JP2620916B2 - 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 in the event of a system accident in a system interconnection system (commercial power line interconnection system).

[0002]

2. Description of the Related Art In general, a system interconnection system as shown in FIG. 5 is used for a customer to interconnect private power generation facilities such as cogeneration (hereinafter referred to as private power generation facilities). That is, in the system interconnection system of FIG. 5, 1a is a private power generation facility, 2 is a system bus, 3 is a distribution substation, 4 is a transformer, 5 is a receiving line sending circuit breaker, 6
Is a transfer receiving device. The transfer receiving device 6 receives a signal from the substation 3 at the time of a system failure in the case of a reverse power flow, and uses the private power generation facility customer's power receiving point circuit breaker 1
4a is canceled. In addition, private power generation equipment 1a
Is a generator 11 driven by an engine (not shown)
a, an automatic voltage regulator (AVR) 12a for controlling the voltage of the generator 11a, a circuit breaker 13a for connecting the generator 11a to the local system, the system bus 2 and the local system 1
0 and receiving point breaker 14a which connects the private branch load 15a
And a circuit breaker 16a for premises load, and furthermore, as protection devices, an undervoltage relay 21a, a frequency reduction relay 22a, an overvoltage relay 23a, an overcurrent relay 24a,
A directional ground fault relay 25a, a reverse power relay 26a, and a generator abnormality detection relay 27a are provided.

A customer 1b is provided with a private power generation facility having the same configuration as the private power generation facility 1a.
Is a customer provided only with power receiving equipment (circuit breaker 14c and in-house load 15c) having no private power generation equipment.

[0004] When the following abnormality occurs in the system interconnection system for private power generation facilities configured as described above, it is necessary to immediately disconnect the private power generation facilities 1a and 1b from the power system. (1) In the event of an accident in the premises of a cogeneration customer (2) In the event of a power system accident

[0005] As a method of detecting the state of an accident at the time of these accidents, it is usually detected by a protective relay device as shown in FIG. That is, when there is no reverse power flow, the overcurrent relay 24a, the ground fault relay 25a, the generator abnormality detection relay 2
7a, a reverse power relay 26a, a frequency reduction relay 22a, etc., detects an abnormality at the time of an accident of the private power generation equipment or system,
The receiving point circuit breaker 14a is opened and disconnected from the system. On the other hand, when there is a reverse power flow, the above-mentioned relay or the like may not detect the disconnection of the substation circuit breaker 5 when the system is abnormal. For this reason, the transfer breaker 6 is provided for protection.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an in-house private power generation system in a distribution system interconnection without providing an expensive transfer shut-off device when there is a reverse power flow. An object of the present invention is to provide a system interconnection protection device capable of detecting a generator alone operation at the time of a system side accident in a facility.

[0007]

To achieve the above object, a system interconnection protection device according to the present invention is directed to a system interconnection system for interconnecting a private power generation facility to a distribution system with a reverse power flow. AC including harmonics from equipment to distribution system
A generator that outputs power and a current on the power receiving side of the distribution system
And the voltage on the receiving side of the distribution system
The current transformer detected by the current transformer and the transformer
The harmonic current and harmonic voltage are extracted from the voltage detected by the detector.
To calculate the impedance and
Compare the dance with the set value and the impedance exceeds the set value
Output a cut-off signal to the circuit breaker to distribute the private power generation equipment
And an impedance detection circuit that is disconnected from the mains .

[0008]

The system interconnection protection device of the present invention focuses on the fact that the system impedance changes during a power failure on the system bus side. The system impedance is constantly monitored, and when a power failure occurs, the detected impedance is set in advance. By changing to a value set by the system impedance map, it is possible to quickly detect that a power failure has occurred in the system.

[0009]

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 of the present invention. A configuration different from the conventional system interconnection system of FIG. In that a harmonic generation device is incorporated in the device, an impedance detection circuit 31a is provided, and the transfer cutoff device 6 is eliminated.
Since there is a reverse power flow, the reverse power relay 26a is abolished. Therefore, the same components as those of the conventional system interconnection system are denoted by the same reference numerals and description thereof is omitted.

In FIG. 1, an impedance detection circuit 31a of a private power generation facility 1a is connected to a point A of a private system bus. Reference numeral 32a denotes a current transformer for detecting a current on the power receiving side, which is detected by the current transformer 32a.
Impedance detection based on harmonic current and voltage
The impedance is detected by a circuit 31a, and this impedance
When the load exceeds the set value, a shutoff command is output to the breaker 14a for receiving power in the premises.

Now, regarding the generation of harmonics inside the generator 11a, it is impossible that a normal sinusoidal waveform does not contain any harmonics. Paying attention to the fact that the harmonic content of each order can be changed by changing the pitch of the stator windings or by shortening the pitch of the stator windings, for example, as shown in FIG. If the gap is kept constant, FIG.
A waveform distorted in a trapezoidal shape as described above is obtained, and a generator having a harmonic generation mechanism can be configured by emphasizing higher harmonics than a normal sinusoidal waveform. Of course, at this time, the waveform irregularity rate of the generator output waveform including harmonics is 10%.
Must be within.

FIG. 3 shows the impedance detection circuit 31a.
In the figure, reference numeral 311 denotes a transformer for detecting a harmonic voltage, 312 denotes a first filter circuit for detecting only the harmonic voltage component of the transformer 311, and 313 denotes a current transformer 3.
This is a second filter circuit that converts the output of 2a into a voltage and detects only a harmonic component of the voltage. 314 and 315 are DC voltage conversion circuits for converting harmonic components of the voltage and current into DC voltage, 316 is an impedance calculation circuit for calculating the impedance of the harmonic component from the voltage component and the current component, and 317 is the calculation circuit 316 Is an output circuit that compares an output level of the output signal with an impedance value set in advance by the setting unit 318 and operates an output relay when the output level exceeds the set value. The output signal of this output circuit 317 is
4a, the private power generation equipment is disconnected from the distribution system
You. Note that the output signal of the output circuit 317 must be
It is not output to the breaker 14a but depends on the communication status.
Or another circuit breaker.

By the way, the impedance on the power receiving point side as seen from the point A in FIG. 1 is a parallel connection of the impedance of the system with the generator and load of another customer as shown in FIG.
Here, 13b, 14b and 16b are circuit breakers of the customer 1b,
14c is a circuit breaker of the customer 1c, and generally, the premises impedance Xbc (XGb, XLb, X
Lc) and system impedance XB
Then, there is a relationship of XB≪Xbc.

The operation of the embodiment configured as described above will be described below. In the grid connection system of the private power generation equipment according to the present embodiment shown in FIG. 1, the private power generation facility 1a on the premises and the private power generation facility 1b on the premises of other customers receive power from the commercial grid side, or Reverse power flow operation that sends surplus power from the power generation equipment to the commercial system side. When the latter reverse power flow operation is performed, the harmonic voltage and the harmonic current from the point A to the power receiving side are detected by the impedance detection circuit 3 shown in FIG.
The impedance is calculated by inputting the value to 1a, and this value is naturally equal to or less than a preset value. However, if the circuit breaker 5 on the system side is opened for some reason in this state, the power receiving point impedance viewed from the point A is only the generators and loads of other consumers, and the impedance detection circuit 31a in FIG. The value changes, and you will know the power outage on the grid side. Therefore, the power receiving point circuit breaker 14a can be quickly disconnected. Note that there is no particular relationship with the presence or absence of a harmonic generation mechanism in the private power generation facility 1b of another customer.

In addition to the above harmonic generation mechanism, a method of superimposing the slot ripple on the fundamental wave without applying skew is also conceivable. The ripple frequency fs in this case is determined by the following equation. Here, ns: number of slots, N: number of rotations (rpm) fs = ns × N × 60

[0016]

As described above, according to the present invention, in a system interconnection system with a reverse power flow in which a private power generation system is connected to a high-voltage distribution system, an exchange including harmonics from a generator is provided.
Output the current to the distribution system, and
Calculate the harmonic impedance of
Distribution by constantly comparing and monitoring the dance and set values
Detects a power outage in the power grid
The power generation equipment and the distribution system
Therefore, the power receiving point circuit breaker can be quickly disconnected without providing an expensive transfer interrupting device between the receiving line sending circuit breaker and the private power generation facility customer power receiving point circuit breaker. Ma
In addition, as in the present invention, an accident is determined based on the
Is that the voltage applied to the impedance changes
The impedance itself does not change just because the current changes.
Erroneous judgment because the current and voltage fluctuations on the other side are offset.
There is an effect that can be prevented.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram including the shape of a magnetic pole and harmonics.

FIG. 3 is a diagram of the impedance detection circuit of FIG. 1;

FIG. 4 is an impedance circuit diagram of FIG. 1;

FIG. 5 is a circuit diagram of a conventional system interconnection protection system 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, 6 ...
Transfer receiving device, 10: premises system bus, 11a: AC generator, 12a: Automatic voltage regulator, 13a, 13b, 14
c, 16a, 16b: Circuit breaker, 14a, 14b: Private power receiving facility customer receiving point circuit breaker, 15a, 15c: Local load, 21a: Undervoltage relay, 22a: Frequency reduction relay, 23a: Overvoltage relay, 24a: Over Current relay, 2
5a: directional ground fault relay, 26a: reverse power relay, 27a
... Generator abnormality detection relay, 31a ... Impedance detection circuit, 32a ... Current transformer.

Claims (1)

(57) [Claims] In a system interconnection system for connecting a private power generation facility to a distribution system with a reverse power flow, the private power generation facility
Generator that outputs AC power including harmonics from the power distribution system
And a current transformer that detects a current on the power receiving side of the power distribution system,
A transformer for detecting a voltage on a power receiving side of the power distribution system;
Such as the current detected by the current transformer and the voltage detected by the transformer
Extract harmonic current and harmonic voltage from
And compare this impedance with the set value.
If the impedance exceeds the set value,
Output from the distribution system
A system interconnection protection device comprising a dance detection circuit .