⚡ electrical engineering

Monitoring method for armoring shielding cable in strong electromagnetic region in substation

This paper proposes and validates a practical monitoring system utilizing a composite five-criteria discrimination method to detect and prevent cable overheating in the strong electromagnetic environments of high-voltage substations, addressing the limitations of conventional detection techniques.

Original authors: Hao Chen, Huaiyu Liu, Xinzheng Guo, Jian DU, Xinhao Lu

Published 2026-07-02

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CC BY 4.0

Original authors: Hao Chen, Huaiyu Liu, Xinzheng Guo, Jian DU, Xinhao Lu

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Problem: The "Magnetic Oven" Effect

Imagine a high-voltage power station as a giant city of electricity. In the middle of this city, there are massive devices called reactors (think of them as giant, powerful magnets). While they do their job, they leak a bit of magnetic energy, creating a "strong electromagnetic region" around them.

If you place a bundle of electrical cables near these magnets, it's like putting a metal loop near a microwave. The magnetic field induces a current to flow in the cable's metal armor and shielding layers. If the cables are installed poorly or get damaged, this induced current can get trapped in a loop, causing the cables to heat up like a toaster. If left unchecked, they can overheat, smoke, or even catch fire.

The Old Way: "The Walk-and-Check"

For a long time, fixing this problem relied on human workers doing manual inspections.

The Analogy: Imagine a security guard walking through a dark warehouse once or twice a day, looking for smoke or feeling the walls to see if they are hot.
The Flaw: This is slow and unreliable. A fire can start and grow between the guard's visits. Also, if the guard isn't looking closely or the smoke is hidden, they might miss it. By the time they find the problem, the cable might already be damaged.

The New Solution: The "Smart Watch" System

The authors (engineers from State Grid Corporation of China) developed a new, automated system to act like a 24/7 smart watch for these cables. Instead of waiting for a human to check, this system constantly "feels" the electrical currents and voltages to spot trouble before it becomes a fire.

How It Works: The Five "Sensors"

The system doesn't just look at one thing; it uses a composite checklist of five criteria (like a doctor checking five different vital signs) to decide if a cable is in danger:

The Voltage Gap Check (Excessive Potential Difference):
- Analogy: Imagine two water pipes connected to the same tank. If the water pressure in one pipe is much higher than the other, it means something is wrong with the connection.
- What it does: The system measures the voltage difference between the "primary" ground and the "secondary" ground. If the gap gets too big, it sounds an alarm.
The Ground Current Check (Box Ground Over-current):
- Analogy: Think of a neighborhood where everyone shares a drainage pipe. If one house starts dumping too much water into the shared pipe, the whole neighborhood's pipe might overflow.
- What it does: It watches the current flowing into the ground from the cable box. If it gets too high, or if a neighboring box is already overflowing (indicating a wider problem), this system gets extra sensitive and sounds the alarm sooner.
The Shield Current Check (Shielding Layer Over-current):
- Analogy: Cables have an inner "shield" like a raincoat. If the raincoat is leaking too much water (current), it's a problem.
- What it does: It measures the total current flowing through the shielding layer's ground wire. If it exceeds a safe limit, it triggers an alert.
The Armor Current Check (Armoring Layer Over-current):
- Analogy: Cables also have a tough outer "armor" like a chainmail suit. If the chainmail is conducting too much electricity, it's overheating.
- What it does: Similar to the shield check, but for the outer metal armor. It sums up the current from all cables in the box to see if the armor is getting too hot.
The Loop Current Check (Loop Over-current):
- Analogy: This is the most dangerous one. Imagine a rubber band that got twisted into a circle. If electricity gets trapped in that circle, it spins faster and faster, creating heat.
- What it does: The system looks for a specific pattern where the currents in the armor and shield add up in a way that suggests a "short circuit loop" has formed. If this pattern is detected, it's a major red flag.

The Real-World Test

The engineers tested this system in two 500kV substations in East China (a very high voltage environment).

The Result: Over three years, the system generated 26 alarms.
The Comparison: When they compared this to the old "walk-and-check" method, the manual method only found a tiny fraction of the problems. The new system caught almost everything, including small issues that humans would have missed until it was too late.

The Bottom Line

This paper presents a method to stop cable fires in power stations by replacing "guessing and checking" with continuous, intelligent monitoring. By watching five specific electrical signals, the system can spot a cable that is about to overheat and warn workers immediately, preventing fires and keeping the power grid safe.

Technical Summary: Monitoring Method for Armoring Shielding Cable in Strong Electromagnetic Region in Substation

Problem Statement
In high-voltage (HV) and ultra-high-voltage (UHV) substations, dry-type air-core reactors generate significant magnetic flux leakage, creating local strong electromagnetic regions. When secondary circuit loops form around these regions—often due to insulation wear between armoring/shielding layers or improper grounding of ground wires—induced loop currents can exceed 20A. This phenomenon leads to severe overheating, cable burning, and potential fire hazards, posing a critical threat to substation safety.

Traditional maintenance relies on manual visual inspections and periodic infrared temperature measurements. The authors identify significant limitations in these conventional methods:

Non-real-time nature: Inspections occur only once or twice daily (up to four times for high-priority tasks), leaving gaps of several hours where a cable can progress from abnormal heating to ignition.
Low accuracy and subjectivity: Detection depends heavily on the skill and mental state of personnel, the specific fault development stage, and whether the measurement location is shielded.
Inefficiency: These methods can only detect a small fraction of heating anomalies, particularly before visible damage occurs.

Methodology
The paper proposes a novel online monitoring system based on the continuous acquisition of specific electrical characteristics and a composite discrimination criteria consisting of five distinct alarms.

Data Acquisition:
The system targets armored shielding cables in terminal boxes within strong electromagnetic regions. It collects:
- The summation of currents in the shielding layer ground wires ( $I_P$ ).
- The summation of currents in the armoring layer ground wires ( $I_K$ ).
- The potential of the primary ground copper busbar and the secondary ground copper busbar to calculate potential differences.
- The ground current of an adjacent terminal box to contextualize the risk.
Composite Discrimination Criteria:
The monitoring logic employs five specific criteria to trigger alarms:
- Excessive Potential Difference Criterion: Monitors the potential difference between primary and secondary ground busbars. If the difference exceeds a threshold (experience value: 1 V), or if an "extra-large" difference occurs, an alarm is triggered. The system dynamically adjusts constraints based on the magnitude of the potential difference.
- Box Ground Over-current Criterion: Monitors the ground current of the terminal box. The alarm threshold is adaptive: it is stricter (lower threshold) if an adjacent terminal box is already experiencing an over-current alarm, and looser if the adjacent box is normal.
- Shielding Layer Ground Wire Over-current Criterion: Triggers if the summation of shielding layer ground wire currents exceeds a set threshold (experience value: 10 A).
- Armoring Layer Ground Wire Over-current Criterion: Triggers if the summation of armoring layer ground wire currents exceeds a set threshold (experience value: 10 A).
- Loop Over-current Criterion: This is the core logic for detecting loop formation. It evaluates the sum of $I_P$ $I_{P}$ and $I_K$ $I_{K}$ .
  - If no potential difference alarm exists, the system checks if individual wire currents are high while the sum is below a specific loop limit (experience value: < 5 A), indicating a localized loop.
  - If a potential difference alarm is active, the thresholds for $I_P$ and $I_K$ are dynamically relaxed to account for phase cancellation and simultaneous insulation damage in multiple cables.

System Implementation
A monitoring system was developed comprising a master workstation in the relay room and multiple Data Acquisition Units (DAUs) deployed in the switchyards of 500kV substations. The DAUs collect the electrical data and transmit it via fiber optics to the central station for analysis and alarm generation.

Results
The system was deployed in two 500kV substations in the Nanjing power grid (Jiangsu, China) from 2020 to 2022. Over a three-year period, the system generated 26 alarms across 9 DAUs.

Detection Capability: The proposed method (Method A) successfully detected various anomalies, including 3 excessive potential difference alarms, 7 box ground over-current alarms, 8 shielding layer over-current alarms, 5 armoring layer over-current alarms, and 3 loop over-current alarms.
Comparison: In contrast, the conventional method (Method B), relying on manual inspection and infrared thermometry, detected only a fraction of these events (e.g., detecting only 1 shielding layer over-current and 1 loop over-current out of the 8 and 3 detected by the new system, respectively).
Specific Findings: One DAU recorded a maximum shielding layer current of approximately 27 A, and another recorded a maximum loop current of approximately 49 A, confirming the system's ability to capture high-risk conditions that would likely have been missed by manual checks.

Significance and Claims
The authors claim that this work lays a foundation for the wide application of monitoring and early warning for cable overheating in high-voltage substations. The key contributions are:

Feasibility of Online Monitoring: Demonstrating that online monitoring of specific electrical characteristics is a viable solution to the limitations of manual inspection in strong electromagnetic regions.
Composite Discrimination: The introduction of a five-criteria logic that effectively distinguishes between different types of faults (potential differences, ground over-currents, and loop formations) rather than relying on a single metric.
Intelligent Maintenance: The successful deployment of the system in 500kV substations verifies its reliability and feasibility, providing a basis for integrating cable monitoring into broader intelligent maintenance frameworks.

The paper concludes by noting that future work will involve generalizing the system's functions, incorporating fiber monitoring, and integrating with edge computing and 5G technologies to improve efficiency and interoperability with other subsystems, such as robot inspection systems.