Ferroresonance severely impacts power quality and can also cause potential damage to electrical equipment when excessive voltages and currents are induced. Ferroresonance is rarely demonstrated provided that all three source phases are energized. However, when series-compensated lines are involved, a special type of ferroresonance can occur where the power system symmetry is remained. In Sweden, there is an increased demand to connect wind farms at the series-compensated sections. However, the transformers that link these wind farms increase the ferroresonance risk during certain operational conditions. The transmission system operator must be aware of these circumstances to ensure safe operation, but the complex nature of such nonlinear phenomena makes it difficult to understand and hard to predict. Therefore, this work offers a plausible understanding of ferroresonance that involves series-compensated lines. It also develops operational guidelines that ensure safe operation by raising awareness of the high-risk operational conditions. Moreover, real-world ferroresonance field measurements are shown from an operational experience that violated the operational guideline. The transformer model implementation is essential when dealing with ferroresonance simulations. Therefore, the transformer model implementation is discussed and the simulation model is validated based on the real-world operational experience.