JP3228772B2 - Method and apparatus for receiving ground return signal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for receiving a ground return carrier signal.

[0002]

2. Description of the Related Art Generally, as means for transmitting monitoring data output from an insulation monitoring device or the like installed near a power receiving transformer where 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. The voltage is applied to the electric circuit via the low voltage side second type ground line of the transformer, and at the receiving point, a modulated carrier signal (hereinafter, referred to as a carrier signal) existing between the ground phase electric line and the third type ground line is detected. A transport method based on a so-called ground return method of demodulating the data and receiving the data is adopted. As an example of the conventional invention, there is an invention disclosed in Japanese Patent Publication No. 2-18009 by the same applicant.

However, in the above-mentioned conventional method, when a carrier signal is detected at a receiving point, a housing ground terminal of various load devices, a ground terminal of an AC noise elimination filter, and the like are connected to a third type ground line. In this case, a commercial wave and a high-frequency noise current 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 correctly demodulate received data.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in consideration of the difference in ground resistance between the transmission side and the reception side when transmitting required data via an electric circuit using the ground return current. 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 enables reliable data transmission.

[0005]

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

That is, in detecting the carrier signal voltage applied to the electric circuit at the receiving point, the voltage between the ground-side electric circuit and the third type ground line at the receiving point is detected, and the third type included in this voltage is detected. In order to remove noise caused by leakage current flowing through the grounding line , the current flowing through the third-class grounding line is detected and converted to a predetermined current / voltage to obtain a noise voltage. Subtraction from the voltage between the three types of ground lines ,
Alternatively, by adding them, a carrier signal voltage from which noise has been removed is detected.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on preferred embodiments shown in the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. Clear distinction 2 on the low pressure side path and second power receiving transformer T is grounded by a ground line 3 in the second type ground point E _2. The monitoring output data of the monitoring device (for example, an insulation monitoring device) SV modulates the carrier by the modulator MOD, and the output is coupled to the ground line 3 via the injection transformer OT, so that the carrier signal is transmitted to the electric lines 1 and 2. Applied. Circuit 1, 2
Are connected to, for example, load devices Z ₁ , Z _2, etc., and ground wires 6, 7 derived from the housing of the device or a noise filter are connected to a ground wire 4 at a third-type 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 circuit 2 and the third type ground line 4 with the amplifier A1 having a high input impedance.

The third type grounding wire 4 has a current transformer ZC
T is coupled, and its output is converted from current to voltage by the amplifier A2. A resistor Rm provided in the amplifier A2 determines a conversion coefficient of the conversion. Both amplifiers A1,
The output of A2 is applied to a subtraction circuit (an addition circuit depending on the polarities of the amplifiers A1 and A2), and the output is demodulated by a demodulator DEM via a commercial frequency rejection filter F to obtain received data 5.

The operation of the embodiment of FIG. 1 is as follows.
The carrier signal voltage applied to the electric circuit by the injection transformer OT coupled to the ground line 3 of the transformer T is ei, the leakage current flowing out of the load devices Z1, Z2, etc. to the third type ground line 4 is 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 is as follows: 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 contained in the output of the subtractor SUB is suppressed, the output of the filter F from which the commercial frequency component has been removed has a carrier wave with less 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. In FIG. 2, the same reference numerals as those in FIG. 1 have the same meaning. FIG.
In contrast to this, the carrier signal receiving device 9 inserts a resistor R ₀ in series with the third-type ground line 4 instead of using the current transformer ZCT to detect the leakage current in, and converts the voltage between both ends of the resistor to the amplifier A _3. This is modified so as to be detected by. Since the third-class ground resistance is generally 200 to 300Ω or less, for example, several tens of Ω is selected as the resistance _R0 . However, the rated power should be of a predetermined size.

[0014] The output of the amplifier A3 is the -R ₀ in. The output is multiplied by a coefficient k ₂ in a coefficient circuit GA. Thus, the output of the coefficient circuit GA becomes -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 an output of the respective amplifiers A1 and factor GA in subtractor SUB, the output e ₀ is (1), with _{(2), e 0 = e - (-} R 0 in k 2) = e _i + (R ₀ k ₂ −r ₃ ) in (3), and by adjusting the coefficient k ₂ or the resistance R ₀ so that k ₂ = r ₃ / R ₀ , the subtracter SUB is obtained. As in the case of FIG. 1, an output in which noise due to leakage current is suppressed is obtained, and the subsequent operation is the same as that of FIG.

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

[0016]

According to the present invention, when receiving the carrier signal of the ground return carrier system, it is possible to compensate for the change in the potential due to the leakage current at the third type ground point.
And transmission can be performed with high reliability.

In addition, since high-frequency noise, such as inverter noise, generated from various load devices included in the leakage current can be reduced at the same time, data transmission with higher reliability can be achieved.

[Brief description of the drawings]

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

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

[Explanation of symbols]

SU monitoring device, MOD modulator, DEM demodulator, O
T injection transformer, T receiving transformer, ZCT current transformer,

Continuation of the front page (56) References JP-A-57-28435 (JP, A) JP-A-58-51630 (JP, A) JP-A-1-1522932 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H04B 3/50-3/60 H02J 13/00

Claims (2)

(57) [Claims] 1. A method of receiving a signal voltage applied to an electric circuit via a ground line of a power receiving transformer between the electric circuit and the ground, wherein a signal voltage is applied between a ground-side electric circuit and a third-class ground line at a receiving point.
Of the first voltage to the first amplifier having a high input impedance
And flows to the third type ground line on the receiving side.
A current is detected, and a second amplifier proportional to the current is detected by a second amplifier.
And receiving the first voltage and adding or subtracting the first voltage and the second voltage to suppress noise included in the first voltage. 2. An apparatus for receiving a signal voltage applied to an electric circuit via a ground line of a power receiving transformer between the electric circuit and the ground, wherein a signal voltage between a ground-side electric circuit and a receiving-side ground line of the electric circuit is provided. Detecting a first voltage having a high input impedance;
And a second amplifier for detecting a second voltage proportional to a current flowing through a receiving-side ground line provided to a load device or the like
And a means for adding or subtracting the first voltage and the second voltage to suppress a noise component included in the first voltage, and a ground return signal receiving apparatus.