JPH10145974A - Control of phase advance capacitor installation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the outflow amount of harmonic current generated from load to an external system, and prevent a trouble due to harmonic overcurrent by controlling inputting and opening of a group(s) of phase advance capacitors according to the magnitude of reactive power and/or the harmonic current per number of the groups of the phase advance capacitors. SOLUTION: A reactive power detector 1 outputs a signal if the magnitude of detected reactive power is in excess of preset magnitude on the phase lag side, and stops the signal if it is in excess on the phase advance side. A harmonic current detector 3 outputs a signal if the magnitude of detected harmonic current is in excess of a preset one, and stops the signal if it is below the prescribed one to some degree. A phase advance capacitor input signal generator 4 receives the signals of the reactive power detector 1 and the harmonic current detector 3. If the signal of either of the reactive power detector 1 or the harmonic current detector 3 is ON, an input signal is given to the switch 13 of a phase advance capacitor installation 21, and if both of the reactive power detector 1 and the harmonic current detector 3 are OFF, an open signal is outputted to the switch 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic control system in which phase-advancing capacitor equipment used for improving the power factor of a load is also used to reduce a harmonic current generated from the load.

[0002]

2. Description of the Related Art In order to improve the power factor of a load, a phase-advancing capacitor is connected in parallel to the load, and the phase-advancing capacitor is divided into two or more groups to open and close according to a change in load. Have been done. In this case, the reactive power of the load including the phase-advancing capacitor is detected, and the phase-advancing capacitor is automatically sequentially turned on and off according to the magnitude of the reactive power, which has been widely used conventionally.

[0003]

Recently, loads generating harmonics, such as inverters, have increased rapidly, and harmonic currents generated from these have flowed out to the power system, increasing voltage distortion and causing faults. For this reason, it is recommended to provide a phase-advancing capacitor equipment with a series reactor on the load side to absorb the harmonic current, thereby reducing the amount of outflow of the harmonic current to the power system. In particular, it is known that a considerably large harmonic current absorbing effect can be obtained by installing a phase-advancing capacitor equipment on the same low voltage side with respect to the harmonic generation load on the low voltage side of the transformer.

For this reason, phase-advancing capacitor equipment which also serves to absorb such harmonic currents has been put to practical use. However, if it is controlled automatically only by the magnitude of the reactive power of the load as in the prior art, However, depending on the load condition, despite the large amount of harmonic current generated, some of the phase-advancing capacitors are opened, so that not only the sufficient harmonic current absorption effect cannot be obtained, but also the There is also a problem in that the phase capacitor equipment generates an overcurrent due to harmonics and causes troubles such as overheating of the series reactor.

[0005]

According to the present invention, a phase-advancing capacitor group comprising a phase-advancing capacitor 11, a series reactor 12, and a switch 13 connected in series constitutes one group, and the phase-advancing capacitor equipment 21 comprises two or more groups. In the control method of the phase-advancing capacitor equipment, the phase-advancing capacitor equipment is connected in parallel to a load, and the phase-advancing capacitor group is automatically turned on and off automatically according to the change of the load. 21
Detects the reactive power of the load, including the load, and the harmonic current of the load only, and sets the magnitude of the reactive power and / or the magnitude of the harmonic current per the number of groups of the phase-advancing capacitors. The control of the phase-advanced capacitor equipment is characterized in that a signal is input when the phase-advanced capacitor group is exceeded, and an open signal for the phase-advanced capacitor group is output when any value falls below the set value. It is a method.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS If the above-described automatic control system is adopted, even if the reactive power is reduced due to the load condition, if the amount of generated harmonic current does not decrease, the phase advance capacitor is not opened. In addition, even if the reactive power is small, if the amount of generated harmonic current exceeds a certain limit, the phase-advancing capacitor will be turned on, so reduce the amount of harmonic current generated from the load to the external system. And the effect of preventing an overheating trouble such as a series reactor due to a harmonic overcurrent of the phase-advancing capacitor equipment can be obtained.

[0007]

Embodiment 1 FIG. 1 is a connection diagram showing an embodiment of a control method of a phase-advancing capacitor equipment according to the present invention. In FIG. 1, a load 22 and a phase-advancing capacitor facility 21 are connected in parallel to a secondary bus of a receiving power system via a receiving transformer Tr. The load 22 is a load for generating harmonics such as an inverter, and the phase-advancing capacitor equipment 21 includes the phase-advancing capacitor 11, the series reactor 12, and the switch 13. PT and CT1 are an instrument transformer and current transformer for detecting the voltage and current on the secondary side of the power receiving transformer Tr,
Connected to reactive power detector 1. CT2 is a current transformer for the instrument for detecting the current of the load 22. The current transformer CT2 changes the input / output current ratio in accordance with the number of input groups of the phase-advancing capacitors. Connected.

[0008] The reactive power detector 1 outputs a signal when the magnitude of the detected reactive power is on the lag side and exceeds a preset magnitude, and detects the magnitude on the leading side and the preset magnitude. If this is exceeded, stop this signal. Harmonic current detector 3
Outputs a signal when the magnitude of the detected harmonic current exceeds a predetermined magnitude, and stops the signal when the magnitude falls below a certain level. The phase advance capacitor input signal generator 4 receives the signals of the reactive power detector 1 and the harmonic current detector 3, and sequentially turns on the switch 13 of the phase advance capacitor equipment 21 if either of these signals is ON. A signal is issued, and when both signals are turned off, an open signal is sequentially issued to the switch 13.

FIG. 2 and FIG. 3 show an example of the configuration of the current ratio switch 2. FIG. 2 (a) shows the switching of the current ratio by the changeover switches 34, 35, 36 using the resistor 31 with tap. FIG. 2B shows a case where the number of parallel shunt resistors 32 is changed over by switches 34, 35 and 36 to change the shunt ratio. FIG. 3 changes the current ratio by switching the taps of the auxiliary current transformer 33 by the changeover switches 34, 35, 36. The changeover switches 34, 35, and 36 are used to open and close according to the number of switches 13 to be turned on, using auxiliary contacts of the switch 13.

The n-th harmonic current generated from the load 22 is represented by In
, N on the power supply side including the reactance of the power receiving transformer Tr
Assuming that the reactance to the next harmonic is Xon, the reactance to the nth harmonic of the first phase capacitor equipment group is Xcn, and the number of input groups of the first phase capacitor group is N, the outflow current Ion to the power supply side, the first phase capacitor group The per-flow inflow current Icn is as follows.

[0011]

(Equation 1)

[0012]

(Equation 2)

In general, the reactance Xc5 of a phase-advanced capacitor using a series reactor having a reactance of 6% becomes considerably smaller than the fifth harmonic (n = 5), which mainly occupies the harmonic current. Although the outflow current Io5 of the current to the power supply side is considerably reduced, the inflow current Ic5 to the phase-advancing capacitor equipment becomes considerably large, and harmonic overcurrent faults such as overheating of the series reactor tend to occur.

Therefore, in order to keep the outflow current Ion to the power supply side and the inflow amount Icn per one group of the phase-advancing capacitors within a certain allowable limit, the phase-advancing capacitor group should be adjusted in accordance with the harmonic current generation In from the load. It is necessary to make the number of input groups N of the number more than an appropriate number. This can be performed by the current ratio switch 2 and the harmonic current detector 3.

[0015]

According to the present invention, as compared with the conventional case where the phase-advancing capacitor is simply turned on and off according to the magnitude of the reactive power of the load, the harmonic current of the load also depends on the magnitude of the harmonic current of the load. Since the phase-advancing capacitor is turned on and off, the phase-advancing capacitor is turned on regardless of the magnitude of the reactive power. The current can be controlled within an allowable limit, and the effect of harmonic countermeasures is large.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment of a control method of a phase-advanced capacitor equipment according to the present invention.

FIG. 2 is a connection diagram showing an example of a configuration of a current ratio switcher constituting the present invention.

FIG. 3 is a connection diagram showing another example of the configuration of the current ratio switch constituting the present invention.

[Explanation of symbols]

 Tr: Power receiving transformer PT: Meter transformer CT1, CT2: Meter current transformer 1: Reactive power detector 2: Current ratio switch 3: Harmonic current detector 4: Signal generator 11: Leading phase capacitor 12: series reactor 13: switch 21: phase-advancing capacitor equipment 22: load 31: resistor with tap 32: shunt resistance 33: auxiliary current transformer 34, 35, 36: switch contact

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroaki Imi 4th floor of Uehara Bldg., 3rd floor, 191 Nakabori-cho, Ichi-dori Karasuma, Higashi-iri, Nakagyo-ku, Kyoto-shi, Kyoto

Claims (3)

[Claims] A phase-advancing capacitor unit comprising a phase-advancing capacitor (11), a series reactor (12) and a switch (13) connected in series as one group, and two or more groups of phase-advancing capacitor equipment (21). In the control method of the phase-advancing capacitor equipment, the phase-advancing capacitor equipment is connected in parallel to a load, and the phase-advancing capacitor group is automatically turned on and off automatically according to the change of the load. Detecting the reactive power of the load including (21) and the harmonic current of only the load,
When either the magnitude of the reactive power or the magnitude of the harmonic current per the number of groups of the phase-advancing capacitors or any one of them exceeds a set value, a signal for turning on the phase-advancing capacitors is issued, and any of them is output. A phase-advance capacitor group open signal is output when the value falls below a set value. 2. A load according to the number of groups of the phase-advancing capacitors on the secondary side of the current transformer for detecting the load current in order to detect the load harmonic current per the number of groups of the phase-advancing capacitors. 2. The control method of a phase advance capacitor equipment according to claim 1, wherein a method of switching a resistance is used. 3. A tap according to the number of input groups of phase-advancing capacitors on the secondary side of a current transformer for detecting load current in order to detect load harmonic current per number of input groups of phase-advance capacitors. 3. The control method of a phase-advanced capacitor equipment according to claim 2, wherein an auxiliary current transformer (33) for switching the phase changer is used.