Cable Fault Distance Locator

HM-A300 full-intelligent cable fault distance locator Includes:

Power cable fault distance locator host(pre-locator)

multiple impulse generator

path locating meter

cable pinpointing meter

integration high voltage power supply

Applications:

Cable Fault Distance Locator is widely used for the test of various types of power cable fault, cable path, cable buried depth, as well as railway, airport control signal and cable failure precision test.

The Cable Fault Distance Locator has three modes of operation as below:

Low voltage pulse：can be used to measure the distance of cable fault, low resistance and short circuits.

Pulse current : in combination with the high-voltage signal generator, can be used to measure the distance of the high resistance and the flashover fault. The

Multiple pulse:multi-pulse ranging method can be used to measure the distance of high-resistance and flashover faults of power cables under the cooperation of the high-voltage signal generator and the multi-pulse generator.

Function of the cable fault distance locator host

1. The test host of Cable Fault Distance Locator can automatically select five sampling frequencies as low as 6.25MHz and up to 100MHz, with self-adaptive pulse width, which can meet the test requirements of cables of different lengths, reduce rough test errors and improve test accuracy.

2. The software realizes automatic identification and search of low-voltage pulse and multiple pulse waveforms, automatic locking of the inflection point of the waveform fault, automatic reading and displaying of the fault distance, three-zone display waveforms on the same screen, and ten low-voltage pulse waveforms randomly displayed on the same screen for selection. Two modes of automatic and manual operating are realized at the same time, so that the waveform can be double-locked. The movement of the double cursor can be accurately locating the fault within 0.15m, which improves the rough measurement accuracy and reduces the waveform error.

Technical indicators for cable fault distance locator host

Working mode: low voltage pulse, pulse current, multiple pulses.

Precise locating error: ±0.2m.

Sampling frequency: 100MHz, 50MHz, 25MHz, 12.5MHz, 6.25MHz, real-time sampling.

Maximum working distance: 60km.

Test blind zone: 5m.

Communication interface: USB.

Power supply: AC 220V±10%, not more than 15W; DC 12V (7AH), not more than 20W.

Function of the cable fault distance Multiple pulse generator

The function of the "multiple pulse generator" is to guide the instantaneous impact high-voltage pulse generated by the "integrated high-voltage generator" to the fault phase of the faulty cable, ensuring that the fault point can be fully broken down, and can extend the arc duration after the breakdown. At the same time, a trigger pulse is generated to start the "ten pulse automatic trigger device" and the cable fault tester, which is one of the key equipment of this set of equipment.

Brief introduction about cable fault distance locator path locating meter

HM-R10 Path Locating Meter of Cable Fault Distance Locator is composed of transmitter and routing receiver. This instrument is a special instrument for low-voltage cable fault locating. Its mainly used for detecting the cable route.

This instrument uses a microcomputer central processing unit and an application-specific integrated circuit. It is characterized by high receiving sensitivity, low static drift, strong anti-interference ability, stable work and high accuracy.

Technical parameter

1. Detection distance: <15km

2. Detection depth: ≤ 3m

3. Routing error: <5cm

4. Transmitter:

Output frequency: transmit frequency 9.82kHz

Output power: 2W

5. Routing receiver:

Input frequency: 9.82kHz

Detection routing error: ± 2cm

Detecting buried depth error: ± 5cm

Brief introduction about cable fault distance locator cable pinpointing meter

HM-C10A Cable Pinpointing Meter is a portable, ultra-quiet, and visualized impulse discharge receiver precise locating instrument. It is specially used in conjunction with a high-voltage impulse generator. It adopts advanced background intelligent noise reduction and sound tracking new technologies, can achieve continuous optimization, perfect sound effects, record the characteristic sound of impact discharge and compare the signal picked up on site.

Technical characteristics

Ultra-quiet noise reduction processing, excellent discharge sound quality, quieter background, monitor headphones are used to quickly and reliably locate the fault point.

Using ultra-quiet technology and BNR intelligent background noise reduction technology, the volume of impact discharge can be adjusted.

A special free-falling ground-penetrating sensor is designed, and equipped with sensor joints for soft pavement, hardened pavement and lawn.

The reliable imported connectors are used to ensure the purity of the sound. The humanized design of the height-adjustable probe handle is very suitable.

Technical parameters

Sensor dynamic range: sound channel>104dB.

Impact discharge sound amplification factor >90dB, and the upper limit of the impact discharge volume is 84dB(A).

LCD display: high-brightness true color screen, 320 x 240 pixels, suitable for outdoor use.

Power supply: Alkaline replaceable battery/Lithium-ion rechargeable battery, convenient for field use.

Brief introduction about High Voltage Power Supply

HM350 is equipped with built-in capacitor, vacuum shock ignition, emergency stop and automatic discharge function, safe and reliable. Cooperating with any cable fault tester produced by our company, it can easily use multiple pulse method or current flashover method for rough measurement, pre-locating or accurately locating of cable fault.

Performance characteristics

1. Integrated design, built-in capacitor, simple wiring.

2. Touch screen, simple setting and operation, intuitive and convenient display.

3. With voltage regulation, automatic voltage stabilization and automatic protection functions.

4. The output high voltage has the function of single pulse and continuous pulse.

5. The output high voltage has a DC output, which can work with an external ball gap, and has a variety of applications.

6. The software controls vacuum impulse ignition and discharge, self-adaptive discharge and pulse period.

7. With emergency stop button, automatic discharge function, safe and reliable.

8. The continuous working time is not less than 6 hours, meeting the longest working time of cable fault test.

9. Engineering chassis design, compact structure, small size, light weight, easy to carry by one person.

Technical parameters

This product is mainly used for impulse discharging when sample high-resistance fault waveforms of power cable of 35KV and below, and for impulsive discharge when precisely locate fault point. It can also be used for the burn-through of high-resistance faults of power cables and external sheath precisely locating for extra-high voltage cables above 110KV. It can burn through the breakdown point in a short time and reduce resistance in the breakdown point.

1. Output mode: pulse output, DC output

2. Output voltage: negative voltage, 0～-35kv continuously adjustable

3. Working current: ≤40mA

4. Working mode: single pulse, continuous pulse, DC output

5. Built-in capacitance: 4uF/35kv

6. Discharge energy: ≤2480J

7. Pulse cycle: 3s～8s adaptive

8. Working power supply: power frequency 220V±10%

10. Display screen: 800×480 resolution touch screen

11. Working temperature: -10℃～40℃

12. Working humidity: ≤80%

13. Altitude: ≤1000m

At present, the power cable fault location methods commonly can be roughly divided into three according to the types of applied signals and pulse acquisition methods, namely, low-voltage pulse method, pulse current method and multiple pulse method which are described in detail below.

2.1 Low-voltage pulse method

2.1.1 Scope of application

The low-voltage pulse reflection method (hereinafter referred to as the low-voltage pulse method) is mainly used to measure the low resistance, short circuit and disconnection faults of cables. It can also be used to measure the length of the cable, the wave speed of the cable, and it can also be used to distinguish the middle end, the T-joint and the terminal end of the cable.

2.1.2 Test principle

According to the transmission line theory, when a pulse voltage is sent to the faulty cable, due to the input impedance Zi at the fault point is no longer the characteristic impedance Zc , it will causes reflection and resulting in a reflected pulse moving to the measuring point. The reflection coefficient is as below:

ρ =(Zi-Zc) / (Zi+Zc) （Formula 2.1）

Δt is the time delay from the instrument transmits the pulse to receiving the reflected pulse of the fault point, it should corresponds to the time required for the pulse to go back and forth between the measurement point and the fault point. Suppose the fault distance is Lx, and the propagation speed of the pulse in the line is v, then the distance to the fault point is (Figure 2.1):

Lx=vΔt/2　　　　　　　　　　　（Formula 2.2）

By identifying the polarity of the transmitted pulse, the nature of the fault can be judged. The reflected pulse of open circuit and disconnection fault has the same polarity as the transmitted pulse, and the reflected pulse of short circuit and low resistance faults has the opposite polarity of the transmitted pulse.

2.2 Multiple Pulse Method

2.2.1 Scope of application

The multi-pulse method is used to measure the distance of high resistance and flashover faults of power cables with the cooperation of a high-voltage signal generator and a two-pulse signal coupler. On the basis of two pulses, by emitting multiple low-voltage pulses during the continuation of the high-voltage arc to select the best fault waveform, making it easier to identify the fault point.

2.2.2 The nature of high voltage arc

When applying high-voltage direct current to the faulty cable to a certain value and the field strength is large enough, a small amount of free electrons in the medium will collide and dissociate under the action of the electric field to produce new electrons and positive ions. These electrons and positive ions collide with other neutral molecules after gaining electric field energy. This process continues to develop, which intensifies the "avalanche" of electron flow in the medium, causing breakdown of the insulating medium. The fault point is instantaneously short-circuited by a strong electron current. In this situation, the cable fault point will be suddenly broken down, the voltage at the fault point drops sharply to almost zero, the current suddenly increases, and a discharge arc occurs. According to the arc theory, the apparent resistance of this arc is very small and can be considered a low resistance or short circuit fault.

2.2.3 Working principle

Sending a low-voltage pulse to the cable while the high-voltage arc is generated and write down the reflected waveform. Because the arc can be considered as a low-resistance or short-circuit fault, the transmitted pulse waveform and the reflected pulse waveform have opposite polarities, and the reflected waveform has a negative polarity the waveform is downward.

After the high-voltage arc is extinguished, the cable returns to a high-resistance or flashover state. At this time, send a low-voltage pulse to the cable, and record reflected waveform. The waveform reflects the pulse waveform of the open circuit at the end of the cable. Display the two waveforms on the screen at the same time. Since the reflected waveforms of the two pulses have obvious differences at the fault point, the location of the fault point can be easily determined. As shown in Figure 2.4

Figure 2.4 Two-pulse waveform

In the actual test, while sending high voltage to the cable to discharge the fault point, it is necessary to use an arc extension device (freewheeling device) to inject current into the fault cable to extend the duration of the arc at the fault point, so as to ensure that the instrument obtains stable low-voltage pulse reflection Waveform.

2.3 Pulse current method

2.3.1 Scope of application

With the cooperation of HM350 integrated high-frequency and high-voltage power supply, pulse current method can be used to measure the high resistance and flashover distance of single-phase grounding, multi-phase grounding or interphase faults of power cables. The waveform is relatively simple.

2.3.2 Test Principle

The high-impedance and flashover faults of the cable have a large fault point resistance (greater than 10 times the cable wave impedance). It can be seen from formula 2.1 that the low-voltage pulse has no obvious reflection at the fault point (the reflected pulse amplitude is less than 5%), so it cannot be used Low-voltage pulse reflection method for distance measurement.

As shown in Figure 2.5, when the voltage applied to the cable increases to a certain value, the fault point is suddenly punctured and discharged, generating a discharge current pulse moving to the measuring point. After the discharge current pulse passes through the measuring point, it is reflected by the capacitor and return to the fault point, then it will be reflected again at the fault point and return to the measurement point. Due to continue to reflect between the capacitor and the fault point, current pulse will pass through the measurement point many times.

The pulse current method is to use high voltage to break down the cable fault. The instrument collects and records the current traveling wave signal generated by the fault break down the current coupler, and analyzes and judges the time for the current traveling wave signal to travel back and forth between the measuring terminal and the fault point. To calculate the distance to failure, pulse current method uses linear current coupler to collect current traveling wave signal in cable.

Figure 2.5 Pulse current principle

The linear current coupler L is placed next to the ground lead of the energy storage capacitor C which connects to the metal sheath of the cable. L is actually an air-core coil, which is connected to the magnetic field generated by the current in the ground wire.

According to the different ways the high voltage DC signal is applied to the cable, it is divided into DC flashover voltage method and Impulse flashover voltage method.

2.3.3 DC flashover voltage method

The DC flashover voltage method is used to measure the flashover breakdown fault. The fault point has a very high resistance, and the flashover breakdown fault occurs when the voltage is increased to a certain value with the high voltage test equipment.

The DC flashover voltage method wiring is shown in Figure 2.6. T1 is a voltage regulator, T2 is a high-voltage transformer, the capacity is 0.5 ~ 1.0 kVA, and the output voltage is 30 ~ 60 kV; C is an energy storage capacitor; L is a linear current coupler. Adjust the output voltage until the cable fault point is broken down.

Figure 2.6 Wiring schematic diagram of DC flashover voltage method