Improvement plan for distribution box
2.1 For the distribution box with distribution transformer capacity of 100kV·A and above, the temperature control relay (JU-3 or JU-4 ultra-small temperature relay) should be installed in the side wall of the heat dissipation window inside the box. The axial flow fan is installed on the box on the left side above the control electric board so that when the temperature inside the box reaches a certain value (such as 40 ° C), the exhaust fan can be automatically activated, and the heat is forcibly discharged to dissipate the box.
2.2 The protection circuit is used to prevent the occurrence of external circuit faults in the power distribution box. Choose a small-sized intelligent phase loss protector. For example, the DA88CM-II motor phase loss protection module (Shanghai product) can be installed in the distribution box to prevent the motor from being burnt due to low voltage phase loss.
2.3 Improve the wiring mode of the low-voltage capacitor bank of the original distribution box, and change its installation position from the pile head on the AC contactor to the low-voltage inlet line of the distribution box and the meter. Prevent the metering device from being inaccurately measured due to phase loss failure or capacitor damage during operation of the capacitor circuit. In addition, the capacitor selection model should be BSMJ series products to ensure reliable and safe operation of components.
2.4 If the power distribution platform on the column is added, when the power distribution box housing is made, 2 mm thick stainless steel plate can be selected, and the distribution box size can be enlarged proportionally (JP4-100/3W type used in agricultural reform project) On the basis of the original box width increase of about 100 mm, from the original 680 mm to 780 mm. The improved distribution box dimensions: 1300 mm × 780 mm × 500 mm), in order to increase the points The electrical safety distance between the outgoing lines and the outlets and the outer casing of the cabinet is beneficial to the operation and maintenance of the electrician and the replacement of the fuses, and also the heat dissipation.
2.5 Select energy-saving AC contactor (similar to CJ20SI type), and pay attention to the AC contactor coil voltage is connected with the corresponding terminal of the selected residual current action protector, pay attention to the correct load matching. When selecting an AC contactor, the product with insulation class A and above should be selected. The rated current of the main circuit contact should be greater than or equal to the load current of the line being controlled. The contactor's solenoid is rated at 380V or 220V, and the coil is allowed to be used in the range of 80% to 105% of the rated voltage.
2.6 Selection of residual current action protector. Products that meet the GB 6829 "General Requirements for Residual Current Action Protectors" and have passed the certification of the China Electrotechnical Products Certification Committee must be selected. A delay-type protector similar to the LJM(J) series of power-saving type and low sensitivity can be selected. The mode of the protector device shall comply with the national GB13955-2005 "Installation and operation of residual current action protection device" standard. The breaking time of the leakage protector, when the leakage current is the rated leakage current, the operating time should not exceed 0.2s.
2.7 The input and output lines of the distribution box are selected from low-voltage cables. The selection of cables should meet the technical requirements. For example, the distribution line of the 30kVA, 50kVA transformer distribution box uses VV22-35×4 cable, the branch line uses the same specification VLV22-35×4 cable; the 80kVA, 100kVA transformer distribution box inlet line uses VV22-50 respectively. ×4, VV22-70×4 cable, the VLV22-50×4, VLV22-70×4 cable is used for the branch outlet, and the cable is connected with the copper and aluminum wiring, and then connected with the bolts in the distribution box. .
2.8 fuse (RT, NT type) selection. The rated current of the low-voltage side total over-current protection fuse of the distribution transformer shall be greater than the rated current 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 the overload multiple and the fuse allowed by the transformer. The characteristics of the device are determined. The rated current of the fuse of the outlet loop overcurrent protection fuse shall not be greater than the rated current of the total overcurrent protection fuse. The rated current of the melt shall be selected according to the normal maximum load current of the loop and shall escape 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.
2.9 In order to analyze the reactive power of the rural low-voltage power grid, install a DTS (X) series active and reactive two-in-one multi-function electric energy meter (installed on the side of the meter panel) in the box for replacement of the original installation. Three single-phase electric energy meters (DD862 series meter) to facilitate on-line monitoring of the load.
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