Why does the small current grounding line selection device effectively improve the identification of high-resistance ground faults?
Publish Time: 2025-09-23
In medium-voltage distribution networks, single-phase ground faults are the most common fault type, accounting for over 80%. High-resistance ground faults, due to their weak fault current, unclear electrical characteristics, and susceptibility to system noise, load fluctuations, and electromagnetic interference, have long been a technical challenge in relay protection. Traditional grounding line selection devices rely on zero-sequence current amplitude or phase comparison, often failing to operate effectively under high-resistance faults. This can lead to long-lasting faults that can potentially develop into phase-to-phase short circuits and even cause fires or personal injuries. By utilizing a comprehensive algorithm combining steady-state and transient data, fuzzy information fusion technology, and a highly reliable, fully embedded architecture, the small current grounding line selection device significantly improves the identification of high-resistance ground faults, making it a key device for ensuring the safe operation of distribution networks.
1. Difficulties in Identifying High-resistance Ground Faults
High-resistance ground faults are typically caused by conductors striking trees, insulator flashover, or cable sheath damage. The large transition resistance in the fault circuit results in extremely low fault currents, which may be below the normal load current fluctuation range. Furthermore, fault currents contain high harmonic content and exhibit strong randomness. Traditional line selection methods based on steady-state zero-sequence current amplitude or direction struggle to accurately capture effective characteristics, easily leading to false or missed selections. Line selection accuracy is particularly degraded in complex distribution networks with multiple feeders, long lines, and a mix of cables and overhead lines.
2. Combining Steady-State and Transient Variables: Comprehensively Capturing Fault Characteristics
Modern small current grounding line selection devices overcome the limitations of a single criterion by employing a comprehensive line selection algorithm that combines steady-state and transient variables.
Steady-state variables include the zero-sequence current fundamental amplitude, phase, and harmonic components that persist after a fault, making them suitable for preliminary assessment of persistent ground faults.
Transient variables refer to the high-frequency transient zero-sequence current and voltage generated at the moment of fault occurrence. Although their amplitude is short-lived, they possess distinct characteristics and are unaffected by load current, making them highly recognizable, especially in high-resistance grounding situations.
By simultaneously analyzing steady-state and transient signals, the device can capture subtle but critical transient characteristics immediately after a fault occurs, compensating for the weakness of steady-state signals and significantly improving sensitivity to high-resistance faults.
3. Multi-Method Fusion and Fuzzy Theory: Improving Decision Reliability
Single line selection methods each have limitations: the zero-sequence current amplitude method is susceptible to CT imbalance, the directional method can reverse direction in resonant grounding systems, and the energy method is sensitive to noise. To address this, advanced line selection devices integrate multiple algorithms (such as the fifth harmonic method, the first half-wave method, wavelet transform, and correlation analysis) and perform fuzzy information fusion on the outputs of each method.
Fuzzy theory effectively handles uncertainty, ambiguity, and incomplete information. The device fuzzifies the "fault probability" of each line using each method, then weights and fuses them using fuzzy inference rules. Ultimately, a comprehensive fault measurement coefficient is calculated for each line. This coefficient quantifies the probability of a ground fault on each line as a value between 0 and 1. The system automatically ranks and outputs the most reliable lines, significantly improving line selection accuracy under complex operating conditions.
4. Fully embedded structure ensures high reliability and anti-interference capabilities.
The device utilizes a highly reliable, industrial-grade, fully embedded structure with high hardware integration and strong electromagnetic interference (EMI) resistance, enabling stable operation in the strong electric field and high-noise environments of substations. High-precision synchronous sampling technology ensures time consistency of data across all lines, providing a foundation for transient quantity analysis. Furthermore, the device seamlessly integrates with backend monitoring systems, enabling real-time upload of fault information and remote diagnosis.
The small current grounding line selection device fundamentally solves the difficulty of identifying high-resistance grounding faults by integrating steady-state and transient information, employing a fuzzy decision-making mechanism, and outputting a fault confidence factor. Leveraging a highly reliable hardware platform, it not only improves line selection accuracy but also provides operators with a scientific and intuitive decision-making basis, effectively preventing fault escalation and improving power supply reliability.
