Method for acquiring single-phase earth fault current of three-phase and three-core cable

Abstract

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.

Description

technical field [0001] The invention belongs to the technical field of power systems, and in particular relates to a method for collecting single-phase grounding fault current of a three-phase three-core cable. Background technique [0002] At present, when a single-phase grounding fault occurs in a three-core power cable in domestic operation, the fault current collection method used for protection is: install a cable-type core-type grounding current transformer at the cable head, and the three-phase core wire of the cable is connected from the current transformer Passing through, this method has the following disadvantages: [0003] (1) Due to the limitation of the acquisition method, the electromagnetic current transformer used is composed of two iron cores. The iron core has gaps, the magnetic circuit reluctance is large, and the excitation impedance is 1-3Ω. To obtain the highest sensitivity, the excitation impedance must be satisfied. It is equal to protecting the sec...

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Problems solved by technology

[0006] The invention provides a method for collecting single-phase grounding fault current of three-phase three-core cables, aiming at solving the fault current collection method used for protection when the single-phase grounding fault of three-core power cables currently in operation in China is: at the cable head Cable-type core-through current transformers are installed at the place, and the three-phase core wires of the cables pass through the current transformers. This fault current acquisition method has low sensitivity, large measurement errors, increased errors, and higher protection settings. Sensitivity issues of protection

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