On load tap changers (OLTC) are key actuators for voltage regulation; in meshed networks, tap steps reshape bus voltages and thereby steer reactive power flows within the grid and across tie lines. This occurs both through the transformation of effective admittances the off nominal tap ratio and through shifts of the low voltage side voltage levels. The thesis develops a mathematically rigorous description of these mechanisms to explain how discrete tap opera-tions affect voltages and VAR flows in meshed 110 kV grids.

Develop a mathematical framework that derives and validates how discrete OLTC steps influ-ence voltage magnitudes and reactive power flows in simple yet representative meshed 110 kV networks, including impacts on Q-exchanges at coupling points. The modeling explicitly considers voltage controlled PV buses and PQ buses with fixed P/Q specifications, yielding general sensitivity relations between tap ratios and VAR redistribution.

• • Im Rahmen der Arbeit werden die folgenden Teilaufgaben bearbeitet:
  • • Build generic, minimal meshed 110 kV topologies (e.g., 3–6 buses with two or more loops and minimum 2 coupling transformers) for analytical derivations and simula-tion based verification.
    • Analyse shifts of reactive power flows within loops and across tie lines caused by discrete OLTC operations, focusing on systematic VAR redistribution.
    • Derive how the OLTC tap ratio enters the power flow equations and their linearisa-tions, and analyse sensitivities of voltage magnitudes and Q flows.
    • Provide detailed transformer modeling, including off nominal tap effects on effec-tive series terms and Y bus entries, and discuss implications for VAR flows.