Using BESS to Help Synchronous Generators Comply with RfG Fault Ride-Through Simulations: A Case Study on Enhancing Transient Stability in the Gas Turbines Located in Barsebäck

Abstract

With the growing integration of renewable energy sources into the power grid, new
challenges for system stability have emerged. To address this, the European Union
has introduced a regulation called Requirements for Generators (RfG). This regulation
sets specific performance standards, one of which is a minimum critical clearing time
related to faults. Some production facilities with low inertial constants struggle to
comply with this requirement.

This thesis investigated how and to what degree a Battery Energy Storage System
(BESS) connected to the generator terminal could enhance the transient stability of
the gas turbines in Barseb¨ack. To do this, the thesis looked into what system and
models should be used. Eventually, a single machine infinite bus (SMIB) system was
simulated in DIgSILENT PowerFactory in accordance with RfG. In this simulation, a
constant current configured Static Generator model was used to represent the BESS.
The BESS was controlled using two constant power factors, during and after the fault.
Each power factor defined the corresponding current reference. The most optimal
power factors during and post-fault were determined by simulation results, which
together provided the best overall control of the BESS.

The results showed that for batteries in the 5–95 MVA range, the critical clearing time
(CCT) increased up to 57 ms and indicated that the voltage profile could be improved
through the use of a BESS. However, if the battery produced high reactive powers
post-fault, it would result in voltage oscillations that have to be dealt with. Due to
model design decisions, the CCT results are conservative, and it might be possible to
increase the CCT even further by utilizing overload capabilities.

Overall, this thesis demonstrates that a BESS can moderately enhance transient stability
by minimizing acceleration and maximizing deceleration of the rotor.
And by this, help meet RfG requirements regarding fault-ride-through simulations.

Popular Abstract

In recent years, the electrical grid has seen a great increase in weather-dependent energy sources, such as wind and solar energy. These sources alone cannot match the electricity demand in a given
moment, which has resulted in new problems with stability and reliability in the electrical grid.

To tackle these challenges, the European Union has introduced new legislation for connecting generators to the grid, which is called Requirements for Generators (RfG). Some technical requirements in RfG have proven difficult for certain power plants to meet. Despite this, these power plants can be important in helping to maintain the stability of the grid. For example, by keeping electricity running in certain areas during a blackout or by helping balance the supply
and demand of electricity. One of these requirements is regarding the ability
to remain connected to the grid if an electrical fault occurs nearby.

To understand this, think of a runner on a treadmill. When the runner is keeping the same pace as
the treadmill, everything is fine. But if the treadmill suddenly stops for a period of time, the runner
might run off the treadmill. Likewise, during normal operation, a generator of
a power plant and the electrical grid are also running in synchronicity, but at a frequency of 50 Hz.
If a tree falls on a transmission line near a power plant, it can cause a three-phase short circuit. This
serious problem can make the generator lose its ability to send power to the grid, if it is not quickly
resolved, the generator can lose synchronicity with the grid, potentially causing great damage.
RfG demands that the amount of time the fault can last before the generator is
disconnected from the grid is at least 200 ms, this is called the critical clearing time.

This thesis investigates, by simulation on a simplified system, how and to what degree a battery can be
used to in order to extend the critical clearing time in synchronous generators to comply with RfG.
The results show that by charging the battery during the fault, and generating reactive power after
the fault, the generator can be optimally braked. It was showed that the critical clearing time can
be extended by almost 60 ms for the system investigated. Because of model decisions, these results
are considered conservative. In conclusion, this signals that batteries can be used to help synchronous
generators comply with RfG.

• author: Martinsson, Norris and Steiner, Hannes
• supervisor: Magnus Genrup
• organization: Department of Energy Sciences
• course: MVKM01 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Transient Stability, Battery Energy Storage System (BESS), Critical Clearing Time (CCT), Fault-Ride-Through, Requirements for Generators (RfG)
• report number: ISRN LUTMDN/TMPH-25/5620-SE
• ISSN: 0282-1990
• language: English
• id: 9194190
• date added to LUP: 2025-06-09 13:36:24
• date last changed: 2025-06-09 13:36:24