Series reactor-type high-impedance transformers, designed with built-in series reactors connected in series with low-voltage windings, serve as core equipment in high-voltage power grids to limit short-circuit currents and reduce local overheating risks. The operating status of the series reactor directly affects the overall health of the equipment and the safety of the power grid. Based on professional research results in the field of power equipment evaluation, this article focuses on the characteristics related to series reactors and concisely explains the operating status evaluation method for such equipment from the perspectives of evaluation system, model construction, and effect verification, providing accurate references for power operation and maintenance.
I. Series Reactor: The Core of Evaluation for Series Reactor-Type High-Impedance Transformers
Series reactor-type high-impedance transformers realize impedance adjustment by connecting series reactors (independent inductive windings) in series with low-voltage windings, combined with a magnetic circuit of steel structural plates and fixed by high-strength tension screws. However, the integrated characteristics of series reactors make them the key to evaluation:
1. Series Reactor Failures Affect Overall Equipment Performance
The windings of series reactors are made of transposed conductors and epoxy glass cloth plates, which have strong short-circuit resistance. However, in the process of forming a magnetic circuit in synergy with the transformer windings, if the series reactor has problems such as excessive winding resistance deviation or insulation dampness, it will directly lead to uneven current distribution, and even cause short circuits in low-voltage leads, failing the series reactor's current regulation function. In a 500kV substation case, abnormal dielectric loss of the series reactor led to a 12-hour equipment outage, resulting in losses exceeding 3 million yuan 4-35.
2. Traditional Methods Cannot Cover Series Reactor-Related Indicators
Existing evaluation methods (such as acoustic vibration signal diagnosis and pattern recognition) either require complex model training or cannot evaluate fault levels, making it difficult to cover electrical and oil-gas indicators related to series reactors. For example, the acoustic vibration diagnosis method proposed by industry researchers cannot quantify the impact of acetylene content in the oil around the series reactor; the pattern recognition method used in some projects also fails to include the excessive grounding current of the series reactor core in level judgment 4-29, 4-30.
3. Power Grid Safety Requires Accurate Evaluation of Series Reactor Status
Such equipment is mostly used in 110kV~500kV backbone power grids, and abnormalities in series reactors may trigger cascading failures. Data from a power company shows that before using the evaluation model, the average annual failure rate of equipment was 3.2 times; after introducing the model, the early warning accuracy rate for series reactor-related failures reached 100%, and the average annual failure rate dropped to less than 0.5 times 4-90.
II. Evaluation System Including Series Reactor Indicators: Four Dimensions Focusing on Key Parameters
Centering on the synergistic characteristics of series reactors and transformers, the evaluation system starts from four categories of first-level indicators, with core second-level indicators directly related to the health of series reactors:
1. Electrical Indicators: Controlling Current Stability of Series Reactors
- Winding DC Resistance: Three-phase deviation ≤ 2% (excessive deviation will occur if the connection between the series reactor and windings is poor);
- Core Grounding Current: ≤ 100mA (the magnetic circuit of the series reactor is associated with the core, and excessive current will cause overheating);
- Winding Absorption Ratio: ≥ 1.3 (preventing insulation dampness of the series reactor windings) 4-41.
2. Oil-Gas Indicators: Monitoring Insulation Status of Series Reactors
- Acetylene Content: ≤ 5 μL/L (overheating of the series reactor windings will increase acetylene content);
- Hydrogen Content: ≤ 150 μL/L (insulation damage of the series reactor will generate hydrogen);
- Total Hydrocarbon Content: ≤ 150 μL/L (reflecting the insulation aging degree of the series reactor) 4-41.
3. Oil-Chemical and Physical Indicators: Ensuring the Operating Environment of Series Reactors
- Oil-Chemical Indicators: Moisture content ≤ 35 mg/L, breakdown voltage ≥ 40 kV (preventing insulation breakdown of the series reactor);
- Physical Indicators: Oil temperature ≤ 85℃, noise ≤ 90 dB (key indicators for heat generation and magnetostriction of the series reactor) 4-41.
III. Evaluation Model Prioritizing Series Reactor Weight: Scientific Weighting and Fuzzy Judgment
With series reactor indicators as the core, the model achieves accurate evaluation through three steps:
1. Indicator Standardization: Unifying the Parameter Scale of Series Reactors
The deviation standardization method is used to convert series reactor-related indicators (such as absorption ratio and acetylene content) into the range of 0~1 to eliminate dimensional differences. For example, the absorption ratio of the series reactor winding gets 1 point when it is ≥ 1.3, and points are deducted proportionally when it is < 1.3 4-42.
2. Combined Weighting: Highlighting the Importance of Series Reactor Indicators
- Objective Weighting (Entropy Weight Method): For indicators with significant impacts on series reactors (such as winding resistance and acetylene content), high weights are assigned based on data fluctuations;
- Subjective Weighting (G1 Method): Combined with expert experience, the weights of indicators related to the magnetic circuit and insulation of the series reactor are increased;
- Objective Correction of Subjectivity: Ensuring that the weight ratio of series reactor-related indicators exceeds 40% 4-47, 4-48.
3. Fuzzy Comprehensive Evaluation: Classifying into Five Levels
Combined with the membership function and score (full score 100), levels are classified according to the series reactor status: Level 1 (85~100 points, no abnormality in the series reactor), Level 2 (65~85 points, slightly excessive indicators of the series reactor), Level 3 (45~65 points, insulation dampness of the series reactor), Level 4 (25~45 points, overheating of the series reactor winding), Level 5 (0~25 points, failure of the series reactor) 4-88.
IV. Model Effect: 100% Accuracy in Series Reactor-Related Evaluation
Tests were conducted on 4 units of equipment in 110kV~500kV substations with 200 pieces of data:
- Single Equipment Evaluation: A 110kV equipment scored 90 points (Level 1) due to normal series reactor parameters, and a 330kV equipment scored 30 points (Level 4) due to insulation breakdown of the series reactor, which were consistent with the actual situation 4-94;
- Batch Sample Evaluation: The number of samples at each level in the 200 pieces of data completely matched the actual situation, with no missed judgments on series reactor-related failures 4-93.
V. Conclusion: Evaluation Value with Series Reactors as the Core
By focusing on series reactor indicators, this model realizes accurate evaluation of the operating status of series reactor-type high-impedance transformers, identifying series reactor-related failures with 100% accuracy and providing clear directions for operation and maintenance. In the future, it is necessary to further apply the model to actual working conditions and optimize the real-time monitoring capability of series reactors to ensure power grid safety.
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