Q7Power System - I

A synchronous grid is an interconnected AC power system in which every generator, regardless of its physical location, rotates in exact synchronism (same electrical frequency and locked relative phase angle) with every other generator on the network, connected via direct AC transmission ties; this allows completely free, instantaneous exchange of both active and reactive power throughout the interconnected network, provides mutual inertial (kinetic energy) support during disturbances (helping to arrest frequency deviations), but also means a severe disturbance (major generator/line loss) in one part of the synchronous grid can potentially propagate and affect stability throughout the entire interconnection.

An asynchronous grid arrangement refers to two or more AC systems that are electrically interconnected only through a non-synchronous link — most commonly an HVDC tie (which fully decouples frequency and phase between the two sides) or, historically, back-to-back frequency converters — such that each side can operate at its own independent frequency and phase reference, without needing to remain in synchronism with the other side. This arrangement is used to interconnect grids of different nominal frequency (e.g., 50 Hz and 60 Hz systems), or to interconnect grids of the same nominal frequency that are otherwise kept deliberately decoupled for stability/reliability reasons (preventing a disturbance in one grid from directly destabilizing the other), while still allowing controlled, adjustable power exchange between them via the converter station's control system. India, for example, historically operated its regional grids asynchronously (via HVDC back-to-back stations) before ultimately achieving full synchronous interconnection of almost the entire national grid.