8a, a first zero-phase current transformer 4, and a power source 7a as power sending equipment.

The distribution system also includes automatic switches 9a to 9h.

The distributed power source site 21 includes, as power receiving equipment, a second zero-phase current transformer 2a, a capacitor-type ground fault detector 11, and a parallel-off circuit breaker 8b, all of which are installed on the high-voltage distribution line 5 within the distributed power source site 21. The distributed power source site 21 also includes an islanding prevention device 18, a power source 7b, a switching protection device 14, a load 22, and a power receiving control device 15, and supplies power to the load 22.

When power source 7b and distribution system 200 are operating in parallel, islanding prevention device 18 detects a power outage on the distribution system 200 side and trips parallel-off circuit breaker 8b. A third zero-phase-sequence current transformer 2b is installed in the connecting conductor from power source 7b to the on-site busbar, and if a fault current flows due to a failure in load 22 or the like, third zero-phase-sequence current transformer 2b detects this. Then, in accordance with the detection signal from third zero-phase-sequence current transformer 2b, switching protection device 14 trips protective circuit breaker 8c to protect power source 7b.

The power receiving control device 15 shuts off the parallel-off circuit breaker 8b based on the output from a zero-phase current sensor (not shown).

In Example 1, a suppression switch 17a for the islanding prevention device 18 is provided on the control line connecting the islanding prevention device 18 and the parallel-off circuit breaker 8b. In addition, a second grounded potential transformer 3b and a high-resistance grounding switch 17b are provided to high-resistance ground the neutral point of the on-site power distribution system only during reverse power flow originating from the distributed power source site 21.

In this distributed power supply distribution system 100, if a single-line ground fault 30a occurs while the distribution substation 1, high-voltage customers 10a, 10b, and 10c, and the distributed power supply site 21 are operating in parallel, the first zero-phase current transformer 4 in the distribution substation 1 detects the fault current and trips the sending circuit breaker 8a. The automatic switches 9a to 9h detect the power outage and open.

In addition, the islanding operation prevention device 18 at the distributed power source site 21 detects islanding operation and shuts off the parallel-off circuit breaker 8b. Isolated operation continues within the distributed power source site 21.

When power is restored, the sending circuit breaker 8a in the distribution substation 1 is closed, and then the automatic circuit breakers 9a to 9h are closed in order of proximity to the distribution substation 1.

When automatic switch 9b is closed a certain time after automatic switch 9a is closed, a fault current flows due to the single-line ground fault 30a. This fault current is detected by distribution substation 1, and sending circuit breaker 8a is shut off. Automatic switches 9a and 9b are opened, but automatic switch 9b is locked open because the time it takes for there to be no voltage after closing is short.

After a certain period of time, the sending circuit breaker 8a in the distribution substation 1 is closed, followed by the automatic circuit breaker 9a, completing the restoration of power. The automatic circuit breaker 9b is locked open and therefore cannot be closed.

A single-line ground fault 30a exists between automatic switchgear 9b and 9c, but whether or not a fault exists beyond automatic switchgear 9c (9c-9h) cannot be detected by time-delayed transmission starting from distribution substation 1.

In Example 1 of the present invention, when reverse power flow occurs, the output of the islanding prevention device 18 is suppressed by the suppression switch 17a, which acts as an islanding prevention device suppressor within the distributed power source site 21. In addition, by activating the high-resistance grounding switch 17b, the neutral point of the on-site power distribution system of the distributed power source site 21 is highly grounded by the second grounding-type potential transformer 3b.

In this state, closing the parallel-off circuit breaker 8b causes a reverse power flow, enabling reverse time-limited sequential transmission starting from the distributed power source site 21.

Specifically, when automatic switches 9d and 9c are closed in sequence, a fault current will flow, so the parallel-off circuit breaker 8b is shut off. Automatic switch 9c is locked open and will not be closed the next time power is restored, with power being restored up to just before automatic switch 9c. Next, when automatic switches 9e and 9f are closed, a fault current will flow, so the parallel-off circuit breaker 8b at distributed power source site 21 is shut off.

Similarly, automatic switch 9f is locked open. Automatic switch 9d is also temporarily opened. Next, when the parallel-off circuit breaker 8b at distributed power source site 21 is closed again and automatic switches 9d, 9e, and 9h are closed in sequence, power is restored to high-voltage consumers 10c and 10b via reverse power flow from distributed power source site 21.

The above procedure detects whether or not an accident has occurred in the healthy power outage section. If the power capacity of the distributed power source site 21 is insufficient, power restoration may be halted and only a portion of the power source capacity of the distributed power source site 21 restored.

Figures 2A and 2B show the system voltage when a line-to-ground fault occurs during reverse time-limited forward transmission starting from the distributed power source site 21 in Figure 1.

Figure 2A is an example of embodiment 1 of the present invention, showing the system voltage when the neutral point of the on-site power distribution system within the distributed power source site 21 is high-resistance grounded by the second grounded-type potential transformer 3b. Figure 2B is an example different from the present invention, showing the system voltage when the neutral point of the on-site power distribution system within the distributed power source site 21 is not high-resistance grounded by the second grounded-type potential transformer 3b.

In Figure 2A, when the single-line ground fault converges, the system neutral potential decays and approaches zero. Even if a single-line ground fault subsequently occurs around 0.55 seconds, no overvoltage occurs.

On the other hand, in Figure 2B, after the single-line ground fault has converged, the neutral point potential of the system does not decay and a DC component remains. If a single-line ground fault occurs around 0.55 seconds in this state, the amplitude of the transient potential oscillation increases by the amount of the shifted neutral point voltage, resulting in a large overvoltage.

Only during reverse time-limited forward transmission originating from the distributed power source site 21, the neutral point of the on-site power distribution system within the distributed power source site 21 is highly resistively grounded at the second grounded potential transformer 3b using the high-resistance grounding switch 17b, thereby preventing overvoltage.

In any state other than reverse time-limited forward transmission originating from the distributed power source site 21, the earth fault current detection sensitivity at the distribution substation 1 decreases, so high-resistance grounding using the second grounded potential transformer 3b at the neutral point of the distribution system within the distributed power source site 21 is not performed.

According to Example 1 of the present invention, if a ground fault occurs in the distributed power distribution system 100, reverse power flow is performed from the distributed power site 21 to the healthy power outage section, and the presence or absence of a fault section in the healthy power outage section is detected by time-limited forwarding (reverse time-limited forwarding) starting from the distributed power site 21.In addition, the high-resistance second grounded potential transformer 3b located at the neutral point can prevent overvoltage in the distribution line when multiple ground faults occur during the reverse time-limited forwarding process, making it possible to safely perform reverse time-limited forwarding.

Therefore, it is possible to provide a distributed power distribution system 100 and a control method for a distributed power distribution system that cooperates with the islanding prevention device 18 and can suppress overvoltages when multiple ground faults occur during reverse power flow from the distributed power site 21.

Example 2
Next, a second embodiment of the present invention will be described.

Figure 3 is a schematic diagram of the distributed power source site 21 of the distributed power source distribution system 100 according to Example 2.

The configuration of the distributed power supply distribution system 100 other than the distributed power supply site 21 is the same as that of Example 1 shown in Figure 1, so illustrations and detailed descriptions will be omitted.

In this second embodiment, a protective transformer 23 is provided within the distributed power source site 21. One end of the protective transformer 23 is connected to the load 22 and the high-resistance grounding switch 17b, and the other end of the protective transformer 23 is connected to the power source 7b via the protective circuit breaker 8c.

In addition, a third grounded potential transformer 3c is connected to the connection point (neutral point) between the other end of the protective transformer 23 and the protective circuit breaker 8c.

In Example 2, the neutral point of the connection line from the protective transformer 23 to the power source 7b is always configured to be high-resistance grounded by the third grounding-type potential transformer 3c, enabling ground fault protection. In addition, reverse time-limited forwarding from the distributed power source site 21 is possible, and in this case, the same effect as in Example 1 can be achieved by turning on the high-resistance grounding switch 17b.

According to Example 2, in addition to achieving the same effects as Example 1, it is possible to improve the ground fault protection performance of the distributed power source site 21.

Example 3
Next, a third embodiment of the present invention will be described.

Figure 4 is a schematic diagram of a distributed power supply distribution system 100 according to Example 3.

In Figure 4, in this embodiment 3, the suppression switch 17a, high-resistance grounding switch 17b, and parallel-off circuit breaker 8b serving as islanding prevention device suppression switches within the distributed power source site 21 are operated by commands from the central load dispatching center's power distribution automation system (power distribution automation department) 24. The central load dispatching center's power distribution automation system 24 controls the opening and closing operations of the suppression switch 17a, high-resistance grounding switch 17b, and parallel-off circuit breaker 8b based on output signals from the islanding prevention device 18.

In addition, the power distribution automation system 24 controls the opening and closing operations of the sending circuit breaker 8a and automatic switches 9a and 9b.

According to this embodiment, in addition to being able to achieve the same effects as in embodiment 1, cooperative control with the central load dispatching center's power distribution automation system 24 becomes possible, further improving reliability and safety.

Example 4
Next, a fourth embodiment of the present invention will be described.

Figure 5 is a schematic diagram of a distributed power supply distribution system 100 according to Example 4.

Example 4 will be explained using Figure 5.

In Example 1, the power receiving control device 15 was configured to trip the protective circuit breaker 8c based on the output from a zero-phase current sensor (not shown). However, in Example 4, the power receiving control device 15 and islanding prevention device 18 within the distributed power source site 21 share the second zero-phase current transformer 2a and capacitor-type ground fault detection device 11.

In other words, the output signal of the second zero-phase-sequence current transformer 2a and the output signal of the capacitor-type earth fault detector 11 are supplied to the islanding prevention device 18 and the power receiving control device 15, and the parallel-off circuit breaker 8b is opened or closed according to the output signal of the second zero-phase-sequence current transformer 2a or the output signal of the capacitor-type earth fault detector 11.

This allows the zero-phase current sensor to be omitted.

According to Example 4, in addition to being able to obtain the same effects as Example 1, the zero-phase current sensor can be omitted, thereby reducing the number of parts.

Note that Example 4 can also be applied to Examples 2 and 3 described above.

1...Distribution substation, 2a...Second zero-phase current transformer, 2b...Third zero-phase current transformer, 4...First zero-phase current transformer, 3a...First grounded type voltage transformer, 3b...Second grounded type voltage transformer, 3c...Third grounded type voltage transformer, 5...High-voltage distribution line, 7a, 7b...Power source, 8a...Sending circuit breaker, 8b...Parallel-off circuit breaker, 8c...Protective circuit breaker, 9a-9h...Automatic switch, 10a, 10b, 10c...High-voltage consumer (electricity Power demand section), 11... Capacitor-type ground fault detector, 14... Switching protection device, 15... Power receiving control device, 17a... Suppression switch, 17b... High-resistance grounding switch, 18... Islanding operation prevention device, 21... Distributed power source site, 22... Load, 23... Protection transformer, 24... Power distribution automation system (Power distribution automation section), 30a, 30b... Single-line ground fault, 100... Distributed power source distribution system, 200... Power distribution system

Claims (6)

a power distribution system that supplies power to a power demand unit via an automatic switch;
a distributed power source site connected to the power distribution system via the high-voltage distribution line and supplying power to a load, the distributed power source site including: a power source; an islanding prevention device; a parallel-off circuit breaker connected to the high-voltage distribution line and opened/closed based on an output signal of the islanding prevention device; a suppression switch of the islanding prevention device; a second grounding type potential transformer; and a high-resistance grounding switch;
Equipped with
A distributed power distribution system characterized in that, in the event of a ground fault, when reverse power flow is caused to flow from the power source at the distributed power site to the distribution system as a starting point, the neutral point of the distributed power site is temporarily grounded via the high-resistance grounding switch using the second grounded potential transformer. 2. The distributed power supply distribution system according to claim 1,
the distributed power source site includes a protective transformer, a third zero-phase current transformer, a third grounded voltage transformer, a protective circuit breaker, and a switchgear;
a power supply connected to the neutral point and the load at the distributed power supply site via the protective circuit breaker, the third zero-phase current transformer, and the protective transformer; and when the third zero-phase current transformer detects a fault current, the switching protection device trips the protective circuit breaker. 2. The distributed power supply distribution system according to claim 1,
A distributed power supply distribution system characterized in that the opening and closing operations of the parallel-off circuit breaker, the suppression switch, and the high-resistance grounding switch at the distributed power supply site are controlled based on an output signal from the islanding prevention device. 2. The distributed power supply distribution system according to claim 1,
the distributed power source site includes a second zero-phase current transformer arranged on the high-voltage distribution line within the distributed power source site, a capacitor-type ground fault detector, and a power receiving control device;
a power receiving control device that receives an output signal from the second zero-phase current transformer and an output signal from the capacitor-type earth fault detector, and opens and closes the parallel-off circuit breaker in accordance with the output signal from the second zero-phase current transformer or the output signal from the capacitor-type earth fault detector; A control method for a distributed power system including a power distribution system that supplies power to a power demand unit via an automatic switch, and a distributed power site that is connected to the power distribution system by a high-voltage distribution line and supplies power to a load, comprising:
A control method for a distributed power distribution system, characterized in that, during a ground fault accident, when a reverse power flow is caused to flow from the power source at the distributed power site to the distribution system, the neutral point of the distributed power site is temporarily grounded via a high-resistance grounding switch using a second grounded-type instrument transformer. 6. The method for controlling a distributed power supply distribution system according to claim 5,
a power supply connected to the neutral point and the load at the distributed power supply site via a protective circuit breaker, a third zero-phase current transformer, and a protective transformer, and wherein when the third zero-phase current transformer detects a fault current, the protective circuit breaker is tripped.