JPH08223809A - System interconnection protection device for generator - Google Patents

Abstract

PURPOSE: To detect the service interruption of a system by shifting reactive power in the lead or the lag direction in accordance with the rise and fall of a frequency and controlling an engine governor when the system is cut off to operate it in the direction in which the frequency and the voltage in single operation are diverged. CONSTITUTION: The different points from the prior art system interconnection system are as follows. The frequency is detected from the output voltage of a generator by a frequency detector 21 to output a reference reactive power Q* through a function generator 22. In order to make reactive power Q detected by a reactive power detector 23 accord with the reference reactive power Q*, a voltage control loop constituted of a voltage control circuit 9 adopting the output of a reactive power control circuit 24 as a reference voltage V* and a speed control loop for controlling the speed of a governor 11 by an effective power control circuit 27 by comparing the output P of an effective power detecting circuit 26 with a reference effective power P*. Single operation is detected by a frequency rising relay 16 and a shortage voltage relay 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system interconnection protection device for system interconnection of private power generation equipment such as garbage power generation and cogeneration.

[0002]

2. Description of the Related Art Generally, a grid interconnection system as shown in FIG. 8 is used by a consumer to grid-connect a private power generation facility such as a cogeneration system. That is,
As shown in the grid interconnection system in the figure, in the substation 39, power is stepped down from the grid power supply 1 via the transformer 2 and is supplied to the general consumer through the circuit breaker 3. The customer supplies power to the load 5 via the circuit breaker 4.

On the other hand, in the private power generation facility, the output of the AC generator 7 is connected to the system power supply 1 via the circuit breaker 6. The output voltage of the AC generator 7 is controlled by controlling the field winding 8 of the AC generator 7 by an AVR (automatic voltage regulator) 9, and the output frequency of the AC generator 7 is an engine that drives the AC generator 7. It is performed by controlling the engine power by the governor 11 of 10.

For failure detection, the current transformer 12 detects the generator current, and the generator abnormality detection circuit 1 is detected from the relationship with the output voltage.
An abnormal current is detected at 3, and the circuit breaker 6 is opened via the fault trip circuit 20.

Further, as a protection circuit, a current transformer 14 is provided on the output side of the circuit breaker 6 in addition to this, and an overcurrent detector (O
C) The fault trip circuit 20 is operated by 19. Further, when the system power supply 1 is abnormal, particularly when the system power supply 1 is cut off, for example, when the circuit breaker 3 is opened, the output of the AC generator 7 is supplied to the load 5 and the frequency and voltage become abnormal. This is detected by the frequency lowering relay (UF) 15, the frequency rising relay (OF) 16, the overvoltage relay (OV) 17, the undervoltage relay (UV) 18, etc., and the breaker 6 is opened via the fault trip circuit 20. The load 5 must be protected and the circuit breaker 3 must be reclosed.

[0006]

However, since there is a case where these relays cannot detect during the independent operation described below, the trip signal is transmitted from the transfer interruption circuit 40 to open the circuit breaker 6. For example, when the circuit breaker 3 is opened, if the output power of the AC generator 7 and the required power of the load 5 are substantially equal in both the active and reactive portions, the frequency and the voltage hardly change. A so-called islanding phenomenon occurs in which operation is not performed and operation continues, and an accident occurs that interrupts the circuit breaker 3 from reclosing.

[0007] In the case of operating in cooperation with the system in this way, a signal indicating that the circuit breaker 3 of the upper substation is open is sent to the customer by the transfer breaker 40 in order to prevent the islanding operation. Then, the circuit breaker 6 is opened. In particular, when the upper substation is far or there are many customers, it is necessary to provide an expensive transfer interruption device.

The present invention has been made in view of the above circumstances, and an object thereof is to independently operate a generator connected to a grid without providing an expensive transfer interruption device for a small-to-medium-sized private power generation facility. An object of the present invention is to provide a system interconnection protection device for a generator that can be reliably detected on the facility side.

[0009]

In order to achieve the above object, a system interconnection protection device for a generator according to claim 1 of the present invention comprises:
In a system interconnection system that interconnects a private power generation facility with a rotary generator to a distribution system, a voltage detector, a current detector, and a frequency detector that detect the voltage, current, and frequency of the output of the private power generation facility, and A reactive power control loop unit by excitation control of a generator, an active power control loop unit by speed governor control of the generator, and a function generator that changes reactive power according to a change in frequency detected by the frequency detector. When the frequency detected by the frequency detector rises in the vicinity of the rated frequency, the reactive power is changed in the forward direction as the frequency rises, and when the frequency is lowered, the reactive power is changed in the delay direction as the frequency falls. Controls the reactive power based on the generator output, detects the power failure on the grid side due to the frequency abnormality relay or voltage abnormality relay, and disconnects from the grid. Characterized in that a to circuit.

According to a second aspect of the present invention, in the system interconnection protection device for a generator according to the first aspect, after disconnecting the system,
A switching circuit for switching from the reactive power control loop unit to the voltage control loop unit and from the active power control loop unit to the frequency control or speed control loop unit is provided.

According to a third aspect of the present invention, in the system interconnection protection device for a generator according to the first aspect, when the frequency rises above the rated frequency by more than a preset frequency, the reactive power is delayed from the forward direction as the frequency rises. The characteristic is inverted in the direction, and when the frequency falls below the rated frequency by more than the set value, the reactive power is controlled so as to be inverted from the delay direction to the advance direction as the frequency falls.

According to a fourth aspect of the present invention, in the system interconnection protection device for a generator according to the first aspect, one of the change amount of the frequency detector output and the function generator output is used as a reference of active power control, or The feature is that both are added and controlled.

[0013]

According to the first aspect of the present invention, the voltage is controlled by the generator field control so as to shift the reactive power in the forward direction when the frequency rises and shift the reactive power in the delay direction when the frequency falls, during which the active power is controlled. By controlling the engine speed governor of the generator so as to be constant, the system is operated in the direction of diverging the frequency and voltage during islanding to detect a system power failure.

According to the second aspect of the present invention, during grid interconnection, active frequency control and a reactive power control loop based on a function during independent operation, the frequency control loop and voltage control are performed after the frequency and voltage are diverged and the system is disconnected. A stable power supply is operated by a loop as an independent type.

According to the third aspect of the present invention, when the frequency shifts by a certain amount or more, the divergence action becomes a converging action, and the divergence width of the frequency is limited. According to the fourth aspect of the present invention, the active power is also slightly changed by the function or the change rate of the frequency to assist the divergence of the frequency.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention (corresponding to claims 1 to 4). The difference between this embodiment and the conventional grid interconnection system of FIG. Instead of providing an expensive transfer interruption device, as shown in FIG. 1, the frequency is detected by the frequency detector 21 from the generator output voltage, and the reactive power reference Q ^* is output via the function generator 22. A voltage control loop composed of a voltage control circuit (AVR) 9 which uses the output of the reactive power control circuit (AQR) 24 as a voltage reference V ^* to match the reactive power Q detected by the detector 23 with Q ^* ; The point is that a speed control loop for controlling the speed of the speed governor 11 by comparing P ^{* of the} active power reference 25 with the output P of the active power detection circuit 26 and controlling the speed of the governor 11 is provided. Points are shown in Figure 8.
Since it is the same as the system interconnection system of No. 3, the same parts are denoted by the same reference numerals, and the duplicated description will be omitted.

Next, the operation of this embodiment will be described with reference to FIGS. FIG. 2 shows the reactive power reference Q ^* of the function generator 22 ^.
FIG. 3 is a characteristic diagram showing an example of the reactive power of the load and the load, and FIG. 3 is a diagram showing the flow of the active and reactive power of the generator and the load in the grid interconnection.

Now, in FIG. 3, assuming that the active power of the generator output is P, the reactive power is Q, the active power required by the load is P _L , and the reactive power is Q _L , the active power ΔP flowing out to the system power supply and Reactive power ΔQ is expressed as follows.

ΔP = P−P _L , ΔQ = Q−Q _L where the inductance between the generator and the system is l,
The load voltage is V and the frequency is f.

Then, normally, ΔP≈0, Δ
Even if the circuit breaker 3 is opened in the state close to Q≈0, the load voltage V and the frequency f hardly change, and the protection relay cannot detect it, and the operation is continued. However, system power supply 1
Since the phase of the load gradually shifts, reclosing the circuit breaker 3 may lead to an accident and may be dangerous and may not be performed, thus deteriorating the stability of the power distribution system.

Now, considering the case where ΔQ = 0 and ΔP = 0 while the generator output is controlled to P = constant and Q = 0, P = V ² / R, | i _C | = | i _L | That is, the operation is performed in a state where the power factor is 1, which resonates at the system frequency. Even in such a case, the system interconnection protection function for detecting and protecting the fact that the circuit breaker 3 is opened and the islanding mode is activated will be described with reference to FIGS. 2 and 4.

[0022] Q _L characteristic of the load in FIG. 2, the rated frequency f _O
When the power factor is 1 and i _C increases and i _L decreases as the frequency f increases, Q _L has a linearly right upper characteristic.

Next, consider the case where the control of the reactive power Q of the generator is controlled to the curve of Q ^* (Q) with respect to the frequency f. Since the frequency f is in the f ₀ and the generator output relationship of the reactive power Q from the required reactive power to Q ₁ load between f ₁ is always Q (advances)> Q _L, the frequency f of the load will rise When you try to balance at the point where the Q = Q _L Te. Frequency f
Since but tries to balance in that the frequency in the opposite becomes reduced Q = Q _L in the case of greater than f _1, f ₁ point is stable point.

Next, when the frequency f is between f ₀ and f ₂ , Q
Since the (delay)> Q _L, frequency f is reduced, Q = Q
Shift in the _L direction and reach point f ₂ . Frequency f is f
In less than ₂ range will be (Q-Q _L) proceeds amount, frequency f is going to rise. Point f ₂ is a stable point. However, the frequency f increases on the right side of the f ₀ point and decreases on the left side, so the f ₀ point becomes unstable, that is, when the control shown in FIG. 2 is possible, the frequency f Will diverge in both directions.

In order to realize this, the frequency detector 21 in FIG. 1 detects the frequency f of the private generator, and the function generator 22 generates a reactive power reference having a characteristic such as Q ^* in FIG. The AQR 24 controls the generator voltage reference V ^* , that is, the generator voltage V by the AVR 9 so that Q ^* and Q coincide with each other.

The principle by which Q changes by changing the generator voltage V is shown in FIG. That is, in order to flow the current I ₂ from the state of the generator voltage V ₁ ′ and the output current I ₁ , the generator voltage V ₂ ′ is achieved by lowering it than V ₁ ′.

Next, how the active power changes by changing the phase of the generator output voltage will be described with reference to FIG. 4 (b). That is, the generator voltage at the generator current I ₁ is V
₁ ', to increase the generated current to I ₂ and increase P, the generator voltage is V ₂ ', that is, the phase is advanced (frequency f
APR2 in the direction of increasing the engine rotation in the ascending direction)
It can be seen that the speed governor 11 may be controlled via 7.
FIG. 1 performs such control.

Next, how the frequency f changes during the isolated operation when such control is performed will be described.
In condition that the isolated operation, when the frequency f is present between f ₀ and f _1, (greater than Q _L required by the load) for outputting a Q becomes proceeds reactive power, the generator voltage V ₁ ' AVR9 operates in the direction of lowering. However, since Q is greater than the load requires Q _L , the generator voltage V ′ is further reduced. On the other hand, since the APR 27 controls the output active power to be constant, when V ′ decreases, the APR 27 tries to increase I ₁ and increases the engine speed to advance the voltage phase, that is, to increase the frequency f. , The frequency f is moved to f ₁ as described with reference to FIG. Therefore, finally, the frequency rising relay (OF) 16 can detect the islanding operation, and transiently, the undervoltage relay (UV) 18 can detect the islanding operation.

Further, if the frequency f is present between f ₀ and f _2, so as to output Q becomes delayed reactive power (delay power than Q _L required by the load is large) in a condition that the isolated operation The AVR 9 operates to increase the generator voltage V '. However, the generator voltage V ′ is further increased because the load tries to output the Q delayed from the required Q _L. On the other hand, the APR 27 controls the output active power to be constant, so that when V ′ rises, the APR 27 attempts to reduce the active current I ₁ to lower the engine speed and delay the voltage phase, that is, to control the frequency f. As a result, the frequency f is moved to f ₂ as described with reference to FIG. Therefore, in the end, the frequency down relay (UF) 1
5 can detect the islanding operation, and transiently overvoltage relay (O
V) 17 can detect islanding.

As described above, even when the private power generation facility connected to the grid is cut off from the grid and is operated independently, even when the generator output and the load in the customer range are substantially balanced in both effective and ineffective portions. The frequency characteristic is added to the Q control and the frequency is shifted by the P constant control to reliably detect the islanding operation by the frequency abnormality relay, and transiently detect the islanding operation as well, and transiently detect the islanding operation, and feed circuit breaker Can be opened and completely disconnected from the grid.

By the way, in the embodiment of FIG. 1, the case where the control of Q = 0 at the point of the rated frequency f ₀ is explained, but in the present invention, when the control for constantly outputting the reactive power is performed by the generator, This can be achieved by adding the steady reactive power control reference to Q ^* of FIG. 1, that is, Q ^{* of} FIG.
_{The slope} of the frequency characteristic of _L is dQ ^* / df is dQ _L / df
The only condition that needs to be rushed is.

FIG. 5 is a block diagram of another embodiment of the present invention. The difference of this embodiment from the embodiment of FIG. 1 is that the frequency detection effective power provided with a frequency change rate detection circuit 31 and an adder 32 is provided. Since the pattern control circuit is added and the other points are the same, the same portions are denoted by the same reference numerals, and duplicate description will be omitted. In the embodiment of FIG. 1, the frequency change occurs in a two-stage loop of frequency detection → reactive power pattern control → voltage change → active power control → frequency change. When it is desired to further increase the islanding operation detection speed of this control, the islanding operation detection speed can be increased by applying the present embodiment.

Next, the reason will be described with reference to FIG.
In the present embodiment, as shown in FIG. 6, in the grid interconnection system of FIG. 1, a part of the output of the function generator 22 is added to the active power reference P ^* as P ′ by the adder 32, and P ^* + P ′ = P ^* '
As the new active power reference P ^* '. Further, the frequency change rate detection circuit 31 detects the frequency change rate and adds P ″ to the adder 32 as the active power correction amount.

These P'and P "are added for the purpose of operating as a kind of feedforward to accelerate the rate of change of frequency. That is, when the frequency starts rising in the direction of f ₀ → f _{1 in} FIG. Both P ′ and P ″ are positive, and the phase of the generator output voltage advances (frequency increases) in order to increase active power, and the frequency can be shifted quickly without waiting for the voltage drop due to reactive power control. It will be possible.
Further, it is needless to say that P ′ and P ″ have the same effect when they are used individually.

FIG. 7 is a block diagram of still another embodiment of the present invention. The difference of this embodiment from the embodiment of FIG.
The limit circuit 33 provided in 24 and the limit circuit 34 provided in the APR 27 are added, and the other parts are the same. Therefore, the same parts are denoted by the same reference numerals and duplicate description will be omitted.

In the embodiment shown in FIG. 1, when the isolated operation is detected, the breaker 6 is opened. In this case, it may be desired to use the output of the generator 7 as a power source for internal use as it is. In such a case, in this embodiment, the limit signal 33b provided in the AQR 24 and the limit circuit 34 provided in the APR 27 are operated by the open signal 6b of the circuit breaker 6 to operate the voltage reference V ^* and the speed (frequency) reference S ^*. Constant and switch to voltage control or frequency control. Although V ^* and S ^* are made constant by the limit circuit 34 in this embodiment, a fixed V
Needless to say, the same effect can be obtained by switching to ^* and S ^* .

[0037]

As described above, according to the present invention,
In a system that operates the generator output by connecting it to the distribution system, if the system is cut off, the control loop that controls reactive power in the forward direction according to the frequency increase near the rated frequency and active power is controlled constantly, By controlling the active power in the increasing direction as the frequency rises, the frequency relay or the voltage relay can detect the islanding operation quickly and disconnect the power receiving point breaker. Moreover, during system operation, active / reactive power is injected into the system, so stability is extremely high.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of FIG.

FIG. 3 is a diagram for explaining the operation of FIG.

FIG. 4 is a diagram for explaining the operation of FIG.

FIG. 5 is a configuration diagram of another embodiment of the present invention.

FIG. 6 is a diagram for explaining the operation of FIG.

FIG. 7 is a configuration diagram of still another embodiment of the present invention.

FIG. 8 is a configuration diagram of a conventional system interconnection system.

[Explanation of symbols]

1 ... System power supply, 2 ... Transformer, 3, 4, 6 ... Circuit breaker, 5 ...
Load, 7 ... AC generator, 8 ... field winding, 9 ... AVR (constant voltage control circuit), 10 ... engine, 11 ... speed governor, 1
2, 14 ... Current transformer, 13 ... Generator abnormality detection circuit, 15 ...
UF (frequency lowering relay), 16 ... OF (frequency rising relay), 17 ... OV (overvoltage relay), 18 ... UV (undervoltage relay), 19 ... Overcurrent relay, 20 ... Fault trip circuit, 21 ... Frequency detector , 22 ... Function generator, 2
3 ... Reactive power detector, 24 ... Reactive power control, 25 ... Reactive power reference, 26 ... Active power detector, 27 ... Active power control, 31 ... Frequency change rate detection, 32 ... Adder, 33, 3
4 ... Limit circuit, 39 ... Substation, 40 ... Transfer interruption signal device

Claims (4)

[Claims] 1. In a system interconnection system for interconnecting a private power generation facility with a rotary generator to a distribution system, a voltage detector, a current detector, and a frequency detector for detecting the voltage, current, and frequency of the output of the private power generation facility. Detector, reactive power control loop unit by excitation control of the generator, active power control loop unit by speed governor control of the generator, and reactive power according to the change in frequency detected by the frequency detector. When the frequency detected by the function generator and the frequency detector rises in the vicinity of the rated frequency, the reactive power is changed in the advancing direction as the frequency rises, and when the frequency falls, the reactive power is delayed in the advancing direction as the frequency falls. Control the reactive power based on the output of the function generator, and detect the power failure on the system side due to the frequency abnormality relay or voltage abnormality relay. A power grid interconnection protection device comprising a circuit for disconnecting from the grid. 2. The generator system interconnection protection device according to claim 1, wherein after the system is disconnected, the reactive power control loop unit to the voltage control loop unit and the active power control loop unit to the frequency control or speed control loop. A system interconnection protection device for a generator, which is provided with a switching circuit for switching to a power supply section. 3. The generator interconnection protection device according to claim 1, wherein when the frequency rises above the rated frequency by more than a set frequency, the reactive power is inverted from the advance direction to the delay direction as the frequency rises. ， When the frequency falls below the rated frequency by more than the set value, reactive power is controlled so as to reverse the characteristics from the delay direction to the advance direction as the frequency falls. 4. The generator interconnection protection device according to claim 1, wherein the active power control standard is controlled by adding either or both of the change in the frequency detector output and the function generator output. A power grid interconnection protection device characterized by: