JPH05175889A - Method and device for receiving ground return signal - Google Patents

Abstract

PURPOSE:To improve a demodulation S/N at a reception part and to enable high-reliability transmission by compensating a potential change due to the leaked current of a class 3 level ground point in the case of transmitting required data through a cable way by utilizing a ground return current. CONSTITUTION:When detecting a carrier signal voltage impressed to cable ways 1 and 2 at a receiving point, a voltage between the ground side cable way 2 and a class 3 level ground line 4 is detected, and a current flowing to the class 3 level ground line 4 is detected for removing noise, which is contained in this voltage, caused by the output fluctuation of the class 3 level ground line 4. Then, these voltage and current are converted to a prescribed current/ voltage, and a noise voltage is obtained. By subtracting this noise voltage from the voltage between the ground side cable way 2 and the class 3 level ground line 4, a carrier signal voltage removing noise is detected. Namely, a noise component caused by the leaked current contained in the output of a subtracter SUB is suppressed, and the carrier signal voltage reducing the noise component is detected at the output of a filter FT removing a commercial frequency component and impressed to a demodulator DEM.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method of receiving a ground return carrier signal.

[0002]

2. Description of the Related Art Generally, as a means for transmitting monitoring data output from an insulation monitoring device or the like installed near a power receiving transformer in which no person is resident to a manned monitoring room or the like, a voltage obtained by modulating a carrier wave with the data is received. It is applied to the electric circuit through the low-voltage side second-class ground wire of the transformer, and at the receiving point, the modulated carrier signal (hereinafter referred to as the carrier signal) existing between the ground-phase electric path and the third-class ground wire is detected. The so-called earth return route is used to demodulate the data and receive the data. As an example of the conventional invention, there is the invention disclosed in Japanese Patent Publication No. 2-18009 by the same applicant.

However, in the above-mentioned conventional method, when detecting the carrier signal at the receiving point, the case ground terminal of various load devices, the ground terminal of the AC noise elimination filter, etc. are connected to the third type ground line. In this case, commercial waves and high-frequency noise currents flowing from these terminals flow through the third-class ground wire. On the other hand, the third-class ground resistance required for these load devices is generally about 300Ω or less, and the second-class ground resistance of the power receiving transformer is about 10Ω or less. The potential of the line will fluctuate. Therefore, when the carrier signal voltage is detected between the ground side electric circuit and the third type ground line at the receiving point, the fluctuation of the potential is added as a noise voltage, so that the S / N of the detected carrier signal voltage is deteriorated. However, it may be difficult to demodulate the received data correctly.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and when utilizing earth return current to transmit required data through an electric line, a difference in ground resistance value between a transmitting side and a receiving side, etc. It is an object of the present invention to provide a method of receiving a carrier signal, which prevents S / N deterioration based on the above and can surely perform data transmission.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention has the following constitution.

That is, when the carrier wave signal voltage applied to the electric path is detected at the receiving point, the voltage between the ground side electric path and the third type ground line at the receiving point is detected and the third type contained in this voltage is detected. In order to eliminate noise caused by fluctuations in the output of the ground wire, the current flowing through the third-class ground wire is detected, this is converted into a predetermined current / voltage to obtain the noise voltage, and this noise voltage is connected to the ground side circuit and The noise-free carrier signal voltage is detected by subtracting from the voltage between the three types of ground lines.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail with reference to the preferred embodiments shown in the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. One line 2 of the low-voltage side electric lines 1 and 2 of the power receiving transformer T is grounded by a grounding line 3 at a second type grounding point E ₂ . The monitoring output data of the monitoring device (for example, insulation monitoring device) SV modulates the carrier wave by the modulator MOD, and its output is coupled to the ground line 3 through the injection transformer OT so that the carrier wave signal is transmitted to the electric lines 1 and 2. Is applied. Circuits 1 and 2
Are connected to load devices Z ₁ and Z ₂ , for example, and the ground lines 6 and 7 derived from the casing of the device or a noise filter are the ground lines 4 and the third-class ground point E ₃ . Grounded. For example, a carrier signal receiving device 8 installed in a manned monitoring room or the like
Detects the voltage between the ground phase electric line 2 and the third type ground wire 4 with the amplifier A1 having a high input impedance.

A current transformer ZC is connected to the third type ground wire 4.
T is coupled, and its output is converted from current to voltage by the amplifier A2. The resistor Rm provided in the amplifier A2 determines the conversion coefficient of the above conversion. Both amplifiers A1,
The output of A2 is applied to a subtraction circuit (which becomes an addition circuit depending on the polarities of the amplifiers A1 and A2), and its output is demodulated by a demodulator DEM through a commercial frequency elimination filter F, and reception data 5 is obtained.

The operation of the embodiment of FIG. 1 is as follows.
Let ei be the carrier signal voltage applied to the electric path by the injection transformer OT coupled to the ground wire 3 of the transformer T, in be the leakage current flowing out from the load devices Z1, Z2, etc. to the third type ground wire 4, and in if the ground resistance of the third kind ground line and r _3, the potential of the ground line 4 becomes r ₃ · in.

Therefore, the output e of the amplifier A1 becomes e = e _i −r ₃ · in (1), and the voltage r ₃ · in of the second term of the equation (1) becomes a noise component. On the other hand, since the output of the current transformer ZCT coupled to the ground line 4 output proportional to the leakage current in flowing through the ground line 4 is obtained, the output voltage of the amplifier A2 becomes -inRmk ₁ (where k ₁ is coefficient). Therefore, the output e ₀ of the subtraction circuit SUB becomes e ₀ = e − (− inRmk ₁ ) = ei + (Rmk ₁ −r ₃ ) in (2),

[0012]

[Equation 1] If the resistor Rm is selected so that the noise component due to the leakage current in included in the output of the subtractor SUB is suppressed, the output of the filter F from which the commercial frequency component has been removed is a carrier with little noise component. The signal voltage is detected and applied to the demodulator MOD.

FIG. 2 is a diagram showing another embodiment of the present invention. 2, the same symbols as those in FIG. 1 have the same meanings. Figure 1
Unlike the case where the carrier signal receiving device 9 detects the leakage current in, instead of using the current transformer ZCT, the resistor R ₀ is inserted in series with the third type ground line 4, and the voltage across the resistor is applied to the amplifier A ₃ It is modified so as to be detected by. Since the third type ground resistance is generally 200 to 300Ω or less, the resistance R ₀ is selected to be, for example, several 10Ω. However, the rated power shall be of a specified magnitude.

The output of the amplifier A3 is -R ₀ in. The output is multiplied by the coefficient k ₂ in the coefficient circuit GA. Therefore, the output of the coefficient circuit GA is -R ₀ in k ₂ . The output of the amplifier A1 is expressed by the equation (1) as in the case of FIG. Therefore, when the respective outputs of the amplifier A1 and the coefficient GA are input to the subtractor SUB, the output e ₀ is expressed by the following equations (1) and (2): e ₀ = e − (− R ₀ in k ₂ ) = e _i + (R ₀ k ₂ −r ₃ ) in (3) and the subtractor SUB is adjusted by adjusting the coefficient k ₂ or the resistance R ₀ so that k ₂ = r ₃ / R _0. As in the case of FIG. 1, the output of is obtained by suppressing the noise due to the leakage current, and the subsequent operation is the same as in the case of FIG.

The above embodiment can be variously modified based on the principle of the present invention. For example, the subtractor SUB1 may replace the adder depending on the polarities of the amplifiers A1, A2, and A3. Further, when the leakage current is extremely large, it is necessary to insert a filter for removing the commercial frequency component in the preceding stage of the amplifiers A1, A2 and A3 as necessary.

[0016]

According to the present invention, when the carrier signal of the earth return carrier system is received, it is possible to compensate the change in the potential due to the leakage current of the third type grounding point.
Can be increased, and highly reliable transmission can be achieved.

Further, since high-frequency noise generated from various load devices contained in the leakage current, such as inverter noise, can be reduced at the same time, further highly reliable data transmission becomes possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

SU monitor, MOD modulator, DEM demodulator, O
T injection transformer, T power receiving transformer, ZCT current transformer,

Claims (2)

[Claims] 1. A method of receiving a signal voltage applied to an electric line via a ground wire of a power receiving transformer between the electric line and ground, wherein a first voltage between the ground side electric line and the ground line at a receiving point. Detecting the current flowing through the ground line on the receiving side to obtain a second voltage proportional to the current, and adding or subtracting the first voltage and the second voltage to obtain the second voltage. A method for receiving a ground return signal, characterized in that noise included in the voltage of 1 is suppressed. 2. A device for receiving a signal voltage applied to an electric line via a ground wire of a power receiving transformer between the electric line and the ground, wherein a part of the electric line between a ground side electric line and a receiving side ground point is provided. A means for detecting a first voltage, a means for detecting a second voltage proportional to a current flowing through a receiving-side ground wire provided in a load device or the like, an addition of the first voltage and a second voltage, or A ground return signal receiving apparatus, characterized in that the noise component included in the first voltage is suppressed by including a means for performing subtraction.