Precautions for 35kV Dual Busbar Operation

Operation of 35 kV double busbar systems requires adherence to strict busbar protection, switchgear handling, and safety standards to ensure reliability and personnel safety.Busbar Configuration and OperationA double busbar system allows flexibility in connecting circuits to either busbar, enabling maintenance or fault isolation without interrupting supply. Each feeder or circuit can be connected to Bus A, Bus B, or via a bus tie. Switching operations must follow a predefined sequence to prevent simultaneous connection of both busbars to a single feeder unless specifically designed for parallel operation .Switchgear HandlingGas-insulated switchgear (GIS) such as Siemens 8DA/B is recommended for 35 kV double busbar systems due to compact design, hermetic sealing, and long service life (≥40 years under normal conditions), .Operation is only allowed with the switchgear enclosure closed to prevent exposure to live parts .Vacuum or SF6 switches are used for load break operations, and visible break switches should be mechanically interlocked to prevent unsafe operation under load .Three-position disconnectors (Open/Closed/Earth) and earthing switches must comply with IEC 62271-102 endurance classes .Busbar ProtectionBusbar differential protection is essential to detect and clear faults quickly, minimizing outage impact .Low-impedance differential relays (e.g., B90) provide phase-segregated, centralized protection, handling multiple segments and CT saturation during external faults .Dynamic bus replica logic ensures secure operation during switching between busbars, avoiding blind spots and unnecessary outages .CT and relay coordination must be verified to prevent false tripping and ensure sensitivity to internal faults .Safety and ComplianceBusbars and connections must be copper or aluminum, corrosion-resistant, and mechanically capable of withstanding short-circuit forces .Maximum permissible temperature rise for bare conductors is 45°C, and rated current calculations must be verified .Circuit-breakers must be trip-free, withdrawable, and capable of isolation, with anti-pumping control where applicable .Segregation between high-voltage and low-voltage circuits must comply with IEC 62271-1 .Protective shutters, insulated handles, and clear marking of bus tie connections are mandatory for safe operation .Operational GuidelinesPre-Operation Checks: Verify busbar selection, breaker status, and relay readiness.Switching Sequence: Operate disconnectors and breakers in the correct order to avoid back-feeding or short circuits.Fault Response: Busbar differential relays should trip only for internal faults; external faults must not cause unnecessary outages .Maintenance Mode: Isolate the bus section using disconnectors and earthing switches before maintenance; ensure interlocks prevent live access .Record Keeping: Maintain logs of switching operations, relay settings, and maintenance activities for compliance and troubleshooting . Following these regulations ensures safe, reliable, and efficient operation of 35 kV double busbar systems while minimizing downtime and protecting personnel.