JP7796579B2 - Protection and Coordination Systems in Microgrids - Google Patents

Description

This specification discloses technology related to a protection coordination system in a microgrid.

Patent Document 1 discloses technology related to a protection coordination system for a typical power distribution system. In this patent, multiple measuring devices are distributed along the power distribution line to measure the power supply voltage from the line and transmit the measurement results to a parent station such as a substation. The parent station detects the fault point based on the measurement results, locks open the sectional switch immediately preceding the fault point, and isolates the fault point from the power distribution system. Therefore, if a short-circuit fault occurs on the consumer side, the substation circuit breaker opens, and then the consumer's sectional switch is locked open. When the substation resumes power transmission, the consumer affected by the short-circuit fault is isolated from the high-voltage power distribution line, allowing the high-voltage power distribution line to operate as normal.

Japanese Patent Application Publication No. 7-318607

In a typical distribution system like the one described in Patent Document 1, the sectional switch can be locked open, allowing a consumer experiencing a short circuit to be isolated from the high-voltage distribution line. However, when a microgrid is configured, if a short circuit occurs on the consumer side of the microgrid, even if the circuit breaker of the power generation equipment in the microgrid opens, the consumer's sectional switch is not locked open, and the consumer experiencing the short circuit cannot be isolated from the high-voltage distribution line. Furthermore, if the interrupting current value of a high-voltage load break switch (LBS) with a current-limiting fuse installed in the consumer's power receiving equipment is greater than the supply current value, the current-limiting fuse will not blow even if a short circuit occurs, and the consumer experiencing the short circuit cannot be isolated from the high-voltage distribution line. As such, current macrogrids do not provide protection coordination when a short circuit occurs on the consumer side, and countermeasures are needed. This specification aims to provide technology for implementing a protection coordination system in a microgrid.

The protection and coordination system disclosed in this specification is a protection and coordination system for a microgrid formed within a power distribution system. This protection and coordination system includes an automatic switch that automatically opens during a power outage and automatically closes when power is restored, and a control unit that outputs a closing operation signal to the automatic switch when power is restored after a power outage in the power distribution system. When the control unit detects that power has been restored to the power distribution system, it outputs a closing operation signal to the automatic switch corresponding to each consumer at predetermined time intervals, starting with the one closest to the power generation equipment.

1 shows a microgrid system according to a first embodiment. 1 shows a microgrid system according to a second embodiment. 10 shows a microgrid system according to a third embodiment. 10 shows a microgrid system according to a fourth embodiment. 10 shows a microgrid system according to a fifth embodiment. 10 shows a microgrid system according to a sixth embodiment.

A microgrid is formed within a distribution system that receives power from a power plant. A microgrid can be connected to and disconnected from the distribution system from the power plant using a switch. Therefore, while the microgrid is connected to the distribution system from the power plant, consumers within the microgrid can use power from the power plant. When the microgrid is disconnected from the distribution system from the power plant, consumers within the microgrid can use power generated within the microgrid. The protection and coordination system disclosed in this specification can identify the consumer in question when a short-circuit fault occurs on the consumer side within a microgrid formed within a distribution system. As a result, the consumer in question can be disconnected from the distribution system, allowing power to be normally supplied from the distribution system to other consumers.

The protection coordination system is equipped with an automatic switch that automatically opens during a power outage and automatically closes when power is restored. The automatic switch may be any type that can connect and disconnect each consumer to the distribution system. For example, the automatic switch may be installed immediately before a sectional switch installed by the electric power company as the division of responsibility between the electric power company and the consumer. Alternatively, the automatic switch may be a replacement for a sectional switch. In other words, the sectional switch itself may be an automatic switch. Alternatively, the automatic switch may be an automatic switch (such as a fused air load switch) located in the consumer's power receiving panel.

The protection and coordination system described above includes a control unit that outputs a closing operation signal to the automatic switch when it detects a power restoration after a power outage in the distribution system. The control unit can be an operation controller that controls the operation of the automatic switch located in the power receiving panel of the above-mentioned customer. Because this operation controller is located in the power receiving panel of each customer, there is no need to install a new operation controller just for the purpose of building a protection and coordination system within the microgrid.

When the control unit detects that power has been restored to the power distribution system after a power outage, it outputs a closing operation signal to the automatic switch. At this time, the control unit is configured to output the closing operation signal at a predetermined time interval, starting with the automatic switch closest to the power generation equipment. For example, the control unit outputs a closing operation signal to the first automatic switch closest to the power generation equipment 5 seconds after detecting the restoration of power, and outputs a closing operation signal to the second automatic switch closest to the power generation equipment 10 seconds after detecting the restoration of power. By varying the timing at which the closing operation signal is output to each automatic switch in this way, for example, if a power outage occurs again after outputting a closing operation signal to the first automatic switch but before outputting a closing operation signal to the second automatic switch, it is possible to identify that a short-circuit fault has occurred at the consumer corresponding to the first automatic switch.

Furthermore, when the control unit identifies a consumer where a short-circuit accident has occurred, it may prohibit the output of a closing operation signal to the automatic contactor corresponding to that consumer the next time power restoration is detected. In other words, if the control unit detects a power outage within a predetermined time after outputting a closing operation signal to the automatic contactor, it may prohibit the output of a closing operation signal to that automatic contactor the next time power restoration is detected. For example, if a power outage occurs again two seconds after outputting a closing operation signal to a first automatic contactor, it is identified that a short-circuit accident has occurred at the consumer corresponding to the first automatic contactor. In this case, if a closing operation signal is output to the first automatic contactor when power restoration is detected again, a power outage will occur again. By prohibiting the closing operation of the automatic contactor corresponding to that consumer when a consumer where a short-circuit accident has occurred can be prevented from occurring again. The consumer where the short-circuit accident has occurred can be reliably isolated from the distribution system, allowing power to be normally supplied from the distribution system to other consumers.

The protection coordination system may also include automatic switchgear on the distribution system in addition to the automatic switchgear corresponding to each consumer. In this case, too, a short-circuit fault on the distribution system can be identified by changing the timing of outputting a closing operation signal to each automatic switchgear (the automatic switchgear corresponding to each consumer and the automatic switchgear on the distribution system). In other words, if a power outage occurs again after an opening operation signal has been output to an automatic switchgear on the distribution system but before an opening operation signal has been output to another automatic switchgear, it can be identified as a short-circuit fault on the distribution system.

A main distribution system and branch distribution systems may be formed within the microgrid. In this case, a closing operation signal may be output to the automatic switch of the main distribution system with priority. In other words, when it is detected that power has been restored to the distribution system, a closing operation signal may be output to the automatic switch corresponding to each consumer in the branch distribution system after the output of the closing operation signal to the automatic switch corresponding to each consumer in the main distribution system has been completed.

(First Example)
A microgrid system 100 will be described with reference to FIG. 1 . The microgrid system 100 includes a storage battery equipment 40 and a reactive power compensator 30 connected to a high-voltage distribution line 3 to which power is supplied from a power plant 2. The high-voltage distribution line 3 is provided with automatic switches 5 and 7 that turn the power supply on and off. The storage battery equipment 40 and the reactive power compensator 30 are connected to the high-voltage distribution line 3 between the automatic switches 5 and 7. Therefore, a microgrid 10 is formed between the automatic switches 5 and 7. Consumers in the microgrid 10 can use their electrical devices with power supplied from the storage battery equipment 40 even when the automatic switches 5 and 7 are opened (power supply turned off). The storage battery equipment 40 can be considered as a power generation facility in the microgrid 10. In the microgrid 10, low-voltage distribution lines 12a, 14a, and 16a are connected to the high-voltage distribution line 3, and consumers receive power from the low-voltage distribution lines 12a, 14a, and 16a. An automatic switch 15 is connected to the high-voltage distribution line 3 between the automatic switches 5 and 7. The automatic switch 15 will be described later.

The high-voltage distribution line 3 has three high-voltage wirings (three-phase wirings) 4, 6, and 8. The low-voltage distribution lines 12a, 14a, and 16a are connected to two phases of the first wiring (first phase) 4, the second wiring (second phase) 6, and the third wiring (third phase) 8. The low-voltage distribution lines 12a, 14a, and 16a can be divided into three groups depending on the high-voltage wiring to which they are connected. Specifically, the low-voltage wiring of the first group 16 (first low-voltage distribution line 16a) is connected to the first wiring 4 and the second wiring 6. The low-voltage wiring of the second group 14 (second low-voltage distribution line 14a) is connected to the second wiring 6 and the third wiring 8. The low-voltage wiring of the third group 12 (third low-voltage distribution line 12a) is connected to the first wiring 4 and the third wiring 8.

A sectionalizing switch (PAS) 20 is provided between the high-voltage distribution line 3 and each of the low-voltage distribution lines 12a, 14a, and 16a. In the event of an electrical fault within each of the customers 25a-25d, the sectionalizing switch 20 opens the electrical circuits between the high-voltage distribution line 3 and each of the low-voltage distribution lines 12a, 14a, and 16a. A power receiving panel 22 is provided between the sectionalizing switch 20 and each of the customers 25a-25d. Typically, the power receiving panel 22 is located on the premises of each of the customers 25a-25d. The power receiving panel 22 includes a fused switch (LBS) 23 and a transformer (pole transformer) Tr. The fused switch 23 automatically opens when an electrical fault occurs in a load 24 used by each of the customers 25a-25d, preventing a secondary fault. The transformer Tr converts the high-voltage distribution line 3 into low-voltage power and supplies it to the low-voltage distribution lines 12a, 14a, and 16a.

Automatic switches 11, 13, 17, and 19 are located on the opposite side of the power receiving panel 22 from the sectional switch 20. Automatic switch 11 corresponds to customer 25a, automatic switch 13 corresponds to customer 25b, automatic switch 17 corresponds to customer 25c, and automatic switch 19 corresponds to customer 25d. In the following description, the automatic switches, including the aforementioned automatic switch 15, may be distinguished by being referred to as the first automatic switch 11, second automatic switch 13, third automatic switch 15, fourth automatic switch 17, and fifth automatic switch 19. Each automatic switch is provided with a switch controller (not shown) that serves as a control unit, and the switch controller has a controller provided within the automatic switch and a slave station connected to the automatic switch. The automatic switch performs closing and opening operations based on an output signal (operation signal) output from the switch controller.

In the microgrid system 100, each consumer 25a-25d normally uses power supplied from the power plant 2. While power is being supplied from the power plant 2, power is charged in the storage battery equipment 40. In the event of a disaster, electrical accident, etc., the automatic switches 5 and 7 are opened, and power supply from the power plant 2 to the microgrid 10 is stopped. When the automatic switches 5 and 7 are opened, the storage battery equipment 40 begins supplying power to each consumer 25a-25d. Thereafter, when power supply from the power plant 2 resumes, the automatic switches 5 and 7 are closed, and power supply from the storage battery equipment 40 is stopped.

While power is being supplied from the storage battery device 40 to the high-voltage distribution line 3, the reactive power compensator 30 monitors the voltage of the high-voltage distribution line 3. If the voltage of the high-voltage distribution line 3 falls outside a specified range, the reactive power compensator 30 supplies reactive power to the high-voltage distribution line 3, restoring the voltage of the high-voltage distribution line 3 to within the specified range. The reactive power compensator 30 has a fast response to voltage changes. Therefore, if the voltage of the high-voltage distribution line 3 falls outside the specified range, the reactive power compensator 30 can immediately restore the voltage to within the specified range.

If a ground fault occurs within the microgrid 10 while power is being supplied from the storage battery device 40 to the high-voltage distribution line 3, i.e., while the microgrid 10 is in operation, the circuit breaker of the storage battery device 40 opens, the automatic switches 11, 13, 15, 17, and 19 open, and a power outage occurs within the microgrid 10. In the microgrid system 100, when the circuit breaker of the storage battery device 40 is closed and power is restored to the high-voltage distribution line 3 (when it is confirmed that there is power on the primary side of the automatic switches 11, 13, 15, 17, and 19), the first automatic switch 11, the second automatic switch 13, the third automatic switch 15, the fourth automatic switch 17, and the fifth automatic switch 19 are closed in this order, starting from the side closest to the storage battery device 40. Specifically, after detecting the restoration of power to the high-voltage distribution line 3, the first automatic switch 11 performs a closing operation after 5 seconds, the second automatic switch 13 after 10 seconds, the third automatic switch 15 after 15 seconds, the fourth automatic switch 17 after 20 seconds, and the fifth automatic switch 19 after 25 seconds. The closing operation of each automatic switch, except for the third automatic switch 15, is controlled by a closing operation signal output from a control device (not shown) located in the power receiving panel 22 of each consumer 25a to 25d. The closing operation of the third automatic switch 15 is controlled by a closing operation signal output from a control device (not shown) located on the high-voltage distribution line 3.

In the microgrid system 100, if a second power outage occurs after a closing operation signal is output to any of the automatic switches 11, 13, 15, 17, and 19, all of the automatic switches 11, 13, 15, 17, and 19 are opened. Then, when power is restored to the high-voltage distribution line 3, a closing operation is again performed on the automatic switches 11, 13, 15, 17, and 19 at the time interval described above. However, depending on the time when the second power outage occurs, the output of a closing operation is prohibited for certain automatic switches. In other words, if a power outage is detected within a predetermined time after the output of a closing operation signal to an automatic switch, the output of a closing operation signal to that automatic switch is prohibited the next time power is restored. Specifically, for an automatic switch that experiences a second power outage within two seconds of performing a closing operation, the closing operation is prohibited even if power is restored to the high-voltage distribution line 3 after the second power outage.

For example, if a second power outage occurs between 5 and 7 seconds after the high-voltage distribution line 3 is restored, the first automatic switch 11 will not be closed even when the high-voltage distribution line 3 is restored. Similarly, if a second power outage occurs between 10 and 12 seconds, the second automatic switch 13 will not be closed; if a second power outage occurs between 20 and 12 seconds, the fourth automatic switch 17 will not be closed; and if a second power outage occurs between 25 and 27 seconds, the fifth automatic switch 19 will not be closed. This allows consumers 25a-25d experiencing a short-circuit fault to be isolated from the high-voltage distribution line 3, and other consumers 25a-25d can then receive power. By identifying consumers 25a-25d experiencing a short-circuit fault and isolating them from the high-voltage distribution line 3, a protection coordination system is established within the microgrid 10. Note that if a second power outage occurs between 15 and 17 seconds after power is restored, the cause of the second power outage is the closing operation of the third automatic switch 15. In this case, the short circuit fault occurred on the high-voltage distribution line 3, so the closing operation of the circuit breaker for the storage battery device 40 is prohibited.

Other embodiments will be described below. The embodiments described below are modified versions of the microgrid system 100. Therefore, in the following description, features common to the microgrid system 100 will be given the same reference numbers as those used for the microgrid system 100, and duplicate explanations may be omitted.

(Second Example)
As shown in FIG. 2 , in the microgrid system 200, automatic switching devices 211, 213, 217, and 219 are provided between the high-voltage distribution line 3 and the power receiving panel 22. The microgrid system 200 can be regarded as a system in which the sectional switch 20 provided in the microgrid system 100 is eliminated. Alternatively, while the microgrid system 100 is provided with a conventional distribution system in which a first automatic switch 11, a second automatic switch 13, a fourth automatic switch 17, and a fifth automatic switch 19 corresponding to each of the consumers 25a to 25d are installed, the microgrid system 200 can also be regarded as a system in which the conventional sectional switch 20 is replaced with the automatic switching devices 211, 213, 217, and 219. Note that in the microgrid system 200, the respective switch controllers perform the closing operation of the automatic switch 211, the automatic switch 213, the automatic switch 215, the automatic switch 217, and the automatic switch 219 in this order. Compared to the microgrid system 100, the microgrid system 200 can reduce the number of components required to build a protection coordination system within the microgrid 10.

(Third Example)
As shown in Fig. 3, in the microgrid system 300, a power receiving panel 322 is provided between the section switch 20 and each of the consumers 25a to 25d. The power receiving panel 322 includes a fused switch (LBS) 23, a transformer (pole transformer) Tr, and an operation controller 27. The microgrid system 300 uses the operation controller 27 to control the timing of the closing operation of the fused switch 23 when power is restored to the high-voltage distribution line 3. The fused switch 23 corresponds to an automatic switch in the power receiving panel 322, and the operation controller 27 corresponds to a control unit that controls the operation of the automatic switch in the power receiving panel 322. Specifically, after a power outage occurs in the microgrid 10 and power is restored to the high-voltage distribution line 3, the LBS 23 of the consumer 25a corresponding to the first automatic switch is closed after 5 seconds, the LBS 23 of the consumer 25b corresponding to the second automatic switch is closed after 10 seconds, the automatic switch 215 corresponding to the third automatic switch is closed after 15 seconds, the LBS 23 of the consumer 25c corresponding to the fourth automatic switch is closed after 20 seconds, and the LBS 23 of the consumer 25d corresponding to the fifth automatic switch is closed after 25 seconds. Compared to the microgrid system 100, the microgrid system 300 can also reduce the number of components required to build a protection coordination system in the microgrid 10.

(Fourth Example)
As shown in FIG. 4 , the microgrid system 400 is a modified example of the microgrid system 100, in which a branch path is formed within the microgrid 10. Specifically, the high-voltage distribution line 3 includes a main high-voltage distribution line 3a and a branch high-voltage distribution line 3b. The components constituting the microgrid system 400 are the same as those of the microgrid system 100. However, in the microgrid system 400, a consumer 25c and a third automatic switch 15 are connected to the branch high-voltage distribution line 3b. As described above, in the microgrid system 100, the closing operation is performed in the order of the first automatic switch 11, the second automatic switch 13, the third automatic switch 15, the fourth automatic switch 17, and the fifth automatic switch 19, starting from the side closest to the storage battery equipment 40. However, in the microgrid system 400, the closing operation is performed preferentially on the automatic switch connected to the main high-voltage distribution line 3a, and then the closing operation is performed on the automatic switch connected to the branch high-voltage distribution line 3b. That is, when it is detected that the distribution system (high-voltage distribution line 3) has restored power, after outputting of a closing operation signal to the automatic switchgears 11, 13, and 19 corresponding to each customer in the main distribution system (customers 25a, 25b, and 25d connected to the main high-voltage distribution line 3a) has finished, a closing operation signal is output to the automatic switchgear 15 on the branch distribution system and the automatic switchgear 17 corresponding to each customer in the branch distribution system (customer 25c connected to the branch high-voltage distribution line 3b). Specifically, each switchgear controller closes the first automatic switchgear 11, the second automatic switchgear 13, the fifth automatic switchgear 19, the third automatic switchgear 15, and the fourth automatic switchgear 17 in this order.

(Fifth Example)
As shown in Fig. 5 , the microgrid system 500 is a modified example of the microgrid system 200, in which the high-voltage distribution line 3 includes a main high-voltage distribution line 3a and a branch high-voltage distribution line 3b. The components constituting the microgrid system 500 are the same as those of the microgrid system 200. Like the microgrid system 400, the microgrid system 500 also performs a closing operation preferentially on the automatic switch connected to the main high-voltage distribution line 3a, and then performs a closing operation on the automatic switch connected to the branch high-voltage distribution line 3b. Specifically, each switch controller performs a closing operation on the first automatic switch 211, the second automatic switch 213, the fifth automatic switch 219, the third automatic switch 215, and the fourth automatic switch 217 in this order.

(Sixth Example)
The microgrid system 600 is a modified example of the microgrid system 300, and the high-voltage distribution line 3 includes a main high-voltage distribution line 3a and a branch high-voltage distribution line 3b. The components that make up the microgrid system 600 are the same as those of the microgrid system 300. Like the microgrid systems 400 and 500, the microgrid system 600 also performs a closing operation preferentially on the automatic switch connected to the main high-voltage distribution line 3a, and then performs a closing operation on the automatic switch connected to the branch high-voltage distribution line 3b. Specifically, after a power outage occurs within the microgrid 10 and power is restored to the high-voltage distribution line 3, the LBS 23 of consumer 25a, which corresponds to the first automatic switch, is closed after 5 seconds, the LBS 23 of consumer 25b, which corresponds to the second automatic switch, is closed after 10 seconds, the LBS 23 of consumer 25d, which corresponds to the fifth automatic switch, is closed after 15 seconds, the automatic switch 215, which corresponds to the third automatic switch, is closed after 20 seconds, and the LBS 23 of consumer 25c, which corresponds to the fourth automatic switch, is closed after 25 seconds.

(Other Modifications)
In the above embodiments, after detecting the restoration of power to the high-voltage distribution line 3, in the first to third embodiments, the closing operation is performed at 5-second intervals from the side closest to the storage battery device 40, and in the fourth to sixth embodiments, the automatic circuit breaker connected to the main high-voltage distribution line 3a is given priority over the automatic circuit breaker connected to the branch high-voltage distribution line 3b, and then the closing operation is performed at 5-second intervals from the side closest to the storage battery device 40. However, the interval between closing operations does not have to be 5 seconds as long as the closing operation is performed at a specified time interval.

In the above embodiment, an example was described in which the timing of the closing operation of each automatic switch is staggered using a control device that controls the operation of a fused switch (LBS) located in a power receiving panel. However, for example, a centralized control device may be installed in the battery storage device, and the centralized control device may control the timing of the closing operation of each automatic switch to be staggered. Specifically, the centralized control device and the fused switch may be connected via a communication line, and the centralized control device may output a closing command to each automatic switch at predetermined intervals via the communication line, allowing the closing operation of each automatic switch to be performed remotely.

In the above embodiment, an example was described in which a storage battery device was used as the power source within the microgrid, but a generator can also be used instead of a storage battery device. The generator is stopped when power is supplied from the power grid, and is operated when the microgrid is in operation. Therefore, if the generator is operated in leading phase during microgrid operation, it will stop, so it must be adjusted to lagging phase operation. Therefore, when supplying power using a generator during microgrid operation, the reactive power compensator automatically switches the operating method from constant voltage control to constant power factor control while detecting the direction of the current flow. This prevents the generator from stopping.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings may demonstrate technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful.

3: Power distribution system 11, 13, 15, 17, 19: Automatic switch 40: Power distribution equipment

Claims (4)

A protection and coordination system for a microgrid formed in a power distribution system,
An automatic switch that automatically opens during a power outage and automatically closes when power is restored,
a control unit that outputs an opening operation signal to the automatic switch when a power outage in the power distribution system is detected, and outputs a closing operation signal to the automatic switch when a power restoration after a power outage in the power distribution system is detected,
A protection coordination system in which, when the control unit detects that power has been restored to the distribution system, it outputs an on-state operation signal to the automatic switch corresponding to each consumer at predetermined time intervals, starting with the one closest to the power generation equipment. An automatic switch is installed in each customer's power receiving panel.
2. A protection coordination system according to claim 1, wherein a control unit for controlling the operation of an automatic switch in a power receiving panel outputs a closing operation signal to the automatic switch. A protection coordination system as described in claim 1 or 2, in which if a power outage is detected within a predetermined time after a closing signal is output to an automatic circuit breaker, the output of a closing signal to that automatic circuit breaker is prohibited the next time a power restoration is detected. A main distribution system and branch distribution systems are formed within the microgrid.
4. A protection coordination system according to claim 1, wherein when it is detected that power has been restored to the distribution system, after output of a closing operation signal to the automatic circuit breaker corresponding to each consumer in the main distribution system has been completed, a closing operation signal is output to the automatic circuit breaker corresponding to each consumer in the branch distribution system.