CN205027853U - A pulse generating circuit for improving cable fault range accuracy - Google Patents

Abstract

The utility model discloses a pulse optimization method and a circuit for improving the accuracy of cable fault distance measurement. When the pulse time domain reflection method is used for cable fault distance measurement, the pulse used for analysis is actually only the reflected pulse of the fault point. It has nothing to do with the transmission pulse, so a circuit can be designed to generate a transmission pulse voltage wave, which is connected to both ends of the primary side of the pulse transformer, one of which is normally injected into the cable, and the other is offset before AD acquisition on the secondary side of the pulse transformer. Inject the transmission pulse of the cable, so that AD collects only the reflected pulse of the fault point in the signal, without the transmission pulse, the waveform is simple, clear, and easy to analyze; at the same time, it does not affect the normal injection of the transmission pulse signal into the faulty cable. The signal input acquisition uses an isolation pulse transformer, which can not only collect the pulse reflection signal on the cable, but also suppress interference, and has high reliability.

Description

A Pulse Generation Circuit for Improving the Accuracy of Cable Fault Location

technical field

The utility model relates to a pulse generating circuit for improving the accuracy of cable fault distance measurement when the pulse time domain reflection method is used for distance measurement of cable faults, and belongs to the technical field of power electronics.

Background technique

Cable power supply has been widely used because of its safety, reliability, and advantages of beautifying cities and industrial and mining layouts. However, with the increasing use of cables, the number of cable faults is also increasing. How to quickly and accurately detect the distance and location of the fault point and find the location of the fault point requires the inspectors to first choose a detection instrument with excellent performance and be able to correctly identify waveform.

Pulse time domain reflectometry is an important method for cable fault location, which is suitable for cable fault location with low resistance and disconnection nature. The cable is used as a transmission line. When a fault occurs, the location of the fault point will cause an impedance mismatch. According to the propagation theory of electromagnetic waves in the transmission line, electromagnetic waves will be reflected at the place where the impedance does not match, and this principle can be used to measure the distance of the cable fault point.

The pulse time domain reflectometry distance measurement is that the pulse generator of the detection instrument generates a pulse voltage wave, which is injected into the fault phase of the cable through the lead wire at the measurement end, and the pulse voltage wave will propagate along the cable line to the far end. When the point is reached, due to the impedance mismatch, a reflected wave will return to the measurement terminal. The detection instrument at the measurement end will record the transmitted pulse and reflected pulse. The fault distance is calculated according to the time difference between the starting position of the transmitted pulse and the reflected pulse on the waveform. The polarity of the disconnected fault reflected pulse is the same as that of the transmitted pulse, and the polarity of the low-impedance fault reflected pulse is the same as that of the transmitted pulse. As shown in Figure 1.

At present, the cable fault distance meter designed based on the pulse time domain reflection method has the main shortcomings in waveform acquisition, display and analysis: the pulse voltage wave emitted by the detection instrument has a certain width, due to the output impedance of the instrument and the waveform of the cable If the impedance does not match, there will be a "smearing effect" of the transmitted pulse at the cable measurement end. When the fault point is very close to the measurement end, the reflected pulse at the fault point will overlap with the transmitted pulse, and the starting position of the reflected pulse cannot be found on the waveform. Causes a significant measurement blind area, as shown in Figure 2; in addition, the instrument collects and displays the transmitted pulse and reflected pulse at the same time. When the fault point is far away from the measurement end, due to the attenuation effect of the cable, the amplitude of the reflected pulse at the fault point will be far If it is smaller than the transmitted pulse, in order to increase the amplitude of the reflected pulse at the fault point, it is often necessary to increase the gain of the instrument amplifier. This will often cause the saturation of the instrument pulse signal acquisition and amplification circuit, and the so-called "blocking" phenomenon will result in signal acquisition distortion, which is not conducive to waveform analysis. .

In order to eliminate the impact of the transmitted pulse on the measurement results and eliminate the "smearing effect", there is also a patented technology that mentions an impedance balance network, as shown in Figure 3, which is simulated by components such as resistors, capacitors, inductors, and pulse transformers inside the instrument. The characteristics of the cable impedance network can realize the matching between the internal impedance of the instrument and the cable impedance, and achieve the purpose of eliminating the influence of the transmitted pulse, but this method cannot solve the above-mentioned "blocking" problem of the preamplifier circuit signal; at the same time, because the simulated impedance and the real impedance of the cable cannot be completely For matching, a large number of transformer components are used. When the cable is long, the inductance and capacitance of the cable and the transformer T2 will cause serious oscillations in the transmission pulse, resulting in messy waveforms that cannot be distinguished.

In actual measurement, the above shortcomings will cause difficulties in waveform analysis, difficulty in determining the start time of the reflected pulse, and easy misjudgment, resulting in unnecessary economic losses.

Contents of the invention

Aiming at the shortcomings of the above-mentioned existing detection instruments, after a lot of exploration and experience summarization, the utility model proposes a pulse generating circuit for improving the accuracy of cable fault distance measurement. On the one hand, it greatly reduces the distance measurement of detection instruments Blind area, no oscillating waveform will be generated during measurement, and at the same time, the "blocking" phenomenon of the pulse signal acquisition and amplification circuit is avoided. The new pulse generating circuit makes the waveform of cable fault distance measurement simple, clear and easy to analyze.

According to the technical solution provided by the utility model, the pulse generation circuit used to improve the accuracy of cable fault location includes: a transmission pulse generation circuit, a first-order passive high-pass filter, a 2-way symmetrical transmission pulse separation circuit, and a cable interface circuit and the pulse transformer, the output of the transmitting pulse generating circuit is connected to a first-order passive high-pass filter, and the output of the first-order passive high-pass filter is respectively connected to both ends of the primary side of the pulse transformer through two symmetrical transmitting pulse separation circuits, one of which transmits The pulse separation circuit is also connected to the cable interface circuit, and the secondary side of the pulse transformer is connected to the AD acquisition circuit; the emission pulse generating circuit outputs the emission pulse by driving the N-channel enhanced mosfet triode with a specific width, and then the first-order passive high-pass The filter filters out the low-frequency components in the signal, and then generates two transmit pulses with the same amplitude and polarity on the primary side of the pulse transformer through two symmetrical transmit pulse separation circuits, and one of the transmit pulses is also injected through the cable interface circuit A faulty cable, the cable interface circuit is also used to receive the reflected pulse signal of the cable fault point.

Specifically, the pulse transformer is an isolated pulse transformer.

In the two transmission pulse separation circuits, the first transmission pulse separation circuit includes: the cathode of the diode D1 is connected to the output of the first-order passive high-pass filter, and the anode of the diode D1 is respectively connected to one end of the TVS tube TVS1, one end of the resistor R5, and the capacitor C2 One end of the capacitor C2, the other end of the capacitor C2 are respectively connected to one end of the resistor R6 and one end of the primary winding of the pulse transformer T1, the other end of the TVS tube TVS1, the other end of the resistor R5, and the other end of the resistor R6 are grounded; the second transmitting pulse separation circuit includes: diode D2 The cathode is connected to the output of the first-order passive high-pass filter, the anode of diode D2 is respectively connected to one end of TVS tube TVS2, one end of resistor R7, one end of capacitor C3 and the cable interface circuit, and the other end of capacitor C3 is respectively connected to one end of resistor R8 and the pulse transformer The other end of the T1 primary winding, the other end of the TVS tube TVS2, the other end of the resistor R7, and the other end of the resistor R8 are grounded.

The utility model has the advantages that: the method utilizes two symmetrical transmission pulse separation circuits to generate two identical transmission pulses at the same time, and utilizes the characteristics of the pulse transformer T1 to cancel each other on the primary side of T1, so that only the cable signal is collected by the AD. The fault point reflects the pulse, but does not transmit the pulse, and the waveform is simple, clear and easy to analyze; at the same time, it does not affect the normal injection of the transmitted pulse signal into the fault cable. The signal input acquisition uses an isolation pulse transformer, which can not only collect the pulse reflection signal on the cable, but also suppress interference, and has high reliability.

Description of drawings

Figure 1 is the ranging waveform of the pulse time-domain emission method.

Fig. 2 is a schematic diagram of the transmitted pulse tailing, overlapping with the reflected pulse, and unable to distinguish the reflected pulse.

Fig. 3 is an impedance balancing network used in the prior art.

Fig. 4 is a schematic diagram of the pulse generating circuit used in the utility model.

Fig. 5 is a module division diagram of the pulse generating circuit of the present invention.

Fig. 6 is an acquisition waveform diagram for implementing the method described in the present invention. Figure 6(a) is the fault location waveform when the fault point is very close to the measurement end, and Figure 6(b) is the fault location waveform when the fault point is far away from the measurement end.

detailed description

Below in conjunction with accompanying drawing and embodiment the utility model is further described.

When the pulse time domain reflection method is used for cable fault location measurement, since the pulse used for analysis is actually only the reflected pulse of the fault point and has nothing to do with the transmitted pulse, a circuit can be designed to generate a transmitted pulse voltage wave, which is divided into two circuits Connected to both ends of the primary side of the pulse transformer, one of the transmission pulses is normally injected into the cable, and the other one cancels the transmission pulse injected into the cable before the AD acquisition of the secondary side of the pulse transformer, so that only the reflected pulse of the fault point is included in the AD acquisition signal, and the No pulses are fired anymore.

The pulse generation circuit of the present utility model comprises a transmission pulse generation circuit 1, a first-order passive high-pass filter 2, 2 symmetrical transmission pulse separation circuits 3, 4, a cable interface circuit 5 and a pulse transformer T1, as shown in Figure 5, The output of the transmission pulse generation circuit 1 is connected to the first-order passive high-pass filter 2, and the output of the first-order passive high-pass filter 2 is respectively connected to the primary side of the pulse transformer T1 through the first transmission pulse separation circuit 3 and the second transmission pulse separation circuit 4 The two ends of the pulse transformer T1, wherein the second transmission pulse separation circuit 4 is also connected to the cable interface circuit 5, and the secondary side of the pulse transformer T1 is connected to the AD acquisition circuit.

In the circuit shown in Figure 4, the N-channel enhanced mosfet transistor VT1, resistors R1, R2, electrolytic capacitor CD1, diode D3, and resistor R3 constitute a transmission pulse generation circuit, which outputs a pulse with a specific width through the drive transistor VT1. Increase the energy of the transmitted pulse, that is, amplify the amplitude of the transmitted pulse from VDD (5V) to V (tens of volts), so as to ensure that the cable fault distance measurement range can be from a few meters to tens of kilometers. Among them, the gate of the N-channel enhanced mosfet transistor VT1 is connected to the initial emission pulse, and at the same time, it is connected to the power supply voltage VDD through the resistor R1, and the drain of VT1 is connected to the positive electrode of the electrolytic capacitor CD1, and the voltage V higher than VDD is connected to the electrolytic capacitor through the resistor R2. The cathode of CD1 is connected to the anode of diode D3 and grounded through resistor R3, and connected to the first-order passive high-pass filter at the same time, the cathode of diode D3 is connected to the voltage V, and the source of VT1 is grounded.

The first-order passive high-pass filter formed by capacitor C1 and resistor R4 suppresses low-frequency components in the circuit.

Diode D1, TVS tube TVS1, resistors R5, R6, capacitor C2 and diode D2, TVS tube TVS2, resistors R7, R8, and capacitor C3 form a 2-way completely symmetrical transmitting pulse separation circuit, so that 2 pulses are generated on the primary side of the pulse transformer T1. Two transmit pulses with the same amplitude and same polarity, using the characteristics of the transformer, the transmit pulse output by the secondary side of T1 is offset, and only the reflected pulse of the cable fault point is included in the signal collected by AD. Wherein, the first transmission pulse separation circuit includes: the cathode of diode D1 is connected to the output of the first-order passive high-pass filter, and the anode of diode D1 is respectively connected to one end of TVS tube TVS1, one end of resistor R5, one end of capacitor C2, and the other end of capacitor C2 respectively Connect one end of the resistor R6 to one end of the primary winding of the pulse transformer T1, the other end of the TVS tube TVS1, the other end of the resistor R5, and the other end of the resistor R6 are grounded; the second transmitting pulse separation circuit includes: the cathode of the diode D2 is connected to a first-order passive high-pass filter The output of the diode D2, the anode of the diode D2 is respectively connected to one end of the TVS tube TVS2, one end of the resistor R7, one end of the capacitor C3 and the cable interface circuit, and the other end of the capacitor C3 is respectively connected to one end of the resistor R8 and the other end of the primary winding of the pulse transformer T1. The other end of the TVS tube TVS2, the other end of the resistor R7, and the other end of the resistor R8 are grounded.

Capacitor C4, varistor RV1, and BNC output socket W1 constitute the interface circuit between the testing instrument and the cable. Through this circuit, the transmitted pulse can be injected into the faulty cable; at the same time, it is used to receive the reflected pulse signal of the cable fault point. The anode of the diode D2 in the second transmission pulse separation circuit is connected to one end of the capacitor C4, the other end of the capacitor C4 is grounded through the varistor RV1, and connected to the cable measurement end through the BNC output socket W1 core, and the shield of the BNC output socket W1 is grounded.

The waveform of cable fault ranging using the utility model is shown in Figure 5. From the perspective of the waveform, the transmitted pulse waveform is completely invisible, eliminating the "tailing response" of the waveform, and there is no waveform oscillation phenomenon, which greatly reduces the measurement Blind area; when detecting long cables at the same time, in order to see a clearer reflection waveform, the gain can be adjusted to the maximum, and the AD acquisition and amplification circuit "blocking" phenomenon caused by the existence of the transmission pulse will not occur. The waveform is concise, clear and easy to analyze.

Claims (3)

1. for improving the pulse generating circuit of cable fault localization precision, it is characterized in that: comprise transponder pulse and produce circuit, single order passive high three-way filter, the transponder pulse separation circuit of 2 tunnel symmetries, cable interface circuit and pulse transformer, the output that transponder pulse produces circuit connects single order passive high three-way filter, the output of single order passive high three-way filter connects the two ends on the former limit of pulse transformer respectively by the transponder pulse separation circuit of 2 tunnel symmetries, wherein riches all the way penetrates pulse-separating circuit also stube cable interface circuit, the secondary of pulse transformer connects the circuit of AD collection, described transponder pulse produces circuit and specific width pulse is exported transponder pulse by driving N channel enhancement mosfet triode, then by the low frequency component in single order passive high three-way filter filtered signal, transponder pulse separation circuit again through 2 tunnel symmetries produces 2 transponder pulses that amplitude is identical, polarity is identical on the former limit of pulse transformer, wherein riches all the way penetrates pulse also by cable interface circuit injection failure cable, and described cable interface circuit is simultaneously for receiving Method of Cable Trouble Point reflected impulse signal.

2. as claimed in claim 1 for improving the pulse generating circuit of cable fault localization precision, it is characterized in that: described pulse transformer adopts Isolated Pulse Transformer.

3. as claimed in claim 1 for improving the pulse generating circuit of cable fault localization precision, it is characterized in that: in described 2 road transponder pulse separation circuits, first transponder pulse separation circuit comprises: diode D1 negative electrode connects the output of single order passive high three-way filter, diode D1 anode connects one end of TVS pipe TVS1, one end of resistance R5, one end of electric capacity C2 respectively, the electric capacity C2 other end is one end of contact resistance R6 and one end of pulse transformer T1 former limit winding respectively, the TVS pipe TVS1 other end, the resistance R5 other end, resistance R6 other end ground connection; Second transponder pulse separation circuit comprises: diode D2 negative electrode connects the output of single order passive high three-way filter, diode D2 anode connects one end of TVS pipe TVS2, one end of resistance R7, one end of electric capacity C3 and cable interface circuit respectively, the electric capacity C3 other end is one end of contact resistance R8 and the other end of pulse transformer T1 former limit winding respectively, the TVS pipe TVS2 other end, the resistance R7 other end, resistance R8 other end ground connection.