JP2015177734A - Automatic power factor control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic power factor control apparatus for controlling insertion and separation of a phase advance capacitor while reducing a calculation load of an apparatus.SOLUTION: An automatic power factor control apparatus 1 for controlling insertion and separation of phase advance capacitors 3, 3 comprises: a power receiving point current threshold calculation unit 8 for calculating a threshold of current at a power receiving point from a load power factor and phase advance capacitor capacitance and the like; an effective value calculation unit 11 for calculating an effective value of a current signal at the power receiving point; and an insertion/separation determination control unit 12 for determining and controlling insertion and separation of the phase advance capacitors. The power receiving point current threshold calculation unit 8 calculates a threshold of power receiving point current and stores the threshold; and the insertion/separation determination control unit 12 compares the effective value of the current signal at the power receiving point calculated by the effective value calculation unit 11 with the power receiving point current threshold, and determines and controls insertion and separation of the phase advance capacitors 3.

Description

  The present invention relates to an automatic power factor control device for controlling the insertion and release of a phase advance capacitor.

Conventionally, high-voltage customers have installed multiple phase-advancing capacitors (SC) to improve the power factor at the power receiving point, and an automatic control system that controls the number of SCs input so as to maintain the power factor at the power receiving point appropriately. A power factor controller (APFC: Automatic Power Factor Controller) is installed. A general control method of APFC is to measure the voltage and current of a power receiving point, calculate reactive power and power factor, and determine the number of SCs to be input according to the magnitude of the reactive power.
Currently, the penetration rate of APFC is as low as 10% of high-pressure customers. For this reason, many SCs are always turned on, and the power factor at the power receiving point is increased at night when the power consumption of high-voltage consumers is small, causing a voltage increase problem in the high-voltage distribution system. Therefore, the installation of APFC that can properly maintain the power factor of the power receiving point requires further cost reduction and expansion of installation merit in order to maintain and improve the power quality of the high voltage distribution system and the like.
From such a background, as one of the measures for reducing the cost of APFC, an automatic power factor control device having a function of calculating a reactive power and a power factor of a power receiving point only from current measurement has been proposed (Japanese Patent Application Laid-Open (JP-A)). 2012-50290 publication).
In the automatic power factor control apparatus disclosed in Japanese Patent Application Laid-Open No. 2012-50290, voltage measurement is not required, so that hardware for taking in voltage and software for calculating a voltage value are not required, and the APFC is low. This contributes to cost reduction.

  JP 2012-50290 A

  In the configuration of the automatic power factor control device disclosed in Patent Document 1, the effective value calculation of the receiving point current input to the current sensor CT2 is always performed, and compared with a predetermined threshold value. If the value exceeds the threshold value, the SC is inserted, and when the value falls below the threshold value, the SC is basically released. Since the expression including the square root and the trigonometric function is constantly calculated, the number of program steps of the control device is reduced. Therefore, it has been difficult to configure the apparatus using hardware such as a low-cost programmable controller (PLC).

It is an object of the present invention to provide an automatic power factor control device that controls the introduction and release of a phase advance capacitor, which can reduce the calculation load of the device and can be configured using low-cost hardware. In order to achieve at least part of the objective, the following measures were taken.
The present invention is an automatic power factor control device for controlling the insertion and release of a phase advance capacitor for power factor improvement provided so as to be connected in parallel with this load on the load side from the power consumer's power receiving point.
A power receiving point current threshold value calculating unit for calculating a current threshold value of the power receiving point from a load power factor and a phase advance capacitor capacity;
An effective value calculation unit for calculating an effective value of the current signal at the power receiving point;
An on / off determination control unit that determines and controls the on / off of the phase advance capacitor, and
With
The receiving point current threshold value calculation unit calculates and holds the receiving point current threshold value,
In the on / off decision control unit, the effective value of the current signal at the power receiving point calculated by the effective value calculating unit is compared with the power receiving point current threshold value to determine and control on / off of the phase advance capacitor. This is the gist.

  Obtain the receiving point current threshold value in advance, and turn the phase advance capacitor on and off while comparing it with the receiving point current threshold value without converting the receiving point current effective value to the load current value. Thus, the calculation load of the apparatus can be reduced, and the automatic power factor control apparatus can be configured using low-cost hardware.

Further, the automatic power factor control device of the present invention may be configured to include a load power factor estimation unit that estimates the load power factor.
In this way, appropriate phase-advancing capacitor on / off control can be performed without assuming the load power factor in advance, and without re-estimating the load power factor even when the load equipment is replaced or expanded. It will be possible.

Further, the automatic power factor control device of the present invention can be configured to include a set value input unit for inputting set values necessary for calculation and control from the outside.
In this way, even when the load power factor estimation unit is not provided, the load power factor can be assumed based on the manufacturer's specifications and short-time measurement results, and can be input and held in advance from the set value input unit.

In the automatic power factor control device of the present invention, the effective value calculation unit may be provided in a current sensor that measures a current signal at the power receiving point.
In this way, by using a sensor having an effective value calculation unit as a current sensor, an effective value calculation unit in the automatic power factor control device is not necessary, and the cost of the device can be reduced.

  It is a block diagram of the automatic power factor control apparatus of 1st Example.   It is a vector diagram which shows the relationship between a receiving point current and load current.   It is an operation | movement flowchart which shows the flow of operation | movement.   It is a block diagram of the automatic power factor control apparatus of 2nd Example.   It is a block diagram of the automatic power factor control apparatus of 3rd Example.

  Next, the form for implementing this invention is demonstrated using an Example.

FIG. 1 shows a configuration example of an automatic power factor control apparatus 1 according to the first embodiment.
An automatic power factor control device 1 for controlling the insertion and release of the power factor improving phase-advancing capacitors 3 and 3 provided so as to be connected in parallel to the load on the load side from the power receiving point of the electric power consumer. A current signal input unit 10 for inputting a current signal at a power receiving point 2 from a current sensor, etc., an effective value calculating unit 11 for calculating an effective value of the current signal, and comparing an effective value and a power receiving point current threshold value, An on / off decision control unit 12 for determining and controlling the introduction and release of the phase advance capacitor, and a threshold value calculation unit for the reception point current for calculating the threshold of the reception point current from the load power factor and the phase advance capacitor capacity 8, a load power factor estimation unit 13 for estimating the load power factor, and a set value input unit 6 for inputting a set value necessary for calculation and control from the outside.

The automatic power factor control device 1 is characterized in that a power receiving point current threshold value is obtained in advance in the power receiving point current threshold value calculation unit 8, and the power reception point current effective value calculated by the effective value calculation unit 11 is obtained as another value. The phase-advancing capacitors 3 and 3 are turned on and off without being converted into values while being directly compared with the power receiving point current threshold value.
In the conventional automatic power factor control device, the load current threshold value is obtained in advance and the load current effective value is compared with the load current threshold value while converting the measured receiving point current effective value into the load current effective value. The phase-advancing capacitor was turned on and off, but the calculation load increases because the effective value of the receiving point current is always converted to the effective value of the load current. It was difficult to configure the control device.

Here, the relationship between the power receiving point current and the load current is shown as a vector diagram in FIG.
The load current is the total current flowing through the electrical equipment operating on the customer premises, and is generally a delay power factor. Therefore, in the vector diagram, the load current is represented by a vector positioned on the delay side. If the phase-advancing capacitors 3 and 3 are not inserted when the load current has a delay power factor, the power receiving point current also has a delay power factor, which causes disadvantages such as an increase in distribution line loss and an increase in power charges. For this reason, the power factor at the power receiving point is adjusted to be close to 1 by inserting the phase advance capacitors 3 and 3 in parallel with the electric equipment through which the load current flows. Since the phase of the current of the phase-advancing capacitors 3 and 3 is 90 degrees with respect to the voltage, the vector diagram is represented by a vector facing the advance side.

In FIG. 2, for the sake of simplicity, the power receiving point current in a state where one phase advance capacitor (SC) 3 having the capacity Qsc (current Isc) is already input is expressed as a power receiving point current (1 SC input), and then In addition, the power receiving point current in a state where one phase advance capacitor (SC) 3 having the same capacity Qsc (current Isc), that is, a total of two power capacitors is input, is expressed as a power receiving point current (2 SC input).
The receiving point current vector when the phase advance capacitors 3 and 3 are turned on is a combination of the phase advance capacitor current vectors that are turned on simultaneously with the load current vector. Therefore, the positional relationship between the power receiving point current (1 SC input) and the power receiving current (2 SC input) is as shown in the figure.

In general high-voltage receiving / transforming equipment, it is possible to directly measure the receiving point current, but it is often difficult to directly measure the load current. This is because the load current is the sum of the currents flowing through a plurality of electrical devices and cannot be measured using only one current sensor.
On the other hand, for example, when considering the case where the power reception point power factor is adjusted to 1, the ineffective portion of the load current vector directly represents the phase advance capacitor current to be input. There are easy features. For this reason, in the conventional automatic power factor control device, the power receiving point current that can be actually measured is converted into a load current that is convenient for control, and the on / off control of the phase advance capacitor has been performed.

In this automatic power factor control device 1, a receiving point current threshold value is held in advance, and the measured receiving point current effective value is directly compared with the receiving point current threshold value without converting to another value. Turn on and off the phase-advancing capacitors 3 and 3.
The operation flow of the automatic power factor control apparatus 1 will be described with reference to the configuration example of FIG. 1, the vector diagram of FIG. 2, and the operation flow of FIG.

(Operation 1)
In step S1, a capacitor capacity Qsc, a circuit voltage V, and a load power factor (power factor angle θ) per unit are input in advance from the set value input unit 6.

ここで、Ｉ_ＬｔｈＮは、Ｎ台目の進相コンデンサ３を投入するための負荷電流しきい値、Ｉ_ＴｔｈＮは、Ｎ台目の進相コンデンサ３を投入するための受電点電流しきい値を表している。
（１）式は、負荷力率がｃｏｓθの場合に、容量Ｑ_ＳＣの進相コンデンサ３を投入すれば、受電点の力率を１に改善できる最大の負荷電流実効値を表している。
（２）式は、その最大の負荷電流実効値を、受電点電流実効値に換算する式である。(Operation 2)
In step S2, the threshold value calculation unit 8 for the power receiving point current is obtained by using the capacitor capacity Qsc per unit, the circuit voltage V, and the load power factor (power factor angle θ) inputted in advance from the set value input unit 6. The power receiving point current threshold value I _TthN is calculated by the following formula and _stored in the memory 9. In addition, the load power factor estimation unit 13 can obtain an estimated value of the load power factor of the load based on Japanese Patent Application Laid-Open No. 2012-50290.

Here, I _LthN is a load current threshold value for _turning on the N-th phase advance capacitor 3, and I _TthN is a receiving point current threshold value for _turning on the N-th phase advance capacitor 3. Represents.
(1), the load power factor when the cos [theta], if charged phase advancing capacitor 3 capacity Q _SC, which represents the maximum load current effective value can improve the power factor of the receiving point to 1.
The expression (2) is an expression for converting the maximum load current effective value into a power receiving point current effective value.

The basis for deriving equation (3) will be described with reference to the vector diagram of FIG.
The symbol in FIG. 2 and the symbol in the expression (3) correspond to I _L → I _LthN and I _T → I _TthN .
In FIG. 2, I _{L, I T,} looking at the relationship between I _SC, receiving point current I _T, the effective amount of the load current, three current of the current minus the before-SC current from reactive component of the load current constitutes a right-angled triangle having the hypotenuse receiving point current I _T. From this, the equation (3) can be easily derived using the three-square theorem.

(Operation 3)
In step S <b> 3, the current signal of the power receiving point current is taken from the current signal input unit 10, and the power receiving point current effective value is calculated by the effective value calculating unit 11.

(Operation 4)
In step S4, the on / off determination control unit 12 compares the power receiving point current effective value with the power receiving point current threshold value that is held in advance. In step S5, the phase advance capacitor 3 is turned on when the power reception point effective value exceeds the power reception current threshold value for a predetermined time, and the phase advance capacitor 3 is opened when the value is lower than the predetermined time.

(Operation 5)
Return to operation 3 and repeat the process. As a result, it is possible to put in the lowest phase advance capacitor 3 that always sets the power factor of the power receiving point to a more advanced side than 1, and it is possible to properly maintain the power factor of the power receiving point. .

FIG. 4 is a configuration example of the automatic power factor control apparatus 1 that does not have the load power factor estimation unit 13.
If the load power factor estimation unit 13 is not provided, the load power factor is assumed based on the manufacturer's specifications and short-time actual measurement results, input in advance from the set value input unit 6, and stored in the input value storage unit 7. That's fine.

FIG. 5 is a configuration example of the automatic power factor control apparatus 1 in which the functions provided in the apparatus are minimized.
Compared with FIG. 4, the effective value calculation unit 11 in the automatic power factor control device 1 is omitted by using a sensor having the effective value calculation unit 13 as a current sensor. The calculation of the effective current value requires a high-speed calculation by the CPU. However, with such a configuration, the calculation becomes unnecessary, and the cost of the apparatus can be reduced.

The merit of the automatic power factor control device 1 of the present invention including the above embodiments is that the calculation for opening and closing the power factor improving phase advance capacitor (SC) 3 can be simplified.
That is, the effective value of the measured current can be directly compared with the threshold value without recalculating it to another value. Once the threshold value is determined by the above equation (3), Since no calculation by a complicated calculation formula is required, the control program can be simplified, and the apparatus can be easily configured with a low-cost PLC.

  Currently, APFC has a low penetration rate, especially for high-voltage customers who install small-capacity power receiving facilities with a total transformer capacity of less than 300 kVA. These small-capacity power receiving facilities have many needs to keep the installation cost lower. For this reason, in order to newly install an APFC in a small-capacity power receiving facility, it is necessary to suppress the installation cost as much as possible. By using the method of the present invention, an apparatus can be realized only by mounting software on a general-purpose low-cost PLC without developing dedicated hardware as an APFC.

1 Automatic power factor controller 2 Receiving point 3 Phase advance capacitor (SC)
5 Switch 6 Set Value Input Unit 8 Receiving Point Current Threshold Calculation Unit 10 Current Signal Input Unit 11 Effective Value Calculation Unit 12 Input / Open Determination Control Unit 13 Load Power Factor Estimation Unit

It is an object of the present invention to provide an automatic power factor control device that controls the introduction and release of a phase advance capacitor, which can reduce the calculation load of the device and can be configured using low-cost hardware. In order to achieve at least part of the objective, the following measures were taken.
The present invention is an automatic power factor control device for controlling the insertion and release of a phase advance capacitor for power factor improvement provided so as to be connected in parallel with this load on the load side from the power consumer's power receiving point.
A receiving point current threshold calculation unit for calculating a threshold value of the current of the load power factor and phase advance capacitor capacitance or et the receiving point,
An effective value calculation unit for calculating an effective value of the current signal at the power receiving point;
An on / off determination control unit that determines and controls the on / off of the phase advance capacitor, and
With
The receiving point current threshold value calculation unit calculates and holds the receiving point current threshold value,
In the on / off determination control unit, the effective value of the current signal at the power receiving point calculated by the effective value calculating unit and the power receiving point current threshold value are compared, and control is performed by determining whether the phase advance capacitor is turned on or off. The gist is to do.

Claims (4)

In the automatic power factor control device that controls the introduction and release of the phase advance capacitor for power factor improvement provided so as to be connected in parallel with this load on the load side from the power receiving point of the power consumer,
A power receiving point current threshold value calculating unit for calculating a current threshold value of the power receiving point from a load power factor and a phase advance capacitor capacity;
An effective value calculation unit for calculating an effective value of the current signal at the power receiving point;
An on / off determination control unit that determines and controls the on / off of the phase advance capacitor, and
With
The receiving point current threshold value calculation unit calculates and holds the receiving point current threshold value,
In the on / off decision control unit, the effective value of the current signal at the power receiving point calculated by the effective value calculating unit is compared with the power receiving point current threshold value to determine and control on / off of the phase advance capacitor. An automatic power factor control device characterized by that.   The automatic power factor control apparatus according to claim 1, further comprising a load power factor estimation unit that estimates a load power factor.   The automatic power factor control device according to claim 1 or 2, further comprising a set value input unit for inputting a set value necessary for calculation and control from the outside.   4. The automatic power factor control device according to claim 1, wherein the effective value calculation unit is provided in a current sensor that measures a current signal at the power receiving point.

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