JPH0550208B2 - - 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. An overcurrent relay that operates faster than an overcurrent relay provided in the power distribution system is provided in the electrical path connecting the circuit breaker, and when the overcurrent relay operates, the interconnection breaker is interrupted, and the circuit breaker is interrupted. By providing an automatic reclosing relay 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 the set value after a predetermined set time has elapsed, It is possible to connect small-capacity power generation equipment to the existing power distribution system without changing the distribution system equipment, and even if a short-circuit accident occurs, it will not have a negative impact on the small-capacity power generation equipment or the system. It is.

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

D Problems to be solved by the invention However, since it is related to the protection system and control system of the existing power distribution system, the parallel operation control system of the conventional power generation equipment and the power distribution system and the protection control system of the private power generation system are not applicable. 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.

Here, in a system in which a power distribution system and a small-capacity power generation facility are interconnected, problems when short-circuit protection is provided by an overcurrent relay 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 AC power source (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 CB _o are parallel power distribution lines (hereinafter referred to as feeders) F ₁ to _{F o}
These circuit breakers are respectively inserted in electric circuits connecting the AC bus bar 1 and the AC bus bar 1. The AC output power of the AC power supply (not shown) is transmitted through a transformer T, a circuit breaker CB ₀ , an AC bus 1,
It is supplied to a load (not shown) via circuit breakers CB ₁ to CB _o and feeders F ₁ to _{F o} . Reference numeral 2 denotes a small-capacity power generation device, which is composed of, for example, a fuel cell power generation device and an inverter (not shown) that converts the DC output power to AC. The AC output power of this small-capacity power generation device 2 is supplied to a load (not shown) through the circuit breaker CBI and the feeder _F1 , which are cut off when the overcurrent relay 51 is activated. The overcurrent relay 51 is
It is operated by the output voltage of the current transformer CT ₀ inserted in the electric line connecting the small capacity power generator 2 and the circuit breaker CBI.
The feeders F ₁ -F _o are provided with current transformers CT ₁ -CT _o , respectively. Overcurrent relay 51F ₁ ~ _{F o} is a current transformer
The circuit breaker is operated by each output current of CT ₁ to CT _o .
Block each of CB ₁ to CB _o . 79F ₁ to 79F _o are reclosing relays for reclosing the circuit breakers CB ₁ to _{CB o} , respectively.

In the device configured as described above, during parallel operation, point A on feeder F ₁ , point B on AC bus 1
When short-circuit accidents occur 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 occurs.

(1) When a short-circuit accident occurs at point A, short-circuit current flows from both the small-capacity power generator 2 and the power grid side. For this reason, the circuit breaker CBI is activated by the overcurrent relay 51.
is cut off, and the circuit breaker CB ₁ is cut off by the overcurrent relay 51F ₁ . There is no problem in this case.

(2) If a short circuit occurs at points B and C,
Similar to the above item (1), short-circuit current flows from both the small-capacity power generation device 2 and the power system. At this time, if the overcurrent relay 51F ₁ on the grid side operates earlier than the overcurrent relay 51 on the small capacity generator 2 side, the fault current disappears due to the interruption of the circuit breaker CB ₁ , and the load connected to the feeder F ₁ (not shown) (omitted) is small, the overcurrent relay 51 will return to its normal state. For this reason, the circuit breaker CBI is not cut off, so power supply from the small capacity power generation device 2 continues, and the power supply voltage on the power grid side and the output voltage of the small capacity power generation device 2 become asynchronous. When the re-closing relay 79F ₁ operates to re-close the circuit breaker CB ₁ after a predetermined period of 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.

(3) Even if a short-circuit accident occurs at point D, a short-circuit current flows from the power system through circuit breakers CB ₁ and CBI, but at this time, if overcurrent relay 51F ₁ operates earlier than overcurrent relay 51, overcurrent relay 51
will return. For this reason, the same problem as in item (2) above arises.

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 interconnection 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 short-circuit accident 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 distribution line and a small-capacity power generator, a current detector inserted in an electric line connecting this breaker and the small-capacity power generator, and an operating time of a circuit breaker of the power distribution system. an overcurrent relay that is set faster than the operating time of an overcurrent relay provided in the current detector and that responds to the output of the current detector to issue a shutdown command to the circuit breaker; and an automatic reclosing relay 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. It is said that

F Effect If a short-circuit accident occurs in a device configured as described above, the overcurrent relay on the small-capacity generator side will operate faster than the overcurrent relay on the distribution system side, so the circuit breaker will be shut off reliably. Ru. In addition, after a predetermined set time has passed after the circuit breaker is shut off,
The circuit breaker is reclosed on 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 a set value. 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 current detector, for example, a current transformer CT ₀ , is inserted in the electrical path connecting the circuit breaker CBI and the small-capacity power generation device 2.
An overcurrent relay 51I is connected to the secondary side of the current transformer CT ₀ to issue a disconnection command to the circuit breaker CBI. The operating time of this overcurrent relay 51I is
As shown in the characteristic diagram in the figure, the operating time is set to be faster than the operating time of the overcurrent relay 51F ₁ provided on the feeder F ₁ side. 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 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. The set time of the timer 12 is determined by a re-closing relay 79 provided on the power distribution system side.
Set it to be larger than one cycle time of F ₁ to 79F _o .

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

(1) If a short circuit occurs at points B and C,
Overcurrent relay 51I operates earlier than overcurrent relay 51F ₁ , and circuit breaker CBI is interrupted. After that, if there is a short-circuit accident at point B, circuit breaker CB ₀ is shut off and feeder F ₁ is not reclosed. Also C
If it is a short-circuit accident, the feeder F ₁ returns to the normal state after the circuit breaker CB ₂ is cut off by the overcurrent relay 51F ₂ . Then, on the feeder F2 _side , the recloser relay _79F2 attempts to reclose the circuit breaker _CB2 . When reclosing is successful, reclosing relay 79
Automatic reclosing relay 79 after the 1st anniversary of F ₂ has passed
The operating condition I is satisfied. Therefore, the circuit breaker CBI is re-closed and the normal state is restored.

(2) Even if a short-circuit accident occurs at point D, overcurrent relay 51I operates faster than overcurrent relay 51F ₁ and circuit breaker CBI is shut off, so feeder F ₁ is not affected in any way. In this case, small capacity power generation device 2
After stopping the inverter (not shown) by a control device (not shown), 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) it is possible to interconnect the small-capacity power generation device with the existing power distribution system without changing the equipment of the existing power distribution system;

(2) If a short circuit occurs on the AC bus 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. Furthermore, the circuit breaker is reclosed only after it has been 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) When a short circuit occurs on the distribution line connected to the small-capacity power generation equipment or on the AC bus on the grid side, the interconnection circuit breaker will not be reclosed, so there will be no negative impact on the grid or the small-capacity power generation equipment.

(4) If a short-circuit accident occurs on a distribution line other than the distribution line interconnected with the small-capacity power generation equipment, the interconnection circuit breaker will be shut off, but the circuit breaker will be disconnected automatically after the distribution line has been reclosed. The recloser relay closes the interconnection circuit breaker again. For this reason, the small capacity power generation device will not remain disconnected. Furthermore, since the power is automatically re-energized, there is no need for a troublesome manual re-energizing operation, and the operating rate of the small-capacity power generation device is improved.

[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. CT ₀ ~ CT _o ...Current transformer, 2...Small capacity power generator,
CBI, CB ₀ to CB _o ...breaker, 51I...overcurrent relay, 79I...automatic reclosing relay, _F1 to F _o ...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. the inserted circuit breaker, the current detector inserted in the electrical line connecting the circuit breaker and the small capacity power generation device, and the operating time of which is faster than the operating time of an overcurrent relay provided on the distribution line of the distribution system. an overcurrent relay that responds to the output of the current detector and issues a shutdown command to the circuit breaker; and an automatic reclosing relay that gives a closing command to the circuit breaker when a vector difference between the output voltage of the small-capacity power generation device and the output voltage of the small-capacity power generation device is less than a set value.