Symbol Analysis Of Drop-out Fuse And Its Engineering Application
1. Standardization system of electrical symbols
High Voltage Fuse The symbol expression in electrical drawings follows international standards such as IEC 60617 and GB/T 4728, and its graphic language needs to accurately convey the structural characteristics and functional properties of the equipment. Symbol design contains core information such as the dynamic drop characteristics, arc extinguishing ability, and installation angle of the fuse, and is an important semantic carrier of electrical engineering design.
2. Standard symbols Composition analysis
1. Basic graphic elements
1/3 of the symbol height
Arc path: indicated by a zigzag line inside the melting tube, with the angle of the line controlled at 60°±5°
Drop indication: a dotted line with an arrow below the melting tube, with the arrow direction forming an angle of 75° with the axis of the melting tube
2. Additional identification rules
Rated current: marked on the right side of the symbol, in the format of I_n=××A
Breaking capacity: indicated by kA value in the lower left corner of the symbol, such as 20kA
Installation method: When installed vertically, the symbol is rotated 90° clockwise and "Vertical" is indicated in the legend
... 4. Implicit technical parameters in symbols
Tilt angle: The 45° tilt of the symbol is not an exact value, but indicates that the device belongs to the gravity tripping mechanism, which is different from the vertically mounted current-limiting fuse.
Contact spacing: The ratio of the contact spacing to the fuse tube height in the symbol (1:2.5) corresponds to the contact stroke design specification of the actual product.
Arc path length: The total length of the jagged line must reach 80% of the symbol height, reflecting the actual arc stretching distance inside the melting tube (usually ≥150mm).
Use norms
1. Representation in the single-line diagram
In the single-line diagram of the power distribution system, the drop-out fuse symbol must be spaced from the following elements:
Between the transformer symbol 2 symbol heights apart
Keep 1.5 times the symbol width of the arrester symbol
Place the ground symbol at 45° to the lower right of the fuse
2. Special expressions in control loops
When used for protection circuit:
The fuse signal contact is wrapped with a dotted frame, and the contact direction is mirror-symmetrical with the main symbol
The action indicator adds an equilateral triangle mark on the top of the symbol
The auxiliary contact is represented by a φ2mm hollow circle, aligned with the center line of the main symbol
VI. Common Misreadings and Corrections
Confusion with load switch: Note that the load switch symbol has a semicircular contact track, while the fuse symbol maintains a straight line motion feature.
Misjudgment of arc extinguishing ability: The number of sawtooth arc paths in the symbol is related to the number of arc extinguishing chambers (each fold represents 1 level of arc extinguishing), not a simple decorative element.
Wrong installation direction: The symbol defaults to outdoor installation mode, and indoor type requires a horizontal line at the bottom of the symbol. This detail is often overlooked.
VII. Engineering semantic extension of symbols
In smart grid design, the symbol derives a new semantic level:
State monitoring interface: The wavy line on the right side of the symbol extends to indicate RS-485 or LoRa communication interface.
Energy dissipation indication: The density of the oblique lines inside the melting tube is positively correlated with the I²t value, and dense oblique lines indicate high segmentation capability.
Environmental adaptability: The change of the dashed and solid lines in the symbol frame indicates the equipment protection level (Solid line IP54, dotted line IP65).
