| 摘要 |
An electrical differential protection apparatus, particularly a circuit breaker or switch having a test circuit, is disclosed. The apparatus (A) comprises a release (1) with a differential current sensing transformer (12), a relay (16) for triggering the circuit breaker cut-off mechanism (2) and a test circuit (33) for monitoring the operation of the release (1). The relay (16) comprises a fixed yoke (25) supporting a coil (29) and an armature (26) movable relative to the yoke (25). During normal operation of the apparatus (A), the armature (26) is magnetically held in engagement with the yoke (25), and when a differential current occurs, the armature (26) actuates the cut-off mechanism (2). The test circuit (33) comprises a means (34) for causing vibration of the armature (26) without triggering the mechanism (2), in order to determine its disengageability from the fixed yoke (25). The vibration is advantageously caused by applying a square-wave voltage across the terminals (29a, 29b) of the coil (29).
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