Zero-sequence transformers The role of cable power generation is to prevent phase grounding to initiate malfunctions or accidents. The zero sequence current transformer mounting position on the bottom plate of the switchgear cabinet, do not install on the stent below the switch cabinet floor or bundled on the cable, which is neither safe and dustproof. The following small series gives you a detailed introduction to the role of zero transformer in cable power transmission, and mounting position.
1, the end of the end of the cable and the metal protective layer of the cable and the cable metal, the closed circuit largely formed shall not be related to the zero-sequence current transformer hill chain (passing).
2, i.e., when the cable grounding is below the zero sequence current transformer, the grounding line should be grounded directly; the grounding point should be grounded by the zero-sequence current transformer when the grounding point is above the zero sequence current transformer. At the same time, a cable metal guard layer and grounding line should be insulated from the cable head to the zero sequence current transformer, and the on-site insulation resistance value should not be less than 50kΩ. The above approach is to prevent the zero sequence current at the time of the cable from leakage in front of the zero sequence current transformer, causing erroneous judges; the stray current flowing through the cable metal proof flow into the earth, nor does the zero sequence current transformer Chain, stray current does not affect the correct judgment.
1. The zero sequence current transformer should be installed on the bottom plate of the switch cabinet, and there should be a reliable bracket fixed. However, some manufacturers or application I units are installed on the brackets under the switchgear floor, and even the zero-sequence current transformer is bundled on the cable, which violates the full closure of the switchgear, which is not safe. It is not dust-proof, not preventing small animals, leaving a lot of hidden dangers.
2. After the cable terminal is passed through the outer attachment zero-sequence current transformer, the relative position of the cable metal shielding ground line and the outer attachment zero sequence current transformer is incorrect. According to the provisions: the metal guards at the three-core power cable terminal must be well grounded; the plastic cable is copper shielded and steel armor soldering ground wire (oil immersed paper insulation cable lead package and armor), the cable is passed When the zero-sequence current transformer, the cable metal guard layer and the ground wire should be insulated, the cable grounding point (the solder joint of cable ground wire and cable metal shield) is below the transformer, and the ground wire should be directly grounded.