Low-voltage pulse method: suitable for precise distance measurement of low-resistance, short-circuit, and broken-line faults, and can also be used for measuring the full length of cables, intermediate joints, T-joints, terminal heads, and for calibrating wave speed. 1. Multiple distance measurement methods:
Low-voltage pulse method: suitable for precise distance measurement of low-resistance, short-circuit, and broken-line faults, and can also be used for measuring the full length of cables, intermediate joints, T-joints, terminal heads, and for calibrating wave speed.
Pulse current method: suitable for distance measurement of high-resistance and flashover faults. It uses a current coupler to collect signals from the test ground wire, completely isolated from the high-voltage part, safe and reliable.
Multiple pulse method: the world's advanced distance measurement method, an improvement of the secondary pulse method. The waveforms are clear and easy to identify, with high distance measurement accuracy.
Clear waveforms, especially in multiple pulse testing, where multiple waveforms are displayed simultaneously in different colors, making identification easier.
7-inch large screen LCD, 160° viewing angle, brightness up to 750cd/m2, meeting sunlight readability requirements.
Pulse current method: suitable for distance measurement of high-resistance and flashover faults. It uses a current coupler to collect signals from the test ground wire, completely isolated from the high-voltage part, safe and reliable.
Multiple pulse method: the world's advanced distance measurement method, an improvement of the secondary pulse method. The waveforms are clear and easy to identify, with high distance measurement accuracy. After using appropriate methods to roughly measure the cable fault distance, it is necessary to determine the approximate location of the fault point based on the cable route, and then proceed with precise fault pinpointing. The reason it is called rough measurement is that the detected fault distance has errors, and manual measurement of the cable route distance on the ground also has errors. Therefore, rough measurement can only tell us the approximate location. Precise pinpointing, as the name suggests, uses methods to accurately determine the fault point location. Cable fault precise pinpointing mainly includes the acoustic method, acoustic-magnetic synchronization method, and audio induction method. The following introduces these methods separately.
The acoustic method is the most basic method for fault pinpointing. When a fault point is broken down by high-voltage impact, it produces a discharge sound. This method uses the discharge sound during breakdown to precisely locate the fault. During pinpointing, the high-voltage generation equipment periodically applies high-voltage signals to the cable, causing the fault point to break down and discharge. The breakdown discharge of the fault gap also produces mechanical vibration. The acoustic detection equipment receives the discharge sound signal transmitted to the ground surface to determine the fault point location. If the fault is open, staff can directly hear the discharge sound with their ears. For closed faults or faults buried deep underground, the discharge vibration sound needs to be enhanced through high-sensitivity acoustic-electric conversion equipment, amplifying the signal and restoring the sound intensity display. During testing, staff usually use headphones and simultaneously observe the meter pointer swing to judge the discharge sound signal. However, the sound signal is short, and environmental noise interference can easily cause misjudgment. With the development of microelectronics technology, intelligent pinpointing instruments can record, store, and compare sound waveform signals from multiple measurements, making it convenient for staff to judge based on signal strength, frequency, attenuation, duration, etc. The acoustic method is particularly suitable for high-resistance faults, and it is recommended to use large-capacity energy storage capacitors (to increase the impact voltage and enhance the vibration wave during discharge; during measurement, the discharge interval should be effectively controlled to eliminate external interference and shorten fault pinpointing time.
When a fault point breaks down, it produces both sound and magnetic field signals. The propagation speed of the magnetic field is negligible, so it is much faster than the sound signal. During fault testing, using the received magnetic field signal as a reference, the time difference between it and the sound propagation is calculated and multiplied by the speed of sound to determine the distance between the fault point and the test end. This is the acoustic-magnetic synchronization method for judging the fault point.
When DC high voltage breaks down the fault point and discharges, it induces a circulating current in the loop formed by the metal sheath and the ground, and generates a pulse magnetic field around the cable. Because this pulse magnetic field is much stronger than other stray magnetic fields in the environment, it can be reliably received. In this way, the audio signal and the pulse magnetic field signal can be received simultaneously and converted for display. If the staff receives the audio signal and the pulse magnetic field display signal consistently, it can be judged as the fault point.
When using the acoustic method for pinpointing, sometimes due to environmental noise interference, road surface structure effects, weak discharge sound at the fault point, etc., it may be difficult for staff to identify the fault point. Using the acoustic-magnetic synchronization reception method can improve the anti-interference capability during fault pinpointing.
When using the acoustic-magnetic synchronization method for fault pinpointing, the time difference between the magnetic and acoustic signals can be used to estimate the fault point location. The time for the magnetic field signal to travel from the fault point to the instrument probe is in microseconds and can be ignored, but the time for the sound to travel to the instrument probe is in milliseconds. Thus, the distance to the fault point can be judged based on the time difference between the magnetic and acoustic signals. The smaller the time difference, the closer to the fault point. The figure below shows the discharge sound signals received by the instrument at two positions near the fault point. The figure shows: when the magnetic field signal peaks, the sound signal begins to appear; the time difference between the magnetic and acoustic signals is measured as [first measurement] for the first measurement and [second measurement] for the second measurement. It can be seen that the second measurement is closer to the fault point.
