British Standards Institution

Electrical installations of ships and mobile and fixed offshore units - Part 1: Procedures for calculating short-circuit currents in three-phase a.c.
 N BS IEC 61363-1

Annotation

Scope and object

This International Standard outlines procedures for calculating short-circuit currents that may occur on a marine or offshore a.c. electrical installation.

The calculation methods are for use on unmeshed three-phase alternating current systems,

a) operating at 50 Hz or 60 Hz;

b) having any system voltage specified in IEC 60092-201 table 2;

c) having one or more different voltage levels;

d) comprising generators, motors (both synchronous and asynchronous), transformers, reactor coils, cables, and converter units;

e) having their neutral point connected to the ship's hull through an impedance (designed to limit the short-circuit current flowing to the ship's hull);

f) having their neutral point isolated from the ship's hull.

The calculation procedures are for a three-phase symmetrical short-circuit condition i.e. threephase conductors shorted together, or shorted to the ship's hull and for which the short-circuit occurs on all three poles simultaneously. The calculation of short-circuit currents resulting from asymmetric short-circuit conditions can lead to higher aperiodic (d.c.) components of the shortcircuit current and is not considered in this standard.

The calculating formulae and methods described produce sufficiently accurate results to calculate the short-circuit current during the first 100 ms of a fault condition. They can be used to calculate the short-circuit current for periods longer than 100 ms when calculating on a bus system to which the generators are directly connected. For time periods beyond 100 ms the controlling effects of the system voltage regulators may be predominant. Calculations including the voltage regulator effects are not considered in this standard.