JP2767214B2 - Grid connection protection device - Google Patents

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 preventing an independent operation of a private power generation facility in the event of a system accident in a system interconnection system (commercial power line interconnection system).

[0002]

2. Description of the Related Art Hitherto, a grid interconnection system as shown in FIG. 7 has been used for a high-voltage customer to interconnect a private power generation facility such as a cogeneration system (hereinafter referred to as a private power generation facility). That is, in the system interconnection system of FIG. 7, 1a is a private power generation facility, 2 is a system bus, 3 is a distribution substation, 4 is a transformer, and 5 is a receiving line sending circuit breaker. The private power generation equipment 1a includes a generator 11a and an automatic voltage regulator 12a for controlling a terminal voltage of the generator 11a.
An engine 13a for driving the generator 11a; and a governor 14 for adjusting the rotation speed of the engine 13a to a predetermined speed.
a and a circuit breaker 15a for connecting the generator 11a to the premises system
, A circuit breaker 16a for connecting the system bus 2 and the premises system bus 10a, a premises load 17a, and a circuit breaker 18a for the premises load 17a. , Overvoltage relay 23a, overcurrent relay 24a, directional ground fault relay 25
a, a generator abnormality detection relay 27a, a frequency rise relay 28a, a frequency detector 30a, and a function generator 31a for a frequency command. Reference numeral 1b denotes a customer provided with a private power generation facility having the same configuration as the private power generation facility 1a described above. Home.

[0003] In the system for interconnecting private power generation facilities configured as described above, if an abnormality occurs in the power system or the customer private power generation equipment, it is detected quickly and the private power generation equipment is disconnected. There is a need to. For this purpose, undervoltage relay 21a, frequency reduction relay 22a, overvoltage relay 23a, overcurrent relay 24a, directional ground fault relay 25
a, a generator abnormality detecting relay 27a and a frequency increasing relay 28a are provided, and when an abnormality occurs, the circuit breaker 16a is opened and disconnected from the system.

[0004] However, in the case of certain abnormalities in the power system,
In some cases, an abnormality cannot be detected with only these protection relays. It is power system and private power generation equipment 1a
When the receiving of active / reactive power is small, an accident occurs at the far end of the power system, and the receiving line sending out circuit breaker 5 in FIG. 7 is opened, or the receiving line sending out is interrupted. This is a case in which the circuit breaker 5 remains closed, but the circuit breaker located further upstream is opened, and the system loses power. Also at this time, it is necessary to immediately disconnect the private power generation facilities 1a and 1b from the power system, that is, the system bus 2. Even if the receiving line sending-out circuit breaker 5 is opened, if the private power generation equipment charges the system bus 2 and continues the operation (hereinafter, this operation is referred to as isolated operation), the power system and the frequency of the private power generation equipment Due to the error of
This is because a phase difference occurs between the two voltages. If a phase difference occurs, the electric power system is restored and a large current flows when the receiving line sending out circuit breaker 5 is closed again, which may cause a secondary accident.

Conventionally, as a method of detecting an islanding operation,
As shown in FIG. 7, a protection device including a frequency detector 30a and a function generator 31a for a frequency command was provided.
In FIG. 7, a frequency detector 30a detects a generator frequency from a generator terminal voltage, and a function generator 31a generates an output signal from a detection value of the frequency detector 30a according to a set function. The governor 14a controls the rotation speed of the engine 13a so that the frequency of the generator 11a becomes a value corresponding to the output signal of the function generator 31a.

Next, the function of the function generator 31a and its function will be described with reference to FIG. This figure shows an example of the characteristic of the function of the function generator 31a, and the horizontal axis of the figure shows the frequency detection value. In the figure, a curve clearly indicated as a frequency command function is a function of the function generator 31a, and shows a relationship between the detected frequency and the frequency command. In addition, b shows the relationship (same) of the generator frequency to the detection frequency. The point at which the vertical and horizontal axes intersect is considered as the rated frequency, and it is assumed that the system is connected to the system and is operating at the rated frequency, and the system and the power are hardly received. Even in this state, even if the system is disconnected and operated independently, the frequency fluctuation is very small and cannot be detected by the conventional frequency lowering relay 22a or the frequency raising relay 28a.

When the function generator 31a is used, even if the frequency slightly rises above the rated frequency due to the fluctuation of the frequency, the function a (the command value is larger than the detected value up to the point d) is used. , The frequency fluctuation is increased, and the frequency is shifted toward the point d. That is, the function generator 31a
Acts as a positive feedback that amplifies a small increase in frequency to a larger increase. Since the point d is a point where the generator frequency and the frequency command are balanced, the frequency settles here. By setting the frequency at point d to a level that can be sensed by the frequency increasing relay 28a, an abnormality can be detected and the power receiving point circuit breaker 16a can be disconnected. Conversely, when the frequency slightly decreases, the frequency shifts to the point c and can be detected by the frequency reduction relay 22a.

When the system is connected to the grid, the frequency is determined by the frequency of the grid, and the frequency of the generator only follows the frequency. Although the frequency fluctuation of the system is slight, even if it fluctuates and the rotation command value to the governor 14a is increased by the function generator 31a, the active power is slightly increased within the range of the droop characteristic of the governor 14a. It just fluctuates. Positive feedback is not applied as in the case of isolated operation, and the frequency fluctuation is not amplified.

[0009]

In the conventional system interconnection protection device configured as described above, a minute frequency fluctuation occurs when the receiving line sending circuit breaker of the substation is opened, or when the power system is operated alone due to a power failure. Amplification and shifting to a level that can be sensed by the protection relay allowed the islanding operation to be detected.

However, in the conventional device, a frequency detector,
A very high-resolution, high-accuracy, high-speed response function generator was required. This is because, in some cases, the fluctuation of the frequency at the time of transition to the islanding operation may be very small.

In recent years, electronic governors have been widely used as governors for power generating prime movers. The electronic governor has good control performance, and is capable of extremely stable operation without frequency fluctuation. Further, in general, an order of several seconds is required as a time limit for detecting the transition to the islanding operation. During such a short time, there is a high possibility that there is no change in load. In that case, the frequency fluctuation becomes very small. In order to detect the small fluctuation and amplify it with the correct polarity, a frequency detector and a function generator with extremely high resolution, high accuracy, and fast response were required. This has raised the price of grid connection protection equipment and has been a factor that has hindered its spread.

The present invention has been made in view of the above circumstances, and an object of the present invention is to instantly operate even when the power generation system and the load are balanced in a customer premises and there is almost no supply and demand of the system and the electric power. It is an object of the present invention to provide a system interconnection protection device capable of detecting a power outage of a power system.

[0013]

According to a first aspect of the present invention, there is provided a system interconnection protection apparatus for connecting a private power generation facility to an electric power system. A governor to be controlled; a frequency detector for detecting the frequency of the generator output; and a function generation for generating a function for a frequency detection value which is an output of the frequency detector and for setting a frequency command value of the governor. And a rocking device that acts to generate small fluctuations in the frequency of the generator,
A protection relay, wherein when the generator is disconnected from the power system, the rocking device generates a small fluctuation in the frequency of the generator, and the function generator generates a frequency command for the generator. value, the value larger than the frequency in which the frequency of the generator has been detected in more than a predetermined frequency, by setting to a value less than the frequency detected at less than a predetermined frequency, us positive
The power failure of the power system is detected by changing the frequency of the generator to a level detected by the protection relay at the time of power failure of the power system.

According to a second aspect of the present invention, in the system interconnection protection device according to the first aspect, the oscillating device is realized by applying a disturbance to a frequency control system of the generator. According to a third aspect of the present invention, in the system interconnection protection device according to the first aspect, the swing device is realized by applying a disturbance to a voltage control system of the generator.

According to a fourth aspect of the present invention, in the system interconnection protection device according to the first aspect, the oscillating device installs a dummy load on an output of the generator and switches the dummy load on and off by a switch. It is characterized by being realized by.

According to a fifth aspect of the present invention, in the system interconnection protection device according to any one of the first to fourth aspects, an active power controller for controlling active power of the generator is provided, and an output signal of the function generator is provided. And the output signal of the active power controller is added to obtain a command value of the governor.

According to a sixth aspect of the present invention, in the system interconnection protection device according to any one of the first to fifth aspects, the private power generation equipment has a circuit breaker for interconnecting the power system, When the vessel is open, the operation of at least one of the rocking device and the function generator is stopped.

According to a seventh aspect of the present invention, in the system interconnection protection device according to any one of the first to sixth aspects, the frequency detector,
At least one of the function generator and the oscillating device is realized by software of a microcomputer.

[0019]

According to the system interconnection protection device of the first aspect of the present invention, while the generator frequency is controlled by the system frequency during the system operation, the speed control of the engine connected to the generator during the independent operation is performed. The characteristic of the function of the frequency command that the function generator has when the isolated operation is caused by generating a minute fluctuation of the generator frequency by the oscillating device. To shift to the level sensed by the protection relay and detect islanding.

According to the system interconnection protection device of the second aspect of the present invention, since the oscillating device applies disturbance to the frequency control system, the frequency slightly fluctuates by the generator when the isolated operation is performed. It works to increase the variation by the characteristic of the function of the frequency command of the function generator, shifts to a level sensed by the protection relay, and can detect islanding.

According to the system interconnection protection device of the third aspect of the present invention, the oscillating device causes disturbance to the voltage control system of the generator. Fluctuating, which causes a slight fluctuation in the generator frequency. It works to increase the variation by the characteristic of the function of the frequency command of the function generator, shifts to a level sensed by the protection relay, and can detect islanding.

According to the system interconnection protection device of the fourth aspect of the present invention, the oscillating device has a configuration in which a dummy load is provided at the output terminal of the generator and is switched on and off by a switch. The load of the generator fluctuates, thereby causing a slight fluctuation in the generator frequency. It works to increase the variation by the characteristic of the function of the frequency command of the function generator, and shifts to a level that the protection relay senses,
Islanding can be detected.

According to the system interconnection protection device of the fifth aspect of the present invention, the active power controller is configured to suppress a change in active power due to a system frequency change during system interconnection. Improve the stability of active power in the system,
In addition, the islanding operation can be detected immediately after the islanding operation.

According to the system interconnection protection device of claim 6 of the present invention, when the circuit breaker for interconnecting the private power generation equipment and the electric power system is open, both the swing device and the function generator or By stopping one of the operations, the stability of the generator at the time of starting and at the time of independent operation can be improved.

According to the system interconnection protection device of the present invention, part or all of the frequency detector, the function generator, and the oscillating device are realized by the software of the microcomputer, so that the cost of the protection device can be reduced. realizable.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a system interconnection protection device for a private power generation system according to an embodiment (corresponding to claim 1) of the present invention. The same components as those of the conventional system interconnection system of FIG. The same reference numerals are given and duplicate explanations are omitted.

This embodiment differs from the conventional system interconnection system shown in FIG. 7 in that it comprises a rocking device 49a, an oscillator 50a, and an adder 51a, and outputs the output signal of the oscillator 50a and the output signal of the function generator 31a. Are added by an adder 51a, and the signal is used as a frequency command for the governor 14a. The other configuration is the same. FIG. 2 shows a waveform example of the output signal of the oscillator 50a of FIG. This waveform may be a sine wave, a rectangular wave, or a random wave as long as it gives a small disturbance to the generator frequency during the isolated operation. FIG. 2 shows three examples of a triangular wave in FIG. 2A, a rectangular wave in FIG. 2B, and a sine wave in FIG. 2C.

According to this embodiment, since the frequency is fluctuated by the oscillator 50a, a minute frequency fluctuation can be constantly generated. Therefore, the frequency detector 30
a, even if the function generator 31a does not have high accuracy, high resolution, and high speed response,
Immediately, the positive feedback loop by the frequency detector 30a and the function generator 31a is activated, and the generator frequency can be shifted to the frequency sensed by the frequency increasing relay 28a or the frequency decreasing relay 22a. Oscillator 50 during grid connection
The output signal a gives a slight disturbance to the active power. However, even if inexpensive circuits are used for the frequency detector 30a and the function generator 31a, the disturbance can be made sufficiently smaller than the rated power value.

FIG. 3 is a block diagram of another embodiment (corresponding to claim 2) of the present invention. In this embodiment, the output signal of the oscillator 50a is added to the output signal of the governor 14a by the adder 51a. The output of the oscillator may be anywhere in the control loop related to the generator frequency as long as the generator frequency is slightly fluctuated during the isolated operation.

FIG. 4 is a block diagram of still another embodiment (corresponding to claim 3) of the present invention. In this embodiment, similarly to the embodiment of FIG. 3, the output of the oscillator 50a is used as a command value of an automatic voltage regulator for controlling the terminal voltage of the generator. At the time of grid connection, the fluctuation of the generator terminal voltage is only the fluctuation of the reactive power, but at the time of independent operation, it is the fluctuation of the active power.
The generator frequency is slightly fluctuated.

FIG. 5 is a block diagram of another embodiment (corresponding to claim 4) of the present invention. In the figure, reference numeral 60a denotes a swing device having a different configuration from the above embodiments. 61a is a dummy load, 62a is a connection switch, and 63a is a signal generator.

In this embodiment, the signal generator 63a momentarily closes the connection switch 62a at a predetermined cycle, and the load 61
A characteristic is that the generator frequency is fluctuated by supplying electric power from the generator to a. As described above, the oscillator may not be configured to connect the oscillator to the control system as long as the oscillator oscillates the frequency.

FIG. 6 is a block diagram of still another embodiment (corresponding to claim 5) of the present invention. In this embodiment, an active power controller 70a is added to the embodiment of FIG.
When the system frequency fluctuates during interconnection by adding the output of 1a and the adder 71a, the fluctuation of the active power generated due to the characteristics of the frequency detector 30a and the function generator 31a is suppressed. . The response of the active power controller 70a may be set to a low speed so as not to affect the isolated operation detection during the isolated operation.

Further, as another embodiment of the present invention (corresponding to claim 6), in each of the above-described embodiments, when the circuit breaker for interconnecting the private power generation equipment and the power system is open, the swinging is performed. The stability of the generator at the time of start-up and at the time of isolated operation may be enhanced by stopping the operation of the power unit and / or the function generator.

Further, as still another embodiment of the present invention (corresponding to claim 7), in the description of each of the above embodiments, the frequency detector, the function generator, and the oscillating device are constituted by independent hardware. However, a part or all of these configurations may be realized by software of a microcomputer.

[0036]

As described above, according to the present invention,
In a system with reverse power flow where the private power generation equipment is connected to the distribution system, even if the private power generation equipment and the load are balanced on the customer premises and there is almost no supply and demand of the power supply and the system, the frequency is controlled by the oscillator. Oscillating, it is possible to constantly generate minute frequency fluctuations.
Therefore, when the private power generator shifts to isolated operation,
Immediately, the positive feedback loop by the frequency detector and function generator is activated, and the generator frequency can be shifted to the frequency sensed by the frequency increasing relay or the frequency decreasing relay. Therefore, independent operation of the generator can be detected without using expensive equipment of high accuracy, high resolution and high speed response for the frequency detector and the function generator.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a system interconnection protection device for private power generation equipment according to an embodiment of the present invention.

FIG. 2 is a diagram showing an output waveform of an oscillator according to the present invention.

FIG. 3 is a configuration diagram of a system interconnection protection device for a private power generation facility according to another embodiment of the present invention.

FIG. 4 is a configuration diagram of a system interconnection protection device for private power generation equipment according to still another embodiment of the present invention.

FIG. 5 is a configuration diagram of a system interconnection protection device for private power generation equipment according to another embodiment of the present invention.

FIG. 6 is a configuration diagram of a system interconnection protection device for private power generation equipment according to still another embodiment of the present invention.

FIG. 7 is a configuration diagram of a conventional system interconnection protection device for private power generation equipment.

FIG. 8 is a diagram showing an example of a function generator of a conventional system interconnection protection device for private power generation equipment.

[Explanation of symbols]

1a, 1b: private power generation facilities, 2: system bus, 3 ... distribution substation, 4 ... transformer, 5 ... receiving line sending circuit breaker, 10
····················································································································· /
16c, 18a: circuit breaker, 16a: private power generation equipment customer receiving point circuit breaker, 17a, 17c: premises load, 21a: undervoltage relay, 22a: frequency reduction relay, 23a: overvoltage relay, 24a: overcurrent relay, 25a ... Direction ground fault relay, 27a ... Generator abnormality detection relay, 28a ... Frequency rise relay, 30a ... Frequency detector, 31a ... Function generator, 49a ... Swing device, 50a ... Oscillator, 51a ...
Adder, 60a: swing device, 61a: dummy load, 62
a: connection switch, 63a: signal generator, 70a: active power controller, 71a: adder.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-31197 (JP, A) JP-A-3-256533 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02J 3/38

Claims (7)

(57) [Claims] In a power generation system for connecting a private power generation facility to a power system, a governor for controlling a frequency of a generator, a frequency detector for detecting a frequency of the generator output, A function generator for generating a function with respect to a frequency detection value as an output and as a frequency command value of the governor, and generating a slight variation in the frequency of the generator.
A oscillating device operative to act as described above , and a protection relay,
When the generator is disconnected from the power system, the oscillating device causes a slight variation in the frequency of the generator, and the function generator sets the frequency command value of the generator to a value equal to or higher than a predetermined frequency. By setting to a value larger than the detected frequency and a value smaller than the detected frequency below a predetermined frequency, the protection relay senses the frequency of the generator at the time of blackout of the power system by applying positive feedback. A system interconnection protection device characterized in that a power outage of the power system is detected by changing to a level. 2. The system interconnection protection device according to claim 1, wherein said oscillating device is realized by applying a disturbance to a frequency control system of said generator. 3. The system interconnection protection device according to claim 1, wherein said oscillating device is realized by applying a disturbance to a voltage control system of said generator. 4. The system interconnection protection device according to claim 1, wherein the oscillating device is realized by installing a dummy load on an output of the generator and intermittently connecting the dummy load by a switch. System interconnection protection device. 5. The system interconnection protection device according to claim 1, further comprising an active power controller for controlling active power of said generator, wherein an output signal of said function generator and said active power controller are provided. Wherein the output signals are added to obtain a command value for the governor. 6. The system interconnection protection device according to claim 1, wherein the private power generation equipment has a circuit breaker for interconnecting with the power system, and the circuit breaker is open. In the state, the operation of at least one of the rocking device and the function generator is stopped. 7. The system interconnection protection device according to claim 1, wherein at least one of the frequency detector, the function generator, and the oscillating device is realized by software of a microcomputer. Grid connection protection device.