Cable fault indicator of low voltage pulse reflection method
in the previous paper, small make up after years of cold and hot shrinkage cable accessories production experience summed up the power cable pulse reflecting the basic principle of current sampling method, a lot of friends look after feeling a lot, and want to know the low voltage pulse reflection method directly problem statement, small make up for this response everyone's requirements, share the rest of the series will give you low voltage pulse reflection method, hope to be of help.
using this method, can be directly from the monitor screen of a cable fault tester visually observed at fault point is open circuit or short circuit fault property, and can also use the photoelectric cursor directly show the fault point distance from testing side. For low resistance, short circuit fault and open circuit fault. Simple and intuitive than a pulse measurement method and the test method.
cable fault indicator display waveform, provided for the judgment is more complicated on the circuit structure of fault tend to have very important reference value.
use a bridge to solve the problem, T joints such as lines, or there is a parallel running cable, or open circuit fault phase or three phase is low resistance fault, etc. ) , low pressure pulse test method can provide a considerable amount of analysis data. Of course, to explain the observed waveforms of all kinds of complicated phenomenon, is the need for technical personnel after basic training and test a large number of practical experience and skills. Now can use a variety of pulse range finder, its depends in part on the dish measurement operators of the practice and experience.
the working principle of low voltage pulse method:
test, send pulse on the fault phase input low voltage, the pulse propagation along the cable until the impedance mismatch, such as the middle head, tee joint, short-circuit point, break point and terminal first. Can cause wave reflection on these points, reflected pulse back to receive cable testing end when the test equipment. Fault point echo pulse and measuring the time interval between pulses sent and fault point from the test on the actual cable is proportional to the distance.
the fault of the nature of the type, can be made of reflected pulse polarity judgment. If send measuring pulse is normal polarity, echo pulse is normal polarity pulse, said is open circuit fault or terminal head open circuit; Echo is negative polarity pulse, it is a short-circuit ground fault.
the fault distance by measuring pulse and the echo pulse estimates the time difference between, this involves the speed of radio waves propagation in the power cable.
in the related theory and the actual measurement, waves in the cable transmission, the transmission speed is only associated with the relative dielectric constant of dielectric, and which had nothing to do with cross-sectional area size. Waves in the propagation speed of oil impregnated paper insulation is about 160 m/us. But if you want to test plastic insulated power cable and other types of power cable, telecommunication cable fault distance, you must to measure electric wave propagation speed within the cable.