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Explosion-proof distribution box fault improvement method
Causes of Failure of Explosion Protection Distribution Boxes and Improvement Plans
The explosion-proof power distribution box is to assemble the switchgear, measurement appearance, maintenance electrical appliances and auxiliary equipment in closed or semi-closed metal cabinets or screens according to the electrical wiring requirements, and constitute the low-voltage power distribution equipment. In normal operation, the circuit can be switched on or off by means of a manual or active switch. Faults or malfunctions are caused by maintaining electrical circuits or alarms. By measuring the appearance of various parameters can be displayed in operation, but also to adjust some of the electrical parameters, to violate the normal operating conditions to prompt or announce the signal. Commonly used in all hair, distribution, substations. In the process of use, many explosion-proof distribution boxes simply present a variety of problems. What are the causes of these problems? How can we improve the explosion-proof distribution box to complete its function? Below is an explanation of this issue.
First and foremost, I want to inform us that the reasons for the outbreak of the explosion-proof distribution box are the following:
1.1 Failure caused by the influence of ambient temperature on the distribution box
Low-voltage electrical equipment in the explosion-proof distribution box consists of fuses, contactors, residual current action maintainers, capacitors and meters. These low-voltage electrical appliances are all planned and manufactured in accordance with GB1497 "Basic Specifications for Low-Voltage Electrical Appliances", and their normal operating conditions have been stipulated accordingly: the upper limit of the ambient air temperature does not exceed 40 °C; the average of the ambient air temperature 24h does not exceed 35 °C The lower limit of ambient air temperature is not lower than -5°C or -25°C.
The power distribution box reformed by the rural power grid works outdoors. It not only suffers from direct sunlight and attacks the high temperature, but also heats itself during the operation. Therefore, during the high temperature season in midsummer, the temperature in the cabinet will reach above 60°C. The temperature greatly exceeds the ambient temperature specified by these appliances and therefore can cause problems due to overheating of electrical components in the distribution box.
1.2 Product Quality Failures
In the rural power grid reconstruction, due to the large number of power distribution boxes required and the short construction period, the demand for power distribution box manufacturers related to low-voltage electrical appliances is urgent and numerous. Therefore, the requirements for product quality are not severe. Some of the products that formed into the operation soon after the onset of illness. If some types of communication contactors are put into operation shortly after the distribution box is put into operation, they cannot be operated due to burnout of the contactor closing coil.
1.3 Faults Caused by Inadequate Selection of Electrical Equipment in the Distribution Box
Because the selection of communication contactor capacity during manufacturing is not very appropriate, the contactor of the same capacity of different outgoing line equipments is contacted, and the unbalanced status of three-phase load is not taken into consideration, and the current rating of some outlet contactors cannot be normal. On the basis of the type of selection, the selection of one current level is improved, thus resulting in a burnout of the communication contactor during the summer high temperature season.
Above, we informed us of the reasons for the failure of the explosion-proof distribution box, then how to improve the explosion-proof distribution box, I will notify the following explosion-proof distribution box improvement plan, the details are the following:
2.1 Regarding the distribution box with a distribution transformer capacity of 100 kV·A or above, the temperature control relay (JU-3 or JU-4 ultra-small temperature relay) of the device should be taken into account in the side wall of the heat dissipation window inside the box. Axial flow fan, the equipment is on the box on the left side above the electrical panel, so that when the temperature inside the box reaches a certain value (such as 40 °C) can actively start the exhaust fan, forcibly discharge heat to make the box heat.
2.2 The use of maintenance circuit to avoid the onset of external circuit breaker power supply problems. Select a small-sized intelligent missing phase maintainer, such as the optional DA88CM-II motor phase loss maintenance module (Shanghai products) equipment in the distribution box to avoid the motor burned out due to low-voltage phase-to-phase operation.
2.3 Improve the wiring method of the low-voltage capacitor bank of the original explosion-proof distribution box, and change the position of the equipment from the contact head on the contactor to the connection between the low-voltage inlet of the distribution box and the meter. To avoid inaccurate measurement of the formation of the metering device due to an out-of-phase fault in the capacitor circuit during operation or damage to the capacitor. In addition, the capacitor selection type should be the BSMJ series to ensure reliable component quality and safe operation.
2.4 If a new distribution platform is installed on the column, a 2 mm thick stainless steel plate can be selected when manufacturing the distribution box enclosure, and the scale of the distribution box should be increased according to the share (in JP4-100/3W type used in the agricultural reform project. On the basis of this, an increase of approximately 100 mm in the width dimension of the original tank, ie the change from the original 680 mm to 780 mm, the improved external dimensions of the distribution box: 1300 mm × 780 mm × 500 mm, in order to increase the number of points The electrical safety interval between the outlets, outlets, and the enclosure of the enclosure is conducive to the maintenance and replacement of the fuses by the agricultural electricians, and they can also dissipate heat together.
2.5 Use energy-saving communication contactor (similar to CJ20SI type) products, and pay attention to the contactor coil voltage connected to the corresponding remaining terminals of the selected residual current action maintainer, and pay attention to the correct load matching. When selecting a contact contactor, products with insulation class A and above should be selected. It is necessary to ensure that the extra current of the main circuit contact should be greater than or equal to the load current of the controlled line. The extra voltage of the electromagnetic coil of the contactor is 380V or 220V, and the coil is allowed to operate within 80% to 105% of the extra voltage.
2.6 The remaining current action maintenance device selection. It is necessary to select the products that meet the specifications of GB 6829 "General Requirements for the Operation of the Remaining Current Operation Maintenance Device" and have been certified by the China Electrotechnical Products Certification Committee. Alternative LJM(J) series power-saving type and low-sensitivity time-delay maintainers are available. The method for maintaining the equipment shall comply with the national specification of GB13955-2005 "Remaining current operation and maintenance equipment equipment and operation". When the leakage current maintains the breaking time, when the leakage current is an additional leakage current, the operating moment should not be greater than 0.2s.
2.7 Explosion-proof distribution box inlet and outlet selection of low-voltage cables, cable selection should meet the skill requirements. For example, the incoming cable of a 30kVA, 50kVA transformer power distribution box uses a VV22-35x4 cable, the split cable outlet uses a VLV22-35x4 cable of the same specification, and the 80kVA and 100kVA transformer power distribution box uses a VV22-50 cable. ×4, VV22-70×4 cable, branch and outlet use VLV22-50×4, VLV22-70×4 cable, its cable is crimped with copper and aluminum wiring and then bolted to the wiring pile head in the distribution box. .
2.8 Selection of fuses (RT, NT type). The total current at the low-voltage side of the distribution transformer shall be greater than the extra current at the low-voltage side of the distribution transformer. Generally, 1.5 times the extra current is taken. The extra current of the melt shall be according to the overload ratio and the fuse of the transformer. Determine the characteristics of the device. Out-of-line circuit over-current maintenance The fuse's melt extra current should not be greater than the total over-current maintenance fuse's extra current. The extra current of the melt is selected according to the normal maximum load current of the circuit and should avoid the normal peak current. The extra current of the shunt capacitor bank fuses can generally be chosen from 1.5 to 2.5 times the extra current of the capacitor.
2.9 In order to analyze the reactive power of rural low-voltage power grids, a DTS(X) series of active and reactive power-in-one multi-function energy meters (equipment on the meter side of the meter) is used to replace the original equipment. Three single-phase energy meters (DD862 series meter) to facilitate on-line operation monitoring of the load.
Today is the time to talk about it. The above is the cause of the outbreak of the explosion-proof distribution box and the improvement plan. We hope to help us.