Application Scenarios:

A 33 kV substation has a bus-section breaker with an automatic transfer scheme. The legacy timing relay in the synchronising circuit verifies that both sides are energised and waits a set delay — but it has no true phase-angle supervision. Under normal conditions the scheme behaves itself. Under stress — a standby generator starting onto a dead bus section, an auto-reclose after a fault, an operator-initiated transfer during a disturbance — it closes on a phase angle it should never have accepted. The result is a current surge into the machine, a mechanical shock to the windings and the shaft, and a breaker that has just absorbed a closing duty it was never rated for. Nothing trips immediately. The damage accumulates silently, and it is discovered years later as insulation failure or a cracked coupling.This is exactly the failure 424K1105​ is engineered to prevent. Because 424K1105​ measures the actual vector difference between the two sources — magnitude, frequency and phase angle, continuously and simultaneously — rather than inferring synchronism from elapsed time, it refuses to release the close circuit unless the sources are genuinely within the window the protection study defined. Where the scheme also needs to energise a dead bus or a dead line, the Type 25V function switch provides that permissive deliberately and visibly, rather than leaving it to an operator’s judgement in an emergency. The pain point it addresses is the most expensive kind of electrical failure: the one that does not announce itself at the moment it happens.

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