JPH0652973B2 - Interconnection device for small-capacity power generation system - Google Patents

Description

Detailed Description of the Invention A. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interconnection device for a small capacity power generation system.

B. SUMMARY OF THE INVENTION The present invention is 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 electric power to a load, wherein the distribution system voltage is lower than a predetermined value. Or, the circuit breaker is cut off when the rate of increase of the current flowing from the small-capacity power generator to the distribution system exceeds a predetermined value, and the distribution system is cut off after a predetermined set time has elapsed since the breaker was cut off. By providing an automatic reclosing relay that gives a closing command to the circuit breaker when the vector difference between the voltage and the output voltage of the small-capacity generator is less than a set value, small capacity can be achieved without changing the existing distribution system equipment. The power generation equipment can be connected to the existing distribution system, and even if a short-circuit accident occurs, it does not adversely affect the small-capacity power generation equipment and the power system.

C. 2. Description of the Related Art In recent years, the demand for electric power has been increasing more and more, but the power generation systems using nuclear power and thermal power, which are currently the mainstream, are restricted in terms of resources and installation places. Therefore, a fuel cell power generation system that can be distributed in power consumption areas and has no pollution and high power generation efficiency is drawing attention. For distributed deployment, the method of connecting to the load end of the existing distribution system is the most economical as a small-scale power generation system.

D. Problems to be Solved by the Invention However, since it is related to the protection method and control method 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 control method of the private power generation system remain unchanged. It could not be applied.

That is, for example, a conventional parallel operation system between large-scale power generation facilities has a configuration in which it is 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 protection control functions (synchronization detection, synchronization input, out-of-synchronization detection, etc.) necessary for parallel operation. A protection control facility that can cope with fluctuations is installed. However, when connecting a small-scale power generation system to an existing distribution system, not only does the distribution system not have a function to check synchronization, but there are also control devices specific to the distribution system, such as an automatic reclosing device and an accident zone indicator. Since it exists, the conventional interconnection method between power plants could not be applied as it is.

Here, in the system in which the power distribution system and the small-capacity power generation facility are interconnected, the problem in the case of performing the short circuit protection by the overcurrent relay will be described with the circuit diagram of FIG. In FIG. 4, 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 _n are circuit breakers that are respectively inserted in the electric lines that connect the distribution lines (hereinafter, referred to as feeders) F _{1 to} F _n arranged in parallel with the AC bus 1. The AC output power of the AC power supply (not shown) is supplied to a load (not shown) via a transformer T, a circuit breaker CB ₀ , an AC bus 1, circuit breakers CB _{1 to} CB _n, and feeders F _{1 to} F _n. . Reference numeral 2 denotes a small-capacity power generator, which is composed of, for example, a fuel cell power generator and an inverter (not shown) that converts its DC output power into AC. The AC output power of the small-capacity power generator 2 is supplied to a load (not shown) via a breaker CBI that is cut off when the home current relay 51 is operating and the feeder F ₁ . The overcurrent relay 51 operates by the output current of the current transformer CT ₀ inserted in the electric path connecting the small capacity power generator 2 and the circuit breaker CBI. Current transformers for feeders F _{1 to} F _n
CT _{1 to} CT _n are provided respectively. Overcurrent relay 51F ₁ ~
51F _n operates according to each output current of the current transformers CT _{1 to} CT _n ,
Each block the circuit breaker CB ₁ to CB _n. 79F _{1 to} 79F _n are reclosing relays for reclosing the circuit breakers CB _{1 to} CB _n , respectively.

In the apparatus configured as described above, during parallel operation, point A on feeder F ₁ , point B on AC bus 1 and feeder F
_{When a} short-circuit accident occurs at each of the points C on ₂ , the following situation occurs.

(1) When a short circuit accident occurs at point A, a short circuit current flows from both the small capacity power generator 2 and the power system side. Therefore, the circuit breaker CBI is cut off by the overcurrent relay 51, and the circuit breaker CB ₁ is cut off by the overcurrent relay 51F ₁ . In this case, there is no problem.

(2) If a short circuit accident occurs at points B and C,
Short-circuit current flows from both the small-capacity generator 2 and the power system as in (1). At this time, the system side overcurrent relay 51F ₁
Is operated faster than the overcurrent relay 51 on the small-capacity generator 2 side, the fault current disappears due to the breaker CB ₁ .
If the load (not shown) connected to the feeder F ₁ is small, the overcurrent relay 51 will recover. Therefore, since the circuit breaker CBI is not cut off, the power supply from the small capacity power generator 2 is continued, and the power supply voltage on the power system side and the output voltage of the small capacity power generator 2 become asynchronous. In this state, the reclosing relay 79F ₁ operates after a lapse of a predetermined time, and the circuit breaker
When CB ₁ is closed again, an excessive current flows between the power grid and the small-capacity generator 2. Therefore, the small-capacity power generator 2 and the power system are adversely affected. In order to solve such a problem, as shown in the characteristic diagram of FIG.
There is a method of setting the operating value of 51 smaller than the operating value of the overcurrent relay 51F ₁ and setting the operating time of the overcurrent relay 51 faster than the operating time of the overcurrent relay 51F ₁ . If this method is adopted, the breaker CBI can be cut off faster than the breaker CB ₁ . However at the substation circuit breaker CB ₁
If the circuit is manually shut off, the circuit breaker CB
I can't shut off. That is, if the circuit breaker CB ₁ is manually cut off when a short circuit accident occurs at the points B and C, the circuit breaker CBI remains turned on and the power supply from the small capacity generator 2 is continued. I will end up. In this case, when the load (not shown) has a large capacity, overcurrent may flow from the small-capacity power generator 2 and the overcurrent relay 51 may operate, but when the load is light, the relay 51 does not operate and shuts off. Vessel CBI is not shut off. Further, even if the load capacity is large as described above, if the output power of the small capacity generator 2 is reduced by the control device (not shown), the overcurrent relay 51 does not operate and the breaker CBI shuts off. Not done.

The present invention has been made in view of the above points, and it is possible to connect a small-capacity power generation facility to an existing distribution system without changing the facilities of the existing distribution system, and even if a short-circuit accident occurs. It is an object of the present invention to provide an interconnection device for a small-capacity power generation system that does not adversely affect the small-capacity power generation equipment or system.

E. Means for Solving the Problems Having a first circuit breaker inserted in a distribution line of a distribution system,
In a interconnection device of a small-capacity power generation system configured to connect a small-capacity power generator and the distribution system to supply electric power to a load, a distribution line connecting the first circuit breaker and the load, and the small capacity. A second circuit breaker inserted in an electric circuit connecting to the power generating device; an undervoltage relay for cutting off the second circuit breaker when the voltage of the distribution system becomes equal to or lower than a predetermined set value; and the small capacity A current change rate detection relay that shuts off the second circuit breaker when the rate of increase of the current flowing from the power generator to the distribution system exceeds a predetermined set value, and a predetermined value after the second circuit breaker is shut off. An automatic reclosing relay that gives a closing command to the second circuit breaker when the vector difference between the distribution system voltage and the output voltage of the small-capacity power generator is less than or equal to a set value after a lapse of a set time; When the relay worked Or the from the automatic reclosing relay 2
The second circuit breaker is cut off when the closing instruction is not issued to the circuit breaker and the current change rate detection relay operates, or at least one of the conditions is satisfied. It is characterized by that.

F. Action In the device configured as described above, even if the first circuit breaker provided on the distribution system side is manually cut off when a short-circuit accident occurs, the distribution system voltage drops and the distribution line and the small-capacity generator are connected. The second circuit breaker inserted in the connecting electric path is reliably broken by the undervoltage relay. Even when the distribution system voltage does not drop at this time, the current flowing from the small capacity generator to the distribution system increases, so the second circuit breaker inserted in the electric path connecting the distribution line and the small capacity generator. Is reliably interrupted by the current change rate detection relay.
Further, after a predetermined set time has elapsed after the second circuit breaker inserted in the electric path connecting the distribution line and the small-capacity generator, the vector difference between the distribution system voltage and the output voltage of the small-capacity generator is detected. The second circuit breaker is closed again on the condition that is less than or equal to the set value. Therefore, the small-capacity power generator does not remain disconnected from the power system, and the operating rate of the power generator is improved.

G. Embodiment An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the same parts as those in FIG. 4 are shown with the same reference numerals, and the description thereof will be omitted. A current change rate detection relay 3 is connected to the secondary side of the current transformer CT ₀ . This relay 3 operates when the increase rate (dI / dt) of the current flowing from the small-capacity generator 2 to the distribution system side exceeds a predetermined set value α, and at that time, a closing command is issued from an automatic reclosing relay 79I described later. The breaker CBI is cut off on the condition that it has not been released. A transformer PT ₁ for voltage detection is connected to a common connection point 4 between the small-capacity generator 2 and the circuit breaker CBI, and
A voltage detection transformer PT ₂ is connected to the common connection point 5 of the cutoff CBI and the feeder F ₁ . An undervoltage relay 27 is connected to the secondary side of the transformer PT ₂ . This relay 27
Operates when the detection voltage of transformer PT ₂ (voltage on the feeder F ₁ side) drops below a preset voltage, and breaker CBI
Shut off. An automatic reclosing relay 79I is provided on the secondary side of the transformers PT ₁ and PT ₂ . This relay 79I
A vector difference between the distribution system voltage (the output voltage of the transformer PT ₂ ) and the output voltage of the small-capacity generator (the output voltage of the transformer PT ₁ ) after a predetermined set time has passed since the breaker CBI was cut off. It is an automatic reclosing relay that gives a closing command to the breaker CBI when is less than the set value. This automatic reclosing relay 79I includes, for example, as shown in FIG. 2, a vector difference voltage detection unit 11 that outputs an output signal when the vector difference between the system voltage and the power generator side voltage is below a predetermined set value, and a circuit breaker CB.
A timer 12 that outputs an output signal after a lapse of a predetermined set time after I is cut off, and a circuit breaker when the AND condition of the output signals of the vector difference voltage detection unit 11 and the timer 12 is satisfied.
It is composed of an AND circuit 13 that issues a closing command to the CBI. The set time of the timer 12 is set to be longer than one cycle time of the reclosing relays 79F _{1 to} 79F _n provided on the power distribution system side.

The circuit breaker CBI is cut off when the undervoltage relay 27 is operated or when the closing command is not issued from the automatic reclosing relay 79I to the circuit breaker CBI and the current change rate detection relay 3 is operated. It shall be carried out when at least one of the conditions of time is met. So circuit breaker CB
A circuit for issuing a cutoff command to I is configured as shown in FIG. 3, for example. In FIG. 3, the circuit breaker CBI closing command is input to one input terminal (inhibit terminal) of the AND circuit 6, and the operation output of the current change rate detection relay 3 is input to the other input terminal of the AND circuit 6. . The output signal of the AND circuit 6 and the operation output signal of the undervoltage relay 27 are input to the OR circuit 7. The output signal of the OR circuit 7 is sent as a break command for the breaker CBI.

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

(1) When a short circuit accident occurs at point A, a short circuit current flows from both the small capacity power generator 2 and the power system side. Therefore, the circuit breaker CB ₁ is cut off by the overcurrent relay 51F ₁ . At this time, when the increase rate (dI / dt) of the current flowing from the small capacity power generator 2 to the point A side increases and exceeds the set value α, the current change rate detection relay 3 operates. If the circuit breaker CBI closing command is not issued, the condition of the OR circuit 7 in FIG. 3 is satisfied, and the circuit breaker CBI is cut off.

(2) When a short-circuit accident occurs at point B, a short-circuit current flows from the AC power source (not shown) on the power system side through the transformer T and the circuit breaker CB _0, and at the same time, the small-capacity generator 2 breaks the circuit breaker CBI. And a short-circuit current flows through the circuit breaker CB ₁ .
Then, the circuit breaker CB ₀ is cut off by the relay (not shown) and the circuit breaker CB ₁ is cut off by the overcurrent relay 51F ₁ . At this time, when the increase rate (dI / dt) of the current flowing from the small-capacity power generator 2 to the point B becomes large and exceeds the set value α, the current change rate detection relay 3 operates in the same manner as in the case of (1) above. Then, the circuit breaker CBI is cut off.

(3) When a short-circuit accident occurs at point C, a short-circuit current flows from an AC power source (not shown) on the power system side through the transformer T, circuit breaker CB ₀ and circuit breaker CB _2, and a small-capacity generator Short-circuit current flows from 2 through circuit breakers CBI, CB ₁ and CB ₂ . Then, the circuit breaker CB ₀ is interrupted by a relay (not shown), and the circuit breaker CB ₁ is overcurrent relay 51F ₁
And the circuit breaker CB ₂ is disconnected by the overcurrent relay 51F.
It is blocked by ₂ . At this time, the small-capacity generator 2
When the rate of increase (dI / dt) of the current flowing from point C to point C exceeds the set value α, the current change rate detection relay 3 operates and the circuit breaker CBI is cut off, as in the case of (1) above. It

(4) As described in (1), (2) and (3) above, in the event of a short circuit accident, the circuit breaker CB ₀ provided on the distribution system side
To CB _n well, breaker CBI small capacity power generator 2 side is reliably cut off. Moreover, if the reclosing relay 79F ₁ attempts to reclose the circuit breaker CB ₁ after the short circuit accident is recovered and succeeds in it, the feeder F ₁ returns to the normal state. Therefore, if it is detected that the vector difference voltage between the voltage of the feeder F ₁ and the output voltage of the small-capacity power generator 2 is equal to or less than the set value after one cycle time of the reclosing relay 79F ₁ , the AND circuit shown in FIG. The condition of the circuit 13 is satisfied, and the circuit breaker CBI is automatically reclosed. As a result, the small-capacity power generator 2 is not left in the disconnected state, and the circuit breaker CBI is automatically re-closed, so that no troublesome manual re-closing operation is required.

(5) Further, it is assumed that the power demand of a load (not shown) connected to the feeder F ₁ is rapidly increased during the interconnected operation of the small capacity power generator 2 and the grid. In this case, there is a possibility that the current flowing from the small-capacity power generator 2 to the load will significantly increase, and the cutoff CBI will be cut off by the operation of the current change rate detection relay 3. However, if the set time of the timer 12 of the automatic reclosing relay 79I elapses after the breaker CBI is cut off, the AND condition of the AND circuit 13 in FIG.
Are automatically re-injected. Therefore, the small-capacity power generator 2 is not left in the separated state.

(6) and where to cut off the circuit breaker CB ₁ provided on feeder F ₁ at short circuit occurs manually. At this time, if the load capacity connected to the feeder F ₁ is larger than the capacity of the small capacity power generator 2, sufficient power cannot be supplied and the voltage of the feeder F ₁ drops. Also, when the output of the small-capacity power generation device 2 is throttled by a control circuit (not shown), the voltage of the feeder F ₁ drops. In such a case, the undervoltage relay 27 operates and the OR condition of the OR circuit 7 in FIG. 3 is satisfied, so that the circuit breaker CBI is reliably cut off. Therefore, the circuit breaker C
When B ₁ is closed again, an excessive current does not flow between the small-capacity generator 2 and the electric power system to adversely affect the device.
After the circuit breaker CB ₁ is reclosed, the operation is the same as in (4) above.

(7) the (6) In the case the load capacity of the feeder F ₁ when the circuit breaker CB ₁ blocked manually is smaller than the capacity of the small-capacity power generation apparatus 2 includes sections undervoltage does not decrease the voltage of the feeder F ₁ Relay 27 does not work. However, if the circuit breaker CB ₁ is manually cut off, only the output power of the small capacity generator 2 is supplied to the load, so that the current flowing from the small capacity generator 2 to the feeder F ₁ is significantly increased. Therefore, the current change rate detection relay 3 operates and the breaker CBI is surely cut off. Therefore, when the circuit breaker CB ₁ is closed again, an excessive current does not flow between the small-capacity power generator 2 and the electric power system to adversely affect the device. After the circuit breaker CB ₁ is reclosed, the operation is the same as in (4) above.

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 facility can be connected to the existing distribution system without changing the facilities of the existing distribution system.

(2) When a short-circuit accident occurs in the distribution line to which the AC bus of the distribution system or the small-capacity generator is connected, the circuit breaker for interconnection can be reliably cut off. Moreover, the circuit breaker is re-closed after it is confirmed that the vector difference between the system voltage and the output voltage of the small-capacity generator is less than the set value. Does not flow. Therefore, it does not adversely affect each facility of the power system and the small-capacity generator.

(3) Even when the circuit breaker on the distribution line side is manually cut off when a short-circuit accident occurs, the circuit breaker for interconnection can be surely cut off by the operation of the current change rate detection relay and the undervoltage relay. As a result, it is not necessary to change the existing distribution facility such as adding a device for detecting the closing / breaking state of the breaker on the distribution line side and transferring the detection signal.

(4) When the circuit breaker on the distribution line side is manually cut off, even if the undervoltage relay cannot be operated due to a light load condition, the current change rate detection relay operates, so disconnection for interconnection The vessel is surely shut off.

(5) Even when the output power of the small-capacity generator is reduced when the circuit breaker on the distribution line side is manually cut off, the undervoltage relay operates, so the circuit breaker for interconnection is reliably cut off. It

(6) Even if the current change rate detection relay operates due to a sudden increase in load capacity, and the circuit breaker for interconnection is cut off, the circuit breaker is reclosed by the automatic reclosing relay. As a result, the small-capacity power generator is not left in a disconnected state, and the circuit breaker is automatically reclosed, so that a troublesome manual reclosing operation is unnecessary.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 3 show an embodiment of the present invention, FIG. 1 is a circuit diagram, FIG. 2 is a block diagram of an automatic reclosing relay, and FIG. FIG. 4 is a block diagram for explaining, FIG. 4 is a circuit diagram showing an example of a conventional interconnection device, and FIG. 5 is an operation time characteristic diagram of a relay. 2 ... Small capacity generator, 3 ... Current change rate detection relay, 11 ...
Vector difference voltage detection unit, 12 ... timer, 27 ... undervoltage relay, 79i ... automatic reclosing relay, CBI ... breaker, CT ₀ ... current transformer.

Claims (1)

[Claims] 1. A small capacity having a first circuit breaker inserted in a distribution line of a distribution system and configured to connect the small capacity power generator and the distribution system to supply electric power to a load. In the interconnection device of the power generation system, the second circuit breaker inserted in the electric path connecting the first circuit breaker and the power distribution line connecting the load and the small-capacity power generation device and the voltage of the power distribution system have a predetermined voltage. An undervoltage relay that shuts off the second circuit breaker when the value falls below a set value, and a second shutoff when the rate of increase of the current flowing from the small-capacity power generator to the distribution system exceeds a predetermined set value. Of the current change rate detecting relay for shutting off the power generator and a predetermined set time after the second breaker is shut off, and the vector difference between the distribution system voltage and the output voltage of the small capacity power generator is less than or equal to the set value. At one time, a closing command is given to the second circuit breaker. An automatic re-closing circuit relay that operates when the undervoltage relay operates, or when the closing command is not issued from the automatic re-closing circuit relay to the second circuit breaker and the current change rate detection relay. Is operated or when at least one of the conditions is satisfied, the second circuit breaker is shut off.