1. © 2005 PRS S.A. Ships’ electrical power network systems protected from damages caused by short-circuit current other than three-phase symmetrical current Presenter: Daniel Czarkowski Polski Rejestr Statków S.A. Electrical and Automation Department Gdańsk, POLAND Conference “Aeronautics and surface transport days” 11-12 April 2005, Warsaw

2. © 2005 PRS S.A. 2 Short-circuit current The short-circuit current analysis is a fundamental requirement of the classification societies. Although the short-circuit condition is an abnormal operating state. The calculations are essential to ensure that ships electrical system is designed assuming safety at see. Why do we need to calculate it?

3. © 2005 PRS S.A. 3 A simple formula I=10xG+4*M I short-circuit current G sum of generator full load current M sum of running motor current If so simple, why to complicate it?!

4. © 2005 PRS S.A. 4 Source of fire 1.Fault of a cable insulation or a poor conductor cause higher current which is a source of heat that damages an insulation. 2.Destroyed insulation causes one phase short-circuit to the ship’s hull that changes into two or even three-phase short- circuit. 3.High temperature caused by an arc is a source of fire. 4.A fire protection system usually detects smoke after a while. The delay might be too long to save human lives or, certainly, the main board equipment. 5.Arc short circuits and asymmetrical currents that occur on the main board are not considered by designers and classification societies while the currents are usually lower than these calculated according to IEC 61363.

5. © 2005 PRS S.A. 5

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7. 7 Scope of IEC 61363-1:1998 Electrical installations of ships and of mobile and fixed offshore units – Part 1: Procedures for calculating short circuit currents in three-phase a.c. “The calculation procedures are for a three-phase symmetrical short-circuit condition i.e. three-phase, 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 components of the short circuit and is not considered in this standard.” Asymmetrical current is not considered!

8. © 2005 PRS S.A. 8 Scope of IEC 60909-0:2001 Short-circuit currents in three-phase a.c. systems – Part 0: Calculation of currents This standard covers: line-to-earth short circuit, occurring in a solidly earthed neutral system or an impedance earthed neutral system. This standard does not cover: a single line-to-earth fault, occurring in an isolated neutral earthed system or a resonance earthed neutral system.

9. © 2005 PRS S.A. 9 Scope of IEC 60909-3:2003 Short-circuit currents in three-phase a.c. systems – Part 3: Currents during two separate simultaneous line-to-earth short circuits and partial short-circuit currents flowing through earth This standard covers: a) currents during two separate simultaneous line-to-earth short circuits in isolated neutral or resonant earthed neutral systems; b) partial short-circuit currents flowing through earth in case of single line-to-earth short circuit in solidly earthed or low- impedance earthed neutral systems. This standard does not cover: short-circuit currents in the electrical installations on board ships or aeroplanes.

10. © 2005 PRS S.A. 10 Aim of the project The aim is to fulfil the gap that exists in IEC 61363 that stems from the requirements set forth after analysis of main boards damaged by short-circuit currents. Thank you for your attention Any further questions please contact me: d.czarkowski@prs.pl

11. © 2005 PRS S.A. 11 Ship electric power system