JPH0548053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an interconnection device for a small capacity power generation system.

B. Summary of the Invention The present invention provides an interconnection device for a small-capacity power generation system configured to interconnect a small-capacity power generation device and a distribution system to supply power to a load. A ground fault overvoltage relay that operates faster than the slight ground fault selection relay provided in the distribution system and the ground fault direction relay provided for each distribution line is installed on the electrical circuit connecting the circuit breaker, and a ground fault overvoltage relay that operates faster than the The circuit breaker is cut off, and after a predetermined set time has passed since the circuit breaker is cut off, the cutoff occurs when the vector difference between the distribution system voltage and the output voltage of the small-capacity power generation device is equal to or less than a set value. By installing an automatic reclosing relay that gives a power-on command to the equipment, it is possible to connect small-capacity power generation equipment to the existing distribution system without changing the equipment of the existing distribution system, and it is possible to prevent ground faults from occurring. The system is designed to avoid any negative impact on small-capacity power generation equipment or the grid.

C. Conventional technology In recent years, the demand for electric power has been increasing more and more, but the currently mainstream power generation systems using nuclear power and thermal power are subject to restrictions in terms of resources, installation locations, etc. For this reason, fuel cell power generation systems are attracting attention because they can be distributed across power consumption areas, are non-polluting, and have high power generation efficiency. For distributed equipment, the most economical method is to connect it to the load end of an existing power distribution system as a small-scale power generation system.

D. Problems to be solved by the invention However, since it is related to the protection and control methods of the existing power distribution system, the conventional parallel operation control method of the power generation equipment and the power distribution system, and the protection and control method of the private power distribution system are not necessary. It was not possible to apply it as is. That is, for example, a conventional parallel operation system between large-scale power generation facilities has a configuration in which they are connected not by a power distribution system but by a nearly dedicated power transmission system. In such a parallel operation system, each power plant has equipment equipped with the protective control functions necessary for parallel operation (synchronization detection, synchronization input, out-of-sync detection, etc.), and the power transmission system also has equipment to prevent out-of-synchronization and frequency Protection and control equipment is installed that can respond to fluctuations, etc. However, when connecting a small-scale power generation system to an existing power distribution system, not only does the distribution system lack a synchronization confirmation function, but it also requires control devices specific to the power distribution system, such as automatic reclosing devices and fault section indicators. Therefore, it was not possible to apply the conventional interconnection method between power plants as is.

By the way, earth fault protection for electrical equipment connected to a non-grounded power distribution system has conventionally been performed using a ground fault direction relay 67G or a ground fault overcurrent relay 51G. That is, since the power distribution system is not grounded, the power generation equipment connected to the power distribution system is also not grounded, and the grounding capacity is also small, so it is normal to provide ground fault protection using the ground fault overcurrent relay 51G.

Here, in a system in which a power distribution system and a small-capacity power generation facility are interconnected, problems when providing ground fault protection using the ground fault direction relay 67G and the ground fault overcurrent relay 51G will be explained with reference to the circuit diagram of FIG. 4. In FIG. 4, it is assumed that the primary side of the transformer T is connected to an alternating current (not shown). The secondary side of the transformer T is connected to the AC bus 1 via a circuit breaker CB ₀ . CB ₁ to CBn are circuit breakers respectively inserted in electric lines connecting parallel distribution lines (hereinafter referred to as feeders) F ₁ to Fn and the AC bus bar 1 . The AC output power of the AC power supply (not shown) is transmitted through the transformer T, the circuit breaker CB ₀ , the AC bus 1, and the circuit breaker CB ₁ .
It is supplied to a load (not shown) via CBn and feeders F ₁ to Fn. 2 is a small capacity power generation device,
For example, it is composed of a fuel cell power generation device and an inverter (not shown) that converts its DC output power to AC. The AC output power of this small-capacity power generation device 2 is supplied to a load (not shown) via the feeder _F1 and the circuit breaker CBI, which is cut off when the ground fault overcurrent relay 51G is activated. Ground fault overcurrent relay 51G
is operated by the output current of a zero-phase current transformer ZCT ₀ inserted in the electrical circuit connecting the small-capacity power generator 2 and the circuit breaker CBI. The AC bus 1 is equipped with a zero-phase voltage transformer.
GPT is provided. Zero-phase current transformers ZCT ₁ -ZCTn are provided in the feeders F ₁ -Fn, respectively.
The ground fault direction relays 67G ₁ to 67Gn connect the output voltage of the zero-phase voltage transformer GPT and the zero-phase current transformer ZCT ₁ to
It operates according to each output current of ZCTn. There is a slight ground fault selection relay 1 on the secondary side of the zero-phase voltage transformer GPT.
0G is provided. 79F ₁ to 79Fn are re-closing relays for re-closing the circuit breakers CB ₁ to CBn, respectively.

In the device configured as described above, during parallel operation, point A on feeder F ₁ , point B on AC bus 1
If a ground fault occurs at point C on feeder F ₂ and point D on the electric line connecting small-capacity power generator 2 and circuit breaker CBI, the following situation will occur.

(1) When a ground fault occurs at point A, the ground fault direction relay 67G ₁ operates and circuit breaker CB ₁ is shut off.
The power supply from the power grid will be cut off. However, since the small-capacity power generation device 2 has almost no ground capacity, a zero-sequence current sufficient to operate the ground fault overcurrent relay 51G does not flow through the zero-sequence current transformer ZCT ₀ . Therefore, since the circuit breaker CBI is not cut off, if the load (not shown) connected to the feeder F ₁ is small, the power supply from the small capacity power generation device 2 will continue. That is, while the ground fault remains, the power supply voltage on the power system side and the output voltage of the small-capacity power generation device 2 become out of sync. When the re-closing relay 79F ₁ operates to re-close the cutoff path CB ₁ after a predetermined time has elapsed in this state, an excessive current flows between the power system and the small-capacity power generation device 2 . For this reason, the small-capacity power generation device 2 and the power system will be adversely affected.

(2) When a ground fault occurs at point B, the ground fault overcurrent relay 51G and the ground fault direction relay 67G ₁ to 6
7Gn does not operate, and after the circuit breakers CB ₁ to CBn are shut off by the slight earth fault selection relay 10G, the circuit breaker CB ₀ is shut off. In this case, the circuit breaker CBI is not cut off, so a problem similar to that described in item (1) above occurs.

(3) If a ground fault occurs at point C, the circuit breaker CB ₂ is simply shut off by the ground fault direction relay 67G ₂ , so there is no problem with parallel operation.

(4) If a ground fault occurs at point D, ground fault current will flow to ground fault point D through the ground capacity on the power system side, so the ground fault overcurrent relay 51G is activated in zero-phase current transformer ZCT ₀ . Sufficient zero-sequence current flows. Therefore, the ground fault overcurrent relay 51G operates and the circuit breaker CBI interrupts the circuit, so that the current system becomes normal and there is no problem.

The present invention has been made in view of the above points, and allows small-capacity power generation equipment to be connected to the existing power distribution system without changing the equipment of the existing power distribution system.
Moreover, it is an object of the present invention to provide a connection device for a small-capacity power generation system that does not adversely affect the small-capacity power generation equipment or the grid even if a ground fault occurs.

E Means for Solving the Problems The present invention provides an interconnection device for a small-capacity power generation system that is configured to interconnect a small-capacity power generation device and a distribution system to supply power to a load. A circuit breaker inserted in an electric line connecting a power distribution line and a small-capacity power generation device, a zero-sequence voltage transformer that detects a zero-sequence voltage of the electric line connecting this circuit breaker and the small-capacity power generation device, and a zero-sequence voltage transformer whose operating time is set to the power distribution line. The operating time of the ground fault directional relay provided in the distribution line of the power system and the operating time of the slight ground fault selection relay provided in the power distribution system are set faster, and the output of the zero-phase voltage transformer A ground fault overvoltage relay that responds and issues a shutdown command to the circuit breaker, and a vector difference between the distribution system voltage and the output voltage of the small-capacity power generation device is set after a predetermined set time has passed after the circuit breaker is disconnected. The present invention is characterized by comprising an automatic re-closing relay which gives a closing command to the circuit breaker when the voltage is below the value.

F Effect When a ground fault occurs in the device configured as above, the ground fault overvoltage relay operates faster than the ground fault direction relay and the slight ground fault selection relay, so the circuit breaker is reliably tripped. . Furthermore, after a predetermined set time has elapsed after the circuit breaker has been disconnected, the circuit breaker is reclosed on the condition that the vector difference between the distribution system voltage and the output voltage of the small capacity power generation device is less than or equal to the set value. Ru. For this reason, the small-capacity power generation device does not remain disconnected from the power grid, and the operating rate of the power generation device improves.

G. Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the same parts as in FIG. 4 are designated by the same reference numerals, and their explanation will be omitted. A zero-phase voltage transformer 3 is provided in the electric line connecting the circuit breaker CBI and the small-capacity power generation device 2. A ground fault overvoltage relay 64I is connected to the secondary side of the zero-phase voltage transformer 3 to issue a disconnection command to the circuit breaker CBI. The operating value of the ground fault overvoltage relay 64I is set lower than, for example, the operating values of the ground fault direction relays 67G ₁ to 67G ₃ and the slight ground fault selection relay 10G.
In addition, the operating time of the ground fault overvoltage relay 64I is
As shown in the characteristic diagram of the figure, ground fault direction relay 67G ₁
~ Set faster than the operating time of 67G ₃ and slight ground fault selection relay 10G. 79I issues a closing command to the circuit breaker CBI when the vector difference between the distribution system voltage and the output voltage of the small-capacity generator is equal to or less than a set value after a predetermined set time has elapsed since the circuit breaker CBI was shut off. It is an automatic reclosing relay. This automatic reclosing relay 79I is, for example, the third
As shown in the figure, a vector difference voltage confirmation unit 11 that issues an output signal when the vector difference between the grid voltage and the voltage on the generator side is less than a predetermined set value, and a circuit breaker CBI
A timer 12 that issues an output signal after a predetermined set time has elapsed since the circuit breaker CBI is cut off, and an AND circuit 13 that issues a closing command to the circuit breaker CBI when the AND condition of the output signals of the vector difference voltage confirmation unit 11 and the timer 12 is satisfied. It is configured. The set time of the timer 12 is set to be longer than one cycle time of the reclosing relays 79F ₁ to 79F ₃ provided on the power distribution system side.

Next, the operation of the apparatus configured as described above will be described.

(1) When a ground fault occurs at point A, the ground fault overvoltage relay 64I operates first, as is clear from the operating time characteristics diagram in Figure 2, so the breaker
CBI is shut down. Then, the ground fault direction relay 67G ₁ operates and the circuit breaker CB ₁ is cut off. Therefore, when the circuit breaker CB ₁ is subsequently reclosed by the reclose relay 79F ₁ , an excessive current will not flow between the power system and the small capacity power generation device 2. If the re-closing of the circuit breaker CB ₁ is successful, the condition is that more than one cycle time of the re-closing relay 79F ₁ has elapsed, and the vector difference between the grid voltage and the output voltage of the small capacity generator 2 is below the set value. circuit breaker
The CBI is re-energized and the circuit returns to its original state.

(2) When a ground fault occurs at point B, the ground fault overvoltage relay 64I operates first and the circuit breaker CBI
is blocked. And then the ground fault direction relay 67
G ₁ to 67G ₃ are inactive, slight ground fault selection relay 1
Operation of 0G causes circuit breaker CB ₀ to shut off.
For this reason, feeder F ₁ becomes voltageless and the operating conditions of automatic reclosing relay 79I are not satisfied.
Circuit breaker CBI is not reclosed. The distribution system will not be adversely affected by this.

(3) When a ground fault occurs at point C, the ground fault overvoltage relay 64I operates first and the circuit breaker CBI
is blocked. Then ground fault direction relay 67G ₂
operates and circuit breaker CB ₂ is shut off. Next, reclosing relay 79F ₂ attempts to reclose circuit breaker CB ₂ , and if reclosing is successful, the operating conditions for automatic reclosing relay 79I are established after one cycle of reclosing relay 79F ₂ has elapsed. . Therefore, the circuit breaker CBI is re-closed and the normal state is restored.

(4) When a ground fault occurs at point D, the ground fault overvoltage relay 64I operates first and the circuit breaker CBI
is blocked. For this reason, ground fault direction relay 67G ₁
will not operate and circuit breaker CB ₁ will not be tripped. As a result, the output power of the AC power supply (not shown) on the power system side continues to be supplied to the load (not shown) via the feeder _F1 without being affected by the ground fault at point D. In this case, on the small-capacity power generation device 2 side, the inverter (not shown) is stopped by a control device (not shown), and then the ground fault at point D is removed. In this way, the output of the small-capacity power generation device 2 becomes non-voltage, so the operating conditions for the automatic reclose relay 79I are not satisfied, and the circuit breaker CBI is not reclosed.

H Effects of the Invention As described above, according to the present invention, the following effects can be obtained. That is, (1) the small-capacity power generation device and the existing power distribution system can be interconnected without changing the equipment of the existing power distribution system.

(2) If a ground fault occurs on the AC busbar of the power distribution system or on the distribution line to which a small-capacity power generator is connected, the interconnection circuit breaker can be reliably shut off.
Moreover, the circuit breaker is reclosed only after it is confirmed that the vector difference between the grid voltage and the output voltage of the small-capacity generator is less than the set value. does not flow. Therefore, there is no adverse effect on the electric power system or the equipment of the small-capacity power generation device.

(3) If a ground fault occurs on a distribution line other than the distribution line connected to the small-capacity power generation equipment, the interconnection circuit breaker will be shut off, but after the distribution line has been reclosed. The interconnection circuit breaker is reclosed by the automatic reclosing relay. For this reason, the small capacity power generation device will not remain disconnected.

(4) If the circuit breaker of the distribution line connected to the small-capacity power generation device is successfully reclosed, the automatic recloser will automatically close the circuit breaker again. This eliminates the need for cumbersome manual reinsertion operations, improving the operating rate of the small-capacity power generator.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a relay operating time characteristic diagram for explaining the main part of the present invention, Fig. 3 is a block diagram showing the main part of the present invention, and Fig. 4 is an example of a conventional interconnection device for a small-capacity power generation system. FIG. CBI, CB ₀ ~ CB ₃ ...Breaker, 79I...Automatic reclosing relay, 2...Small capacity generator, 67G ₁
~67G ₃ ...Ground fault direction relay, 3...Zero-phase voltage transformer, 10G...Slight ground fault selection relay, 64I...
...Ground fault overvoltage relay, _F1 to _F3 ...Feeder.

Claims (1)

[Claims] 1. In a interconnection device for a small-capacity power generation system configured to connect a small-capacity power generation device and a distribution system to supply power to a load, an electric line connecting the distribution line of the distribution system and the small-capacity power generation device is connected. an inserted circuit breaker, a zero-sequence voltage transformer that detects the zero-sequence voltage of an electric line connecting the circuit breaker and the small-capacity power generating device, and a ground-fault directional relay whose operating time is provided on the distribution line of the distribution system. and the operating time of the micro-ground fault selection relay provided in the power distribution system, and is responsive to the output of the zero-phase voltage transformer to issue a disconnection command to the circuit breaker. The overvoltage relay and the circuit breaker are configured to issue a closing command to the circuit breaker when a vector difference between the distribution system voltage and the output voltage of the small capacity generator is equal to or less than a set value after a predetermined set time has elapsed since the circuit breaker has been disconnected. An interconnection device for a small-capacity power generation system, characterized in that it is equipped with an automatic reclosing relay that provides an automatic reclosing relay.