Patent ID: 8149550

Claim:
A protective device, comprising: a circuit breaker for an electrical connection of a transformer to a load, the transformer being operated on the secondary side in star-connected fashion, and the electrical connection taking place via at least three phase conductors and a neutral conductor; and an overcurrent device, arranged between the transformer and the load and between a first switching device and the load, the overcurrent device including first magnetoelectric transducers arranged on each phase conductor and the neutral conductor between the first switching device and the load, the transducers each being arranged to emit a transducer current, the overcurrent device in each case establishing the presence of a first ground-fault current using the transducer currents, the first switching device to interrupt at least the phase conductors between the transformer and the load in the event of the presence of a first ground-fault current, second magnetoelectric transducers being provided between the star connection and the first switching device on each phase conductor, the neutral conductor and a star-point conductor connected at the star point, the star-point conductor being connected to ground, wherein the presence of a second ground-fault current is determined using the transducer currents of the second transducers, and wherein, in the event of the presence of a second ground-fault current, a signal for disconnecting the transformer is formed, said overcurrent device including a second switching device on the primary side of the transformer, which is tripped by the signal.