Power Increase and Stability Analysis In a Nuclear Generation System

This master's thesis evaluates whether the nuclear power generation system Forsmark 3 remains compliant with the body of laws governing alternating current (AC) generators in the interconnected power grid following a potential power increase. Increasing the net thermal power output of a nuclear plant reduces the margin for compliance, making it essential to assess whether the stipulated requirements are fulfilled before any such increase is decided on. There is no decision regarding a possible power increase at Forsmark 3 today. Therefore, the purpose of this report is to serve as an analysis for the potentiality of such initiatives. A key focus is on the subset of the governing regulations addressing the system behaviour before and after a zero-impedance three-phase fault near the generator, afssessing ‘transient stability’ or ‘fault-ride-through capability’. These requirements are presently defined by the European Commission under the "Requirements for Generators" (RfG) and implemented in Sweden by The Energy Markets Inspectorate (Ei) under the regulation EiFS 2018:2. Previously, Svenska kraftnät (Svk) developed and enforced these standards which were named SvKFS 2005:2. Forsmark 3 predates the RfG and typically follows the older Svk regulations. Although, the proposed power increase may involve technical changes that could necessitate compliance with RfG standards. Therefore, compliance has been evaluated against both regulatory frameworks. The analysis is conducted on Forsmark 3 using simulations in the simulation software PowerFactory (PF), developed by DigSILENT GmbH. The model integrates a detailed electrical- physical representation of Forsmark 3 with a national grid equivalent model exterior to Forsmark 3 provided by Svk; originally in PSS/E format, and converted to PF. The Forsmark model has been developed over many years by in-house power system specialists. Results show that Forsmark 3 meets the requirements of both SvKFS 2005:2 and EiFS 2018:2. The discussion highlights the significant influence of grid conditions and generator inertia on compliance with the regulations. Therefore, a recommendation is that further investigations are made with consideration of grid configuration methods and strategies to positively contribute to the fault-ride-through capability of the generator at Forsmark 3. As well as an upgrade to a turbine with more rotational energy for future technical modifications.