JPH06148255A - Method and apparatus for applying signal in monitoring device for insulation or grounding resistance of cable way - Google Patents

Abstract

PURPOSE:To correct effect of level of ground resistance and characteristic of ground impedance by a method wherein both or one of a low frequency signal and a carrier signal to be detected near an injection transformer and the size of a signal to be applied to the injection transformer is adjusted automatically so that the resulting voltage value reaches a specified value to keep the signal constant to be injected between a cable way and the ground. CONSTITUTION:An output of a modulator 9 is applied to an amplifier 5 through a variable gain circuit 11. On the other hand, a carrier signal voltage is detected with a high input impedeance amplifier 12 between a ground side cable way 2 near an insulation monitor and a third type earth wire E3 and an output thereof is applied to a filter 13 which lets a frequency band of the carrier signal alone pass and an output thereof is applied to a rectifier/amplifier circuit 14 to obtain a DC voltage proportional to the carrier signal voltage between the cable way 2 and the ground E3. The DC voltage is applied to another input terminal of a variable amplification circuit 11 to form a gain control loop. This keeps the level of the carrier signal at a receiving point constant thereby achieving a correction of the effect of a second type ground resistance or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal applying device in an insulation monitoring or ground resistance measuring device of a one-grounded electric circuit.

[0002]

2. Description of the Related Art Conventionally, as a device for monitoring the insulation of a constant piezoelectric path, for example, it is different from the commercial frequency via an injection transformer connected to a ground wire of the second type construction for installing one end of the constant voltage side electric path of a power receiving transformer. applying an AC voltage for measurement of the low frequency of several 10H _z to path, in the leakage current that flows back to the grounding line by the AC voltage, monitoring the circuit of the insulation resistance by detecting the component of the AC voltage and the phase and, applying a carrier signal having kH _Z modulated with data monitoring results to path through the injection transformer, the receiving portion provided on the office or the like of the extension of the path, is detected between the path and the earth The carrier wave signal is demodulated to obtain insulation monitoring data. A proposal by the same applicant for such a device is disclosed in Japanese Patent Application No.
3-1982.

However, in the conventional device, even if a low frequency signal for measurement and a carrier signal are applied to the electric path through an injection transformer, the ground impedance (consisting of insulation resistance and ground capacitance) of the electric path is remarkable. When it is low and the ground resistance of the second type ground wire is high, the signal level between the electric line and ground is significantly attenuated, and it becomes difficult to secure a sufficient S / N on the extension of the electric line and detect the carrier signal. There were cases.

The conventional device will be briefly described as follows. FIG. 3 is a block diagram showing a conventional insulation monitoring device, and the conventional means for applying a signal to an electric circuit will be described with reference to this figure. In the figure, T is a transformer for converting high-voltage electricity to low-voltage, and one of the low piezoelectric paths 1 and 2 is grounded by a ground wire 3. 4 is, for example, 10 to 30H
The low frequency signal generator of _Z applies the low frequency voltage E ₁ to the ground line 3 through the amplifier 5 and the injection transformer 6. Insulation resistance R between the electric line and ground due to the low frequency voltage applied to the ground line
₀ , a current flows to the ground via the ground capacitance C ₀ , and this is returned to the ground line as a leakage current. Therefore, the leakage current is detected by the current transformer 7 coupled to the ground line, the discrimination unit 8 separates only the low-frequency signal component, and the output of the low-frequency oscillator 4 performs synchronous detection to inject the injected low current. A leak current component in phase with the frequency voltage is detected, and when this value reaches a predetermined value, the output of the discrimination unit is generated as an alarm signal. Modulator 9 for example, the same time to generate a carrier frequency 1～3KH _Z modulated at the output of the discriminator 8, applies a carrier signal voltage E ₂ to path by adding the output to the amplifier 5. On the other hand, in the receiving unit 10 provided between the desired point on the extension of the electric line and the ground, the carrier data signal voltage is detected between the electric line 2 and the earth, and then demodulated to reproduce the alarm data and display it. Drives alarm boards, etc.
In this example, a low-frequency signal for monitoring such as an insulation resistance is generated from the low-frequency signal generator 4 and a carrier for monitoring information transmission is generated from the modulator 9, and both are applied to the electric line via the amplifier 5. It goes without saying that the amplifier may be provided separately.

FIG. 4 shows an equivalent circuit of a current path that circulates to the ground line by the low frequency signal voltage E ₁ and the carrier signal voltage E ₂ injected in the above alarm signal transmission system. In this figure, r ₂ is the second type ground resistance value, R ₀ is the insulation resistance of the electric path, C ₀ is the electrostatic capacitance to ground, and r ₃ is between the electric path 2 of the receiver 10 and the ground E ₃ . It is a resistance value, and is mainly a third type ground resistance when detecting a carrier voltage.

Therefore, although the low-frequency signal voltage E ₁ and the carrier signal voltage E ₂ are applied to the output end of the injection transformer 6, the second-type ground resistance r ₂ is high and the ground capacitance C ₀ is extremely large. When the insulation resistance R ₀ is small, the voltage e at the receiving point of the carrier wave is greatly attenuated, and the low frequency voltage E ₁ applied to the electric line is also dependent on the insulation resistance R ₀ and the ground due to the difference in the distance between the transformer and the receiver installation position. Since the value of the electrostatic capacitance C ₀ is different, it can be seen that the values are not the same on all the electric circuits. Further, in particular, when the frequency of the carrier signal is high, the reactance due to the capacitance becomes small, so that the attenuation amount of the low frequency signal becomes large and the voltage at the receiving point becomes further smaller.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to eliminate this drawback, and the signal voltage injected between the electric line and the ground is affected by the impedance characteristic between the electric line and the ground and the magnitude of the grounding wire grounding resistance. It is an object of the present invention to provide a signal applying method and apparatus that accurately transmit monitoring information by making the value almost constant without being changed.

[0008]

SUMMARY OF THE INVENTION In order to achieve this object, the present invention detects a low frequency signal voltage and / or a carrier signal voltage detected between an electric line and ground near the ground of the injection transformer. Then, the magnitude of the signal applied to the injection transformer is automatically adjusted so that this voltage value becomes a predetermined value.

[0009]

The present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 is a diagram showing an embodiment of the present invention,
1, the same symbols as those in FIG. 3 have the same meanings or functions. FIG. 1 is a block diagram including means for compensating for attenuation of a carrier signal voltage on an electric path.

The difference between the configurations of FIG. 1 and FIG. 3 is that the output of the modulator 9 is applied to the amplifier 5 via the variable gain circuit 11 and the ground side electric path 2 near the insulation monitoring device is installed.
The high-impedance amplifier 12 detects the carrier signal voltage between the third-type grounding line E ₃ and the third type grounding line E _3, and a filter 13 that allows the output to pass only the frequency band component of the carrier signal.
Is applied to the rectifying / amplifying circuit 14 to obtain a DC voltage proportional to the carrier signal voltage between the electric line 2 and the ground (E ₃ ), and this voltage is applied to the other input terminal of the variable amplifying circuit 11. The gain control loop is configured so that the gain of the variable amplifier circuit 11 is controlled by applying the gain control loop to the gain control loop. With this configuration, the variable gain circuit 11 controls so that the level of the carrier wave signal supplied to the amplifier 5 is increased when the output of the rectifying / amplifying circuit is small, and is decreased in the opposite case. The circuit of this control circuit itself can be realized by forming a conventionally known gain control loop. By this means, the carrier signal level existing between the electric line 2 and the ground at the receiving point is made constant, and as described above. The magnitude of the second type ground resistance r ₂ and the influence of the ground impedance are corrected.

To further explain the correcting action, in the equivalent circuit shown in FIG. 4, the load side voltage of the carrier signal of the second type grounding resistance r ₂ , that is, the insulation resistance R ₀ between the circuit and the ground, and the ground. The voltage across the capacitance C ₀ increases / decreases according to the magnitude of the reactances.

The low-frequency signal voltage applied to the ground line 3 will increase or decrease in substantially the same manner depending on the values of R ₀ and C ₀ , whether near the ground line 3 or near a distant reception point. Therefore, if this voltage value is monitored in the vicinity of the ground line 3 and the carrier applied voltage is increased or decreased by the variable gain circuit 11 so that this voltage becomes a constant value, the above-mentioned conventional defects are eliminated and the reception point is achieved. The carrier signal level can be kept constant.

FIG. 2 is a diagram showing a second embodiment. The difference of this example from FIG. 1 is that the variable gain circuit 11 is inserted between the low frequency oscillator 4 and the amplifier 5.

Further, in this example, the electric line 2 and the earth (E
₃ ) A filter 15 for detecting the voltage between the two by the high input impedance amplifier 12 and detecting the output of the low frequency signal component.
Are separated and detected by and the output is added to the rectification / amplification circuit 14.
This output is applied to the other input terminal of the variable gain circuit 11 to form a gain control loop, and the low-frequency measurement signal voltage existing between the electric line and the ground is controlled to be constant. That is, in this example, the variable gain circuit 11 is controlled by the low frequency signal voltage instead of the carrier wave.

The operation and effects of this embodiment are as follows. That is, in this example, the voltage between the electric path of the insulation resistance measuring low-frequency signal itself and the ground is monitored so as to be constant, but at the same time, the insulation between the electric path and the ground is made similar to the first embodiment described above. It is possible to keep the carrier voltage, which changes depending on the resistance and the capacitance to ground, to be almost constant. Since the insulation resistance measuring low-frequency signal frequency and the carrier wave signal frequency are different, they cannot be kept completely constant, but can be kept in a range where there is no practical problem.

Further, according to this method, it is possible to prevent the accuracy of the insulation resistance measurement itself from being lowered due to the increase of the ground resistance r _{2 in the} insulation resistance measurement. That is, for example, in an area with a large ground resistance, such as a volcanic ash plateau, it is impossible to perform an accurate insulation resistance measurement because the voltage between the ground and the electric line decreases as the low-frequency signal for measurement that flows back to the ground line increases. However, if the measurement signal voltage between the electric line and the ground is kept constant as described above, this problem can be solved. The present invention also provides the first,
The embodiment shown in FIG. 2 may be carried out simultaneously, in which case the output of the high input impedance amplifier 12 may be applied simultaneously to the input of the filter 13 and the second 15 filter input of FIG. Incidentally, in carrying out the present invention, various modifications can be made without being limited to the above-mentioned embodiment, and the target electric circuit is not limited to the single-phase electric power transmission line, and the single-phase three-wire or the three-phase three-wire electric circuit, It can be widely applied to electric lines other than power lines.

[0017]

The voltage of the carrier signal modulated by the alarm signal injected into the electric line or the low-frequency measuring signal voltage can be kept constant without being affected by the ground resistance, etc. S / N of the receiver input at is improved,
Various types of information can be transmitted over long distances.

[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.

FIG. 3 is a diagram illustrating a conventional device.

FIG. 4 is a diagram showing a signal path.

[Explanation of symbols]

1, 2 ... Low piezoelectric path, 7 ... Current transformer 3 ... Ground wire, 6 ... Injection transformer, 8 ... Discrimination unit, 4 ... Low frequency signal oscillator, 5 ... Amplifier, 9 ... Modulator 10 ... Receiving part, 11 ... Variable gain circuit 13, 15 ... Filter.

Claims (3)

[Claims] 1. A low-frequency AC voltage is applied to the electric line via a ground wire of the electric line whose one end is grounded, and the insulation of the electric line is monitored by using a leakage current returned to the ground line by the low-frequency voltage. , A carrier voltage modulated by the information of the monitoring result is applied to the electric line via the ground line, and the carrier voltage is detected and demodulated on the extension line of the electric line to detect a signal indicating the insulation state. In the device, the magnitude of the low frequency voltage applied to the electric line is automatically adjusted so that the low frequency voltage detected between the electric line and the ground in the vicinity of the means for injecting the low frequency signal has a predetermined value. A method for applying a signal in an electric circuit insulation or earth resistance monitoring device characterized by the above. 2. The low-frequency AC voltage applied to the injection transformer so that the low-frequency AC voltage detected between the ground-side electric path in the electric path near the injection transformer and the ground has a predetermined value. The signal applying device according to claim 1, wherein the size of the signal is automatically adjusted. 3. A low frequency voltage is applied between a ground whose one end is grounded via a ground wire and the ground, and the leakage current returning to the ground wire is used to monitor the insulation state or ground resistance of the wire, In a device adapted to apply a carrier wave modulated by the information of the monitoring result between the electric line and the ground, and to derive the carrier wave between the extension of the electric line and the earth, a low frequency signal or Means for detecting the low frequency signal between the electric path near the means for applying the carrier signal and the earth or a signal corresponding to the carrier signal level, and a low frequency signal applied to the electric path so that the signal level becomes a specified level. A signal application device in an insulation or ground resistance monitoring device of an electric circuit, characterized by comprising a means for controlling a voltage or a carrier signal voltage.