I. Paghimo sa Pagkasira: Electrodinamiko nga Epekto (Nagpapatuman sa GB/T 1094.5 / IEC 60076-5)
Ang direktang dahon sa pagkabagol sa katapusan sa winding sa mataas na kuryente mao ang instantaneong electrodinamikong epekto gikan sa short-circuit current. Kon magkakadaghan ang single-phase grounding fault sa sistema (tulad niining lightning overvoltage, insulation breakdown, ug uban pa), ang grounding transformer, isip ang ruta sa fault current, gigub-an og high-amplitude ug steep-rise-rate nga short-circuit currents. Sumala sa Ampère's force law, ang mga winding conductors gigub-an og radial (inward compression) ug axial (tensile/compressive) electrodinamikong puwersa sa matigas na magnetic field. Kon ang electrodinamikong puwersa adunay higayon nga mosobra sa mechanical strength limit sa winding structure (conductors, spacers, press plates, binding systems), mahimong makaresulto kini sa irreversible deformation, displacement, o distortion sa mga windings, sa dili pa makita isip winding end collapse—usa ka typical failure mode sa transformer-type equipment sa panahon sa short-circuit faults.
II. Associated Fault Triggers: Resonant Overvoltage ug Energization with Residual Faults (Nagpapatuman sa Overvoltage Protection Standards sama sa DL/T 620 / IEC 60099)
System Resonant Overvoltage (Ferroresonance / Linear Resonance)
Ang sayop nga pagkatugma sa mga parameter sa sistema (line capacitance, PT inductance, arc suppression coil inductance, ug uban pa) mahimong magtrigger sa ferroresonance o linear resonance, naghimo og persistent overvoltage. Kini nga overvoltage giingon-ingo nagpuyo sa insulation weak points (aged insulators, arresters, bushings, ug uban pa), nahimo og intermittent arc grounding o repeated breakdowns, naghatag og high-frequency impact currents sa grounding transformer. Wala ra kini nagproducce og electrodinamikong epekto apan usab nagpasabot sa pag-accelerate sa thermal ug electrical aging sa winding insulation (inter-turn, inter-layer, ug main insulation), nagpakit-an sa dielectric strength ug mechanical strength, mas prone sa pagkabagol sa sunod nga impacts o normal operation.
Energization with Persistent Faults after Lightning Strike
Pagkahuman sa lightning strike nga nagresulto og permanenteng grounding fault sa line, kon ang fault point wala gituklas (e.g., ang circuit breaker wala mogana o fault indication unclear), ang maintenance personnel kasalaan sa pagrestore sa power (energization with faults), nagpuyo sa grounding transformer sa continuous power-frequency fault current (far exceeding the design limit). Ang sustained overcurrent nag-trigger sa I²Rt Joule heating effect, nagdala sa winding temperature nga molihok sa taas ngadto sa insulation tolerance limit (e.g., 105°C for Class A), rapid leading to thermal aging, carbonization, ug loss of insulation performance, finally resulting in winding short-circuit and burnout (thermal collapse). Kini nga kondisyon nagdala og devastating damage sa equipment.
III. Optimization Scheme: Enhancing Equipment Tolerance and Perfecting Protection Strategies (Integrating Equipment Selection, Relay Protection, and Condition Monitoring Standards)
Improving Equipment Body Short-Circuit Resistance (Complying with GB/T 1094.5 / IEC 60076-5)
Selection Requirements: Prioritize high short-circuit resistance models verified by strict short-circuit withstand tests (e.g., IEC 60076-5) for subsequent purchases, focusing on winding structure design (reinforced press plates, axial clamping systems, radial support structures, transposition conductor processes), material strength, and manufacturing processes.
Optional Series Current-Limiting Reactor: Install a current-limiting reactor in the neutral circuit of the grounding transformer to effectively suppress the amplitude and rise rate of fault currents, reducing electrodynamic impacts on windings. The impact on the system grounding mode and relay protection must be verified simultaneously.
Optimizing Relay Protection Configuration and Setting (Complying with Relay Protection Standards DL/T 584 / DL/T 559)
Setting Principle: The overcurrent protection settings (zero-sequence overcurrent, inverse-time overcurrent) of the grounding transformer must be strictly lower than the equipment's thermal and dynamic stability limits (calculated per GB/T 1094.5).
Gradation Coordination: The protection time delay of the grounding transformer (e.g., 100A/10s) must reliably coordinate with the upstream line protection (outgoing circuit breaker). Ensure that the line protection (zero-sequence Stage I: 0.2s, Stage II: 0.7s) can quickly clear grounding faults on the line, preventing the grounding transformer from enduring unnecessary stress. The grounding transformer protection, as a close backup, should have an operation time delay greater than the longest time delay of the line protection (including the gradation Δt).
Optimization of Grounding Transformer Body Protection Settings:
Strengthening Fault Fast-Clearing Capability (Complying with DL/T 584 / DL/T 559)
Directional Zero-Sequence Protection Configuration: Deploy and reliably activate directional zero-sequence current protection (Stage I/II) in line protection. The direction element accurately distinguishes between faulted and non-faulted lines, ensuring that the faulted line circuit breaker trips reliably within ≤0.2s during single-phase grounding faults, completely isolating the fault source—this is the core protection measure to prevent grounding transformer damage.
Deploying Intelligent On-Line Monitoring and Early Warning Systems (Complying with Condition Monitoring Standard DL/T 1709.1)
Real-Time Winding Hot Spot Temperature Monitoring: Install optical fiber or platinum resistance temperature sensors at key positions of the high-voltage winding ends to achieve real-time monitoring with ±1~2℃ accuracy. Set multi-level alarms (warning/alert) and tripping thresholds (calculated based on insulation class thermal models), automatically triggering protection actions when limits are exceeded to prevent thermal collapse.
Neutral Point Electrical Parameter Monitoring and Asymmetry Alarm: Continuously monitor neutral point current and system displacement voltage (zero-sequence voltage), and configure asymmetry over-limit alarm functions. When persistent/frequent abnormal neutral point electrical parameters are detected (indicating intermittent grounding, resonance, or insulation degradation), issue immediate warnings for early fault intervention.
Optimization Conclusions and Implementation Recommendations
