JPH06339227A - Instantaneous voltage drop compensator - Google Patents

Abstract

PURPOSE:To effectively detect a voltage drop in a utility power source and to prevent interruption of a cogenerator system in an apparatus having cogenerator power source connected in parallel with the utility power source. CONSTITUTION:A high speed switch 6 is inserted to an electric circuit for connecting a utility power source 1 to a cogenerator power source 3, and a reactive power detector 11 for detecting a reactive power to flow from the source 3 to the source 1 is provided. At the time of a voltage drop in the source 1, a potential difference occurs between both the sources 1 and 3, but in the case, since an impedance of the system mainly has an L component, a cross-current of the reactive power is generated. Flow of the reactive power is detected by the detector 11 to open the switch 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an instantaneous voltage drop compensator for protecting a power supply connected in parallel with a system power supply, such as a cogeneration system, from a voltage drop of the system power supply.

[0002]

2. Description of the Related Art In a combined heat and power system, a combined heat and power supply 3 is connected in parallel to a load 2 connected to a system power supply 1 as shown in FIG. In the device configured as described above, when the voltage of the system power supply 1 decreases, the load on the combined heat and power supply 3 side increases, and the combined heat and power supply system goes down due to occurrence of overcurrent.

In order to prevent this, a voltage drop is detected by an instrument transformer 4 and a voltage drop detection circuit 5 as shown in the figure, and the high speed switch 6 is shut off at the time of detection. This prevents current from being supplied from the combined heat and power supply 3 to the system power supply side to bring down the system.

[0004]

However, in the method of directly monitoring the voltage as shown in FIG. 4, when the impedance of the system power source is small, a large current flows with a small voltage change, so that the detection sensitivity cannot be increased and the system is May not be protected.

The present invention has been made in view of the above points, and an object thereof is to provide an instantaneous voltage drop compensating device capable of surely detecting a voltage drop and preventing the combined heat and power supply system from being down.

[0006]

DISCLOSURE OF THE INVENTION The present invention relates to a device for protecting a combined heat and power supply connected in parallel to a system power supply from a voltage drop of the system power supply, including (1) an electric path connecting the system power supply and the combined heat and power supply. An interposed high-speed switch, and a reactive power detection circuit for detecting reactive power flowing from the combined heat and power supply to the system power supply, the high-speed switch is opened by a detection signal of the reactive power detection circuit,
(2) A high-speed switch inserted in an electric path connecting the system power supply and the combined heat and power supply, a reactive power detection circuit that detects reactive power flowing from the combined heat and power supply to the system power supply, and a voltage of the combined heat and power supply. A voltage drop variation detection circuit for detecting a voltage variation is provided, and the high-speed switch is opened when an AND condition of detection signals of the reactive power detection circuit and the voltage reduction variation detection circuit is satisfied.

[0007]

[Action]

(1) In the invention of claim 1, when the voltage of the system power supply decreases, a potential difference occurs between both power supplies. At this time, since the impedance of the system is mainly the L component, a cross current of the reactive power is generated. This outflow of reactive power is detected by the reactive power detection circuit, and the high-speed switch is controlled to open. Therefore, it is possible to reliably prevent the combined heat and power supply from going down.

(2) In the invention of claim 2, when the voltage of the system power supply drops and the reactive power flows out, both the voltage drop fluctuation detection circuit and the reactive power detection circuit issue a detection signal and the AND condition is satisfied. As a result, the high-speed switch is controlled to be opened, and the combined heat and power supply is reliably prevented from going down.

When the load connected to the system power supply suddenly decreases, the voltage of the combined heat and power supply rises temporarily and reactive power is supplied from the combined heat and power supply to the system. Therefore, the detection signal is output from the reactive power detection circuit, but the voltage drop variation detection circuit does not output the detection signal, and therefore the AND condition is not satisfied. Therefore, careless opening of the high-speed switch can be avoided.

Furthermore, since it is a system that takes AND with the detection of the outflow of the reactive power not only by detecting the voltage drop fluctuation, there is no problem even if the detection sensitivity is increased.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the invention described in claim 1 will be described below with reference to the drawings. 1, the same parts as those in FIG. 4 are indicated by the same reference numerals. In FIG. 1, reference numeral 11 denotes a reactive power detection circuit that detects reactive power by the current transformer 12 and the instrument transformer 4 that are inserted in the system electric circuit. The high speed switch 6 is cut off by the detection signal of the reactive power detection circuit 11.

Now, when the voltage of the system power supply 1 drops, a potential difference occurs between the two power supplies 1 and 3. At this time, since the impedance of the system is mainly the L component, a cross current of the reactive power is generated. This outflow of reactive power is caused by the reactive power detection circuit 1
1, the high speed switch 6 is controlled to open.
Therefore, the combined heat and power supply 3 is reliably prevented from going down.

When the voltage drop is recovered, the high-speed switch 6 is turned on by another circuit (not shown), and the steady state is restored.

Next, an embodiment of the invention described in claim 2 will be described. 2, the same parts as those in FIG. 1 are designated by the same reference numerals. 2 is different from FIG. 1 in that a voltage drop fluctuation detection circuit 21 that detects fluctuations in voltage drop based on the output of the instrument transformer 4 is provided, and the detection output of the detection circuit 21 and the detection output of the reactive power detection circuit 11 are provided. The AND circuit 22 is used to cut off the high-speed switch 6 when the AND condition is satisfied, and the other parts are configured the same as in FIG.

Now, when the voltage of the system power supply 1 drops and reactive power flows out, both the voltage drop fluctuation detection circuit 21 and the reactive power detection circuit 11 generate detection signals and the AND circuit 2 is operated.
The AND condition of 2 is satisfied. This enables high-speed switch 6
Is controlled so that the combined heat and power supply 3 is prevented from going down.

An unnecessary operation of the high speed switch when the load 2 suddenly decreases will be described. In this case, the combined heat and power supply 3 causes the voltage to temporarily rise as shown in FIG. Therefore, from the combined heat and power supply 3 to the grid,
Reactive power is supplied as shown in (c). In the device of FIG. 1 described above, the reactive power detection circuit 11 detects the reactive power of FIG. 3 (c) and shuts off the high speed switch 6 as shown in FIG. 3 (d). In this case, there is no need to shut off the high speed switch 6. In this respect, since the voltage drop variation detection circuit 21 does not detect the voltage drop in the device of FIG. 2, the AND condition of the AND circuit 22 is not satisfied and the high speed switch 6 is not inadvertently cut off.

As a result, the high-speed switch 6 can be turned off only when the system voltage drops, and stable protection can be achieved. In addition, the voltage is only judged whether it is rising or falling, and the condition that reactive power is flowing out is combined, so it is possible to increase the detection sensitivity, and stable control is possible compared to the conventional method that only detects voltage drop. it can.

When the voltage drop is recovered, the high-speed switch 6 is turned on by another circuit (not shown), and the steady state is restored.

[0019]

As described above, according to the invention of claim 1,
Since a high-speed switch inserted in a circuit connecting the system power supply and the combined heat and power supply and a reactive power detection circuit for detecting reactive power flowing from the combined heat and power supply to the system power supply are provided, regardless of the impedance of the system power supply. Since the voltage drop can be reliably detected, it is possible to reliably prevent the combined heat and power supply system from going down.

According to the second aspect of the present invention, there is provided a reactive power detection circuit for detecting reactive power flowing from the combined heat and power supply to the system power supply, and a voltage drop variation detection circuit for detecting variation in voltage drop of the combined heat and power supply. Since the high-speed switch is opened when the AND conditions of the detection signals of the reactive power detection circuit and the voltage drop fluctuation detection circuit are satisfied, the voltage drop can be reliably detected regardless of the impedance of the system power supply, so the combined heat and power supply system. Can surely be prevented from going down.

Further, the high-speed switch can be controlled to be turned off only when the system voltage drops without inadvertently disconnecting the system power supply, and stable protection can be performed. Furthermore, since voltage detection is only a judgment of rise or fall, and the condition that reactive power is flowing out is combined, detection sensitivity can be increased, and stable control is possible compared to the conventional voltage drop detection only method. Can be done.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the invention described in claim 1.

FIG. 2 is a circuit diagram showing an embodiment of the invention described in claim 2.

FIG. 3 is a time chart illustrating a malfunction when a load changes suddenly.

FIG. 4 is a circuit diagram showing an example of a conventional instantaneous voltage drop compensating device.

[Explanation of symbols]

 1 ... System power supply 2 ... Load 3 ... Combined heat and power supply 6 ... High-speed switch 11 ... Reactive power detection circuit 21 ... Voltage drop fluctuation detection circuit 22 ... AND circuit

Claims (2)

[Claims] 1. A device for protecting a combined heat and power supply connected in parallel to a system power supply from a voltage drop of the system power supply, a high-speed switch interposed in an electric path connecting the system power supply and the combined heat and power supply, and the combined heat and power supply. An instantaneous voltage drop compensating device comprising: a reactive power detection circuit for detecting reactive power flowing from a power supply to a system power supply; and a high-speed switch is opened by a detection signal of the reactive power detection circuit. 2. A device for protecting a combined heat and power supply connected in parallel to a system power supply from a voltage drop of the system power supply, a high-speed switch inserted in an electric path connecting the system power supply and the combined heat and power supply, and the combined heat and power supply. A reactive power detection circuit for detecting reactive power flowing from a power supply to a system power supply; and a voltage drop fluctuation detection circuit for detecting a voltage drop fluctuation of the combined heat and power supply, the reactive power detection circuit and the voltage drop fluctuation detection circuit The instantaneous voltage drop compensating device is characterized in that the high-speed switch is opened when the AND condition of the detection signal is satisfied.