JP4483056B2 - Power factor adjustment device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention detects a reactive power, a reactive current or a power factor in a power system, and adjusts a power factor for improving the power factor by inserting or shutting off a power factor improving capacitor in the power system based on the detected values. It relates to the device.
[0002]
[Prior art]
4 is a configuration diagram of a conventional power factor adjustment apparatus disclosed in, for example, Japanese Patent Laid-Open No. 7-182057, FIG. 5 is a vector diagram illustrating the relationship of conventional power factor adjustment, and FIG. 6 is an arithmetic process of an arithmetic processing unit. It is a flowchart which shows a procedure.
In FIG. 4, 1 is a power system subject to power factor adjustment, 2 is a transformer for an instrument installed in the power system 1, 3 is a current transformer for the instrument, and 10 is a power factor adjustment device.
Reference numeral 4 denotes a power factor improving capacitor, and a plurality of capacitors 4a to 4n are connected to each other by electromagnetic contactors 6a to 6n via the control circuit unit 5 according to the output of the power factor adjusting device 10, respectively. Yes. Reference numerals 7a to 7n denote DC reactors connected to the capacitors 4a to 4n, 8 denotes a transformer connected to the power system 1, and 9 denotes a load connected to the transformer 8.
[0003]
The power factor adjusting device 10 is controlled by a microprocessor (not shown) and converts a detected voltage and a detected current from the instrument transformer 2 and the instrument current transformer 3 with a predetermined conversion ratio, respectively. 11 and the second conversion circuit 12, the A / D converter 13 for converting the analog signal from the first conversion circuit 11 and the second conversion circuit 12 into a digital signal, and the detection voltage and detection converted into the digital signal An arithmetic processing unit 14 that outputs a signal for controlling the insertion and interruption of the power factor improving capacitor 4 to the power system 1 based on the current and a target power factor setting value and a light load breaking power setting value, which will be described later, and this calculation Based on the control signal from the processing unit 14, the control output relay unit 15 that controls the insertion and interruption of the power factor improving capacitor to the power system 1 and the calculation processing result of the calculation processing unit 14 are displayed. It includes a display unit 16, the arithmetic processing unit 14 and a setting unit 17 for setting a target power factor and light load shedding power setting.
Here, the light load cut-off power set value is a power factor improving capacitor 4 in order to prevent the power factor improving capacitor 4 from being kept on when the load is light and a significant advance power factor. Is the minimum active power value for shutting down all of the above.
[0004]
Next, the operation of the power factor adjusting device will be described with reference to FIGS. In FIG. 5, 30 indicates the reactive power on the vertical axis, the leading power factor above the zero point, the lagging power factor below, and 31 the active power on the horizontal axis. Reference numeral 34 denotes a target power factor, which is set by the setting unit 17, and the capacitor connecting point 33 is a line connecting the angle with the zero point. A value 37 obtained by multiplying the charging point 33 by a phase constant reactive power value corresponding to the capacitor capacity and a margin constant (generally 1.2 times) for preventing hunting advances and moves in the power factor direction is defined as a capacitor cutoff point 32. Control is performed.
[0005]
Reference numeral 36 denotes reactive power, which is calculated from the target power factor 34 set by the setting unit 17 and the active power 35 calculated from the measured value. Reactive power 36 is obtained as reactive power = active power × √ (1 / target power factor ² -1). A value 38 obtained by subtracting a value 37 obtained by multiplying the value of the reactive power 36 by a constant (generally 1.2 times) from the currently charged capacitor capacity is compared with the capacitor cutoff point 32, and the capacitor cutoff point is required. Decide no. Reference numeral 40 denotes a light load breaking power setting value of the active power value set by the setting unit 17, and a light load breaking point 39 is a line connected vertically.
[0006]
Based on the target power factor set by the setting unit 17 and the light load breaking power set value 40, the calculation processing unit 14 sets a closing point and a light load breaking point 39 (step S1), and an instrument transformer. 2, the detected voltage from the current transformer 2 and the detected current from the current transformer 3 are converted by the first conversion circuit 11 and the second conversion circuit 12, respectively, and then converted into a digital signal by the A / D converter 13. The apparent power, active power, reactive power, and power factor are calculated based on the detected voltage and the detected current (step S2).
[0007]
These calculated numerical values are displayed on the display unit 16, and if the calculated active power value is less than the light load cutoff point 39 (step S3), a capacitor cutoff signal is output to the control circuit unit 15 (step S6). If the active power value exceeds the light load breaking point 39, a comparison is made as to whether the reactive power exceeds the capacitor breaking point 32 (step S5). A cutoff signal is output to the control circuit unit 5.
On the other hand, if the active power value exceeds the light load cutoff point 39 and the reactive power exceeds the capacitor charging point 33 in the delay power factor direction (step S7), the capacitor charging signal is controlled in step S8. Output to the circuit unit 5.
[0008]
That is, the on / off control is executed appropriately or in combination from among the plurality of capacitors 4 so that the apparent power vector exists in the non-hatched part of FIG. Since a capacitor bank is formed by a plurality of capacitors 4a to 4n, each of the capacitors 4a to 4n has a predetermined order for life averaging, or a capacitor having an optimum capacity for power factor improvement at that time. The capacitor to be controlled is selected by selecting it. For this reason, the capacitor that remains in the input state until the end does not necessarily have the minimum capacity, and in some cases, only one capacitor with the maximum capacity may remain in the input state.
[0009]
[Problems to be solved by the invention]
Since the conventional power factor adjusting device is configured as described above, when a small value is set as the light load break point set value 40, the active power is not in a light load state in which the light load break point 39 is slightly exceeded. When the capacity of one capacitor remaining in the capacitor bank is large, the value obtained by multiplying the capacitor capacity by a margin constant for preventing hunting (for example, 1.2 times) is large. The sum of the reactive power value, the calculated target reactive power value and the absolute value of each does not reach this value, and the capacitor is not cut off, resulting in an extreme advance power factor as shown at point P in FIG. There are problems such as an increase in circuit voltage and generation of harmonics.
[0010]
The present invention has been made to solve the above problems, and in a light load state in which the active power has not reached the light load cutoff point, a capacitor having a relatively large capacity remains and is extremely advanced. Prevent power factor.
[0011]
[Means for Solving the Problems]
The power factor adjusting apparatus according to the present invention is configured to set an allowable advance power factor from the advance power factor setting means in addition to a preset target power factor and light load breaking power value, and a minimum capacity capacitor in the capacitor bank to be controlled. When the calculated active power value exceeds the light load cut-off power value, and the calculated reactive power is in the capacitor input area and is ahead of the allowable advance power factor, the currently connected capacitor is selected. The capacitor with the smallest capacity is selected and connected by cutting off.
[0012]
And when the calculated active power value exceeds the light load cut-off power value, the calculated reactive power is in the capacitor input area and is ahead of the allowable advance power factor, and the currently connected capacitor is the minimum capacity capacitor Indicates that the capacitor is not cut off.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a power factor adjustment apparatus according to the present invention, FIG. 2 is a vector diagram illustrating an operation of power factor adjustment, and FIG. 3 is a flowchart showing contents of arithmetic processing.
In the figure, 1 to 17, 30 to 40 and steps S1 to S12 of FIG. Reference numeral 18 denotes an advance power factor setting unit that inputs and sets an allowable upper limit value of the advance power factor of the power system 1. Reference numeral 19 denotes a memory device that stores the capacitance values of the capacitors 4a to 4n, the on / off sequence, and the current on / off state. It is.
In FIG. 2, reference numeral 41 denotes the advance power factor setting value set by the advance power factor setting unit 18, and the line connecting the zero point is the advance power factor allowable limit control point 42. In other words, the cutoff of the capacitor 4 is urged so that the apparent power vector of the power system 1 does not exceed the advance power factor allowable limit control point 42 to become a significant advance power factor.
[0014]
Next, the operation of the present invention will be described with reference to FIGS. For example, if the power load of the power system 1 gradually decreases and, for example, the current load power vector is at point A, the active power B of this load power exceeds the light load cut-off point 39, so that the total cut-off of the capacitor is Not done. The reactive power C has not reached the cutoff point 32. However, it is in a position that exceeds the advance power factor allowable limit control point 42. Accordingly, the capacitor is cut off and replaced so that the lead power factor allowable limit control point 42 is not exceeded.
[0015]
The flow of this capacitor shut-off / replacement process, which is the main point of the present invention, will be described with reference to FIG. When the active power is equal to or higher than the light load cut-off point 39 and the reactive power is the advance power factor (steps S1 to S4), it is compared whether or not the advance reactive power exceeds the cut-off point 32 (step S5). The capacitor is cut off (step S6). When the advanced reactive power falls below the cut-off point 32, it is compared whether the advanced reactive power exceeds the advanced power factor allowable limit control point 42, and if the advanced reactive power is less than the advanced power factor allowable limit control point 42, it is left as it is. The capacitor input state is maintained (step S20). When the advance reactive power is greater than the advance power factor allowable limit control point 42, it is checked whether or not the currently input capacitor has the minimum capacity in the capacitor bank. S21). When the capacitor is not the minimum capacitor, the currently connected capacitor is cut off, and the capacitor having the minimum capacitance is selected from the standby capacitors (steps S2 2 and S2 3 ).
[0016]
When the capacitor is cut off in step S21, if the capacitor has the minimum capacity, the capacitor is once cut off and then turned on again, so that the frequency of opening and closing of the capacitor increases, and the durable life of the capacitor is shortened.
Therefore, it is determined whether or not the capacitor that is currently input has the minimum capacity among the capacitors to be controlled. If the capacitor has the minimum capacity, the capacitor that has been already input is not cut off. Thereby, frequent opening and closing of the minimum capacitor can be avoided.
[0017]
In addition, although the advance power factor setting part 18 is provided separately in the said Example, you may include this in the setting part 17 which sets a target power factor and a light load cutoff electric power setting value.
The advance power factor set value 41 has been described as being settable by the setting unit 17, but may be a fixed value determined in advance.
[0018]
【The invention's effect】
In the conventional device, a significant advance in a triangle (XYZ) range surrounded by the capacitor cutoff point 32, the light load cutoff point 39, and the advance power factor allowable limit control point 42 of FIG. The power factor state can be resolved.
[0019]
In addition, since the light load breaking point 39 can be set small corresponding to the minimum capacity capacitor in the capacitor bank, it is possible to achieve a large delay power factor without introducing a capacitor at all in the range of the active power that does not reach the light load breaking point 39. Electricity usage is reduced, and power rate discounts can be benefited in electricity bill transactions.
The reason is that the electricity charge = basic charge + power consumption charge, and the basic charge is calculated by contract power x contract power unit price x {1- (monthly power factor -0.85)} (base month) The power factor is set to 85%). The formula of 1- (monthly power factor -0.85) is generally called power factor discount, and the power factor of 1% is calculated from this value based on the power factor value of 85% delay, that is, 0.85. If the unit is exceeded, the basic fee is discounted in units of 1%. Conversely, if the unit rate is reduced by 1%, it is increased by 1%. Since there is little power usage in a state where the power factor is bad, the benefit of power factor discount can be obtained.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a power factor adjusting device according to the present invention.
FIG. 2 is a vector diagram illustrating an operation of power factor adjustment according to the present invention.
FIG. 3 is a flowchart showing the calculation process contents of power factor adjustment according to the present invention.
FIG. 4 is a configuration diagram of a conventional power factor adjustment device.
FIG. 5 is a vector diagram for explaining a conventional power factor adjustment operation.
FIG. 6 is a flowchart showing the contents of a conventional power factor adjustment calculation process.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electric power system, 4 Capacitor, 10 Power factor adjustment apparatus 14 Computation processing part, 18 Advance power factor setting part, 19 Memory apparatus 32 Capacitor cutoff point, 33 Capacitor insertion point, 34 Target power factor 39 Light load cutoff point, 40 Light load Breaking power set value 41 Leading power factor set value, 42 Leading power factor allowable limit control point

Claims (2)

Measures voltage and current in the power system, calculates active power and reactive power from the measured values, and controls on / off of capacitors to the above power system based on preset target power factor and light load cutoff power value In the power factor adjustment device that adjusts the power factor,
A lead power factor setting means for setting an allowable lead power factor of the power system, and means for storing and selecting a capacitor having the minimum capacity among the capacitor banks to be controlled,
When the calculated active power value exceeds the light load cut-off power value, and the calculated reactive power is in the capacitor input area and is ahead of the allowable advance power factor, the currently connected capacitor is cut off and the minimum A power factor adjusting device characterized in that a capacitor having a capacity is selected and connected. When the calculated active power value exceeds the light load cut-off power value, the calculated reactive power is in the capacitor input area and is ahead of the allowable advance power factor, and the currently connected capacitor is the minimum capacity capacitor 2. The power factor adjusting device according to claim 1, wherein the capacitor is not cut off.

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