​Parallel operation​ involves connecting two or more independent AC power sources (e.g., generators, grids) to share electrical loads seamlessly. This process—synchronization—demands precise matching of voltage magnitude, frequency, and phase angles between systems before interconnection. Critical for grid expansion, backup power, and renewable integration, it enables redundant supply during failures.

A ring-closing operation involves closing a normally open switch within a closed-loop electrical network fed by a single power source. This creates parallel paths to redistribute loads without interruption, primarily for maintenance or network reconfiguration. Key prerequisites are voltage difference under 5%, phase angle alignment below 5 degrees, and pre-calculation of induced circulating currents to avoid equipment damage. Distinct from connecting independent systems, this procedure requires advanced monitoring but avoids synchronization complexity. Strict protocols using real-time sensors and simulations ensure safe execution, making it fundamental for resilient distribution networks like ring-main units (RMUs) in urban grids.

This article compares the ​synchronism check function​ in line protection devices and the ​synchronizing function​ in dedicated synchronizing equipment. The ​synchronism check function​ serves as a safety interlock for circuit breaker closing operations, while the ​synchronizing function​ enables precise generator synchronization and critical tie-line interconnections with active parameter regulation. Explore core principles, application scenarios, and technical distinctions between these critical power system components.

Transformer protection is critical for maintaining power system reliability. A well-designed ​transformer protection configuration​ must balance speed, selectivity, and sensitivity to prevent equipment damage and outages. ​Primary protection​ (e.g., differential and gas protection) acts instantly for internal faults, while ​backup protection​ (e.g., overcurrent, zero-sequence) provides redundancy for extended coverage. This guide covers key principles, settings, and coordination to optimize ​transformer protection​ schemes for different transformer types and voltage levels.