The Protection of Transmission Lines Connected to DFIG-Based WTGs
Bibliographic record
Abstract
Recently, many countries have proposed various plans to address the issue of climate change, and increasing the capacity of renewables is one of the major common components of such plans. The uncertainty and variability of generation, introduced by renewable energy sources (RESs), pose significant protection challenges to the power systems. Although many studies have identified the challenges associated with the protection of power systems with RESs and have proposed various algorithms to address these challenges, only a few of them comprehensively discuss all the protection challenges within one system. To begin with, a single test system is developed and used to illustrate the protection challenges and to provide a review of the existing protection schemes, which have been proposed in the literature to tackle the protection challenges associated with power systems with RESs. \nAfter introducing the protection challenges associated with the integration of RESs in the power system, this thesis focuses on the protection of transmission lines connected to doubly-fed induction generator (DFIG)-based wind turbine generators (WTGs). DFIG-based WTGs, or namely Type III WTGs, which connect to the power systems via reduced-size converters, raise additional protection challenges such as the maloperation of distance relays due to the frequency deviation of the current measurement caused by the short-circuit characteristics of the DFIGs, and the impact of the fault resistance on the calculated impedance. The protection challenge associated with the frequency deviation caused by the short-circuit characteristics of DFIG is further discussed in detail, and a modified permissive underreaching transfer trip (PUTT) scheme is presented to address the challenge. With the addition of a frequency tracking element, the modified scheme correctly prevents the maloperation of the distance elements during external faults and enables the trip of the relay during internal faults. Besides, the protection challenges associated with conventional distance relays at the terminal of DFIG-based WTGs that are caused by the fault resistance and the frequency deviation associated with the short-circuit characteristics of the DFIG, are addressed and investigated. A modified distance protection scheme is presented to address these protection challenges by using an averaging filter to correct the current phasors and removing the error term caused by the fault resistance in the measured impedance. Pure-fault circuits are used to calculate the pure-impedance of the WTG and pure-fault sequence networks are used to estimate the fault current flowing through the fault resistance. Simulation results show that, for various fault scenarios with different fault resistances, the developed modified distance protection scheme is able to accurately estimate the positive-sequence impedance between the fault and relay location, with fast operations.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".