Online monitoring of circuit breakers

• core objective:: To realize continuous, real-time monitoring and assessment of the mechanical and electrical condition of HV/EHV circuit breakers, aiming to shift from the traditional "periodic maintenance (TBM)" mode to the more efficient and reliable "condition-based maintenance (CBM)" mode.

• Monitoring dimensions: The system uses a multi-dimensional sensor network to comprehensively collect key operating parameters of the circuit breaker, mainly including: the mechanical characteristics of the operating mechanism, the state of the insulating medium (e.g., SF6 gas), the electrical conductivity of the main circuit, and the integrity of the auxiliary and control circuits.

• technological base: Based on modern sensing technology, high-speed data acquisition, edge computing, and intelligent diagnostic algorithms, the massive amount of data collected is analyzed to extract the characteristic quantities of equipment health status and predict potential failure trends.

• system architecture:: A layered distributed structure is usually adopted, including a sensor layer at the front end, a local data acquisition and processing layer, a network layer responsible for data transmission, and an application analysis master layer at the center.

• applied value: Its core value lies in early warning of potential defects of circuit breakers, avoiding malignant accidents such as refusal to act and false activation, optimizing maintenance strategies, reducing whole-life operation and maintenance costs, and providing key technical support for the safe and stable operation of power grids.

I. Need for and objectives of online monitoring

High-voltage circuit breaker is the most critical control and protection equipment in the power system, and its operation status is directly related to the safety of the whole power grid. The traditional Time-Based Maintenance (TBM) model has many drawbacks: on the one hand, it may unnecessarily dismantle and overhaul equipment in good condition, resulting in a waste of resources and the introduction of new defects; on the other hand, it is impossible to detect sudden or gradual deterioration between two maintenance cycles, and the potential danger of accidents still exists.

The fundamental goal of an online circuit breaker monitoring system is to achieve theCondition-Based Maintenance (CBM), ie:

1. Real-time state awareness:: Continuously obtaining data on the operating conditions of circuit breakers to fully grasp their "health index".

2. Early warning of defects:: Alerts at the budding stage of faults through trend analysis and diagnosis of characteristic volume anomalies.

3. Avoiding unplanned outages: Effectively preventing large-scale grid outages caused by circuit breaker refusal or malfunction.

4. Optimize O&M decisions:: Provide an accurate data basis for the development of maintenance plans, moving from "maintenance on time" to "maintenance on demand".

II. Core monitoring objects and technical principles

A comprehensive circuit breaker online monitoring system typically covers the following key components:

1. Online monitoring of mechanical properties
The vast majority of circuit breaker failures (approximately 801 TP3T) stem from defects in the mechanical operating mechanism.

• Closing and opening coil current waveform analysisThe current waveforms of the opening and closing coils are captured by non-intrusive Hall current sensors. The waveform is the "fingerprint" of the whole process of the operating mechanism, which contains many key time points such as core action and auxiliary switch switching. By analyzing the characteristic point time (e.g. suction and closure time) and current amplitude of the waveform, the circuit breaker'sBreaking and closing time, three-phase non-simultaneity, and determine whether there are problems such as core jamming, insufficient energy storage, or poor contact in the auxiliary circuit.

• Energy storage motor condition monitoring:: Monitor the starting current, operating current and energy storage time of energy storage motors. Excessive energy storage time or abnormal currents are usually indicative of problems with the motor itself or the drive train, such as poor lubrication or jamming.

• Vibration and Travel Characterization Monitoring:: Vibration signals during operation are captured by installing acceleration sensors on mechanism boxes or operating levers. By analyzing the vibration signals in the time-frequency domain, mechanical defects such as loosening of components and detachment of fasteners can be identified. For more precise monitoring, non-contact sensors (e.g., laser, ultrasonic) can be used to directly measure the stroke-time (s-t) curve of the main contact to obtain theClosing and closing speed, overtravel, reboundand other core mechanical parameters.

2. On-line monitoring of electrical performance

• SF6 gas density and micro water monitoring:

  • Density monitoring: For SF6 circuit breakers, the insulation and arc extinguishing properties of the gas are directly dependent on itsintensityrather than pressure (pressure is strongly influenced by temperature). An in-line density relay continuously monitors the density of SF6 gas and indicates the presence of a leak if it falls below an alarm threshold.

  • Microwater monitoring: Trace amounts of water in oil can degrade SF6 insulation and produce corrosive decomposition products. The in-line micro water sensor continuously monitors the water content (ppm) in the gas and prevents internal insulation degradation.

• Main circuit conductivity monitoring:

  • Contact temperature monitoring: Real-time monitoring of contact temperature rise by installing wireless passive temperature sensors (SAW or RFID technology) at the movable and static contact connections of circuit breakers. Abnormal temperature rise is the most direct and reliable indicator of increasing contact resistance in the main circuit, which can effectively warn of serious defects such as contact burning and poor contact.

  • Vacuum monitoring: For vacuum circuit breakers, the principle of magnetron discharge or the principle of electric field induction can be utilized to assess on-line whether the vacuum of the vacuum interrupter chamber is qualified.

3. Auxiliary and control circuit monitoring
Monitoring the DC operating supply voltage, the health of the secondary circuits, and the operating status of the heaters ensures that circuit breakers are reliably actuated and controlled when needed.

III. System architecture

Circuit breaker online monitoring systems typically utilize a typical Internet of Things (IoT) four-layer architecture:

1. Perception layer (sensors): Consists of various types of sensors (current, temperature, vibration, density, displacement sensors, etc.) mounted on the circuit breaker body and the operating mechanism, and is responsible for the capture of raw physical signals.

2. Acquisition layer (in situ units): Consists of an intelligent data acquisition terminal (DAU) deployed near the circuit breaker. It is responsible for conditioning sensor signals, analog-to-digital conversion, data packaging, and performing some edge computing and local alarm functions.

3. Network layer (communications): Responsible for remote transmission of data from the acquisition unit to the master station. Usually adopts fiber optic Ethernet, power line carrier (PLC) or 4G/5G wireless communication.

4. Application layer (master software): Deployed on the server of the monitoring center, providing a graphical interface. The master station is responsible for centralized storage, display, trend analysis, intelligent diagnosis, alarm release and report management of all circuit breaker data in the whole station, and it is the decision-making center for realizing condition maintenance.

Frequently Asked Questions (FAQ)

1. What is the difference between on-line monitoring and traditional off-line handover/preventive testing?
The two are complementary. Offline test (such as circuit resistance test, voltage withstand test) provides a "static snapshot" of the circuit breaker at a specific point in time, with high data accuracy, which is the benchmark of equipment status. Online monitoring provides a "continuous video" of the equipment under real operating conditions, which can capture dynamic changes and progressive deterioration trends that cannot be detected offline. The goal of online monitoring is to guide and optimize the conduct of offline tests.

2. Can this system be retrofitted to older circuit breakers?
Completely. Modern online monitoring systems are designed with full consideration of theTraceability retrofit. Most of the sensors, especially the current, vibration and wireless temperature sensors, are installed in a non-invasive or minimally invasive way without major changes to the circuit breaker body, so they can be easily retrofitted to older circuit breakers in operation to enhance their intelligence.

3. How does the system accurately determine SF6 gas leakage?
The system is available online throughDensity RelayInstead of a pressure gauge to monitor. Because gas pressure varies with temperature in a closed container (Charlie's Law), and density is the mass of gas per unit volume, it is a truer reflection of the insulation and the margin of the interrupting medium. The master software can calculate the annual leakage rate by analyzing the long-term trend of the density data. Once the leakage rate exceeds the standard or the density value is below the set alarm threshold, the system will issue an alarm.

4. What is the difference between monitoring and diagnosis?
monitorsIt is the process of data acquisition, i.e., "seeing" and "hearing", which answers the question "What is happening to the device?" (e.g., the closing time is 10ms longer). ThediagnosticIt's the process of analyzing data and making decisions, or "thinking," that answers the questions "Why is this happening?" and "What is going to happen?" (e.g., a long closing time due to poor lubrication of the operating mechanism that, if left untreated, could lead to a failed closing within a month). A complete online monitoring system must include powerful intelligent diagnostics to truly enable predictive maintenance.