The invention discloses a method for acquiring a single-phase earth fault current of a three-phase three-core cable. The head end of a three-phase three-core cable shielding layer is serially connected with a zero-sequence
current transformer, the three-phase three-core cable shielding layer is earthed through the zero-sequence
current transformer and is used for acquiring the
capacitance current without being influenced by a load imbalance current when the single-phase earth fault of the three-phase three-core cable is caused, so that the insulation property of the three-phase three-core cable can be well reflected; a
voltage limiter is arranged on the far end of the three-phase three-core cable shielding layer, when the
voltage of the three-phase three-core cable shielding layer raises to a
limit value, the
voltage limiter is of
low impedance to guide current to the earth, the zero-sequence
current transformer is not limited by the impedance, the number of turns of a primary side can be increased freely, so that the sensitivity of the protection of a low-current grounding and isolated neutral
system is improved; and meanwhile, an iron core of the zero-sequence current
transformer can adopt a cold-rolled particle oriented
silicon steel sheet with high magnetic conduction property, so that high-frequency
transient current when the earth fault is caused can be well reflected, the protection sensitivity is improved, and the strong popularization and application value is achieved.