JP3104833B2 - Composite instrument - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite instrument capable of measuring electric energy and reactive electric energy in one housing.

[0002]

2. Description of the Related Art A compound meter of this type is generally used to obtain an average power factor of a load connected to a power supply line, and measures the power amount and the reactive power amount of the power supply line. Then, the average power factor of the load is to be obtained by calculation based on the reactive power amount.

FIG. 6 shows a block diagram of a conventional composite instrument of this type. In the figure, 11 is a voltage detection unit that converts the voltage V of the power supply line into a voltage signal proportional to the voltage value, 12 is a current detection unit that converts the current I of the power supply line into a voltage signal proportional to the current value, Reference numeral 13 denotes a watt hour meter that obtains power by multiplying the voltage signals output from the voltage detector 11 and the current detector 12. That is, the watt-hour meter unit 13 multiplies the voltage signals output by the voltage detection unit 11 and the current detection unit 12 to convert the voltage signal into a voltage signal proportional to the power, and converts the voltage signal proportional to the power into a frequency. Frequency converter 132 for converting to a signal
And a count display section 133 for counting the frequency signal and displaying the count value.

[0004] On the other hand, reference numeral 14 denotes a reactive energy meter section, which is configured as follows. That is, the delay unit 141 performs a phase shift conversion of the voltage signal output by the voltage detection unit 90 by 90 degrees, and multiplies the voltage signal subjected to the phase shift conversion by 90 degrees and the voltage signal output by the current detection unit 12 into reactive power. A power multiplying unit 142 for converting the voltage signal proportional to the reactive power, a frequency converting unit 143 for converting the voltage signal proportional to the reactive power to a frequency signal, and a counting display unit 144 for counting the frequency signal and displaying the count value It is composed of In this way, the power amount and the reactive power amount of the power supply line can be measured.

[0005]

The power P and the reactive power Q have a phase angle of π / 2 = 9 as expressed by the following equation.
It is well known that it is shifted by 0 degrees.

[0006]

P = VI cos θ Q = VI sin θ sin θ = cos (θ−π / 2) As described above, since the phase angle is shifted by 90 degrees between the power and the reactive power, as shown in FIG. The meter operates in the range from the leading power factor 0 to the lagging power factor 0 around the power factor 1, and the reactive power meter operates in the range from the power factor 1 to the power factor -1 around the leading or lagging power factor 0. It is supposed to work.

In FIG. 7, the upper half, which is the operating range of the watt hour meter, is a forward current range (a state in which the power company is supplying power), and the lower half of the reverse direction is a reverse current range (the state of the power company). (A state in which power is supplied), and a situation in which such a reverse current flows when a customer having a private power generation facility has a surplus in private power generation.

[0008] For this reason, when this kind of combined meter is used for a customer having a private power generation facility, the power meter operates when the surplus power of the private power is generated and the power is returned (supplied) to the power company. When only the reactive power meter operates without performing the above operation, the reactive power amount increases. Therefore, since the power factor is the ratio of the active power to the apparent power, it is as if a load having a bad power factor was used.

In general, a power company makes a power factor contract so that the power factor of a load used by a consumer is used as close to 1 as possible in order to use the generated power efficiently, and the power factor is lower than the contract. Take a fine when used at the rate.
Therefore, when using such a composite instrument in a customer having a private power generation facility, it is necessary to take measures to prevent a reverse current from flowing through the composite instrument, and an expensive capital investment is required. . SUMMARY OF THE INVENTION An object of the present invention is to provide a composite instrument that can accurately measure an electric energy and a reactive electric energy and can prevent an erroneous calculation of a power factor.

[0010]

In order to achieve the above object, according to the present invention, a control means determines whether or not a load current of a power supply line is a reverse current based on a frequency signal of an active power amount calculating means and controls the load. The gist is that the reactive power calculating means is stopped when the means determines the reverse current.

[0011]

In such a configuration, when the control means determines that the direction of the load current is the reverse current based on the frequency signal of the active power calculation means, the control means stops the reactive power calculation means. The electric energy and the reactive electric energy can be accurately measured regardless of the direction.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. Note that the same components as those in the related art are denoted by the same reference numerals, and description thereof is omitted. FIG. 1 is a block diagram showing one embodiment of the composite instrument of the present invention. The configuration different from the conventional composite meter is the reverse current discriminator 1 provided on the output side of the frequency converter 132 of the wattmeter 13.

That is, the reverse current discriminating unit 1 is provided with a watt hour meter unit 13.
It determines whether or not the current I in the power supply line is a reverse current from a frequency signal proportional to the power output by the frequency conversion unit 132, and outputs a count control signal to the count display unit 144 of the reactive power meter unit 14. The counting display section 144 of the reactive energy meter section 14 stops counting when it receives the reverse current discrimination signal from the reverse current discriminating section 1.

FIG. 2 is a circuit diagram of the reverse current discriminating section 1. In FIG. 1, a reverse current discriminating unit 1 includes a retrigger type monostable multivibrator 21, a resistor Ra, and a capacitor C.
And a D-type flip-flop 22. Electricity meter unit 13
Is input to the trigger input terminal T of the retrigger-type monostable multivibrator 21 and the clock input terminal CK of the D-type flip-flop 22. Re-trigger type monostable multivibrator
The output terminal Q1 outputs a pulse of a reference time determined by the resistance Ra and the capacitor C from the rising of the frequency signal.
And the data input terminal D of the D-type flip-flop 22
Give to. Each time the frequency signal proportional to the power output from the frequency conversion unit 132 of the watt-hour meter unit 13 input to the clock input terminal CK rises, the D-type flip-flop 22 inputs the data input terminal D immediately before the rise. The output terminal Q2
Is configured to be output.

FIG. 3 is a diagram showing operation waveforms of the reverse current discriminating section 1. As shown in the figure, when a frequency signal IN proportional to the power output from the frequency conversion unit 132 of the watt-hour unit 13 rises, the retrigger type monostable multivibrator 21 sets the resistance R
A pulse having a reference time Tr determined by a and the capacitor C is output to the output terminal Q1. D-type flip-flop 22
Is a frequency signal IN input to the clock input terminal CK.
Each time the signal rises, the state of the data input terminal D connected to the output terminal Q1 of the retrigger type monostable multivibrator 21 immediately before the rise is output to the output terminal Q2. Therefore, when the interval of the frequency signal IN is longer than the reference time Tr, the output terminal Q2 of the D-type flip-flop 22, that is, the determination signal of the reverse current determination unit 1 is 0 level, indicating that the current is reverse. When the interval of the frequency signal IN is shorter than the reference time Tr, the output terminal Q1 of the retrigger type monostable multivibrator 21 becomes zero level in FIG. 3c, but is retriggered in FIG. , The output terminal Q1 of the retrigger-type monostable multivibrator 21 continues to be at one level until FIG. 3e. In FIG. 3b, the output terminal Q2 of the D-type flip-flop 22, that is, The judgment signal of the current judging section 1 becomes 1 level, indicating that the current is a positive current.

As described above, in the composite instrument of this embodiment,
In order to check the direction of the current flowing in the power supply line, the interval between frequency signals proportional to the power output from the frequency conversion unit 132 of the watt-hour meter unit 13 is compared with a reference time. However, as can be seen from the equation P = VI cos θ for calculating the power P,
When the reverse current flows, the current I becomes negative, so that P = −VI cos θ and the power P also becomes negative power. However, the frequency signal output by the frequency conversion unit 132 of the watt hour meter unit 13 is Since there is no negative frequency, the result is as shown in FIG. 4A, and it is not preferable that a positive power portion near power 0 is determined to be a reverse current. Therefore, the characteristics of the watt-hour meter unit 13 are shown in FIG.
The output frequency is adjusted to 0 with a slight negative power by adjusting as in b, and it is determined whether the current is a reverse current or a positive current at a frequency between the frequency Fb when the power is 0 and the frequency 0. Things.

That is, the reverse current discriminating unit 1 uses the reference time Tr
By comparing and determining the interval between frequency signals proportional to the power output by the frequency conversion unit 132 of the watt hour meter unit 13,
The direction of the current is easily determined. Then, the determination signal is supplied to the counting display section 144 of the reactive energy meter section 14 and the operation of the reactive energy meter section 14 is stopped by stopping the counting operation of the counting display section 144 at the time of reverse current. It is to let.

As described above, in the composite meter according to the present invention, the reactive power meter can be made not to operate at the time of reverse current, so that correct metering can be performed even if the meter is used for a customer having a private power generation facility where reverse current occurs. Erroneous calculation of the power factor can be prevented.

Next, another embodiment is shown in FIG. The light load shown in FIG. 1 is obtained by changing the characteristic of the frequency conversion unit 132 in FIG. 1 in a light load portion near power 0 as shown in FIG. 4c so that the output frequency becomes 0 with a slight negative power. 5 is a configuration diagram of a frequency converter with characteristic correction 34. FIG.

The frequency converter 34 with light load characteristic correction is shown in FIG.
An input terminal of the frequency conversion unit 32 is provided with a light load characteristic correction unit composed of resistors Rb and Rc and a diode D. In such a configuration, the resistance Rb and the resistance R
The power supply voltage is divided by c and the power
Generates a voltage VWa equal to the voltage output at the positive power Wa near the positive power 0, and applies this voltage VWa through the diode D to the input terminal of the frequency conversion unit 132, whereby the characteristic below the positive power Wa is obtained. 4c.

The frequency converter 34 with light load characteristic correction shown in FIG.
When used in place of the frequency conversion unit 132 shown in FIG. 1, as can be seen from the characteristic diagram of FIG. 4, the characteristic of FIG. Has appeared as an error, but in the frequency converter with light load characteristic correction 34, it is possible to obtain a characteristic having no error at a positive power Wa or more. Therefore, the power Wa
By making the above point out of the characteristic guarantee range as a watt-hour meter, a composite meter with less errors can be obtained.

In these embodiments, the reverse current discriminating section 1 discriminates the current direction based on the reference time Tr determined by the resistor Ra and the capacitor C. However, a reference frequency generating means is provided instead. The current direction may be determined based on the reference frequency fr corresponding to the reciprocal of the time Tr. However, the determination of the current direction in this case is opposite to that based on the reference time Tr.

[0023]

As described above, according to the present invention, an auxiliary transformer for outputting a voltage signal proportional to a load voltage of a power supply line;
An auxiliary current transformer that outputs a voltage signal proportional to the load current of the power supply line, and a voltage multiplier that multiplies a voltage signal from the auxiliary current transformer and a voltage signal from the auxiliary transformer and outputs the voltage from the power multiplier. A power conversion means for converting a signal into a frequency signal by a frequency conversion unit to calculate an active power, a phase shift signal obtained by shifting a voltage signal from the auxiliary transformer by π / 2, and an auxiliary current transformer. And a reactive power amount calculating means for calculating a reactive power amount by multiplying the voltage signal by a power multiplying unit, and a load current direction of the power supply line from the frequency signal of the frequency conversion unit of the active power amount calculating means. Control means for stopping the reactive power calculation means when the direction is the reverse direction, and the control means determines the direction of the load current as the reverse current based on the frequency signal of the frequency converter of the active power calculation means. I decided to
The amount of power and the amount of reactive power can be measured accurately, and erroneous calculation of the power factor can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a composite instrument of the present invention.

FIG. 2 is a circuit configuration diagram of a reverse current discriminating unit 1 in FIG. 1;

FIG. 3 is a diagram for explaining the operation of a reverse current discriminating unit 1 in FIG. 1;

FIG. 4 is a diagram for explaining the operating characteristics of the composite meter shown in FIG. 1;

FIG. 5 is a circuit configuration diagram of a frequency converter showing another embodiment of the composite instrument of the present invention.

FIG. 6 is a configuration diagram of a conventional composite instrument.

FIG. 7 is a diagram for explaining an operation range of a general watt hour meter and a reactive watt hour meter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reverse current discrimination part, 13 ... Watt-hour meter part, 14 ... Reactive power meter part 132 ... Frequency conversion part

Claims (4)

(57) [Claims] An auxiliary transformer for outputting a voltage signal proportional to a load voltage of the power supply line; an auxiliary current transformer for outputting a voltage signal proportional to a load current of the power supply line; Active power calculating means for multiplying a voltage signal and a voltage signal from the auxiliary transformer by a power multiplier, converting an output signal from the power multiplier into a frequency signal by a frequency converter, and calculating an active power amount; A reactive power amount calculator for calculating a reactive power amount by multiplying a phase shift signal obtained by shifting a voltage signal from the auxiliary transformer by π / 2 and a voltage signal from the auxiliary current transformer in a power multiplier. Means, and control means for determining the load current direction of the power supply line from the frequency signal of the frequency conversion unit of the active power calculation means, and stopping the reactive power calculation means when the current direction is in the opposite direction. And the control means includes: The frequency signal of the frequency conversion unit of the amount calculation means is compared with a reference time signal, and when the frequency signal of the frequency conversion unit is equal to or greater than the reference time signal, the load current direction of the power supply line is determined to be the opposite direction. A composite instrument characterized by the following. 2. An auxiliary transformer for outputting a voltage signal proportional to a load voltage of a feeder line, an auxiliary current transformer for outputting a voltage signal proportional to a load current of the feeder line, Active power calculating means for multiplying a voltage signal and a voltage signal from the auxiliary transformer by a power multiplier, converting an output signal from the power multiplier into a frequency signal by a frequency converter, and calculating an active power amount; A reactive power amount calculator for calculating a reactive power amount by multiplying a phase shift signal obtained by shifting a voltage signal from the auxiliary transformer by π / 2 and a voltage signal from the auxiliary current transformer in a power multiplier. Means, and control means for determining the load current direction of the power supply line from the frequency signal of the frequency conversion unit of the active power calculation means, and stopping the reactive power calculation means when the current direction is in the opposite direction. And the control means includes: The frequency signal of the frequency conversion unit of the amount calculation means is compared with a reference time signal, and when the frequency signal of the frequency conversion unit is equal to or less than the reference frequency signal, the load current direction of the power supply line is determined to be the opposite direction. A composite instrument characterized by the following. 3. The frequency conversion unit of the active power calculation means stops output when a load current direction of the power supply line becomes a reverse direction and reaches a predetermined negative power value. The composite instrument according to claim 1, wherein: 4. A means for dividing a predetermined power supply voltage is provided on an input side of a frequency converter of the active power calculating means, and a voltage signal from the voltage dividing means is applied to a power multiplying section of the active power calculating means. The composite instrument according to any one of claims 1 to 3, wherein the output signal is equivalent to the output signal of (i) and is supplied to the frequency conversion unit via a diode.