Author: Noyafa–Noyafa Cable Tester
What are the working methods of the underground pipeline detector? The underground pipeline detector has three working modes: wave crest method, wave trough method and step voltage method. ⑴ Wave crest method: When the detector receiver is located directly above the pipeline, the signal indication is the largest and the sound is also the largest. What are the working methods of the underground pipeline detector? There are three working modes of underground pipeline detector: wave crest method, wave trough method and step voltage method.
⑴ Wave crest method: When the detector receiver is located directly above the pipeline, the signal indication is the largest and the sound is also the largest. Care should be taken to adjust the gain so that the signal is only detected above or near the line. The wave peak method is to use the horizontal coil to receive the strength of the horizontal component of the electromagnetic field, and to detect the peak value of the cable without interference.
When it is directly above the cable, when the front of the receiver is perpendicular to the cable, the magnetic field response intensity is the largest. This is not only because the coil is closest to the cable and the magnetic field where the coil is located is strong, but also because the magnetic field lines of the magnetic field pass through the magnetic flux of the receiving coil. big. When the receiver moves to both sides of the cable for detection, the magnetic field response strengths on both sides are symmetrical and gradually decrease. This is not only because the coil is far away from the cable at this time, and the magnetic field received by the receiver coil becomes weaker, but also because the direction of the magnetic field lines of the magnetic field is no longer perpendicular to the plane of the coil, and the magnetic flux passing through the coil becomes smaller, resulting in a mountain-like peak. signal response.
so called“Crest method”. (2) Valley method: When the detector receiver is directly above the cable, the signal indication is the smallest, and the sound indication of the receiver does not have any sound indication. Pay attention to adjusting the gain, so that the receiver has no signal and sound indication directly above the cable, and there is sound when it is located on both sides of the line.
The valley method uses a vertical coil to measure the vertical component of the electromagnetic field. The magnetic field on the target cable is composed of countless circular magnetic lines of force concentric with the cable. When the receiver is directly above the cable, the signal response is the smallest, and there is a peak on each side. This is due to the fact that the vertical component of these magnetic field lines passing through the vertical receiving coil of the receiver directly above the cable is zero, at this time the magnetic flux passing through the vertical coil of the receiver is zero, and the signal response has a minimum value (zero value or minimum value) ; When the receiver moves on both sides of the cable, the response of the instrument will gradually increase as the receiver moves away from the cable. This is because the direction of the magnetic field line at this time and the vertical coil plane of the receiver have formed a certain angle. The magnetic flux of the vertical coil gradually becomes larger. At the same time, as the receiver coil is far away from the underground cable, the strength of the magnetic field detected by the receiver gradually becomes weaker. When this factor becomes the main factor affecting the change of the magnetic flux passing through the coil, the response of the instrument will gradually become smaller, resulting in such as Valley-like signal response.
so called“Valley method”⑶ Step voltage method: pass“A”The frame can detect the ground fault and sheath damage fault of the directly buried cable. Will“A”The frame is connected to the receiver, and the receiver receives the“A”The frame detects the leakage signal overflowing from the fault point sent by the transmitter, which can easily locate the fault of the direct buried cable to the ground and the damage of the outer skin. The direct buried cable fault location is especially suitable for the fast and accurate location of the ground insulation fault of the street lamp cable, the direct buried power cable, the direct buried communication cable and the direct buried optical cable.
It is especially useful for the dead grounding of directly buried cables. When testing with the traditional high-voltage flashover method, because the discharge energy of the single-phase metallic grounding fault point is proportional to the square of the discharge current and the grounding resistance, and the grounding resistance is very small, the fault clicks. When discharging through the gap, the sound is lighter, and it cannot be fixed or even fixed.
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