JPH08166413A - Temperature compensator for voltage phase difference of voltage transformer - Google Patents

Abstract

PURPOSE: To easily correct the metric error of an electronic watt-hour meter caused by the phase angle temperature characteristics of a voltage transformer where the phase of secondary voltage advances with respect to the primary voltage due to ambient temperature rise. CONSTITUTION: A capacitor C is connected between the output lines of secondary voltage V2 of a voltage transformer 2. Phase of the secondary voltage V2 is delayed by the internal resistance R of the voltage transformer 2 and the capacitor C. Since the internal resistance R increases as the ambient temperature increases, the phase lag also increases. Capacitance of the capacitor C is selected appropriately, and increase of the phase lead angle is offset by the increase of phase lag angle caused by the ambient temperature rise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an electronic system for measuring the amount of electric power by multiplying the secondary voltage of a transformer for an instrument whose primary input is an AC voltage to be measured with electric power and the alternating current to be measured with electric power. An instrument transformer as a device for compensating that the phase angle (phase difference) of the secondary voltage with respect to the primary voltage of an instrument transformer used in an electric energy meter or the like increases to the leading side due to an increase in ambient temperature. Voltage phase difference temperature compensator.

In the following drawings, the same reference numerals indicate the same or corresponding parts.

[0003]

2. Description of the Related Art FIG. 4 is a block circuit diagram showing a structure of a conventional main part of an electronic watt hour meter. In the figure, 3 is the power measured primary current I ₁ as an alternating current of interest and potential insulated, current transformer for detecting output as secondary current I _2, 2
Is also the primary voltage V ₁ as the AC voltage of the power measurement target.
Is a potential transformer, which is a voltage transformer for detecting and outputting as a secondary voltage V ₂ . Further, 1 is the secondary voltage V of the transformer 2 for the instrument.
Enter the ₂ and the secondary current I ₂ of the current transformer 3, multiplies them together power determined from this secondary voltage V ₂ secondary current I ₂ (hence potential transformer 2, varying meter It is a W / F converter that converts and outputs a pulse train 1a proportional to the electric power on the primary side of the flowmeter 3 assuming ideal operation. In addition,
GND is a ground as a common potential end of the W / F converter 1 and each secondary winding of the instrument transformer 2, the instrument current transformer 3.

[0004]

FIG. 5 shows an instrument transformer 2
Angle of the secondary voltage V _{2 with} respect to the primary voltage V ₁ (vertical axis)
It is a characteristic view which shows the relationship (it calls phase angle temperature characteristic) between (phi) and ambient temperature (horizontal axis) T. That is, when the ambient temperature T increases by ΔT, the advance phase angle φ has a property of advancing by a minute angle Δφ.

FIG. 6 is a characteristic diagram showing the relationship between the error (vertical axis) and the ambient temperature (horizontal axis) of the electronic watt hour meter based on the phase angle temperature characteristic of FIG. Even if the ambient temperature T rises, the advance phase angle φ as a phase difference between the secondary voltage V ₂ of the instrument transformer 2 and the primary voltage V ₁ must be constant, that is, φ + Δφ, which is the primary Primary current I for voltage V ₁
The phase angle with a delay of ₁ (that is, the power factor angle of the load on the primary side) is ψ
Assuming that the phase difference between the primary current I ₁ and the secondary current I _{2 of the} current transformer 3 is negligible, the secondary voltages V ₂ and 2
The phase angle between the next currents I ₂ is ψ + φ + Δφ.

Therefore, this secondary voltage V₂And the secondary current I₂To
Therefore, the measured power W is V₂・ I ₂cos (ψ + φ +
Δφ), and as shown in the following equation (1),
Therefore, there is a problem that a negative error occurs in the measured power.
It This error ε is the phase angle due to the rise in ambient temperature.
Electric power V before the advance of change Δφ occurs₂・ I₂cos (ψ
+ Φ) as a reference.

[0007]

[Equation 1] Error ε = [V ₂ · I ₂ cos (ψ + φ + Δφ) −V ₂ · I ₂ cos (ψ + φ)] / V ₂ · I ₂ cos (ψ + φ) × 100% ≈−tan (ψ + φ) · Δφ × 100% (1) Therefore, an object of the present invention is to provide an electronic watt-hour meter that can easily solve this problem.

[0008]

In order to solve the above-mentioned problems, the power phase difference temperature compensating device according to claim 1 has a primary voltage (V ₁ ) and a secondary voltage of an instrument transformer (2 etc.). (V ₂ )
The change (Δφ) in the phase difference (φ) between the output voltage and the ambient temperature (change ΔT) is compensated by connecting a passive element between the output lines of the secondary voltage of the measuring transformer.

Further, in the voltage phase difference temperature compensating device of the second aspect, in the voltage phase difference temperature compensating device of the first aspect, the passive element is a capacitor (C). Further, in the voltage phase difference temperature compensating device according to claim 3, in the voltage phase difference temperature compensating device according to claim 1 or 2, the meter transformer inputs an AC voltage of a power measurement target as a primary voltage, The secondary voltage is applied to the W / F converter (1 or the like) of the electronic watt hour meter that measures the power.

[0010]

[Operation] A capacitor is connected between the output lines of the secondary voltage of the voltage transformer and the voltage of this capacitor is used as the secondary voltage for W
Input to the / F converter. That is, it is utilized that the internal resistance of the winding of the meter transformer increases due to the increase of the ambient temperature, which causes the voltage across the capacitor to lag the primary voltage of the meter transformer.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block circuit diagram showing a configuration of a main part as an embodiment of the present invention and corresponds to FIG. FIG.
4, a capacitor C is connected between the output lines of the secondary voltage V ₂ of the instrument transformer 2 as compared with FIG. Further, the internal resistance of the instrument transformer 2 is shown as R.

FIG. 2 is a characteristic diagram showing the relationship between the internal resistance R (vertical axis) and the ambient temperature T (horizontal axis). That is, when the ambient temperature T increases by ΔT, the internal resistance R of the instrument transformer 2 also increases by ΔR. Now, letting Δφs be the change in the delay phase angle of the secondary voltage V ₂ due to the increase ΔR of the internal resistance R of the instrument transformer 2 and the capacitor C, the following equation (2) holds.

[0013]

Tan (Δφs) = ωC · ΔR (2) where ω: angular velocity (2πf) of the power supply (frequency f), and if the delay phase angle change Δφs is sufficiently small, the equation (2) becomes ) Can be approximated.

[0014]

## EQU3 ## Δφs = ωCΔR (2A) Therefore, 2 for the primary voltage V ₁ due to the increase in the ambient temperature T.
The advance phase angle change Δφ of the next voltage V ₂ and the equation (2A)
If the capacitor C is selected so that the lag phase angle change Δφs of the secondary voltage V ₂ due to C becomes equal to the lead phase angle change Δφ.
Is canceled out, and the error amount of the electronic watt hour meter due to this change is corrected. FIG. 3 shows the temperature characteristic of the error ε of the electronic watt-hour meter based on this correction, and the error ε becomes constant even if the ambient temperature T rises.

[0015]

According to the present invention, a change in the phase angle in which the phase of the secondary voltage of the meter transformer advances with respect to the primary voltage due to the rise of the ambient temperature, a capacitor is placed between the secondary output lines of the meter transformer. Since the connection is made for compensation, it is possible to easily realize a highly accurate electronic watt-hour meter even if an inexpensive and compact instrument transformer is used.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a main part configuration as an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the internal resistance of the instrument transformer and the ambient temperature.

FIG. 3 is a characteristic diagram showing the relationship between the measurement error and the ambient temperature of the electronic watt hour meter of FIG.

FIG. 4 is a conventional block circuit diagram corresponding to FIG.

FIG. 5 is a characteristic diagram showing the relationship between the lead phase angle of the secondary voltage with respect to the primary voltage of the voltage transformer and the ambient temperature.

FIG. 6 is a characteristic diagram showing a relationship between a measurement error and an ambient temperature of the electronic watt hour meter based on the characteristic of FIG.

[Explanation of symbols]

1 W / F converter 2 potential transformer 3 current transformer C capacitor R potential transformer secondary voltage φ instrument transformer internal resistance V ₁ 1 primary voltage V ₂ instrument transformer voltage transformer Angle of secondary voltage with respect to primary voltage of transformer Δφ Change of phase angle φ T Ambient temperature ΔT Change of ambient temperature T

Claims (3)

[Claims] 1. A passive element is connected between the output lines of the secondary voltage of the instrument transformer to detect the change in phase difference between the primary voltage and the secondary voltage of the instrument transformer due to the ambient temperature. A voltage phase difference temperature compensating device for an instrument transformer, which is characterized by being compensated. 2. The voltage phase difference temperature compensating device according to claim 1, wherein the passive element is a capacitor. 3. The voltage phase difference temperature compensating device according to claim 1, wherein the voltage transformer inputs the AC voltage of the power measurement target as a primary voltage and measures the secondary voltage. A voltage phase difference temperature compensating device for an instrument transformer, which is provided for a W / F converter of an electronic watt hour meter.