Low-voltage power cable

Selection of the conductor cross-sectional area for low-voltage power cables must consider four conditions simultaneously: economic current density, safe current carrying capacity, voltage loss, and mechanical strength. During calculation, one condition is prioritized while verifying that the other three conditions are also met.

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Product Introduction

The selection of conductor cross-sectional area for low-voltage power cables must consider four conditions simultaneously: economic current density, safe carrying capacity, voltage loss, and mechanical strength. Calculations should prioritize one condition while verifying the other three meet requirements.
1) High and low voltage transmission and distribution lines are selected according to economic current density, ensuring power loss and capital investment remain within a reasonable range.
2) For nearby loads, conductor cross-section is primarily selected based on heating conditions (safe carrying capacity), ensuring the temperature remains within a reasonable range.
3) For high-current loads and low-voltage power lines, conductor cross-section is primarily selected based on voltage loss, ensuring the voltage at the load point remains within acceptable limits.
4) For large spans and small loads, mechanical strength must also be considered based on the stress on the conductor, ensuring the conductor can withstand the tensile force.
Economic current density and voltage loss are both related to the length of the conductor. That is, for the same cross-sectional area and current, the longer the line, the greater the power loss and voltage drop. For example, for a 50kW load at a distance of 50 meters, with 50mm² copper wire, the voltage loss is 2V, and the power loss is 0.
4KW; If it's 100 meters, the voltage loss is 4V, and the power loss is 1.6KW; If it's 400 meters, the voltage loss is 8V, and the power loss is 3.2KW;
Carrying capacity is related to the conductor's cross-sectional area. The larger the cross-sectional area, the smaller the unit carrying capacity. For example, the carrying capacity of a 1m² copper wire is 18A, a 10mm² copper wire is 80A, a 100mm² copper wire is 320A, and so on.
Economic Current Density
The calculation is relatively complex; generally, national standards are directly adopted:
3000 and below, 3000-5000, 5000 and above
Bare copper wire 3.
0A/mm² 2.25 A/mm² 1.75 A/mm²
Bare aluminum wire 1.65 A/mm² 1.15 A/mm² 0.9 A/mm²
Copper cable 2.5 A/mm² 2.25 A/mm² 2.0 A/mm²
Aluminum cable 1.
92 A/mm² 1.73 A/mm² 1.54 A/mm²
Safe Carrying Capacity of Conductors
The current density allowed for a conductor to operate continuously for a long time is called the safe carrying capacity.
Generally, it is stipulated that: copper wire selects 5～8A/mm²; aluminum wire selects 3～5A/mm².
Mechanical Strength (Rural Requirements)
Conductor Type 10KV Below 1KV
Aluminum stranded wire 35 25
Steel-cored aluminum stranded wire 25 25
Copper wire 16 16 or ￠3.2mm
Simplified Calculation Formula for Voltage Loss Percentage and Conductor Cross-sectional Area Selection
△U=PL/CS S=PL/C△U
△U——Voltage loss percentage
P——Active power transmitted (Kw)
L——Transmission distance (m)
C——Constant, single-phase aluminum wire 8.
3, three-phase four-wire aluminum wire 46; single-phase copper wire 12.8, three-phase four-wire copper wire 77
S——Conductor cross-sectional area (mm²).