JP3001712B2 - 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 reliably measuring active power and reactive power with a single instrument.

[0002]

2. Description of the Related Art A compound meter of this type is used to determine an average power factor of a load connected to a power supply line, and measures an active power amount and a 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. 4 shows a block diagram of a conventional composite instrument. That is, 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.
Reference numeral 12 denotes a current detection unit that converts the current I of the power supply line into a voltage signal proportional to the current value. 13 is an active energy meter section,
A power multiplying unit 131 that multiplies the voltage signals output from the voltage detecting unit 11 and the current detecting unit 12 to convert the voltage signal into a voltage signal proportional to the power, and a frequency converting unit 132 that converts the voltage signal proportional to the power into a frequency signal And a count display unit 133 that counts this frequency signal and displays the value. Reference numeral 14 denotes a reactive energy meter unit, which includes a delay unit 141 that performs a phase shift conversion of the voltage signal output from the voltage detection unit 90 by 90 degrees, a voltage signal that has been subjected to the phase shift conversion by 90 degrees, and a voltage signal output from the current detection unit 12. And a frequency conversion unit 143 that converts the voltage signal proportional to the reactive power into a frequency signal.
And a counting display unit 1 for counting the frequency signal and displaying the value.
44. In this way, the active power amount and the reactive power amount of the power supply line can be measured.

[0004]

The active power P
And the reactive power Q are given by the following equation:
= 90 degrees is well known.

[0005]

## EQU1 ## P = V1 cos θ

[0006]

## EQU2 ## Q = V1 sin θ

[0007]

## EQU3 ## sin θ = cos (θ−π / 2)

As described above, since the phase angle is shifted by 90 degrees between the active power and the reactive power, as shown in FIG. 5, the active power meter measures a power factor of 1 from a leading power factor of 0 to a lagging power factor of 0. , And the reactive power meter operates in a range from a power factor of 1 to a power factor of -1 with a leading or lagging power factor of 0 as a center.

In FIG. 5, the upper half, which is the operating range of the active watt hour meter, is the forward current range (in a state where the power company is supplying power), and the lower half is the reverse current range (where the power company is supplying power). (A state in which power is supplied), and such a state in which a reverse current flows when a surplus of self-generated power occurs in a customer having a private power generation facility.
For this reason, in the conventional composite meter, when a customer having a private power generation facility has excess private power and returns (supplies) power to the power company, the active power meter unit 3 is disabled and does not operate. Only the watt-hour meter unit 4 operates. Therefore, the amount of reactive power increases, and it is as if a load with a bad power factor was used.

[0010] In general, a power company makes a power factor contract so that the power factor of a load used by a customer 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 a customer having a private power generation facility uses such a composite instrument, it is necessary to take measures to prevent a reverse current from flowing through the composite instrument, which is an expensive capital investment.

An object of the present invention is to provide a composite instrument that can accurately measure the active power and the reactive power with a single instrument regardless of the forward current or the reverse current, thereby preventing erroneous calculation of the power factor. .

[0012]

To achieve the above object, the present invention provides an auxiliary transformer for outputting a voltage signal proportional to a load voltage of a power supply line, and an auxiliary transformer for outputting a voltage signal proportional to a load current of the power supply line. An auxiliary current transformer, active power amount calculating means for calculating an active power amount by multiplying a voltage signal from the auxiliary current transformer and a voltage signal from the auxiliary transformer by a power multiplying unit; A reactive power calculating means for calculating a reactive power by multiplying a phase shift signal obtained by shifting the voltage signal by π / 2 and a voltage signal from the auxiliary current transformer in a power multiplier, and an active power calculating means And the control means for determining the load current direction of the power supply line from the output signal of the power multiplying unit and stopping the reactive power calculation means when the current direction is the opposite direction.

[0013]

In such a configuration, the power multiplying unit of the active power calculating means multiplies the voltage signal from the auxiliary transformer by the voltage signal from the auxiliary current transformer, and the control means uses the power supply line based on the multiplied signal. And the reactive power calculating means is stopped when the current direction is opposite, so that the active power and reactive power can be measured by one instrument regardless of the current direction of the feed line. Can be measured accurately, and erroneous calculation of the power factor can be prevented.

[0014]

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

FIG. 1 is a block diagram of a composite instrument according to the present invention. In FIG. 1, reference numeral 1 denotes a voltage detector, which is a voltage V of a power supply line.
A current detection unit 2 converts the voltage signal into a voltage signal proportional to the current I of the electric wire.
The active watt-hour meter unit 3 includes a power multiplying unit 31 that multiplies the voltage signals output from the voltage detecting unit 1 and the current detecting unit 2 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. A frequency conversion unit 32 converts the frequency signal into a signal, and a count display unit 33 counts the frequency signal and displays a value. Reference numeral 4 denotes a reactive energy meter unit, which includes a delay unit 41 for phase-shifting the voltage signal output from the voltage detection unit 1 by 90 degrees,
A power multiplying unit 42 that multiplies the voltage signal subjected to the phase shift conversion and the voltage signal output from the current detecting unit 2 to convert the voltage signal into a voltage signal proportional to the reactive power, and converts the voltage signal proportional to the reactive power into a frequency signal. It comprises a frequency conversion unit 43 for conversion, and a count display unit 44 for counting this frequency signal and displaying the value. Reference numeral 5 denotes a reverse current determination unit which determines whether or not the current I in the power supply line is a reverse current from a voltage signal proportional to the power output from the power multiplying unit 31 of the active watt-hour meter unit 3 and displays the count of the reactive power meter 4 The counter 44 outputs a count control signal to the unit 44.
Is a discrimination control input unit that outputs a signal for controlling the discrimination operation of the reverse current discrimination unit 5. The count display section 44 of the reactive power meter section 4 stops counting when it receives the reverse current determination signal from the reverse current determination section 5. Next, the reverse current determination unit 5 and the determination control input unit 6 will be described in detail with reference to FIGS.

FIG. 2 is a circuit diagram of the reverse current determining unit 5. In FIG. 2, a reverse current discriminating unit 5 has a voltage comparator 51 and a reference negative voltage −Vr.
There voltage signal (hereinafter, the power voltage referred to as signal Vw) proportional to the output electric power and receives a determination control signal C _IN output by the determination control input unit 6 to be described later, when the determination control signal C _IN is determined allowed Level of power voltage signal Vw and reference negative voltage−
Vr is compared and determined. When the power voltage signal Vw is equal to or lower than the reference negative voltage -Vr, it is determined that the current is a reverse current and the reverse current determination signal OUT is output. That is, as shown in Equation 1, when the reverse current flows, the current I becomes negative, so that the effective power P also becomes negative power. If the discrimination control signal C _IN indicates that the discrimination is not permitted, a signal indicating that there is a positive current is output without performing comparison discrimination.

FIG. 3 is a circuit diagram of the discrimination control input unit 6.
In FIG. 3, the discrimination control input unit 6 is constituted by a switch SW. For example, when the switch SW is closed, a discrimination control signal C _OUT that permits discrimination is output, and when the switch SW is opened, discrimination is not permitted. The control signal C _OUT will be output. Therefore, the power voltage signal V
When w also becomes negative, the reverse current can be determined.

As described above, the reverse current discriminating unit 5 compares the level with the reference negative voltage −Vr of the voltage signal proportional to the power output from the power multiplying unit 31 of the active watt-hour meter unit 3 to determine the current. The direction can be easily known. The operation of the reactive power meter unit 4 is stopped by inputting the determination signal of the reverse current determining unit 5 to the count display unit 44 of the reactive power meter unit 4 and stopping the counting operation of the count display unit 44 at the time of reverse current. I was made to. For this reason, an accurate power factor can be obtained, and a special device is not required even when a customer having a private power generation facility uses such a composite instrument.

The discriminating operation of the reverse current discriminating section 5 can be controlled by the discriminating control input means 6.
At the time of the test, the correct operation of the active power meter unit 3 and the reactive power meter unit 4 can be performed without performing the determination operation of the reverse current determining unit 5.

The composite meter according to the present invention does not need to be limited to the present embodiment. For example, the frequency signal output from the frequency converter 32 of the active energy meter 3 is compared with the reference frequency signal to determine the reverse current. The determination may be performed. In addition, if a power factor calculation unit for calculating a power factor from the output signal of the active watt-hour meter unit 3 and the output signal of the reactive watt-hour meter unit 4 is provided, the power factor can be reliably measured with one instrument.

[0021]

As described above, according to the present invention, the control means supplies the power based on the signal indicating the multiplication of the output signals of the auxiliary transformer and the auxiliary current transformer, which is output by the power multiplication of the active power calculation unit. The direction in which the load current of the electric wire flows is determined, and when the direction is the opposite direction, the reactive power calculation means is stopped. Therefore, regardless of the direction of the load current in the power supply line, one meter can be used. An active power amount and a reactive power amount can be measured accurately, and a composite instrument that can prevent erroneous calculation of the power factor can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a reverse current discriminating unit 5 of FIG. 1;

FIG. 3 is a circuit diagram of a discrimination control input unit 6 of FIG.

FIG. 4 is a block diagram showing a configuration of a conventional composite instrument.

FIG. 5 is a diagram showing an area where active power and reactive power can be measured.

[Explanation of symbols]

3 Active power meter section, 31 Power multiplying section, 4
... Reactive power meter section, 5...
Discrimination control input section

Claims (3)

(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; A power multiplying unit for multiplying a voltage signal and a voltage signal from the auxiliary transformer by a power multiplying unit to calculate an active power amount; and a phase shift of the voltage signal from the auxiliary transformer by π / 2. A reactive power amount calculating means for calculating a reactive power amount by multiplying a phase shift signal and a voltage signal from the auxiliary current transformer by a power multiplying unit; and an output signal from a power multiplying unit of the active power amount calculating means. A control means for determining a load current direction of the power supply line, and stopping the reactive power calculation means when the current direction is the reverse direction. 2. The control unit compares an output signal of a power multiplying unit of the active power calculation unit with a reference voltage signal,
2. The composite meter according to claim 1, wherein when the output signal of the power multiplying unit is equal to or less than the reference voltage signal, the load current of the power supply line is determined to be in the opposite direction. 3. The composite instrument according to claim 1, further comprising a discriminating operation control means for controlling a discriminating operation of said control means.