How does the cable fault tester locate cable routing and estimate cable burial depth-Chemical Instrument Network

Cable fault testerHow to find cable routing and estimate cable burial depth

Connect the output cable core of the testing system to one phase of the cable, and connect the ground wire to the cable ground wire (lead package). If the resistance value of the faulty phase is very low, a resistor of several hundred ohms can be connected in series between the output ground wire and the cable ground wire. First, adjust the output potentiometer to the minimum, turn on the power, and then adjust the amplitude knob to the appropriate position. At this time, the instrument outputs a 15KHZ sine signal, which generates an electromagnetic field around the cable. Adjust the "volume" and "fine adjustment" knobs of the path signal receiver to make the sound in the headphones clear and pleasant, and then locate the cable path and estimate the depth of cable burial.

● Find the cable path

When the probe is at point B above the cable, the coil of the probe is parallel to the electric field, and the coil does not cut the power line. The induced current in the coil is small, and there is almost no sound in the earphone at this time. When the probe is at point A or C, the sound in the headphones is louder.

The line connected by points with lower sound is the path of the cable.

Estimate the depth of cable burial

Tilt the probe 45 degrees to the right above point B of the cable, then move it back perpendicular to the direction of the cable. When it reaches point A, the probe is facing the cable, and the sound of the headphones is relatively low.

The distance from point B to point A, which is the backward distance, is the depth of cable burial.

This method can be used to estimate the burial depth of cables.

PSHZC cable fault testerIntroduction

PSHZC cable fault testerSystem Composition

The PSHZC cable fault tester consists of a laptop, a testing system, a path signal generator, a path signal receiver, and a positioning instrument. It can complete two tasks: cable fault testing and cable data management.

Laptops are used for measurement control, data processing, and cable data management.

The fault testing system, when combined with a laptop, can measure the distance between the fault point and the testing end at one end of the faulty cable, as well as measure the length of the cable and the propagation speed of radio waves in the cable.

The path signal generator can generate intermittent sine wave signals with a maximum amplitude of 30V and a frequency of 15KHZ, which are used to locate cable paths.

The path signal receiver is used to receive path signals, search for cable routing, and estimate cable burial depth.

The locator is used for locating the fault point.

PSHZC cable fault testertechnical performance

1. Fault testing system

It can test various faults of power cables, as well as open and short circuit faults of communication cables and local telephone cables.

The speed of radio wave propagation in any cable with a known length can be measured.

Test distance: not less than 40 kilometers

● System error: less than 0.5 meters

Sampling frequency: 25MHz

Test blind spot: less than 5 meters

Power supply: AC 220V ± 10%

2. Pathfinder signal generator.

● Signal frequency: 15KHz

● Oscillation mode: intermittent

Output power: 30W

Power supply: 220V ± 10%

3. Positioning device

Sensitivity test: A signal source with an internal resistance of 50 Ω outputs a 300Hz signal, and the fixed-point instrument maintains an output of 2V and a signal-to-noise ratio better than 20:1, with an input signal not exceeding 10 μ V.

● Input impedance: not less than 1.2K Ω. ● Use 2 × 2000 Ω headphones.

Working voltage: 9V ± 10%. ● Operating environment temperature: -10 ℃ to 40 ℃

After starting Windows 98, double-click on the Test Management System on the desktop, and the screen will display the main control interface. Press the "Test" button to enter the testing mode; Press the "Manage" button to enter the daily management of cable data and testing data; Press' Help 'to enter the help system; Press' End 'to exit the test management system.

*Partial cable fault testing

PSHZC cable fault testerTest Principle

This instrument adopts the principle of time-domain reflection (TDR) to emit a series of electrical pulses to the tested cable and receive the reflected pulses caused by impedance changes in the cable. Based on the propagation speed of the electric wave in the cable and the time represented by the characteristic inflection points of the two reflected waves, the distance from the fault point to the test end can be measured as:

In the formula S=VT/2:

S represents the distance from the fault point to the testing end

V represents the propagation speed of radio waves in cables

T represents the time required for radio waves to propagate back and forth in the cable

In this way, with V known and T already measured, the fault point distance test can be calculated. The distance S between the ends. All of this can be automatically completed by the computer with minimal manual intervention, and the testing of faults can be done quickly and accurately.

PSHZC cable fault testerIntroduction to Test System Control Panel

The test panel can be divided into four parts: menu bar, status bar, graphic display area, and function key area.

1. Menu bar

The menu bar includes two menu items: "Data Management" and "Test Help".

The "Data Management" menu includes four menu items: "Print", "Read Disk", "Save", and "End".

Select 'Print' to print out the displayed content on the screen using a printer; Select 'Save' to store the test waveforms and data on the computer's hard drive or floppy disk as data storage; Select 'Read Disk' to retrieve waveforms that existed on the disk during previous testing; Select 'End' to exit this control panel.

Test Help ": Click on this menu to display the user manual for the test management system, which can be printed out.

2. Status bar

The status bar displays four types of information, with the testing method on the left; The second is the radio wave velocity corresponding to the selected cable medium (if measuring velocity, medium information will not be displayed). The third is the fault distance (or cable length), with the test date displayed on the right.
3. Graphic display area

The graphic display area is used to display the waveform obtained from sampling, analyze and process the waveform, and display the processing results.

4. Function key area

The function key area consists of 14 keys, which can be divided into three categories.

Initialize data: including two keys for testing method and media selection.

Testing method: There are two options, "fault testing" and "speed testing".

There are three basic testing methods: "low voltage pulse", "flashing", and "direct flashing".

Low voltage pulse "includes two pulse widths to choose from:" 2 μ s "and" 0.2 μ s "; 'Flashing' includes three menu items: 'Inductance voltage sampling', 'Resistance voltage sampling', and 'Current sampling'; Direct flashing "includes two menu items:" voltage sampling "and" current sampling ".

Medium selection:

When initializing the program, it is set to "oil immersed paper type". If it is a cable with other media, it can be selected according to the media of the cable. There are five options available: "Oil immersed paper type", "Non drip type", "Cross linked ethylene", "Polyvinyl chloride", and "Self selected medium".

Choosing one of the menu items is equivalent to selecting a speed, which is the propagation speed of radio waves in the cable.

Data sampling and testing: There are a total of eight buttons:

Sampling button: used during system testing. Every time the "sample" button is pressed, the system collects data and can draw a waveform in the graphical display area.

Expansion button: To calculate the fault distance, press this button to expand the displayed waveform before calculating. Press once to double the waveform, and press four times to form a cycle.

Scroll "button: After the waveform is expanded, the characteristic waveform of the fault point may appear on other screens outside of the * screen. Pressing this button will move the displayed content to the left screen by screen until the fault waveform is displayed on the screen, then locate it with the cursor *.

Return button: Press this button when the cursor needs to quickly return to the left end of the screen.

Location key: Calculate distance from the starting point key. Press this key when the cursor moves to the starting inflection point of the feature waveform.

Left and Right Shift Keys: These two keys are used to control the left and right movement of the cursor. When they are pressed, the cursor moves, moving one unit per press. In addition, to quickly move the cursor, you can drag it with the mouse to the appropriate position and release it.

Reset button: System reset button. No matter what state the system is in, pressing this key can enter the system main interface.

Waveform comparison: There are four keys.

Storage button: Press this button to store the test waveform and data in the computer. ("Storage" is different from "flash drive". "Flash drive" stores data on a disk for long-term preservation, while "storage" only stores data in computer memory, and data will be lost after shutdown.)

Call key: Used in conjunction with the Store key. Press this key to display the last stored content on the screen for analysis and calculation.

Comparison button: Pressing this button will display both the measured waveform and the waveform stored in the instrument on the screen, allowing users to compare and analyze these two waveforms.

Pan "key: Press this key to enter the left and right movement function of the graphic. Click the" Left Move "key to align the starting points of two waveforms.

PSHZC cable fault testerFault testing

The basic steps of fault testing are to measure the insulation resistance of the faulty cable with a megohmmeter or multimeter, determine the nature of the fault, and determine the testing method; Test the fault distance; Detecting the path of cable burial near the fault point; Fixed point.

This testing system has three basic methods for fault testing: low voltage pulse, direct flash, and impulse flash. Combined with different sampling methods, there are a total of eight testing methods.

Disconnect all connections at the cable terminals before testing.

There are two knobs on the panel of the testing system, "Input Amplitude" and "Displacement", which are used to adjust the signal amplitude and up and down position for the next sampling, respectively.

1. Low voltage pulse mode

Low voltage pulses are used to test the speed of radio wave propagation in cables, the total length of cables, low resistance faults, and open circuit faults.

Connect the communication cable of the testing system to the serial port behind the laptop. Connect the faulty phase (tested phase) of the cable and the ground wire to the red and black terminals of the water resistance plate, respectively. Connect the output of the water resistance plate to the input of the testing system. The input line of the testing system can also be directly connected to the fault phase and ground wire.

● Measure speed

For some cables, the speed of radio wave propagation is unknown and must be determined through testing. But before testing, the total length of the cable must be known.

Select "Low Voltage Pulse" and "Measurement Speed" in the "Testing Method" menu, and choose "0.2 μ s" or "2 μ s" according to the length of the cable. Generally, 0.2 μ s is used for cables below 500 meters. After entering the total length of the cable, press the "Sample" button and adjust the "Displacement" and "Amplitude" knobs to ensure that the amplitude and baseline of the signal are in a position that is easy to observe.

Move the cursor to the falling edge of the low-voltage pulse and press' locate ', then move the cursor to the front edge of the reflected signal, and the screen will display the propagation speed of the radio waves in this cable. If the transmitted and received waveforms are too close, you can press the "Expand" button to expand the waveform before calculating.

● Fault detection

When testing for faults, select "Low Voltage Pulse" and "Test Fault" from the "Test Method" menu, and choose the appropriate pulse width. After pressing "Sample", the screen will display the fault waveform.

The reflected signal of an open circuit fault has the same polarity as the transmitted pulse, while the reflected signal of a short circuit fault has the opposite polarity as the transmitted pulse.

Note: Due to the same wiring and waveform when measuring the total length of the cable as when measuring open circuit faults, the menu for measuring the total length was not separately listed in the design.

The waveforms for open circuit faults (along the entire length of the cable) and short circuit faults in low-voltage pulse testing are as follows.

2. Flashing method

The flashing method is used to test high resistance leakage faults, and most cable faults can be tested using the flashing method.

Previously, voltage sampling using flash inductors was more common, but now current sampling is generally used because it is not directly connected to high voltage, resulting in higher safety factors for both personnel and equipment. If there are multiple faults on a cable or if the cable is extensively damp, the flash resistance sampling method can be used.

3. Direct flash mode

The direct flashing method is used to test high impedance flashover faults.

When using the direct flashing method, it is important to monitor the high voltage current to prevent excessive current from burning out the high voltage transformer.

4. Test cable routing and burial depth

● Find the cable path

The line connected by points with lower sound is the path of the cable.

Estimate the depth of cable burial

The distance from point B to point A, which is the backward distance, is the depth of cable burial.

This method can be used to estimate the burial depth of cables.

5. Fault location

We have used various testing methods to measure the distance of the fault point, but due to various factors such as measurement errors, residual cables, bends, etc., the fault may not be accurately located on the ground, and a fault locator must be used to accurately determine the fault point.

When locating faults, high-voltage equipment is used to apply an impulse DC negative high voltage to the cable, and a locator is used to detect the sound point of the cable fault near the measured fault point.

It is advisable to discharge high voltage once every 1 second.

Turn on the power of the locator, adjust the volume knob appropriately, and place the locator at the measured cable fault point. There should be a sound of discharge from the fault point. If you cannot hear the position of the movable locator, wait until the discharge sound in the headphones is maximized, and this is the fault point.

6. Precautions

When testing cable faults, relevant safety rules must be followed.

In high-voltage testing, all equipment should be well grounded to avoid burning out the testing equipment. If possible, separate the power supply of the high-voltage generator from that of the testing instrument.

When conducting high-voltage testing in environments with flammable materials, security measures should be taken.

Every time the resistance flash is used, the measured value of the water resistance should be taken.

Pay attention to personal safety.

It is recommended to disconnect the external power supply of the computer when applying high voltage, without using an external mouse.

Part 2 Cable Data Management

The cable data management part utilizes database principles to conduct daily management of cable data, including cable distribution maps, numbers, starting and ending positions, burial depths, dates, cable media, joint positions, maintenance records, and other archival information, so that management personnel can understand all the data of the cable.

Click the "Manage" command button on the system interface to enter the operation interface of the management system.

The cable data management part utilizes database principles to manage cable data.

Click the 'Management' command button on the main interface of the system to enter the operation interface of the management system. Click the 'System Login' button, and the system will prompt you to enter your password; Click the 'Change Password' button, enter the original password, then enter the new password, and confirm; Click the 'Exit' button to exit cable data management. The interface for cable data management is the substation information interface, which displays all substation information. You can add records, edit records, save records, delete records and other operations on substation information. Click on the pre test record to view all pre test records, and click on cable information to enter the cable information interface.

The second interface for cable data management is the cable information interface, which displays all cable information of a substation. You can add records, edit records, save records, delete records, and search records for cable information. Clicking on cable basic information will take you to the cable basic information interface.

The third interface for cable data management is the cable basic information interface, which displays a cable basic information. You can add records, edit records, save records, delete records and other operations on cable information. Click on the cable distribution map to view the cable distribution map. The cable distribution map is used to display the user's testing range and cable distribution, and can be used for finding and determining faulty cables. Click on the pre test record to view all pre test records of the cable.