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1. Causes of electrical failure of explosion-proof electrical distribution box 1.1 Faults caused by product quality At the time of the rural electricity network transformation, due to the large number of electrical distribution boxes required and the short construction period, the distribution box factory needed urgent and quantity-related delivery of low-voltage electrical appliances. Too much, resulting in the phenomenon that the product quality requirements are not strict, causing some products to malfunction shortly after put into operation. If some types of AC contactors were put into operation shortly after the distribution box was put into operation, they could not be operated because the contactor closing coil was burned out.
1.2 Faults caused by improper selection of electrical equipment in explosion-proof distribution boxes Due to the inappropriate selection of AC contactor capacity in manufacturing, AC contactors of the same capacity are installed for different outlet circuits, and the imbalance of three-phase loads is not considered. However, the current rating of some of the outlet contactors could not be increased on the basis of the normal selection model, and the selection of a current level was improved, resulting in the occurrence of AC contactor burnout in the summer hot season.
2. Disposal scheme of explosion-proof distribution box 2.1 The protection circuit is used to prevent the external circuit failure caused by the power supply of the distribution box. Choose a small-sized intelligent phase loss protector, such as the optional DA88CM-II motor phase loss protection module (Shanghai products) installed in the distribution box to prevent the motor from being burned out due to low-voltage phase-to-phase operation.
2.2 Select energy-saving AC contactor (similar to CJ20SI type) products, and note that AC contactor coil voltage is connected to the corresponding terminal block of the selected residual current action protector. Pay attention to correct load matching. When selecting AC contactors, products with insulation class A and above shall be used, and the rated current of the main circuit contact shall be guaranteed to be greater than or equal to the load current of the controlled line. The electromagnetic coil of the contactor has a rated voltage of 380V or 220V, and the coil can be used within the range of 80% to 105% of the rated voltage.
2.3 Selection of residual current action protector. The products that meet the standards of GB6829 "General Requirements for Residual Current Operation Protectors" and have been qualified by the China Electrotechnical Products Certification Committee must be selected. Alternative LJM (J) series power-saving type and low sensitivity time-delay protectors are available. The protection device shall conform to the national standard GB13955-2005 "Installation and operation of residual current protection device". Leakage protection device breaking time, when the leakage current is rated leakage current, the action time should not exceed 0.2s.
2.4 The low-voltage cable is used for the incoming and outgoing cables of the distribution box. The selection of the cable should meet the technical requirements. For example, for the distribution box of 30kVA and 50kVA transformers, use the VV22-35x4 cable for the power distribution box, the VLV22-35x4 cable of the same specification for the branch line, and the VV22-50 for the line of the 80kVA and 100kVA transformer box. ×4, VV22-70×4 cable, branch outlets use VLV22-50×4, VLV22-70×4 cables respectively, the cable is crimped with the copper-aluminum connection nose and then bolted to the wiring pile head in the distribution box .
2.5 fuse (RT, NT type) selection. The rated current of the low-voltage side overcurrent protection fuse of the distribution transformer shall be greater than the rated voltage of the low-voltage side of the distribution transformer, generally 1.5 times of the rated current. The rated current of the melt shall be in accordance with the overload tolerance and fuse allowed by the transformer. Determine the characteristics of the device. The rated current of the fuse of the outlet circuit over-current protection fuse shall not be greater than the rated current of the total over-current protection fuse. The rated current of the melt shall be selected according to the normal maximum load current of the circuit and should avoid the normal peak current. The rated current of the shunt capacitor bank fuses can generally be selected from 1.5 to 2.5 times the rated current of the capacitor.
Quickly judge the failure of the explosion-proof distribution box circuit
Explosion-proof distribution box is a total circuit distribution box for all users. The distribution box is a mass parameter on the data. It generally constitutes a low-voltage electrical connection according to the electrical wiring. The switchgear, measuring instruments, protective electrical appliances and auxiliary equipment are required to be assembled in enclosed or semi-enclosed metal cabinets or screen panels to constitute low-voltage distribution. box. During normal operation, the circuit can be switched on or off by means of a manual or automatic switch.