The widespread application of capacitor banks in transmission substations has increased the risk of harmonic resonance under different network operating conditions. Accurate identification of resonance-prone operating states is therefore essential for maintaining power quality and system reliability. This paper presents a practical methodology for harmonic resonance assessment based on frequency sweep analysis and the Resonance Risk Index (RRI). First, the resonance frequencies of different capacitor-bank operating states are determined using a detailed DIgSILENT PowerFactory model of a real transmission network. The RRI is then calculated by considering the resonance frequency, harmonic distortion level, and network short-circuit capacity. Unlike conventional approaches that evaluate resonance risk only under normal operating conditions, the proposed method further investigates the influence of transmission-line outage, transformer outage, and 20-kV bus-coupler opening on resonance risk. The results demonstrate that network topology significantly affects both the resonance frequency and the corresponding RRI. While some switching operations increase resonance risk, others reduce it by shifting the resonance frequency away from dominant harmonic orders. These findings indicate that resonance risk is a dynamic characteristic rather than a fixed network property and highlight the importance of considering practical operating conditions in harmonic resonance assessment. The proposed approach provides transmission system operators with a practical decision-support tool for identifying high-risk operating states and selecting appropriate operational or technical mitigation measures.