JPS61221524A - Apparatus for linking small-capacity generation system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] A. Industrial application field The present invention relates to an interconnection device for a small capacity power generation system.

B1 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 power distribution system to supply power to a load, comprising: an output end of the small-capacity power generation device; A capacitor is connected between the ground and the ground to ensure that sufficient current flows to the ninth relay that shuts off the interconnection circuit breaker in the event of a ground fault, and to set the operating time of the relay to the optimal operating time. and an automatic system that issues a closing command to the circuit breaker when the vector difference between the distribution system voltage and the output voltage of the small-capacity power generator falls below a set value after a predetermined set time has elapsed since the circuit breaker was shut off. By installing a reclosing relay, small-capacity power generation equipment can be connected to the existing distribution system without changing the existing distribution system equipment, and even if a ground fault occurs, the small-capacity power generation equipment or This is to avoid any negative impact on the system.

C0 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 deployment, the most economical method for small-scale power generation systems is to connect to the load end of the existing distribution system.

The problem that the D0 invention aims to solve However, since it is related to the protection method and control method of the existing power distribution system, it is difficult to implement the parallel operation control method of the conventional power generation equipment and the power distribution system, or the protection control method of the private power generation system. It could not be applied 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 protective control functions (synchronization detection,
In addition, power transmission systems are equipped with protection control equipment that can respond to synchronization and frequency fluctuations. However, when connecting a small-scale power generation system to an existing distribution system, not only does the distribution system not have a synchronous WA recognition function, but it also requires control devices specific to the 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 of 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 that interconnects the power distribution system and small-capacity power generation equipment, the ground fault direction relay 67G and the ground fault overcurrent relay 51
Problems in providing ground fault protection using G will be explained with reference to the circuit diagram in FIG. In Fig. 4, 1 of transformer T
It is assumed that the next side is connected to an AC power source (not shown). The secondary side of transformer T is connected to AC bus 1 via circuit breaker CB6.
It is connected to the. CBl-CBn are 7'C circuit breakers inserted in the t-paths connecting parallel distribution lines (hereinafter referred to as feeders) Fs to Fn and the AC bus 1, respectively.

The AC output power of the AC power supply (not shown) is supplied to the transformer T.
, J disconnector CB, , AC bus 1. Circuit breaker CB, ~CB.

and is supplied to a load (not shown) via feeder F1%Fnt-. Reference numeral 2 denotes a small-capacity power generation device, which is composed of a fuel cell power generation device 1, for example, and an inverter (not shown) that converts its DC output power to AC. This small capacity power generation device! ! The AC output power of No. 2 is supplied to the circuit breaker CBI and the feeder F, which are cut off when the ground overcurrent relay 51G operates.
1 to a load (not shown). The ground fault overcurrent relay 51G is operated by the output current of the zero-phase current transformer ZCTo inserted in the electric path connecting the small-capacity power generation device 2 and the circuit breaker CBI. The AC bus 1 is equipped with a zero-phase voltage transformer G.
PT is provided. The feeders F1 to FnK are each provided with zero-phase current transformers Z'CT and ZCTn.

The ground fault direction relays 67G, ~67Gn connect the output voltage of the zero-phase voltage transformer GPT and the zero-phase current transformers ZCT, ~ZCTn.
It operates with each output current. Phase voltage transformer GP
A slight ground fault selection relay 10G is provided on the secondary side of T. 79F and 79Fn are re-closing relays for re-closing the circuit breakers CB and CBn, respectively.

In the apparatus configured as above, during parallel operation, point A on feeder F1, point B on flow line 1, feeder F
, when a ground fault occurs at point 0 above and point D on the electric line connecting the small-capacity power generator 2 and circuit breaker CBI, the following situation occurs.

(1) If a ground fault occurs at point A, the ground fault direction relay 67G operates to shut off the circuit breaker CB1, cutting off the power supply from the power system. However, since the small-capacity power generation device 2 has almost no ground capacity, the zero-sequence current sufficient to operate the ground fault overcurrent relay 51G flows through the zero-sequence current transformer Z.
There is no flow to CTo. Therefore, since the circuit breaker CBIFi is not cut off, if the load (not shown) connected to the feeder F1 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 asynchronous. In this state, when the re-closing relay 79F operates to re-close the circuit breaker CB after a predetermined period of time has elapsed, an excessive current flows between the power system and the small-capacity power generation device 20. 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 relays 67G1 to 67Gn do not operate, and the circuit breakers CB1 to 67Gn are activated by the slight ground fault selection link 10G.
After CBn is cut off, circuit breaker CBo is cut off. In this case, since the circuit breaker CBI is not cut off, a problem similar to that described in item (1) above occurs.

(3) If a ground fault occurs at point 0, the ground fault direction relay 6
Since the cut-off ICB is only cut off by 7 Gt, there is no problem with parallel operation.

(4) If a ground fault occurs at point D, the ground fault current will flow to the ground fault point through the ground capacity of the power system.
A zero-sequence current sufficient to operate the earth fault overcurrent relay 51G flows through the zero-sequence transformer 6 Z CT.

For this reason, the ground fault overcurrent relay 51G operates and the circuit breaker CBI
Since the power system is cut off, the power system is in a normal state and there are no problems.

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 distribution system without changing the equipment of the existing distribution system, and moreover, without causing ground faults. The purpose of the present invention is to provide an interconnection device for a small-capacity power generation system that does not adversely affect small-capacity power generation equipment or the grid.

Next Means for Solving Problem E1 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 power distribution system to supply power to a load. A circuit breaker inserted in the electric line connecting the distribution line and the small-capacity power generation device, and a zero-phase current transformer inserted in the electric line connecting the circuit breaker and the small-capacity power generation device, The output of the zero-phase current transformer is set to be slower than the operating time of the ground fault direction relay provided on the distribution line of the power system and further than the operating time of the slight ground fault selection relay provided on the distribution system, and Respond and move forward! e A ground fault overcurrent relay that gives 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 set to a set value after a predetermined set time has elapsed since the circuit breaker has been disconnected. The present invention further comprises: an automatic reclosing relay that issues a closing command to the circuit breaker when: f:l! It is considered as an “If” sign.

20 actions above +7)! In the device configured in No. 5, when a ground fault occurs, sufficient current flows through the zero-phase current transformer via the capacitor, so the ground fault overcurrent relay operates reliably and the circuit breaker is cut off. In addition, after the circuit breaker is disconnected and a predetermined set time has elapsed, the circuit breaker recloses on the condition that the vector difference between the distribution system voltage and the output voltage of the small capacity generator is less than or equal to the set value. be done. 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 shown with the same reference numerals, and the explanation thereof will be omitted. The zero-phase current transformer Z CTo
A capacitor C3 is connected between the small-capacity power generation device 2 side of the electric circuit in which the power supply is inserted and the ground. This capacitor CI
The capacity is set to a value such that a sufficient zero-sequence current flows to operate the ground fault overcurrent relay 51G in the event of a ground fault on the system side.

A capacitor C1 is connected between the circuit breaker CBI side of the circuit in which the zero-phase transformation ATO is inserted and the ground. This capacitor C2 is a capacitor that becomes necessary when the zero-sequence current flowing through the ground capacitance of the feeder F80 is insufficient to operate the ground fault overcurrent relay 51G in the event of a ground fault accident. The operating value of the ground fault overcurrent relay 51G is set to a value that can sufficiently respond to the zero-sequence current flowing through the capacitor CI in the event of a ground fault on the system side, and also to a value that can sufficiently respond to the zero-sequence current flowing from the feeder F side (feeder (determined by the sum of the ground capacitance of F and the capacitance of capacitor C8). The operating time of the ground fault overcurrent relay 51G is set to be slower than the operating time of the ground fault direction relays 67G to 67Gn and faster than the operating time of the slight ground fault selection relay 10G, as shown in the characteristic diagram of FIG. put.

79I issues a closing command to the circuit breaker C1l when 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 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 includes, for example, as shown in FIG. 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. Said timer 1
The set time 2 is set to be larger than the cycle time of the reclose relays 79F8 to 79Fn01 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, as is clear from the operating time characteristic diagram in FIG. 2, first the ground fault direction relay 67G8 operates and the circuit breaker CB is shut off. Next, since a sufficiently large zero-sequence current flows through the zero-sequence current transformer ZCT through the capacitor C1, the ground fault overcurrent relay 51G operates reliably. Since the circuit breaker CBI is thereby disconnected, an excessive current does not flow between the power system and the small capacity power generation device 2 when the circuit breaker CB is reclosed by the reclose relay 79F1. If the re-closing of the circuit breaker CB is successful, one cycle time or more of the re-closing relay 79F1 has elapsed;
In addition, on the condition that the vector difference between the system voltage and the output voltage of the small-capacity power generation device 2 is less than or equal to the set value, the cutoff WacBI is turned on again, and the circuit returns to its original state.

(2) When a ground fault occurs at 8 points, the ground fault direction relay 67G1 is inoperative and the slight ground fault selection relay 10G is activated, but before that, the ground fault overcurrent relay 51G is caused by the zero-sequence current flowing through the capacitor C1. operates first. Therefore, the circuit breaker CBI is cut off first, and then the circuit breaker CB is cut off, so that the feeder F becomes voltageless. Therefore, the operating conditions for automatic reclose relay 79I are no longer met, so that circuit breaker CBI is not reclosed and the power distribution system is not adversely affected.

(3) When a ground fault occurs at the 0 point, the ground fault direction relay 67G operates first, so the circuit breaker CB is cut off. At this point, the ground fault overcurrent relay 51G is restored, so the circuit breaker CBI is not cut off. For this reason, the small capacity power generation device 2 connected to the feeder F is
It will not be unnecessarily disconnected due to the effects of a ground fault that occurred on the 8th side.

(4) When a ground fault occurs at the 0 point, first the ground fault direction relay 67G is operated, the circuit breaker CB is cut off, and the small capacity power generation device 2 is operated independently. However, since the zero-sequence current due to the sum of the ground capacity of the feeder Fl and the capacitor C2 flows to the zero-sequence current transformer ZCT0, the ground fault overcurrent relay 5
1G is activated and circuit breaker CBI is also shut off.

H6 Effects of the Invention As described above, according to the present invention, the following effects can be obtained. That is, (1) a small-capacity power generation device and an existing power distribution system can be interconnected without changing the equipment of the existing power distribution system.

(2) If a ground fault occurs on an AC bus in a power distribution system or on a distribution line to which a small-capacity power generation device is connected, the interconnection circuit breaker can be shut off reliably. 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) Even if a ground fault occurs on a distribution line other than the secondary distribution line that is interconnected with a small-capacity power generation device, the interconnection circuit breaker will not be tripped.For this reason, the small-capacity power generation device It will not be unnecessarily disconnected due to the influence of the ground fault.

(4) If the circuit breaker of the distribution line connected to the small-capacity power generation device is successfully reclosed, the operation of the automatic reclosing relay automatically closes the circuit breaker for the distribution line again. Therefore, there is no need for the troublesome re-powering operation after obtaining the power, and the operating rate of the small-capacity power generation device is improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a relay operating time characteristic diagram for explaining the present invention in detail, FIG. 3 is a block diagram showing the main parts of the present invention, and FIG. FIG. 4 is a circuit diagram showing an example of a conventional interconnection device for a small-capacity power generation system. C1* C@ ... Capacitor, Z CTo -Z
CTn=zero phase current transformer, CB I, CBo=CBn
...jl disconnector, 67G1-67Gn...ground fault direction relay, 51G...ground fault overcurrent relay, 10G...slight ground fault selection relay, 2...small capacity power generator, F, ~Fn
...Feeder, 79I...Automatic reclosing relay.

Claims (1)

[Claims] In a 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, the power generation device is inserted into an electric line connecting the distribution line of the distribution system and the small-capacity power generation device. a zero-phase current transformer inserted in the electrical circuit connecting the circuit breaker and the small-capacity power generation device, and an operating time of a ground-fault directional relay installed on the distribution line of the distribution system. an earth fault overcurrent relay that is set slower and faster than the operation time of a micro-earth fault selection relay provided in the distribution system, and that responds to the output of the zero-phase current transformer to issue a disconnection command to the circuit breaker; and an automatic restart that issues a closing command to the circuit breaker when 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 a set value after a predetermined set time has elapsed since the circuit breaker was disconnected. A interconnection device for a small-capacity power generation system, comprising a closing relay, and a capacitor connected between the earth and an electric line connecting the zero-phase current transformer and the small-capacity power generation device.