RW 12-10 Drop Fuse

I. Overview

Dropping fuse and pulling composite drop fuse are outdoor high-voltage protective appliances. It is installed on the high-voltage side of distribution transformer or the branch line of distribution line. It is used for short-circuit, overload protection and load-sharing current of transformer and line. The drop fuse consists of an insulating bracket and a fuse tube. The static contacts are installed at both ends of the insulating bracket and the movable contacts are installed at both ends of the fuse tube. The fuse tube consists of an inner arc extinguishing tube and an outer phenolic straight tube or an epoxy glass cloth tube. The pull composite drop fuse enhances the elastic auxiliary contacts and extinguishes the shield for dividing and closing the current.

When the drop fuse is in normal operation, the fuse pipe is tightened by the fuse to form a closed position. When the system fails, the fault current causes the fuse to fuse rapidly and form an arc. The arc of the arc extinguishing pipe hand is heated and decomposes a large number of gases, which forms a high pressure in the pipe and blows longitudinally along the pipe. The arc is rapidly elongated and extinguished. After the fuse is fused, the lower movable contact loses tension and turns down two times. The locking mechanism releases the fuse pipe and the fuse pipe falls down, forming an obvious starting position. When the load needs to be pulled, the contact is pulled by insulating rod. At this time, the active and static contacts are still in contact. The contact is pulled by insulating rod, and the auxiliary contacts are separated. Arc is generated between the auxiliary contacts. The arc is elongated in the narrow gap of the extinguishing cover. At the same time, the gas is produced by the extinguishing cover. When the current passes zero, the arc is extinguished.

II. Usage

Outdoor drop fuse is suitable for short circuit protection of overload of transmission line and power transformer in power system with voltage frequency of 35KV and below 50HZ. It divides rated load current and has a mechanical life of more than 2000 times.

III. Conditions of Use

1. Applicable to the upper limit of ambient temperature of 40 degrees C and the lower limit of - 30 degrees Celsius.

2. No more than 1000m above sea level and no more than 35m/s wind speed

3. Fuses are not suitable for places with fuel or explosion hazards, places with violent vibration or shock, abnormal chemical gases, severe air pollution and smoke areas.

IV. Brief introduction of structure

The fuse is composed of base and arc extinguishing device. There may be a rotating spring bracket at the lower end of the arc extinguishing tube. The fuse is always in a tense state to ensure the self-locking of the arc extinguishing tube at the closing position, the overload or short circuit between the circuit and transformer, the fuse is fused and the fuse is rapidly heavy. The arc extinguishing tube is designed to beat air layer by layer to solve the contradiction between breaking large and small current on the same fuse.

V. Model Description
Fuse Selection

The short circuit capacity of the installation site shall be within the rated cut-off capacity of the drop fuse. If the upper limit is exceeded, the fuse pipe may explode due to excessive current and gas production; if it is below the lower limit, the arc may not be extinguished due to excessive current and insufficient gas production. Therefore, when choosing the rated capacity of drop fuse, we should not only consider the matching of the upper limit interruption current with the limit large short circuit current at the installation site, but also pay attention to the relationship between the lower limit interruption capacity and the limit small short circuit current at the installation site. Considering that drop-type fuse is the main protection for internal faults of distribution transformer, the protection range is from low-voltage fuse transformer side to high-voltage fuse transformer side, and as the back protection of low-voltage fuse, the lower limit interruption capacity should be chosen as the minimum limit value of short-circuit current with two-phase short circuit at low-voltage outlet.

8. Selection of fuses

The selection of fuse should ensure that the inner bushing of distribution transformer or the bushing of high and low voltage outlet can be fused quickly when short circuit occurs. In practice, the following principles are often adopted: the capacity of distribution transformer is less than 160KA, the fuse is selected by 2-3 times the rated current of transformer, and the capacity of distribution transformer is more than 160KVA, and is selected by 1.5-2 times. This is the key problem to decide whether the fuse protection can be effective or not. In 0.1S, the fuse current should be no less than 20 times of the rated current. This data is a necessary condition to ensure the matching of fuse and head circuit breaker.