Product Overview

The ABB 424K1105​ is a Circuit Shield™ Series 25S (ANSI Device Number 25S) Synchronizing Check—or Synchro-Check—relay manufactured by ABB for use in power generation and substation secondary systems. Its primary function is to supervise the voltage magnitude, frequency difference, and phase angle displacement between two AC sources (typically the generator side vs. grid side, or bus A vs. bus B across a tie breaker) and issue a permissive output only when all three parameters are within pre-set tolerance windows—thereby preventing dangerous out-of-synchronism breaker closure that could damage generators, transformers, or cause system disturbances.Installed in the closing circuit of a circuit breaker’s 52a/52b control scheme, the ABB 424K1105​ receives line-to-line voltage from both sides via potential transformers (typically 100 V or 110 V secondary) and continuously compares the two waveforms. When the magnitude difference (ΔV), slip frequency (Δf), and phase displacement (Δφ) all fall inside the adjustable setpoints, the relay’s output contact closes, allowing the auto-synchronizer or manual close pushbutton to complete the breaker coil circuit. If any parameter drifts outside limits—for example during a fast frequency drift or large phase-angle mismatch—the contact opens immediately, blocking the close command. The ABB 424K1105​ is an electromechanical / solid-state hybrid design typical of the Circuit Shield 25S family, offering front-panel potentiometers for window adjustment, a selectable time delay (0–10 seconds) to mask transient conditions, and clear LED status lamps for voltage presence, sync window satisfaction, and relay pick-up/drop-off.Designed for panel or 35 mm DIN-rail mounting inside switchgear cubicles, control cabinets, or generator control panels (GCP), the ABB 424K1105​ operates from a 110 V AC 50/60 Hz control supply and provides two Form C (changeover) contacts—typically configured as one NO (permissive close) and one NC or auxiliary alarm—rated at 10 A for direct interruption of the breaker close-coil circuit or auxiliary annunciation. It remains widely specified as a mandatory “hard-wired sanity check” even in modern digital protection schemes where an independent, diverse synchronism-check device is required per NERC PRC-002 or utility-specific protection philosophies. The ABB 424K1105​ thus serves as both a primary synchronism guard in legacy retrofits and a fail-safe secondary check behind microprocessor-based synchronoscopes in new EHV/HV substations and combined-cycle power plants.

Technical Specifications

Main Features and Advantages

Three-parameter synchronism supervision:The ABB 424K1105​ does not merely check phase angle—it simultaneously evaluates voltage magnitude difference (to prevent closing across a dead or severely depressed bus), slip frequency (to ensure the two sources are not drifting apart too quickly for safe closure), and phase displacement (to keep the angular difference below the mechanical/transient-stability limit of the connected equipment). All three windows must be satisfied concurrently for the permissive contact to close, providing a far more rigorous safeguard than simple phase-angle-only checks found on basic synchroscopes.Adjustable deadbands with front-panel access:Both the voltage-difference window (typically 0–20 % of PT voltage), slip-frequency limit (0.02–0.5 Hz), and phase-angle tolerance (±5° to ±30°) are set via clearly labeled front-panel potentiometers on the ABB 424K1105. This allows the protection engineer to tailor the relay to the specific inertia and transient characteristics of the generation unit or network section—tightening the window for large turbo-generators (where asymmetrical closing can impose severe shaft torque) and widening it slightly for utility bus-tie applications where short-term transients are acceptable.Defeatable time-delay element for nuisance-trip prevention:An adjustable 0–10 second timer on the ABB 424K1105​ can be inserted after the sync window is met, requiring the condition to persist for the set duration before the contact picks up (or, inversely, imposing a brief hold-after-window-lost before drop-out). This masks momentary crossings caused by system switching transients or minor PT-induced harmonics, reducing spurious blocking of legitimate close commands during automatic synchronizing sequences driven by a separate synchronizer (e.g., ABB REG-S or equivalent).Independent hard-wired safety layer:Even in fully digital control rooms equipped with numerical protection relays (IEDs) that include built-in 25S functions, many utilities mandate a separate, diverse-technology synchronism-check device such as the ABB 424K1105​ in series with the breaker close circuit. Because the ABB 424K1105​ is an autonomous, non-programmable relay with visible setpoint knobs and LED confirmation, it provides defense-in-depth against software bugs, configuration errors, or IED firmware corruption in the primary synchronizer—a key compliance point in NERC-regulated bulk-power systems.