DFIG Wind Turbine Modeling and Fault Protection

The objective of this project is to design a detection and protection scheme for faults on Type III and Type IV wind turbines. We plan to use SEL relays for both detection and protection and will run simulations using both RSCAD and model power system to help us achieve our goals.

Background
Currently in the power industry, "green" energy generation has a higher priority over traditional generation from fossil fuels such as coal or natural gas. One of the most common "green" production methods is to harness the wind. Today there are numerous wind farms with hundreds of wind turbine generators producing green energy. These wind farms are a huge monetary investment. Therefore protecting these wind turbines and keeping these green technologies in production under varying conditions has become a concern. The newer types of wind turbines (Type III and IV) can be modeled as a Doubly Fed Induction Generator (DFIG). Currently, the effects of faults on type III/IV wind turbines and the responses of the DFIGs to faults are not completely understood.

Nearly all new megawatt-scale wind power plants being developed employ either variable-speed doubly-fed asynchronous (Type III) or full converter-based (Type IV) wind turbine generators (WTGs). These two WTG types can produce energy over a wide range of wind speeds, allow for fast and independent control of active and reactive power, limit fault current, and comply with low-voltage ride-through (LVRT) requirements set forth by industry regulatory agencies.

For faults near the WTG terminals, the fault current can be several times the rated full-load current and is only limited by the system and the WTG impedances. The fault current characteristics for Type I and Type II WTGs are accurately represented in most commercially available short-circuit analysis tools used by protection engineers. Type III and Type IV WTGs, on the other hand, have much more complex fault current characteristics and are governed by the proprietary controls of the converters used in these generators.

For Type III and Type IV WTGs, the fault current contributions are usually limited to 1.1 to 1.2 times the rated full-load current, following any transients. This makes it very difficult to use a number of the widely available short-circuit analysis tools employed by protection engineers without causing erroneous breaker trips.

Design Goals
- Design a detection scheme using existing SEL relay technology.

- Design a fault protection scheme using existing SEL relay technology.

Deliverables
- Comparison and verification of RSCAD DFIG model.

- Detection scheme that quickly detects a single type of fault on the system.

- Working protection scheme that takes protects the DFIG following fault detection.

Specifications
Below is our refined specification sheet. After our design review, we are confident that we can meet these requirements.



RTDS and RSCAD
Before testing the effects of faults on the DFIG, we will first model the system in RSCAD software and run simulations using the RTDS system. This will give us a better idea of how the system will react to various types of faults before we do physical testing using the model power system. The simulations are carried out in a RSCAD Runtime file. An example of a runtime output can be seen in the figure to right.

Model Power System
Once we have a good idea of what to expect, we plan to connect the DFIG to the model power system and test faults in different locations throughout the system. This should verify or disprove the validity of our computer simulations.

SEL Relays
We are currently doing research on which relay will allow us to detect and protect faults most effectively. We are currently looking at two different relay options: the SEL 421 and the SEL 411L. Both have a variety of detection and protection technologies that will help us solve the problem. Once we determine which detection technology will work best for our project, we should be able to make a definitive choice of which relay we plan to use.

Document Archive
Agenda
 * Agenda 9-16-2014
 * Agenda 9-23-2014
 * Agenda 9-30-2014
 * Agenda 10-7-2014
 * Agenda 10-16-2014
 * Agenda 10-21-2014
 * Agenda 10-28-2014
 * Agenda 11-4-2014

Meeting Minutes
 * Meeting Minutes.9.23.14
 * Meeting Minutes.9.30.14
 * Meeting Minutes.10.7.14
 * Meeting Minutes.10.16.14
 * Meeting Minutes.10.21.14
 * Meeting Minutes.10.28.14
 * Meeting Minutes.11.4.14