In the early stages of a system restoration, why are high transmission voltage issues more prevalent than low voltage issues?

High transmission voltage issues tend to be more prevalent than low voltage issues during the early stages of a system restoration primarily due to excessive MVAR supply from the energization of transmission lines.

When restoring a power system, operators often bring lines back into service to re-establish transmission capabilities. Energizing these lines can introduce reactive power (measured in MVARs) into the network. If the supply of reactive power exceeds demand, it can lead to over-voltage conditions, particularly in the transmission system. This over-voltage can manifest as high voltage issues that can complicate system stability and integrity, necessitating careful management of reactive power to avoid such situations.

In contrast, low voltage issues typically arise from insufficient reactive power or load imbalances during periods of high demand, but during the initial restoration phase, the predominance of available generation and the change in system conditions from re-energizing lines makes the management of reactive power supply and its effects on voltage levels a more pressing concern.