In modern power systems, the reliability of distribution and transmission switchgear is paramount. As grids evolve toward higher efficiency, digitalization, and resilience, condition monitoring has become a cornerstone of asset management.
Sensors, when properly integrated, enable non-intrusive diagnostics, ensuring that equipment operates safely and efficiently while minimizing downtime.
This content explores the landscape of Non-Intrusive Sensor Technologies for HV and MV Switchgear, highlighting their applications, advantages, and limitations.
The Role of Sensors in Switchgear Monitoring:
Switchgear typically spends most of its operational life in a steady state. This makes continuous diagnostics challenging, as meaningful data often emerges only during switching events or through long-term aging indicators. Sensors bridge this gap by capturing critical parameters during rare but decisive operations, while also monitoring gradual changes such as temperature rise or gas density variations.
Reliability is non-negotiable: sensors must not become the weak link in the monitoring chain. Their accuracy, robustness, and integration into control systems determine the effectiveness of predictive maintenance strategies. With the rise of IoT and digital interfaces, sensors are increasingly capable of multiplexing measurements, offering engineers richer datasets for analysis.
Sensor Technologies in High-Voltage Switchgear:
Ablation Sensors
Contact ablation is monitored by applying high-frequency signals to closed contacts and analyzing impedance changes. Deviations from standard values indicate degradation, providing early warnings of contact wear.
Gas Density Monitoring
Gas density sensors are critical in SF₆-insulated switchgear. Traditional mechanical density meters are being replaced by electronic sensors with digital interfaces (RS485, CAN). These advanced sensors compute density using pressure and temperature inputs, detect liquefaction risks, and even calculate annual gas losses with accuracies below 0.4% FS.
Pressure and Humidity Sensors
- Piezo-resistive sensors measure resistance changes under mechanical force.
- Capacitive sensors detect variations in electrode spacing.
- Gas humidity sensors (dew point) use cooled mirrors and optical detection to monitor condensation, though robustness against SF₆ decomposition products is essential.
Dynamic Pressure Sensors
Piezoelectric sensors capture AC signals across wide bandwidths, ideal for transient phenomena such as internal arcs or restrike detection.
Optical Position Sensors
Applied to breaker drive shafts, optical slot sensors outperform mechanical auxiliary contacts, offering higher accuracy and consistency.
Rogowski Coils
These coreless current sensors measure di/dt, making them suitable for fast transients, harmonics, and arc localization. Their wide bandwidth (up to several MHz) enables precise monitoring of circuit breaker arcing times.
These technologies are shown in Table 1:
Table 1: Sensor Technologies in HV Switchgear
Sensor Technologies in Medium-Voltage Switchgear:
Infrared (IR) Temperature Sensors
Thermopile-based IR sensors detect radiation by measuring linear changes in resistance. Their accuracy and speed justify their cost, but proper integration is crucial to avoid misleading readings due to environmental influences.
Fiber-Guided IR Sensors
Optical fibers transmit IR radiation to detectors, useful where line-of-sight is obstructed (e.g., inside spouts). Despite high costs and poor sensitivity below 40°C, they remain valuable for specialized applications.
SAW (Surface Acoustic Wave) Sensors
Passive reflective antennas detect frequency shifts caused by temperature changes. These sensors are effective in generator circuit breakers and HV disconnectors, with ranges of a few meters.
RFID Temperature Sensors
Wireless, low-cost RFID sensors provide simple temperature monitoring. While attractive for cost-sensitive applications, their long-term reliability requires validation.
Contact Force Sensors
Strain gauges measure mechanical forces in breaker kinematics, enabling detection of failure modes.
Rotary Encoders
Travel curves derived from rotary sensors reveal parameters such as contact speed, stroke, and bounce. Technologies include:
- Magnetic (RVDT): robust but sensitive to extreme magnetic fields.
- Optical encoders: immune to magnetic interference but mechanically less robust.
- Resistive sensors: rarely used due to wear concerns.
These technologies are shown in Table 2:
Table 2: Sensor Technologies in MV Switchgear
Common Sensors Across HV and MV Switchgear:
Certain sensor technologies are applied universally:
- Vibration sensors: inexpensive accelerometers, similar to those in smartphones, integrated into switchgear for mechanical diagnostics.
- Partial Discharge (PD) sensors: detect HF signals, acoustic waves, or UHF activity. Interpretation remains complex, as environmental and material factors influence results.
- Acceleration sensors: widely available and cost-effective, but require careful signal interpretation.
- Auxiliary current sensors (Hall effect): measure DC and AC currents in actuation coils. While contactless and versatile, they are sensitive to external magnetic fields and residual flux.
Economic and Technical Considerations:
High-voltage applications demand superior isolation and performance, driving up sensor costs. In MV systems, simpler and cheaper sensors can often suffice. However, comprehensive monitoring requires multiple sensors, each tailored to specific parameters. While IoT integration promises cost reductions and enhanced functionality, isolation and performance requirements in HV environments limit the extent to which these benefits can be realized.
Conclusion:
The evolution of sensor technologies for HV and MV switchgear reflects the broader transformation of power systems toward digitalization and predictive maintenance. While HV applications demand high-performance, isolated solutions, MV systems benefit from cost-effective and simpler sensors. Engineers and managers must balance technical requirements with economic constraints to ensure that monitoring systems deliver actionable insights without compromising reliability. As IoT integration advances, the future of switchgear monitoring lies in smarter, more connected sensors—capable of turning raw data into predictive intelligence.
