Street lamp cable fault tester using time domain reflection principle

PSHZC street lamp cable fault tester system composition

The PSHZC street light cable fault tester consists of a notebook computer, a test system, a path signal generator, a path signal receiver, and a positioning instrument. It can complete the test of cable faults and the management of cable data.

Notebook computer for measurement control, data processing and cable data management.

The fault test system can cooperate with the notebook to measure the distance of the fault point from the test end at the faulty cable end. It can also be used to measure the length of the cable and the propagation speed of the electric wave in the cable.

The path signal generator generates a 15KHZ, intermittent sine wave signal with a maximum amplitude of 30V to find the cable path.

The path signal receiver is used to receive the path signal, find the cable direction and estimate the cable depth.

The locator is used for precise positioning of the fault point.

PSHZC Street Light Cable Fault Tester Technical Performance

1, fault testing system

● It can test all kinds of faults of power cables and open circuit and short circuit faults of communication cables and local telephone cables.

● Measure the speed of wave propagation in any cable with a known length.

● Test distance: not less than 40 kilometers

● Systematic error: less than 0.5 meters

● Sampling frequency: 25MHz

● Test blind spot: less than 5 meters

● Power: AC 220V±10%

2, path meter signal generator.

● Signal frequency: 15KHz

● Oscillation mode: intermittent

●Output power: 30W

● Power supply: 220V ± 10%

3, positioning instrument

Test Sensitivity: The signal source of 50 Ω internal resistance outputs 300 Hz signal, and the fixed point instrument is not more than 10 μV when the output is maintained at 2V and the S/N ratio is better than 20:1.

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

● Operating voltage: 9V ± 10%. ● use of ambient temperature: -10 °C ~ 40 °C

After starting Windows98, double-click the test management system on the desktop and the main control appears on the screen. <Press "Test" button to enter the test mode; press "Manage" button to enter the daily management of cable data and test data; press "Help" to enter the help system; press "End" to exit the test management system.

The first part of the cable fault test

PSHZC street light cable fault tester test principle

The instrument adopts the time domain reflectometry (TDR) principle to emit a series of electrical pulses to the cable under test, and receives the reflection pulse caused by the impedance change in the cable, and then according to the propagation speed of the wave in the cable and the characteristic inflection point of the two reflected waves. On behalf of the time, the distance from the fault point to the test end can be measured as:

S=VT/2 type:

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

V represents the propagation speed of the electric wave in the cable

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

In this way, the fault point distance test can be calculated if V is known and T has been measured. The distance S from the end. All this can be done automatically by the computer with a little manual intervention, and the test failure is quick and accurate.

PSHZC Street Light Cable Fault Tester Test System Control Panel Introduction

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

1, the menu bar

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

"Data Management" menu: including "print", "read disk", "Save", "end" four menu items.

Select "Print" to print the contents of the screen with a printer; select "Save" to save the test waveforms and data on the computer's hard disk or floppy disk as data; select "Read Disk" to recall the previous test The waveform in the disk; select "End" to exit the control panel.

"Test Help": Click this menu to display the test management system's instruction manual and print it out.

2, the status bar

The status bar shows four aspects of information, the left is the test mode; the second is the speed of the radio wave corresponding to the selected cable media (if the speed is measured, the media information is not displayed) The third is the fault distance (or cable length) , the test date is shown on the right.
3, the graphic display area

The graphic display area is used to display the sampled waveforms, analyze the waveforms and display the processing results.

4, function keypad

The function keypad consists of 14 buttons and can be divided into three categories.

Initialization data: Including the test method and media selection two keys.

Test method: There are two choices, "fault detection" and "measurement speed."

There are three basic test methods, "low-voltage pulse", "flash flash", "straight flash."

“Low-voltage pulse” includes two pulse widths “2μs” and “0.2μs”; “flashflash” includes three menu items: “inductor voltage sampling”, “resistance voltage sampling” and “current sampling”; ” Including “Voltage Sampling” and “Current Sampling” two menu items.

Media selection:

When the program is initialized, the setting is: "oil-impregnated paper type". If it is a cable of other media, it can be selected according to the media of the cable. There are five options: "oil-impregnated paper type", "drip-free type", "cross-linked ethylene", "PVC", "self-selected media" five menu items.

Selecting one of the menu items is equivalent to choosing a speed, which is the speed of propagation of the wave in the cable.

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

"Sampling" key: Used during system testing. Each time you press the "Sampling" button, the system collects data once and you can plot the waveform in the graphic display area.

“Extended” key: In order to accurately calculate the distance to fault, press this key to expand the displayed waveform and then calculate it. Each press of the waveform expands by one and presses four times for one cycle.

“Scroll” button: After the waveform is expanded, the fault point feature waveform may be in other screens than the first screen. Press this button to move the display content to the left one screen at a time until the fault waveform is displayed on the screen. , the precise positioning of the cursor.

“Home” key: Press this button when you want the cursor to quickly return to the left end of the screen.

"Location" key: Calculate the distance from the start key. Press this button when the cursor moves to the start point of the feature waveform.

"Left shift" key and "right shift" key: These two keys are used to control the left and right movement of the cursor. When you press them, the cursor moves, one unit per press. In addition, in order to quickly move the cursor, you can drag the cursor with the mouse and release it at the appropriate position.

"Reset" button: System reset button. No matter what state the system is in, press this key to enter the main interface of the system.

Waveform comparison: There are four keys.

“Save” key: Press this key to store the test waveform and data in the computer. ("Save" is different from "Save". "Save" is to store data on a disk, which can be stored for a long time, while "Storage" is just storing data in the computer's memory. Data will be lost after shutdown.)

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

“Compare” key: Press this key to display the waveform currently being measured and the waveform stored in the instrument on the screen at the same time. Users can compare and analyze the two waveforms.

“Translate” key: Press this key to enter the left/right movement function of the graph. Click the “left shift” key to align the starting points of the two waveforms.

PSHZC street light cable fault tester fault test

The basic steps of fault testing are: measuring the insulation resistance of the faulty cable with a shake meter or a multimeter, determining the nature of the fault, determining the test method, testing the fault distance, detecting the route of the cable buried near the fault point, and fixing the point.

The test system fault test has three basic methods: low-voltage pulse, direct flash, and flash flash. In combination with different sampling methods, there are eight types of test methods.

Disconnect all cables from the cable terminal before testing.

The panel of the test system has two knobs “input amplitude” and “displacement”, which are used to adjust the signal amplitude and the up and down position of the next sampling.

1, low pressure pulse method

Low-voltage pulses are used to test the speed of propagation of electrical waves in the cable, the full length of the cable, low-impedance faults and open-circuit faults.

Connect the communication cable of the test system with the serial port on the back of the notebook computer. The fault phase (measured phase) of the cable and the ground cable are respectively connected to the red and black terminals of the water stop plate, the output of the water block switch and the input of the test system. Connected. It is also possible to directly connect the test system's input line to the fault phase and ground.

●Speed ​​measurement

For some cables, the speed of wave propagation is unknown and must be determined by testing. But before testing, you must know the full length of the cable.

In the "Test Method" menu, select "Low-Pressure Pulse" "Measuring Speed" and select "0.2μs" or "2μs" depending on the cable length. Generally, use 0.2μs for 500m or less. After typing the full length of the cable, press the Sampling button to adjust the Displacement and Amplitude knobs so that the amplitude and baseline of the signal are in an easy-to-observe position.

Move the cursor to the falling edge of the low-voltage pulse and press “Position”. Then move the cursor to the front of the reflected signal. The propagation speed of the electric wave in this cable can be displayed on the screen. If the transmitted and received waveforms are too close, press the "Extended" key to expand the waveform before calculating.

●Fault detection

When measuring the fault, select “Low-voltage pulse” “Fault detection” in the “Test mode” menu, select the appropriate pulse width, and press “Sampling” to display the fault waveform.

The reflection signal of the open circuit fault has the same polarity as the transmission pulse, and the reflection signal of the short circuit fault has the opposite polarity to the transmission pulse.

Note: Since the wiring and waveform of the full-length cable are exactly the same as when measuring the open circuit fault, the full-length menu is not listed separately in the design.

The waveforms of open-circuit fault (full-length cable) and short-circuit fault waveforms for the low-voltage pulse test are as follows.

2, flashing way

The flashover method is used to test high-impedance leakage faults. Most of the cable faults can be tested using the flashover method.

In the past, the use of flash lightning-induced voltage sampling was more common. Current sampling is generally used because current sampling does not directly connect with high voltage, and the safety factor of the human body and equipment is higher. If there are multiple faults on one cable or a large area of ​​the cable is affected by moisture, a flash impulse resistance sampling method can be used.

3, direct flash mode

The direct flash method is used to test high-fault flashover property failures.

When using direct flash method, we must pay attention to monitor high-voltage current to prevent the current is too large and burn out the high-voltage transformer.

4, test cable path and buried depth

The test system outputs the cable core wire to one phase of the cable and the ground wire to the cable ground (lead bag). (If the resistance of the fault phase is very low, a resistance of several hundred ohms can be connected in series between the output ground and the cable ground.) First, turn the output potentiometer to the minimum, turn on the power and adjust the amplitude knob to the appropriate value. Position, at this time the instrument outputs a 15KHZ sinusoidal signal. This signal generates an electromagnetic field around the cable. Adjust the "volume" and "fine-tuning" knobs of the path signal receiver so that the sound in the earphone is clear and pleasing. You can find the cable path and Estimate the depth of cable laying.

● 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, the coil does not cut the power line, and the induced current in the coil is small. At this time, there is almost no sound in the earphone. When the probe is at point A or point C, the sound in the headset is louder.

The line connected by the point where the sound is small is the path of the cable.

● Estimate the depth of cable buried

Point the probe right at point B on the cable and tilt it to the right at 45 o. Then move back perpendicular to the cable. When retreating to point A, the probe is facing the cable.

The distance from point B to point A, that is, the distance to retreat is the depth at which the cable is buried.

This method can estimate the depth of cable buried.

5, fault location

We have used various test methods to measure the distance of the fault point, but due to the influence of various factors such as measurement error, cable residual cable, cornering, etc., the fault cannot be accurately found on the ground, and fault location must also be used. Instrument to determine the point of failure.

In the fault location, a high-voltage device is used to add a shock DC negative high voltage to the cable, and the sounding point of the cable fault is detected near the measured fault point with a locator.

The time for high pressure discharge is preferably once per second.

Turn on the power of the locator, adjust the volume knob appropriately, and place the locator at the fault point of the measured cable. There should be a sound at the fault point discharge. If the position of the movable locator cannot be heard until the discharge sound in the earphone is maximized, Here is the point of failure.

6, matters needing attention

● Observe the safety rules when testing cable faults.

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

● When using high-voltage tests in environments with flammable substances, there should be security measures.

● Measure the value of water resistance each time you use resistance flash.

● Pay attention to personal safety.

● It is recommended to disconnect the external power of the computer when high voltage is applied. It is better not to use an external mouse.

Part II Cable Data Management

The cable data management part is to use the database principle to carry out daily management of cable data, including cable distribution map, number, starting and ending position, depth of burial, date, cable media, connector location, maintenance records, and other file information, so that managers can understand the cable All information.

Click the "Manage" command button on the system interface to enter the management system's operating interface.

The cable data management part uses the database principle to manage cable data.

Click the "Manage" command button on the main interface of the system to enter the operating interface of the management system. Click the "System Login" button, the system will prompt you to enter the password; click the "Change Password" button, enter the original password, and then enter the new password , OK; click "Exit" button to exit cable data management. The first interface of cable data management is the substation information interface, displaying all substation information. Substation information can be added to record, edit records, save records, delete records, etc., click pre-test records, you can view all the pre-test records, click on the cable information, you can enter the cable information interface.

The second interface of cable data management is the cable information interface, showing all the cable information of a substation. The cable information can be added to record, edit record, save record, delete record, search record, etc. Click cable basic information to enter the cable basic information interface.

The third interface of cable data management is the cable basic information interface, which shows a cable basic information. The cable information can be added to record, edit record, save the record, delete the record, etc., click the cable distribution chart, you can view the cable distribution diagram, the cable map is used to display the user's test range and cable distribution, can be used for faulty cable Find and OK. Click on the pre-test record to view all the pre-test records for this cable.