The selection of drop fuse (switch)
The 10kV drop fuse is suitable for outdoor places where the ambient air is free of conductive dust, corrosive gases and flammable and explosive hazards, and the annual temperature variation is within ± 40℃. Its selection is in accordance with the rated voltage and rated current two parameters, that is, the rated voltage of the fuse must be matched with the rated voltage of the protected equipment (line). Fuse with the rated current should be greater than or equal to the rated current of the fuse. And the rated current of the fuse can be 1.5 to 2 times the rated load current. In addition, the selected fuse should be calibrated according to the three-phase short-circuit capacity of the protected system. Ensure that the three-phase short-circuit capacity of the protected system is less than the upper limit of the rated disconnecting capacity of the fuse, but must be greater than the lower limit of the rated disconnecting capacity. If the rated breaking capacity of the fuse (generally refers to its upper limit) is too large, it is likely that the three-phase short-circuit capacity of the protected system is smaller than the lower limit of the rated breaking capacity of the fuse, resulting in the fuse fusing when it is difficult to extinguish the arc, eventually causing fuse burning, explosion and other accidents. At present, some power supply units are still in the peak of the transformation of the agricultural network, in the selection of this type of fuse, must strictly control the quality of the product, to protect the qualified equipment into the network, and at the same time to pay attention to its rated breaking capacity of the upper limit and lower limit value.
Installation of drop out fuse
(1)The fuse should be installed tightly (so that the fuse is about 24.5N pull), otherwise it is easy to cause contact heating.
(2) The fuse should be installed on the crossbar (frame) firmly and reliably, without any shaking or shaking phenomenon.
(3) fuse tube should be down 25 ° ± 2 ° angle of inclination, in order to facilitate the melt fuse fuse can fall quickly by its own weight.
(4) The fuse should be installed on the crossbar (frame) at a vertical distance of not less than 4m from the ground, and if it is installed above the distribution transformer, it should be kept at a horizontal distance of more than 0.5m from the outermost contour of the distribution transformer to prevent the fuse from falling off in case of other accidents.
(5) The length of the fuse tube should be adjusted moderately, requiring the tongue of the duckbill to hold more than two-thirds of the contact length after closing, so as to avoid the malfunction of falling down by itself in operation, and the fuse tube should not be topped off by the duckbill to prevent the fuse tube from falling down in time after the fuse melts.
(6) The melt used must be the standard product of the regular manufacturer and have a certain mechanical strength, generally requiring the melt to withstand at least 147N of tension.
(7) 10kV drop fuse installed in the outdoor, the required distance between the phase is greater than 70cm.
4 drop fuse operation generally does not allow the operation of the drop fuse with load, only allow it to operate no-load equipment (line). But in the agricultural network 10kV distribution lines branch lines and distribution transformers with a rated capacity of less than 200kVA are allowed to operate with a load according to the following requirements.
(1) Operation by two persons (one supervising, one operating), but must wear tested and qualified insulating gloves, insulating boots, goggles, and use qualified insulating rods of matching voltage level.
(2) When pulling the switch, the general rule is to pull off the middle phase first, then the leeward side phase, and finally the windward side phase. This is because the distribution transformer is changed from three-phase operation to two-phase operation, and the arc spark generated when pulling off the middle phase is minimal and does not cause inter-phase short circuit. The second is to pull off the leeward side phase, because the middle phase has been pulled apart, the distance between the leeward side phase and the windward side phase has doubled, even if there is overvoltage, the possibility of inter-phase short circuit is also very small. When the windward side phase is finally pulled off, there is only capacitive current to ground, and the spark generated is already very slight.
(3) When closing the gate, the operation sequence is reversed when pulling the gate, first closing the windward side phase, then closing the backwind side phase, and finally closing the middle phase.
(4) operation of the fuse tube is a frequent project, not pay attention to it will cause contact burns caused by poor contact, so that contact overheating, spring annealing, prompting contact more poor contact, forming a vicious circle. Therefore, pull and close the fuse tube with moderate force, after closing, carefully check the duckbill tongue can be tightly clasped tongue length of more than two-thirds, can pull the gate rod hooked on the duckbill down a few times, and then gently try to pull, check whether to close. Failure to close the gate in place or not closed securely, the fuse on the static contact pressure is not enough, it is easy to cause contact burns or fuse tube fall down.