GB/T 15544.1-2013 Short-circuit current calculation in three-phase a.c.systems—Part 1:Calculation of currents

Scope

This part of GB/T 15544 is applicable to the calculation of short-circuit current in low- and high-voltage three-phase AC systems with a rated frequency of 50 Hz or 60 Hz.
When the system nominal voltage is 500 kV or higher and contains long-distance AC transmission lines, special consideration is required.
The equivalent voltage source method at the short-circuit point proposed in this part is a simple and practical method for calculating short-circuit current, and the calculation results generally have acceptable accuracy. If the same calculation accuracy can be obtained, other calculation methods, such as the superposition method, are not excluded. The short-circuit current calculated by the superposition method depends on a specific power flow, so it may not be the maximum short-circuit current.
The short-circuit forms covered in this part include balanced short-circuit faults and unbalanced short-circuit faults.
For a line conductor-to-earth short-circuit caused by human or accidental factors, the physical characteristics and impacts of the following two situations are different (leading to different calculation purposes) and must be clearly distinguished:
——In a system with a directly grounded or impedance-grounded neutral point, the conductor is short-circuited to the ground;
——In a system with an ungrounded or resonantly grounded neutral point, a conductor-to-earth short-circuit fault occurs. The calculation of this short-circuit fault is not within the scope of this part.
In a system with an ungrounded or resonantly grounded neutral point, when two independent single-phase-to-earth short-circuit faults occur simultaneously, the short-circuit current is calculated according to IEC 60909-3.
Short-circuit current and short-circuit impedance can also be determined through system tests, measurements by system analysis instruments, or digital computers. In existing low-voltage systems, the short-circuit impedance ca

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