AS 3851-1991

Specifies standard methods for the calculation of short-circuit currents in three-phase a.c. systems, both radial and meshed with and without contribution from generators and motors, which are suitable for either computer or manual calculation.

This Standard specifies a standardized procedure for the calculation of prospective short-circuit currents in the fault for-(a) low voltage a.c. systems; and (b) high voltage three-phase a.c. systems, operating at a nominal frequency of 50 Hz.The procedure is intended to be, as far as possible, in a form to facilitate its use by non-specialist engineers.NOTE: The procedure is applicable generally to other frequencies close to 50 Hz; however, care should be exercised in the use of frequency-dependent factors.Except in Appendix A, the basis of the calculation procedure in this Standard is ohmic. Appendix A converts this procedure to per-unit calculation.NOTE: Worked examples are provided in Appendices D and E on ohmic and per unit basis respectively.The current, calculated in this Standard forms the basis for the determination of the currents in the paths feeding the fault.This Standard specifies a standardized method for the calculation of the joule integral (I2t) of a short-circuit current.This Standard does not cover-(i) short-circuits deliberately created under controlled conditions as in short-circuit testing stations; (ii) short-circuits in the electrical installations of ships and aircraft; (iii) non-simultaneous short-circuits, which can lead to higher aperiodic components of short-circuit current; or (iv) methods for analysis of short-circuit currents in non-linear systems.

First published as AS 3851-1991.
Incorporating: Amdt 1-1992