What occurs when transmission line conditions are below SIL?

When transmission line conditions are below the Surge Impedance Limit (SIL), the line tends to produce reactive power, measured in VAR (volt-amperes reactive). This occurs because, at lower load levels than the SIL, the capacitive nature of the transmission line becomes more prominent.

Transmission lines exhibit both inductive and capacitive characteristics. When the operating conditions are below the SIL, the capacitive effect dominates, leading to the production of VAR. This can be beneficial in some scenarios as it can help support voltage levels in the system, especially when there are reactive power deficiencies elsewhere.

Maintaining a balance between reactive power generation and consumption is essential for stable voltage control in the power grid. Thus, the ability of the line to produce VAR under these conditions is a key aspect of optimizing transmission efficiency and reliability.