JPH063389A - Detecting method and device for phase error of current transformer - Google Patents

Abstract

PURPOSE:To detect a phase error simply and accurately without using an expensive measuring instrument. CONSTITUTION:The device 1 is provided with a conversion transformer 3 for current and a conversion transformer 4 for voltage for taking out current and voltage with a phase difference of 60 degrees by transforming two phases out of a three-phase power supply 2. Further, it is provided with a first watthour meter 7 for integrating an electric energy with a secondary current which is output from a current transformer 5 with a current which is output from the conversion transformer 3 for current as a primary current and a voltage which is output from the transformer 4 for voltage conversion as an input and a second watthour meter 8 integrating the electric energy with the secondary current which is output from a current transformer 6 with a current which is output from the conversion transformer 3 for current as the primary current and a voltage which is output from the conversion transformer 4 for voltage as input.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting a phase error of a current transformer used in a test apparatus such as a power management meter and a watt hour meter.

[0002]

2. Description of the Related Art Conventionally, a phase error of a current transformer (hereinafter referred to as CT) is detected by converting a primary current and a secondary current into a voltage having an appropriate magnitude, inputting the voltage to an oscilloscope, and reading the deviation. Was there. In addition, a method of comparing the standard device and the sample under test is also used as a test of the electricity meter.

[0003]

However, since the phase shift is very small with respect to the magnitude of the amplitude read by the oscilloscope, there is a problem in that it cannot be read accurately. Therefore, in order to improve the reading accuracy, a method of inputting the rectangular wave from the converted voltage to an oscilloscope through an amplifier is also taken, but there is a problem in accuracy and cost of the amplifier itself.

On the other hand, in the method of comparing the reference device with the DUT as a test of the watt-hour meter, an expensive waveform generator and an amplifier for power amplification are required to create the current-voltage waveform of the input power. Therefore, an object of the present invention is to provide a current transformer phase error detection method and apparatus that can detect a phase error more easily and accurately without using an expensive measuring instrument or the like.

[0005]

A current transformer phase error detection method according to claim 1, wherein two phases of a three-phase power supply are transformed to 60.
The current and voltage with a phase difference of degrees are taken out, the secondary currents are taken out from the reference current transformer and the test current transformer, respectively, using this current as the primary current, and these secondary currents and the transformed voltage are taken out. The active energy of each is measured, and the phase error of the test current transformer is determined by comparing these active energy.

According to another aspect of the present invention, there is provided a current transformer phase error detection device comprising a current conversion transformer and a voltage conversion transformer for transforming two phases of a three-phase power source to extract a current and a voltage having a phase difference of 60 degrees. A first electric power for integrating the electric energy with the secondary current output from the test current transformer having the current output from the current conversion transformer as the primary current and the voltage output from the voltage conversion transformer as inputs A quantity meter and a secondary current output from a reference current transformer whose primary current is the current output from the current conversion transformer, and a voltage output from the voltage conversion transformer are input, and the electric energy is integrated. It is equipped with two electric power meters.

[0007]

According to the structure of the present invention, by utilizing the fact that the phase difference of the three-phase power source is 120 degrees, the two phases are transformed to 12 degrees.
By reversing the polarity of either the voltage or current signal having a phase difference of 0 degrees, the current and voltage having a phase difference of 60 degrees can be extracted. When the active power is calculated for each of the test current transformer and the reference current transformer using these as signal inputs, the power with a phase difference of 60 degrees, that is, a power factor of 0.5 can be obtained. If the phase of the test current transformer is deviated, for example, by 3 degrees, an error of about 9% is obtained as the power having a power factor of 0.5. Therefore, the phase error of the current transformer is detected by comparing the active power amounts of the two thus obtained and back calculating from these errors.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a current transformer phase error detection apparatus 1 according to an embodiment of the present invention. In the figure, 2 is a three-phase power supply, and 3 is a three-phase power supply 2 with one phase being transformed. A current conversion transformer for taking out a current signal for power input, 4 is a voltage transformation transformer for taking out a voltage signal for power input by transforming one phase of the three-phase power source 2, 5 is a test current transformer, and 6 is The reference current transformer 7 uses the current output from the current conversion transformer 3 as a primary current and the secondary current output from the test current transformer 5 and the voltage output from the voltage conversion transformer 4 as inputs. A first watt-hour meter that integrates the amount of electric power, 8 is a secondary current output from the reference current transformer 6 and an output from the voltage conversion transformer 4 with the current output from the current conversion transformer 3 as the primary current. Second electric energy that integrates the electric energy with the input voltage It is.

In the current conversion transformer 3 and the voltage conversion transformer 4 described above, the phase shift of the three-phase power source 2 is 12
Utilizing the fact that it is 0 degrees, current is taken out from one phase of the three-phase power supply 2 and voltage is taken out from the other phase. FIG. 2A shows the phase relationship, but if one of the polarities of the current and voltage is inverted and transformed, as shown in FIG. 2B, a current and a voltage with a phase difference of 60 degrees are generated. Obtainable. By properly selecting the output terminal of the power supply, it is possible to easily obtain a phase difference of 60 degrees in advance or delay.

The first watt-hour meter 7 uses the current output from the current conversion transformer 3 as a primary current and the test current transformer 5
The current input unit 9 into which the secondary current output from the voltage conversion transformer 4 is input, and the voltage input unit 10 into which the voltage output from the voltage conversion transformer 4 is input are provided.
Is multiplied by. The output of the multiplier 11 is converted into a frequency signal by the V / F converter 12, and integrated by the integration counter 14 via the frequency divider 13 to obtain the amount of active power.

The second watt-hour meter 8 is also configured similarly to the first watt-hour meter 7, and the current output from the current conversion transformer 3 is output as the primary current from the reference current transformer 6. The secondary current and the voltage output from the voltage conversion transformer 4 are input, and the electric energy is integrated. In the first watt-hour meter 7 and the second watt-hour meter 8, as described above, the power input signal has a phase difference of 60 degrees, that is, a power factor of 0.5 (cos6).
It is calculated as active power of 0 ° = 0.5). Therefore, if the phase of the test current transformer 5 is deviated by, for example, -3 degrees, the active power is obtained by the voltage V, the current I, and the power factor cosΦ by VI · cosΦ, where cos60 ° =
Cos 57 ° = 0.545 with respect to 0.5, and an error of 9% appears as electric power. On the contrary, as power
When the error is%, arccos 0.505 = 59.67.
It can be seen that there is a shift of -0.33 degrees as the phase difference.

When the power factor angle is close to 0 degree, the error of the power factor angle due to the phase error of the current transformer output is only a small error in terms of electric power. Since the phase error can be treated as a large amount of electric power, this is used to input the current voltage from the three-phase power source 2 as a signal input to a power factor angle of 60 degrees. In this way, the error of the active electric energy between the first electric energy meter 7 and the second electric energy meter 8 is obtained, and the error is calculated back to obtain the test current transformer 5.
The phase shift of can be obtained. If the accuracy of the watt-hour meter used is good, it is possible to detect the phase error with high accuracy by checking the accuracy of the watt-hour amount and testing over time.

[0013]

According to the current transformer phase error detection method and apparatus of the present invention, the phase error detection of the current transformer is performed by using two electric power amounts for the test current transformer and the reference current transformer. Since the phase shift is calculated by back-calculating from the error of the active power by comparing the output power of the meter, it is not necessary to read the phase shift directly with an oscilloscope as in the conventional method, and the measuring instrument and power supply used. The phase error of the current transformer can be detected easily without requiring an expensive device.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a current transformer phase error detection device that is an embodiment of the present invention.

FIG. 2A is a diagram showing an output phase of a three-phase power supply,
(B) is a figure which shows the phase relationship of the current voltage signal obtained by transforming from a 3-phase power supply in an Example.

[Explanation of symbols]

 1 Current Transformer Phase Error Detector 2 3 Phase Power Supply 3 Current Conversion Transformer 4 Voltage Conversion Transformer 5 Test Current Transformer 6 Reference Current Transformer 7 First Electricity Meter 8 Second Electricity Meter

Claims (2)

[Claims] 1. A two-phase three-phase power supply is transformed to extract a current and a voltage having a phase difference of 60 degrees, and this current is used as a primary current for secondary current from a reference current transformer and a test current transformer, respectively. The present invention is characterized in that a current is taken out, each active current amount is measured from each of the secondary currents and the transformed voltage, and the active current amount is compared to obtain the phase error of the test current transformer. Current transformer phase error detection method. 2. A conversion transformer for current and a conversion transformer for voltage for extracting a current and a voltage having a phase difference of 60 degrees by transforming two phases of a three-phase power supply, and a current output from the conversion transformer for current. A first watt-hour meter that integrates the amount of electric power with the secondary current output from the test current transformer as the primary current and the voltage output from the voltage conversion transformer as inputs, and from the current conversion transformer A second watt-hour meter that integrates the amount of electric power with the secondary current output from the reference current transformer that uses the output current as the primary current and the voltage output from the voltage conversion transformer as inputs A current transformer phase error detection device characterized by the above.