What is online cable monitoring

• core objective: To realize continuous, real-time monitoring and fault warning of the critical operating status of high-voltage power cables and their accessories (terminals and joints), with the aim of enhancing the operational reliability of cable lines and realizing the shift from reactive repair to proactive preventive maintenance.

• Monitoring dimensions: Mainly covers the cableinsulation condition,Temperature of conductor and connection pointas well asIntegrity of the external sheathThese are the three core elements that affect the life and safe operation of cables.

• Key technologies:

  • Insulation monitoring: Partial Discharge (PD) on-line monitoring is the core of the system, which detects weak discharge signals inside the insulation by means of a variety of sensors such as Ultra High Frequency (UHF), High Frequency (HFCT), and Acoustic (AE).

  • Temperature monitoring:: Distributed fiber optic temperature measurement (DTS) technology is used to achieve continuous temperature distribution monitoring of the entire path of the cable, or infrared thermal imaging, wireless passive temperature measurement and other technologies are used to monitor critical points.

  • Sheath monitoring: Determine whether there is grounding, corrosion or external damage to the metal sheath by monitoring the sheath loop current or injecting a DC signal.

• -system architecture: Adopt layered distributed architecture, including front-end sensors, on-site data acquisition and processing units, high-speed communication network and back-end intelligent diagnostic master station, to realize comprehensive sensing, intelligent analysis and visualization of data.

• applied value:: Be able to warn weeks or even months in advance of the deterioration of cable insulation, joints overheating and other serious faults, effectively avoiding sudden cable breakdown accidents, and providing core technology for the safe operation of urban power grids, important transmission corridors, nuclear power, rail transportation and other key infrastructure.

I. The need for online monitoring of cables

High-voltage power cables, especially buried in the underground cable lines, has the characteristics of "hidden engineering". Once a fault occurs, it is not only difficult to locate and take a long time to repair, but also may cause extensive power outages and huge economic losses. The traditional manual inspection and periodic offline test (such as AC withstand voltage test) has a blind spot, and can not detect the dynamic development of internal defects in operation in a timely manner.

The core purpose of the cable online monitoring device is to capture the early deterioration characteristic signals occurring inside the cable under the operating condition of non-stop power to realize:

• early warning of malfunction: Alerts before insulation drops to a critical point.

• precise positioning: Indicate the exact location where the defect occurred (e.g., which joint, how many meters from the terminal).

• Condition Assessment: Comprehensive assessment of the overall health of cable lines to provide data support for asset management and condition maintenance.

II. Core monitoring technologies and principles

1. On-line monitoring of insulation condition: Partial Discharge (PD) monitoring
Partial discharge is the "main culprit" leading to the eventual breakdown of cable insulation. It refers to the cable insulation within (such as air gaps, impurities) or accessories in the occurrence of weak, localized spark discharge.

• Monitoring Principles: Localized discharges are accompanied by a variety of physical signals when they occur, and the online monitoring system captures these signals to infer the presence and severity of the discharge.

  • Ultra High Frequency (UHF): High-frequency electromagnetic waves (300 MHz-3 GHz) generated by electrical discharges are radiated along the surface of cable accessories. These signals can be detected with high sensitivity by installing UHF sensors at cable terminals or joints. This method has a high signal-to-noise ratio and is highly resistant to interference.

  • High Frequency Current Transformer Method (HFCT):: The discharge generates pulsed currents that flow through the cable's ground wire to earth. These high frequency pulsed current signals can be coupled out by clamping the HFCT to the cable ground wire. This method is easy to install and widely used.

  • Acoustics (AE): Discharge generates ultrasonic waves. By attaching acoustic sensors to the surface of the cable attachment, the sound of the discharge can be "heard". By combining multiple acoustic sensors, it is possible to acoustically localize the discharge point in three dimensions.

• Diagnosis and localization: The back-end system analyzes the collected PD signals **PRPD mapping (Phase Resolved Partial Discharge Mapping)**, and the shape of the mapping can be used to determine the type of discharge (e.g., internal air gap discharge, discharge along the surface, etc.). Through the time difference of arrival (TDOA) of multiple sensor signals, the propagation distance of the discharge source along the cable line can be accurately calculated to realize fault localization.

2. Online temperature monitoring
The temperature of a cable's conductors is a key factor in determining its current-carrying capacity, while abnormal temperature rises at joints and other connections are the most common precursors to failure.

• Distributed Temperature Sensing (DTS - Distributed Temperature Sensing):: This is the realization of the cablefull pathThe most advanced technology for temperature monitoring. A temperature-sensitive optical fiber is laid in the same trench as the power cable, and the DTS mainframe transmits laser pulses into the fiber, and the temperature at each point on the fiber can be calculated by analyzing the intensity and time of the Raman scattered light that is backscattered by the laser pulses in the fiber. Its advantage is that it can provide a continuous temperature curve without monitoring blind zone, especially suitable for long distance and important cable lines.

• infrared thermography: For cable terminations and accessories exposed to air, in-line infrared cameras can be used for non-contact temperature measurement to monitor their surface temperature distribution in real time and visually detect hot spots.

3. On-line monitoring of sheathing and earthing systems
The metal sheath (or shield) of the cable is essential to protect the insulation and equalize the electric field.

• Sheath circulation monitoring:: Induced loop currents in the sheath are monitored by installing a current transformer on the cable sheath grounding wire. Abnormally high ring currents may indicate a multi-point ground fault in the sheath, which can lead to additional losses and localized overheating.

• Sheath integrity monitoring:: For cross-interconnected grounding systems, monitoring the operation of their protectors or injecting signals of a specific frequency can determine whether there is damage to the sheath, water ingress or insulation damage.

III. System architecture and data applications

An online cable monitoring device usually consists of the following components:

1. sensor layer:: Various types of sensors (UHF, HFCT, DTS fiber optic, temperature probes, etc.) installed along cable lines.

2. Data Acquisition and Edge Computing Layer: A data acquisition unit deployed in the field (e.g., cable tunnels, terminal towers) responsible for high-speed data acquisition, signal pre-processing, feature extraction and local alarms.

3. communications network layer: Transmission of field data to the monitoring center using fiber optics, power carrier or wireless public network (4G/5G).

4. Main site diagnostics and presentation layer: Intelligent diagnostic software is deployed in the backend server to perform comprehensive analysis, trend prediction and fault location on massive data, and provide users with visualized cable health status reports and early warning information via Web and mobile apps.

Frequently Asked Questions (FAQ)

1. How far in advance can an online cable monitoring system warn of a fault?
This depends on how quickly the fault develops. For partial discharges triggered by gradual aging of insulation and moisture, the process from the detection of a weak PD signal to the eventual development of a breakdown fault may last weeks, months or even longer, providing a sufficient window of time for scheduling maintenance. For unexpected events such as damage due to external forces, the warning time is very short.

2. What is the essential difference between distributed fiber optic temperature measurement (DTS) and traditional point temperature measurement?
Point temperature measurement(e.g. thermocouples, infrared) can only measure the temperature at a specific point, with a blind spot for monitoring between points. WhereasDTSTurns the entire fiber into a sensor, capable of delivering a signal along the cable path.Every meter or less.The continuous temperature data from the cable is a leap from "point" to "line". This is crucial for detecting localized hot spots in cables (e.g. defects inside joints, influence of external heat sources).

3. Does the installation of an online monitoring system require cable outages?
Most monitoring systems can be installed on cableelectrified operationThe situation is carried out in a number of ways. For example, HFCTs are clamped to the ground wire, UHF and acoustic sensors are mounted on the surface of the accessory, and infrared cameras are non-contact. Only the temperature sensing fibers of a distributed fiber optic temperature measurement system need to be synchronized with the cable laying or added next to the cable in a subsequent project.

4. How is the system's monitoring data translated into maintenance decisions?
The system master software is at the heart of decision making. It not only displays data, but more importantly has a built-in expert knowledge base and intelligent diagnostic algorithms. For example, when the system detects a PD signal, it automatically analyzes its PRPD profile, gives a diagnosis of "suspected air gap discharge inside the accessory", and marks the fault location. When the DTS detects an abnormal increase in temperature at a certain point, it will combine the historical data and load current at that point to determine whether it is a normal increase in temperature caused by the load or a defective heating of the joint. These accurate "diagnostic reports" directly guide the operation and maintenance personnel to develop "where to repair, repair what" precise maintenance program.

 Inotera is committed to providing industry-leading online cable monitoring solutions. We integrate advanced monitoring technologies to create a highly integrated and intelligent product system designed to elevate your cable operation and maintenance management to a whole new level.

Our core strengths:

• Comprehensive and multidimensional monitoring. Our system integrates various modules such as high frequency/ultra-high frequency partial discharge, distributed fiber optic temperature measurement (DTS), sheath ring current and grounding current monitoring, etc., to achieve 360-degree monitoring of cable insulation, temperature and sheath status without dead angle.

• Core Algorithms and Precision Diagnostics. Equipped with self-developed intelligent diagnostic engine, it can automatically perform PRPD mapping analysis, accurately identify the type of discharge, and through the multi-sensor fusion localization algorithm, it can enhance the fault location accuracy to meter level, providing you with clear and executable diagnostic reports.

• Modular design and flexible configuration. Whether it's focused monitoring of a single critical line or comprehensive coverage of an entire cable network, we offer modular, scalable solutions from sensors to master station software. The products can be flexibly adapted to different voltage levels and application scenarios (e.g. urban cable tunnels, substations, offshore wind power, etc.).

• Integrated Intelligent Platform. Provides a unified visualization monitoring platform, presenting complex monitoring data in the form of intuitive graphics, trend curves and 3D maps. The system supports Web and mobile access, realizing real-time push alarms and automatic generation of reports, allowing you to control the health of the cable anytime, anywhere.

We not only provide excellent products, but also provide the whole process of professional services from site investigation, program design, installation and commissioning to the later data analysis and technical support.

Contact us today for a smart monitoring solution customized for your cable lines.