Cable joint local emission monitoring

Date: October 29, 2025 09:04:12

The core of localized emission monitoring in cable joints is to detect the inside of the joints through thelocalized electrical discharge signal (LES), to determine its insulation status and detect potential faults in advance to avoid power outages.
This question cuts to the heart of the matter. Cable joints are the weak link of cable lines, and local discharge monitoring is a key means to ensure their safe operation.

I. The central importance of monitoring

  1. Joints are a high failure point: Cable joints are prone to insulation defects such as air gaps, impurities and poor contact during fabrication and operation, which are the main source of cable line faults.
  2. Local Discharge is a precursor to failure: Partial discharges are an early sign of insulation degradation, occurring months or even years before a fault occurs, and can be used as a basis for early warning.
  3. Avoiding vicious accidents: The local discharge monitoring can detect potential problems in advance and arrange for planned maintenance to avoid large-scale power outages or fires caused by joint breakdowns.

II. Mainstream monitoring technologies

Currently, there are four main monitoring technologies commonly used in the industry, each with its own application scenarios:
  • Ultra-high frequency (UHF) monitoring: Detection is realized by receiving the ultra-high frequency electromagnetic wave (300MHz-3GHz) generated by the local discharge, which has strong anti-interference ability and can precisely locate the discharge point.
  • Ultrasound monitoring: Capture the mechanical vibration (ultrasonic signal) generated by the local discharge, suitable for on-site inspection, easy to operate, but susceptible to environmental noise interference.
  • Ultra-high frequency (VHF) monitoringIt receives 30MHz-300MHz high frequency signals with low signal attenuation and can realize long-distance monitoring, but the anti-jamming ability is slightly weaker than that of UHF.
  • Transient Earth Voltage (TEV) MonitoringThe system is suitable for rapid screening of cable joints in switchgear cabinets by detecting the transient voltage induced by the localization on the grounded metal surface, non-contact measurement.

III. Technical comparison table

Monitoring technology core principle Key Benefits Applicable Scenarios
Ultra High Frequency (UHF) Receive UHF electromagnetic waves generated by local discharges Strong anti-interference ability and high positioning accuracy Fixed monitoring in substations and cable tunnels
ultrasound (scan) Receive ultrasonic vibrations from local amplifiers Easy to operate, non-contact On-site inspections, ad hoc spot checks
Very High Frequency (VHF) Receive high-frequency electromagnetic signals generated by local amplifiers Low signal attenuation and long monitoring distance Online monitoring of long distance cable lines
Transient Earth Voltage (TEV) Detection of transient voltages induced on grounded surfaces Small size and fast response Quick screening of cable glands in switchgear cabinets

How to choose a cable joint local discharge monitoring manufacturer

First, clarify their core needs

Before choosing a manufacturer, it is important to be clear about what you want and avoid being sidetracked by the manufacturer's "all-purpose propaganda".
  1. Clarify monitoring scenarios: is the cable tunnelOn-line stationary monitoringOr is it a live one?Mobile inspectionor of the connectors in the switchgearRapid screeningThe technology for different scenarios (e.g. UHF/VHF for online, ultrasonic/TEV for inspection). Different scenarios correspond to different technologies (e.g. UHF/VHF for on-line, ultrasonic/TEV for inspection).
  2. Determining the type of technologyFor example, if you need precise positioning, you should prioritize manufacturers that specialize in UHF technology, and if you need long-distance monitoring, you should focus on manufacturers with mature VHF technology.
  3. Listing of functional requirementsIf you need remote data transfer, AI diagnostics, fault location, historical data traceability, etc., then you need to know whether you need these features. Clarify "required functions" and "optional functions" to avoid paying for useless functions.
  4. Consider environmental adaptation: Whether there is strong electromagnetic interference, high humidity, dust, etc. at the site, you need to confirm whether the protection level (e.g., IP65/IP67) and anti-interference capability of the manufacturer's products are up to standard.

II. Focus on assessing the 4 core competencies of manufacturers

This is the key to screening manufacturers and directly determines the reliability of products and services.

1. Technical strength: looking at "hard skills"

  • Priority is given to those withIndependent R&D capabilitymanufacturers, not just assembly manufacturers. You can check whether they have core technology patents (e.g. signal processing algorithms, sensor design, etc.).
  • Find out if their technology is industry-proven, for example, if they have been involved in monitoring programs for large projects such as power grids and power plants.

2. Product performance: looking at "key indicators"

Don't just listen to the manufacturer's claims of "high accuracy", but keep your eyes on the specific indicators for comparison.
  • (level of) sensitivity: The ability to detect weak localized emission signals (e.g., ≤5pC) is central to the detection of early defects.
  • anti-interference capability: Availability of proven technical solutions for immunity to electromagnetic interference, environmental noise (e.g. motor, switching operations).
  • stability: The MTBF of the product, the online monitoring equipment should be guaranteed to operate stably for at least 1-2 years.

3. Service capacity: looking at "full process support"

Localized monitoring is not "buy it and forget it"; follow-up services are critical.
  • Pre-support: The possibility of visiting the site and developing a personalized monitoring programme based on the actual situation, rather than directly marketing a standardized product.
  • Installation and commissioning: Whether to provide a professional team to install and complete commissioning work such as signal calibration and data networking.
  • Post-operation and maintenance: Availability of 24-hour technical support, regular on-site inspections, data interpretation, and response time for maintenance after equipment failure (e.g., on-site within 48 hours).

4. Industry cases: looking at "practical effects"

  • Required from the manufacturerThe case for the same scenarioFor example, if you are a municipal cable tunnel monitor, focus on its use cases in similar tunnels rather than other industry cases.
  • It is best to contact the user in the case, side to understand the product operating results, manufacturers of service attitude and other real feedback.

III. 3 practical steps for selection

  1. Initial screening (narrowing): According to "Scene + Technology Type", screen 3-5 manufacturers that meet the requirements through official websites, industry exhibitions and other channels, and exclude the options that are obviously mismatched.
  2. In-depth examination (validation of capabilities): Invite the shortlisted manufacturers to communicate with each other at home, requesting product testing reports, patent certificates, cases in the same industry, and on-site demonstration of the signal acquisition and data analysis functions of the equipment.
  3. Integrated decision making (more than "value for money" rather than "price")Compare and contrast the technology, products and services of each manufacturer, focusing on the comprehensive price/performance ratio of "necessary functions + stability + operation and maintenance costs", avoiding only the cheapest or the most expensive, and prioritizing the one with the "highest degree of demand matching".