During the reconstruction of rural power grids, the number of distribution boxes required at the time was large and the construction period was short. The distribution box manufacturers needed urgent and large quantities of low-voltage electrical appliances. As a result, the requirements for product quality were not strict, resulting in Some products failed shortly after they were 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.
1.3 Failures Caused by Improper Selection of Electrical Equipment in the Distribution Box
Due to the improper choice of AC contactor capacity in manufacturing, AC contactors of the same capacity are installed for different outlet loops, and the unbalanced three-phase load is not taken into consideration, and the current rating of some outlet contactors cannot be normal. On the basis of the selected model, an increase in the choice of the current level results in the occurrence of AC contactor burnout during the summer hot season operation.
Above, we told you the reason why the explosion-proof power distribution box failed. Then how to improve the explosion-proof power distribution box? Next, I'll tell you about the improvement plan of the explosion-proof power distribution box, specifically the following points:
2.1 For distribution box with distribution transformer capacity of 100kV·B and above, the temperature control relay (JU-3 or JU-4 subminiature temperature relay) shall be installed in the side wall of the heat dissipation window inside the box. The axial fan is installed on the box on the left side above the control electrical panel so that the exhaust fan can be automatically activated when the temperature inside the box reaches a certain value (for example, 40°C), and heat is forcibly exhausted to dissipate the heat of the cabinet.
2.2 The use of protection circuit to prevent the external box circuit breaker power supply from occurring. 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.
2.3 Improve the connection mode of the low-voltage capacitor bank of the original explosion-proof distribution box, and change the installation position from the AC contactor's pile head to the connection between the low voltage line of the distribution box and the meter. To prevent the metering device from measuring inaccurately due to a lack of phase fault in the capacitor circuit during operation or damage to the capacitor. In addition, the capacitor selection model should be BSMJ series products to ensure reliable and safe operation of components.
2.4 If a new distribution platform is installed on the column, a 2 mm thick stainless steel plate can be selected when the distribution box is manufactured, and the size of the distribution box can be enlarged proportionally (in JP4-100/3W type used in agricultural reform projects. 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 dimensions of the distribution box: 1300 mm × 780 mm × 500 mm, in order to increase the number of points The electrical safety distance between the outlets, outlets and the enclosure of the enclosure is beneficial to the maintenance and replacement of the fuses by the agricultural electricians, and it can also dissipate heat.
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