NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
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NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
With the acceleration of social modernization, the demand for electric power is getting bigger and bigger. Because of its connection, transmission, distribution and other functions, it has been widely widely used, and the failure generated by the power cable has a large proportion of all power supply failures. The acceleration of the social modernization process is increasingly bigger.
Because of its connection, transmission, distribution and other functions, it has been widely widely used, and the failure generated by the power cable has a large proportion of all power supply failures. Therefore, during the use and operation of the power cable, how to determine the location of the fault point, determine the type of fault, has become a very critical technology. Let's take a look at the commonly used power cable faults and positioning methods.
I. Common fault spacings, positioning methods. 1, low voltage pulse method: ranging. (1) Principle: Using the time domain reflection (TDR) principle, transmit a series of electrical pulses from the measured cable, receive reflection pulses due to changes in impedance, and then according to the propagation speed of the radio wave and the characteristics of two reflection waves The time indicated by the inflection point can measure the distance of the fault point to the test end is S = VT / 2.
(2) method. The low voltage pulse is used to test the speed of the radio wave propagating in the cable, the cable length, low-resistance fault (the fault phase resistance is less than 1K), open fault and short circuit failure. 2, high pressure flash mode: fixed point.
Cable high resistance failure (high resistance failure: DC resistance is greater than cable characteristic impedance is high resistance fault (cable intermediate or ground insulation resistance is greater than 100KΩ), Almost more than 90% of all failure rates. High-blocking faults and high resistance faults with flushing can be used, and the high resistance value of the cable can be used. Depending on the property of the fault, it can be divided into a pulsed high pressure flashing (Flash) and DC high-pressure flashing (direct flashing).
(1) Rough test. Current sampling method. Since the current sampling wiring is simple, safe and reliable, the waveform is easy to identify, it is recommended to use current sampling.
When the wiring diagram is complete, press the speed button to select the transfer speed or the key speed value. Turn the input amplitude knob to approximately 1/3, then press the sample button, the instrument enters the waiting sampling state. Adjust the ball gap (if it is discharged, it will make a crisp, the working box is greater than 10A-15A, otherwise it is not discharged, please re-adjust the gap, increase the impact voltage, input the amplitude knob, and then power the fault cable boost The voltage rises to a certain value, a flash discharge, and the instrument recording waveform.
The input amplitude can be adjusted according to the size of the waveform, repeatedly sampled until a relative standard waveform is obtained. Note: Adjusting the ball gap is generally 1 mm to 3kV when the power cable fault lookup is performed. Please appropriately adjust according to the measured cable voltage level. (2) Accurate fixed point.
The accuracy is the key step of cable fault detection. After the rough test is completed, the cable is continuously pressurized, so that the fault point is continuously discharged, the frequency is approximately 3 to 4 seconds. Carrying the sound number display synchronous fixed-point instrument to the roughness, 10 meters, carefully listen to the discharge sound of the fault point, and listen to the sound point of the cable. The commonly used power cable fault finding method will introduce you to you, pay attention to Xiaobian, continue to introduce you to you next time.
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