Microcomputer-Based Protection Solution for Transformers
- Background and Core Challenges
Transformers are critical components of power systems, and their reliable operation is essential to grid security. Traditional transformer protection faces multiple technical challenges, including internal short-circuit current identification, inrush current discrimination, overload protection, and CT saturation issues. In particular, conventional percentage differential protection is susceptible to harmonic interference, which may lead to protection system maloperation or failure to operate, severely compromising system stability.
2. Solution Overview
This solution employs advanced microcomputer-based protection technology, integrating multiple techniques to achieve comprehensive transformer protection. It consists of three core modules: harmonic-restrained differential protection, adaptive CT saturation detection system, and optical fiber temperature monitoring integrated protection.
2.1 Harmonic-Restrained Differential Protection Technology
Utilizing second harmonic blocking technology, this method effectively distinguishes fault currents from inrush currents by real-time detection of second harmonic content in differential currents. Key features include:
- Adjustable harmonic content threshold (15%-20%) tailored to transformer characteristics.
- Fourier transform-based harmonic analysis ensuring detection accuracy.
- Dynamic blocking logic to prevent protection maloperation.
Application Results: In a 765kV ultra-high voltage transformer protection case, this technology reduced maloperation rates by 82%, significantly enhancing protection reliability.
2.2 Adaptive CT Saturation Detection System
Based on current waveform distortion analysis and pre-fault CT load monitoring, this system dynamically adjusts restraint coefficients:
- Monitors CT operating status in real time to identify saturation characteristics.
- Employs waveform distortion rate calculation for precise saturation judgment.
- Dynamically adjusts protection parameters to ensure reliability under saturation conditions.
Performance Metrics: In UHV applications, this method ensures reliable operation even under severe CT saturation, reducing operation time to within 12ms and significantly improving fault response speed.
2.3 Optical Fiber Temperature Monitoring Integrated Protection System
Distributed optical fiber sensors are embedded in critical transformer winding locations for real-time temperature monitoring:
- Direct measurement of winding hotspot temperatures with ±1°C accuracy.
- Multi-level temperature thresholds (e.g., 140°C trip setting).
- Integration with differential protection for accelerated tripping based on temperature.
- Automatic cooling system activation to prevent temperature rise.
Practical Results: Implementation at a converter station extended transformer service life by 30% and prevented insulation failures caused by overheating.
3. Technical Advantages
- Enhanced Reliability: Multiple protection mechanisms work together to mitigate single protection deficiencies.
- Rapid Response: High-speed data processing algorithms significantly reduce operation time.
- Adaptability: Automatic adjustment of protection parameters based on operating conditions.
- Preventive Protection: Temperature monitoring enables fault prediction, transforming passive protection into active prevention.
4. Application Cases
This solution has been successfully deployed in multiple UHV projects and 765kV ultra-high voltage substations. Operational data shows:
- Correct operation rate of 99.98%.
- Average fault identification time reduced by 40%.
- Maloperation incidents decreased by over 85%.
- Significant extension of equipment service life.
