1. The Operating Steps for the Three Phases of HV Dropout Fuse Cutouts
To cut off the power supply, disconnect the middle phase first and then the two phases on both sides. To supply power, make the phases on both sides first and then the middle phase. The reason why the middle phase is disconnected first to cut off is mainly because the current is smaller than those of the side phases (part of the load of the circuit is transferred to the two phases) when the middle phase is cut off, and the arc is small and there is no danger to the two phases. When operating the second phase (side phase), the current is relatively large, and at this time the middle phase has been disconnected, and the other two dropout fuses are far apart, which can prevent interphase short circuit caused by arc elongation. When encountering strong winds, disconnect the middle phase, then the leeward phase, and finally the windward phase. When supplying power, first make the windward phase, then close the back wind phase, and finally close the middle phase, so as to prevent the short circuit caused by the wind blowing the arc.
2. The Operating Steps for Cutting off and Supplying Power for Power Distribution Transformers
Under normal circumstances, to cut off the power, disconnect the low-voltage switch on the load side should be opened first, and then the high-voltage drop-out fuse on the power supply side should be opened. In the case of multiple power sources, cutting off the power supply in the above order can prevent the transformer from reversely feeding power. In case of a fault, the protection may not be provided, prolonging the fault removal time and expanding the accident. Supplying power from the power supply side step by step can reduce the impact starting current (load), reduce voltage fluctuations, and ensure safe operation of equipment. In case of failure, trip or stop operation immediately to make it convenient for inspection, judgment and treatment according to the power transmission range. To cut off the power, cut off the power supply at the load side. Cutting off the power supply from LV to HV step by step can avoid a large amount of current in the switch and reduce the amplitude and frequency of operating over-voltage. During the operation, try to avoid pulling and closing the drop-out fuse cutout with load during operation. If it is found that the cutout is mis-closed under load during operation, even if it is wrongly closed, or even an arc occurs, it is not allowed to pull off it again. If a cutout with load is accidentally pulled, an arc will occur when the moving contact just leaves the fixed contact, and in such case, it close it immediately to eliminate the arc and avoid the expansion of the accident. However, if the cutout has been fully disconnected, it is not allowed to close the cutout that has been pulled by mistake. For power distribution transformers with a capacity of 200 kVA and below, the breaking and closing load currents of the cutout are allowed on the high-voltage side of the transformer.
3. There should be no impact when the operator pulls or close the cutout. The impact will damage the cutout, such as breaking and cracking the insulator, deflecting the cutout, breaking the operating ring, etc. When opening and closing the cutout, the operator should not use too much force to cause impact so as not to damage the cutout, and the opening and closing must be in place.
The process of closing the cutout is slow (at the beginning), fast (when the moving contact is close to the static contact), and slow (when the moving contact is close to the closing end). The process of pulling the cutout is slow (at the beginning), fast (when the moving contact is close to the static contact), and slow (when the moving contact is close to the pulling end). Being fast is to prevent the short circuit and burned contacts the s due to electric arc, and being slow is to avoid the impact of operation from causing mechanical damage to the cutout.