In China’s 3–35 kV power supply networks, most systems operate with an ungrounded neutral. Standards allow up to 2 hours of operation after a single-phase ground fault, which lowers operating costs and improves supply reliability. However, as system capacity increases and overhead lines are progressively replaced by cables, the system-to-ground capacitive current grows significantly.
When a single-phase ground fault occurs, a large capacitive current makes the fault arc difficult to extinguish, which can evolve into intermittent arc-grounding. The resulting arc-ground overvoltage and ferroresonance overvoltage pose serious risks to grid safety. Among them, single-phase arc-ground overvoltage is the most critical—non-fault phases can rise to 3–3.5× their normal phase voltage. Sustained exposure at this level can damage equipment insulation; cumulative degradation creates weak points that may lead to ground insulation breakdown, phase-to-phase short circuits, motor insulation failure, cable explosions, PT saturation and ferroresonance causing PT burnout, and arrester explosions.
Traditionally, networks install arc suppression coils at the neutral to compensate capacitive current and reduce the likelihood of arcing. Yet due to the inherent limitations of arc suppression coils—especially their difficulty in effectively compensating the current (notably the high-frequency components) that harms equipment—the mitigation is often insufficient.
Based on extensive study of such coils, we developed the RWXHG Intelligent Arc Suppression Device, designed to address long-duration overvoltage from arc-ground faults by providing smarter, more effective suppression and protection for ungrounded systems.
Application Scope
- Applicable to 3–35 kV medium-voltage power systems.
- Suitable for ungrounded neutral systems, resonant grounded systems (via arc suppression coil), and high-resistance grounded systems.
- Suitable for networks dominated by cable lines, mixed cable and overhead lines, or overhead line-dominated networks.
Basic Functions
- During normal operation, the device monitors PT signals and provides system alarm, trip, and lockout functions. It includes single-phase ground fault detection, transition fault point location, arc suppression, harmonic suppression, over-voltage alarm, and fault recording functions.
- Records parameters such as fault time, fault type, fault phase, line voltage, and neutral current, facilitating fault analysis.
- When a single-phase ground fault occurs, the device responds within 30 ms, determines fault type, and automatically selects arc suppression measures (arc suppression coil, grounding resistance, or other methods).
- Suppresses sustained arc grounding, reducing the risk of insulation breakdown, short circuits, or equipment explosions.
- Provides PT disconnection monitoring, preventing false actions due to PT failures.
- Features PTK smart switching technology, which suppresses sustained overvoltage caused by arc-ground faults, protecting equipment safety.
- Supports RS-485 communication and MODBUS protocol for data acquisition and remote monitoring.
Additional Functions
- Can be configured with an automatic neutral selection circuit.
- Works with RMRXL low-current grounding selection device to improve fault detection accuracy.
- Optional “elimination” mode: special technology discharges residual charge and prevents ferroresonance damage to PTs.
- User-customizable additional harmonic suppression modules are available.
Working Principle
- The controller continuously monitors secondary voltages of PTs in open-delta connection.
- When a single-phase ground fault occurs, changes in PT secondary voltages (Ua, Ub, Uc) are analyzed to determine the fault type.
- For metallic ground faults, the device quickly isolates the fault point, issues trip signals, and protects equipment and personnel.
- For intermittent arc-ground faults, the system detects fault characteristics and automatically operates the suppression unit within 30–40 ms, preventing overvoltage escalation.
- For resonant grounded systems, the device suppresses transient and steady-state overvoltages, ensuring safe system recovery.
Main Features
- Data recording: Records voltage, current, and fault parameters for analysis and troubleshooting.
- High-speed response: 30–40 ms action time, rapidly suppressing arc-ground faults.
- Automatic recovery: Capable of quickly extinguishing transient arcs and restoring system operation.
- Extended operation: Allows networks to run up to 2 hours with single-phase ground faults, reducing outage time and costs.
- Comprehensive protection: Not affected by system topology or running conditions.
- High reliability: Equipped with auxiliary PT monitoring to prevent malfunctions.
- Smart fault selection: Automatically identifies grounding characteristics, improving accuracy.
- Flexible design: Supports multiple working modes for different network configurations.
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