The short-circuit current breaking capacity of the low-voltage side circuit breaker of the distribution transformer is too small; the influence of the thermal stability current of the cable is not verified in the low-voltage distribution system, which leads to the small cross-sectional area of some distribution circuit cables in the low-voltage distribution system.
Since the data of the system short-circuit capacity and short-circuit impedance need to be provided by the power supply department, the electrical design of most civil construction projects does not make accurate short-circuit current calculations at present.
Correct method: Calculate the short-circuit current of the low-voltage side for the transformers of different capacities of each project, including at least the peak value of the short-circuit current: ip
Steady State Short-Circuit Current RMS: Ik
When choosing a circuit breaker, at least the rated ultimate short-circuit breaking capacity of the circuit breaker should be guaranteed: Icu
Not less than: Ik
For each project, a cable with the smallest cross-sectional area and a short path should be selected for short-circuit current thermal stability verification, and a load terminal with the longest distribution path should be selected for voltage drop analysis. If the cable cross-sectional area does not meet the requirements, the cable cross-sectional area should be adjusted.
Under the condition that the system capacity is infinite, the circuit current parameters at the outlet of the low-voltage side of the transformer corresponding to different capacity and short-circuit impedance voltage parameters must be greater than the short-circuit capacity of the actual project whose short-circuit capacity of the system is not infinite. It can be used to check the low-voltage distribution. The breaking capacity of the electrical circuit breaker.
For another example, it can be seen from the selection table for short-circuit current of low-voltage copper core XLPE cables that for transformers of 1000kVA and below, the cross-sectional area of the distribution cable on the low-voltage bus shall not be less than 10mm2; for transformers greater than 1000kVA, the The cross-sectional area of the distribution cable shall not be less than 16mm2.
For large-scale or important public construction projects, short-circuit current calculation is recommended when short-circuit current has a great influence on equipment selection.
Take advantage of our unrivaled knowledge and experience, we offer you the best customization service.
LEAVE A MESSAGE
Please fill out and submit the form below, we will contact you in 48 hours, thank you!
They are all manufactured according to the strictest international standards. Our products have received favor from both domestic and foreign markets.