I. Overview

Drop out fuses and load drop out fuses are outdoor high-voltage protection devices. It is installed on the high voltage side of the distribution transformer or on the main branch of the distribution line, used for short-circuit and overload protection of transformers and lines, as well as for breaking and closing load currents. The drop out fuse consists of an insulation bracket and a fuse tube. The static contact is installed at both ends of the insulation bracket, and the dynamic contact is installed at both ends of the fuse tube. The fuse tube consists of an inner arc extinguishing tube and an outer layer of phenolic paper tube or epoxy glass cloth tube. Load drop type fuses enhance the elasticity of auxiliary contacts and arc extinguishing covers, used for opening and closing load currents.

When a drop out fuse operates normally, the fuse tube is tensioned by the fuse to form a closed position. When the system malfunctions, the fuse quickly melts and forms an arc due to the fault current. The arc extinguishing tube is heated by the arc and decomposes a large amount of gas, creating high pressure inside the embassy and forming a longitudinal blow along the pipeline. The arc is quickly stretched and extinguished. After the fuse is blown, the lower moving contact loses tension and flips down twice, locking the mechanism and releasing the fuse tube, causing the fuse tube to fall and form a clear breaking position. When a load needs to be pulled, use an insulating rod to pull the contact. At this time, the active and stationary contacts are still in contact. Continue to pull the contact with the insulating rod, and the auxiliary contacts also separate. An arc is generated between the auxiliary contacts, and the arc is elongated in the narrow slot of the extinguishing hood. At the same time, the extinguishing hood produces gas. When the current crosses zero, the arc is extinguished.

II. Purpose

Outdoor drop out fuses are suitable for use in 35kV and below voltage and frequency 50Hz power systems as overload and short-circuit protection for transmission lines and power transformers. They are only used for opening and closing rated load currents and have a mechanical life of ≥ 2000 times.

3、 Usage conditions

1. Suitable for environments with an upper limit of 40 ℃ and a lower limit of -30 ℃.

2. Altitude not exceeding 1000m, wind speed not exceeding 35m/s

3. Fuses are not suitable for the following locations

3.1 Places with fuel or explosion hazards.

3.2 Places with severe vibrations or impacts.

3.3 Areas with heterogeneous electrochemical gas interactions and severe air pollution and smoke.

4、 Structure Introduction

A fuse is composed of two main parts: a base and an arc extinguishing device. The lower end of the arc extinguishing tube is equipped with a spring bracket that can rotate, which always keeps the fuse in a tight state to ensure the self-locking of the arc extinguishing tube in the closed position. In case of overload or short circuit between the line and the transformer, the fuse melts and quickly withdraws from the arc extinguishing tube. The arc extinguishing tube is designed with a step-by-step exhaust to solve the contradiction of breaking large and small currents on the same fuse.