Description

The 424K1105​ is a Type 25V Synchronism Check Relay within ABB’s Circuit Shield series, manufactured by ABB. It is an electromechanical/solid-state hybrid protection relay designed for generator paralleling and bus-section automatic transfer applications, where closing a breaker between two unsynchronized sources can destroy generator windings or trip the utility. The “K” in the 424K prefix denotes the 25V type (which adds dead-bus and dead-line detection versus the base 25S), and “1105” denotes the 110V AC (50/60 Hz) coil and 10A contact rating. The 424K1105​ monitors two PT (potential transformer) secondary_inputs—typically 100/110V from each side of a tie or generator breaker—and compares voltage magnitude, frequency, and phase angle. Only when all three fall within configurable windows does the relay close its output contacts to “allow” the breaker close circuit. It mounts on standard 35 mm DIN rail and remains a high-demand MRO spare for power-gen, substations, and industrial 10/35 kV switchgear that haven’t migrated to fully electronic sync-check (e.g., ABB CM-SFS or protection relays).

Application Scenarios

At a 12 MW combined-heat-and-power plant feeding a regional paper mill, the original 1998 sync scheme for the three 4 MW Caterpillar gensets used 424K1105​ relays in each genset’s 13.8 kV secondary switchgear cubicle—one 424K1105​ per genset, comparing the genset PT (110V secondary) against the utility-tie PT on the same bus. The plant runs island mode at night (utility rates) and parallels during the day for peak-shaving; the sync-check relay is the hard-logic gate between “utility breaker closed” and “genset breaker close-permitted.” In 2021, during a utility-voltage swell event, one of the three 424K1105​ units started nuisance-dropping the “sync-ok” contact—internal timing pot had drifted on the 0.1–1.5 s ramp, and the phase-window comparator was rejecting a perfectly good 2° phase delta as “out of sync.” The fix was a like-for-like swap: 424K1105 (110V AC coil matches the cubicle’s 110V control power; a 424K2105 at 220V wouldn’t have fit without rewiring the PT-burden resistors). The maintenance electrician noted the DIN-clip made the swap 4 minutes—no panel rewire, just unlatch the terminal-block carrier (the 25V series uses a detachable terminal shell), swap the relay, re-latch. The plant’s charter: “We looked at upgrading to an ABB CM-SFS electronic sync relay, but that needs a 24V DC supply we don’t have in these old cubicles, plus a DIN-cutout resize. The 424K1105​ drops in, works, and costs 180 vs 650 for the electronic retrofit. We’ll migrate when we redo the 13.8 kV gear in 2028.”

Parameter

Technical Principles and Innovative Values

• Innovation Point 1: 25V Type Adds Dead-Bus/Dead-Line to Basic Sync Logic.​ The Circuit Shield 25 series comes in two flavors: 25S (basic — checks voltage magnitude, frequency, phase; all three must be “in window” to allow close) and 25V (adds dead-bus and dead-line logic, catalog prefix 424K). The 424K1105​ is the 25V variant with 110V AC coil. Dead-bus means “if the bus side PT sees <~30% voltage, skip the sync check and allow close” (useful for black-start or bus-tie auto-close when one side is de-energized). Dead-line is the reverse (source side dead, bus alive). That logic lives in the 424K1105​ as jumper/terminal selections—no extra relay needed. For a plant with both parallel and standby modes on the same tie, the 25V type is the right spare; a 25S (424J1105) would reject close on a dead-bus and force a manual override.
• Innovation Point 2: Vector-Difference Sensing, Not Single-Parameter.​ Unlike a plain undervoltage relay or a phase-sequence relay, the 424K1105​ computes the vector difference between the two PT inputs—it’s watching magnitude Δ, frequency Δ, andphase-angle Δ simultaneously. Each has a settable window (voltage band, frequency band, phase-angle window in degrees). Only when all three windows are satisfied does the “sync-ok” Form C close. This three-parameter AND-gate is what prevents “voltage-ok-but-30°-off” scenarios that would torque-shear a generator if the breaker slammed in. The dual-range time-delay pots (0.1–1.5 s fine + 1–15 s coarse) let the relay ride through momentary swells/sags without dropping sync-ok during a normal transient.
• Innovation Point 3: Detachable Terminal Carrier + DIN Form Factor.​ The 424K1105​ uses ABB’s Circuit Shield standard DIN housing: the relay body unlatches from a terminal carrier (the 25-series “drawout test case” concept in miniature). In a live cubicle, you unlatch the carrier, pull the relay, seat the new one, re-latch—the PT 110V and the contact wiring stay on the carrier, so no screw-driver work on live 110V AC terminals. For a midnight swap in a 13.8 kV switchgear room, that’s the difference between “4 minutes” and “20 minutes + a permit.”