JPH07264778A - Capacitor protective device - Google Patents

Abstract

PURPOSE:To avoid the generation of the abnormal heating, etc., of a capacitor by extracting only even higher-harmonic currents flowing through the capacitor, adding higher-harmonic currents from load currents to the even higher-harmonic currents and removing higher-harmonic currents from system currents for infecting higher-harmonic currents having an antiphase into a system by an active filter. CONSTITUTION:Only even higher-harmonic currents are extracted from capacitor currents 13 flowing through a capacitor 7 by an even higher-harmonic current detector 22. Higher-harmonic currents from load currents to higher-harmonic generating load 6 are added to the even higher-harmonic currents, and the higher-harmonic currents of system currents 14 are removed for infecting antiphase higher-harmonic currents 12' into a system by an active filter 24. Accordingly, possibility that the even higher-harmonic currents are made to flow through the capacitor 7 and the abnormal heating, etc., of the capacitor 7 are generated can be avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor protection device for protecting a phase-advancing capacitor bank connected to a system from harmonic currents, and more specifically, to reactive power, power factor, or voltage in the system. The present invention relates to a capacitor protection device that reduces and protects a harmonic current that is input to a phase-advancing capacitor to improve the above.

[0002]

2. Description of the Related Art Generally, in a predetermined electric equipment, a reactive power, power factor, voltage, etc. are adjusted by installing a phase advancing capacitor in order to improve the reactive power, power factor, or voltage by operating a load. . On the other hand, some loads, such as an inverter, generate a harmonic current, which may cause the harmonic current to flow into the phase-advancing capacitor and cause abnormal heating or deterioration of the capacitor.

Therefore, an active filter is used as a means for preventing abnormal heating and deterioration of a capacitor due to the inflow of a harmonic current from a harmonic current source.

Explaining this example with reference to FIG. 5, a transformer 3 is connected to a system 1 via a circuit breaker 2, and is connected from a main line 4 to a bus 5. Connected to the bus 5 are a load 6 such as an inverter that generates a harmonic current, a power factor improving capacitor 7, and a reactor 8 for reducing inrush current in series with the load 7.

A current transformer 9 is arranged on the main line 4, and the current transformer 9 is connected to an active filter 10.
The output of active filter 10 is connected to bus 5. In addition, 11 has shown the circuit breaker.

First, when the load 6 is operated, a load current I1 flows to the load 6 and a harmonic current is generated. A current including the harmonic current is detected by the current transformer 9 provided in the main line 4 and input to the active filter 10. In the active filter 10, only the harmonic current component is extracted, and the opposite phase harmonic current component of the harmonic current component is injected into the bus 5 as the active filter current I2.

In this case, load current I1 = fundamental wave current Ia
+ Harmonic current Ib and capacitor current I3, overall system current I4 = load current I1 + capacitor current I3-active filter current I2.

As a result, system current I4 = fundamental wave current Ia
+ Harmonic current Ib + Capacitor current I3-Active filter current I2.

Since the harmonic current Ib = active filter current I2, the system current I4 = fundamental wave current I
It becomes a + capacitor current I3. Therefore, the system current I4
Does not include a harmonic component, and prevents a harmonic current from flowing into the capacitor 7.

[0010]

However, the capacitor protection device described with reference to FIG. 5 has the following problem.

First, in the capacitor protection device described in FIG. 5, the harmonic current generated in the load 6 can be removed. However, when the transformer in the host system is turned on, the hysteresis characteristic of the transformer causes Even harmonic current may transiently enter the capacitor 7.

On the other hand, the reactor 8 is generally inductive to the fifth, seventh, eleventh, thirteenth, etc. odd harmonic components from the load 6 such as an inverter.
It is selected to have a resonance at the fourth harmonic. Therefore, the even harmonic current Id from the host system is
If it goes into, the resonance phenomenon may occur transiently, an excessive current may flow into the capacitor 7, and the capacitor 7 may be abnormally heated, resulting in deterioration or damage.

Therefore, an object of the present invention is to provide a capacitor protection device which removes a harmonic current which causes a resonance phenomenon and prevents an excessive current from flowing into the capacitor to protect the capacitor.

[0014]

According to the present invention, there is provided a harmonic current generating load and a capacitor for reactive power compensation, which are connected to the system, and the harmonic current flowing through this capacitor is reduced for protection. In the capacitor protection device, the means for extracting only the harmonic current from the harmonic current generating load,
A means for extracting only even harmonic current from the harmonic current flowing into the capacitor, and a harmonic current and an opposite phase obtained by adding the even harmonic current extracted by this means and the harmonic current from the harmonic current generating load. And an active filter for injecting higher harmonic current into the system.

According to a second aspect of the present invention, there is provided a capacitor protection device having a harmonic current generating load and a capacitor for reactive power compensation, which are connected to the system, and which reduces and protects the harmonic current flowing to the capacitor. A means for extracting only the harmonic current from the harmonic current generating load, a means for extracting only the even harmonic current from the harmonic current flowing into the capacitor, and a means for outputting a switching signal when the even harmonic current is extracted, Wave current generator Injects a harmonic current in the opposite phase to the harmonic current from the load into the system, while providing an active filter that injects the even harmonic current extracted by the switching signal and the even harmonic current in the opposite phase into the system It was done like this.

[0016]

According to the first aspect of the present invention, only the even harmonic current flowing to the capacitor is extracted, and the harmonic current from the harmonic current generating load is added to the even harmonic current. Harmonic currents are removed from the system current to inject the wave current into the system. Therefore, it is possible to avoid the possibility that even harmonic currents flow into the capacitor and cause abnormal heating of the capacitor.

According to the second aspect of the present invention, only the harmonic current is extracted from the harmonic current generating load, and only the even harmonic current is extracted from the harmonic current flowing into the capacitor. And
When only the even harmonic current is extracted, the switching signal is output. The active filter injects the harmonic current from the harmonic current generating load in opposite phase to the harmonic current, while injecting the even harmonic current and the opposite phase even harmonic current extracted by the switching signal into the system. To do. Therefore, it is possible to avoid the possibility that even harmonic currents flow into the capacitor and cause abnormal heating of the capacitor. In addition, since the active filter only needs to process either the even harmonic current or the odd harmonic current, the capacity of the active filter can be reduced.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a system diagram of a capacitor protection device showing a first embodiment of the present invention, and the same reference numerals as those of the corresponding conventional example shown in FIG. 5 indicate the same or corresponding portions.

In the figure, a current transformer 20 for detecting the load current I1 is arranged on the load 6 side, and a current transformer 21 for detecting the capacitor current I3 flowing to the capacitor 7 is arranged on the capacitor 7 side. Harmonic current detection circuit 22 that connects the transformer 21 to the input side, and an adder 23 that adds the output from the even harmonic current detection circuit 22 and the output of the current transformer 20.
And an active filter 24 connected to the output side of the adder 23.

Here, the even harmonic current detection circuit 22 is
Of the capacitor current I3 detected from the current transformer 21,
Only even harmonic currents are extracted. The active filter 24 extracts a harmonic current component from the currents added by the adder 23, and injects the active filter current I2 ′ of the opposite phase to the bus 5 side.

First, the load current I1 including harmonics due to the load 6 such as an inverter connected to the bus 5 is detected by the current transformer 20 and input to the adder 23. The capacitor current I3 to the power factor improving capacitor 7 is detected by the current transformer 21 and input to the even harmonic current detection circuit 22.

Here, the even harmonic current detection circuit 22 is
As shown in FIG. 2, the waveform reproduction circuit 22a, the phase shift circuit 22b, the adder 22c, and the multiplier 22d are included.

First, the DC component is removed from the capacitor current containing harmonics by the waveform reproducing circuit 22a, and only the AC current component containing harmonics is extracted.

The alternating current containing the harmonics is subjected to sampling digital processing by the next phase shift circuit 22b,
Then, a 180 ° electrical angle shift process is performed on the fundamental wave, and the fundamental wave is converted again to analog.

Then, the output from the waveform reproduction circuit 22a and the output from the phase shift circuit 22b are added by the adder 22c. As a result, the odd harmonic current including the fundamental wave is removed by the adder 22c, while the even harmonic current having the double peak is extracted, and the multiplier 22
It is halved by d to obtain the original harmonic even harmonic current.

The even harmonic current obtained by the even harmonic current detecting circuit 22 and the current detected by the current transformer 20 are added by the adder 23 and input to the active filter 24.

In the active filter 24, a harmonic current component is extracted from the input added current, and the harmonic current of the opposite phase is taken as the active filter current I2 'and the bus 5
Inject.

As a result, the load current I1 = fundamental wave current Ia
+ Harmonic current Ib, capacitor current I3 = fundamental wave current I
c + even harmonic current Id, system current I4 = load current I1
+ Capacitor current I3-Active filter current I2 '
Becomes

Therefore, the active filter current I2 '=
The harmonic current Ib + the even harmonic current Id are compensated, and the system current I4 = fundamental current Ia + fundamental current I
Therefore, harmonic current is not included in the system current I4.
As a result, even harmonic currents are prevented from entering the capacitor 7, and deterioration or damage due to abnormal heating of the capacitor 7,
It is possible to avoid noise and the like.

In this way, the even harmonic current detection circuit 22
To extract only the even harmonic current Id flowing to the capacitor 7 and add it to the harmonic current Ib from the load current to the load 6 so that the active filter 24 injects the antiphase harmonic current I2 ″. The harmonic current of the current I4 is removed, so that it is possible to avoid the possibility that the even harmonic current Id flows into the capacitor 7 and causes abnormal heating of the capacitor 7.

It should be noted that the reason why the even harmonic current is extracted from the capacitor current I3 and the odd harmonic is ignored is that most of the even harmonic current flows into the capacitor 7 and When added by the adder 23, the active filter 2 interferes with the odd harmonic component of the load current I1.
This is because there is a possibility that the process in 4 will be impossible.

Next, a second embodiment of the present invention will be described with reference to FIG.

In FIG. 3, the same reference numerals as those in the conventional example shown in FIG. 5 indicate the same or corresponding portions, and the current transformer 20 for detecting the load current I1 of the load 6 and the capacitor current I3 to the capacitor 7 are detected. The even current harmonic detection circuit 22A, and the output from the even harmonic current detection circuit 22A or the current from the current transformer 20 according to the switching signal from the even harmonic current detection circuit 22A. A switch 25 for switching to any of the outputs and an active filter 24A are newly provided.

Here, the even harmonic current detection circuit 22A
In the same manner as in the first embodiment described with reference to FIG. 2, while detecting and extracting only the even harmonic current from the capacitor current I3,
The switching signal is output to the switch 25 only for a predetermined time after the detection.

The switch 25 is connected to the output side (A side in the figure) of the current transformer 20, and is switched to the output side (B side in the figure) of the even harmonic current detection circuit 22A by the input of the switching signal. .

The active filter 24A is a switching device 25.
The harmonic current component is extracted from the current selectively input by and the anti-phase harmonic current I2 ″ of the opposite phase is extracted from the bus 5
It is something to inject to the side.

First, the load current I1 including harmonics due to the load 6 such as an inverter connected to the bus 5 is detected by the current transformer 20 and input to one (A side) of the switch 25.

The capacitor current I3 to the power factor improving capacitor 7 is detected by the current transformer 21 and input to the even harmonic current detection circuit 22A.

Here, the even harmonic current detection circuit 22A
Specifically, as shown in FIG. 4, it is composed of a waveform reproduction circuit 22a, a phase shift circuit 22b, an adder 22c, a multiplier 22d, and a switching signal generator 22e.

First, the waveform reproducing circuit 22a removes the DC component from the capacitor current containing harmonics, and extracts only the current component containing harmonics. The current, including harmonics,
Next, sampling digital processing is performed by the phase shift circuit 22b, 180 electrical angle shift processing is performed on the fundamental wave, and the fundamental wave is converted again to analog.

Subsequently, the output from the waveform reproduction circuit 22a and the output from the phase shift circuit 22b are added by the adder 22c. As a result, the odd harmonic current including the fundamental wave is removed by the adder 22c, while the even harmonic current having the double peak is extracted, and the multiplier 22
It is halved by d to obtain the original harmonic even harmonic current.

When the even harmonic current extracted at this time exceeds a predetermined value, the switching signal generator 22e outputs the switching signal to the switching device 25 only for a predetermined time. As a result, the switch 25 is switched from the output side of the current transformer 20 (A side in the drawing) to the output side of the even harmonic current detection circuit 22A (B side in the drawing) and the even harmonics from the even harmonic current detection circuit 22A. The current is input to the active filter 24A.

The active filter 24A extracts only the input even harmonic current, and injects the opposite phase harmonic current into the bus 5 as the active filter current I2 ".

As a result, load current I1 = fundamental wave current Ia
+ Harmonic current Ib, capacitor current I3 = fundamental wave current I
c + even harmonic current Id, system current I4 = load current I1
+ Capacitor current I3-Active filter current I2 "
Becomes

Therefore, the active filter current I2 "=
When the harmonic current Ib or the even harmonic current Id is compensated, the system current I4 = fundamental current Ia + fundamental current Ic, and the system current I4 does not include the harmonic current.

As a result, even harmonic currents are prevented from entering the capacitor 7, and deterioration, damage, noise, etc. due to abnormal heating of the capacitor 7 can be avoided.

In addition, either the even harmonic current or the odd harmonic current is applied to the active filter 24.
Since A may be processed, the capacity of the active filter 24A can be reduced.

In the second embodiment, when the even harmonic current reaches a predetermined value, the output is switched to the output side of the even harmonic current detection circuit 22A only for a predetermined time. It is also possible to switch to the output side of the even harmonic current detection circuit 22A only when.

[0050]

As described above, according to the invention of claim 1, since the active filter injects the antiphase harmonic current into the system, the harmonic current is removed from the system current.
Therefore, it is possible to avoid the possibility that even harmonic currents flow into the capacitor and cause abnormal heating of the capacitor.

According to the second aspect of the present invention, while the harmonic current from the harmonic current generating load is injected into the system, the harmonic current in opposite phase to the harmonic current is generated. Wave current is injected into the system. Therefore, it is possible to avoid the possibility that even harmonic currents flow into the capacitor and cause abnormal heating of the capacitor. In addition, since the active filter only needs to process either the even harmonic current or the odd harmonic current, the capacity of the active filter can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a capacitor protection device showing a first embodiment of the present invention.

2 is a configuration diagram showing an even harmonic current detection circuit of FIG. 1. FIG.

FIG. 3 is a configuration diagram of a capacitor protection device showing a second embodiment of the present invention.

4 is a configuration diagram showing the even harmonic current detection circuit of FIG. 3. FIG.

FIG. 5 is a configuration diagram of a capacitor protection device showing a conventional example.

[Explanation of symbols]

 1 system 7 capacitor 8 reactor 20 current transformer 21 current transformer 22 even harmonic current detection circuit 23 adder 24 active filter 25 switcher

Claims (2)

[Claims] 1. A capacitor protection device having a harmonic current generating load connected to a system and a capacitor for reactive power compensation, and reducing and protecting the harmonic current flowing to the capacitor, wherein the harmonic current generation is performed. Means for extracting only harmonic current from the load, means for extracting only even harmonic current from the harmonic current flowing into the capacitor, and even harmonic current extracted by this means and harmonics from the harmonic current generating load And an active filter for injecting a harmonic current having a reverse phase and a harmonic current obtained by adding the wave current to the system. 2. A capacitor protection device having a harmonic current generating load connected to a system and a capacitor for compensating reactive power, and reducing and protecting the harmonic current flowing to this capacitor, wherein the harmonic current generating Means for extracting only the harmonic current from the load, means for extracting only the even harmonic current from the harmonic current flowing into the capacitor, and outputting a switching signal when only the even harmonic current is extracted, and the harmonic current An active filter that injects a harmonic current having a phase opposite to that of the harmonic current from the generated load into the system while injecting an even harmonic current having a phase opposite to that of the extracted even harmonic current by the switching signal into the system. A capacitor protection device comprising: