IEC 61892-4-2019 pdf free.Mobile and fixed offshore units – Electrical installations -Part 4: Cables.
Careful consideration shall be given to cables subjected to voltage surges associated withhighly inductive circuits to ensure that they are of a suitable voltage rating.
The choice of standard cables of appropriate voltage designations for particular systemsdepends upon the system voltage and the system earthing arrangements.
The rated voltage of any cable shall not be lower than the nominal voltage of the circuit forwhich it is used.To facilitate the choice of the cable, the values of U recommended for cablesto be used in three-phase systems are listed in Table 1 in which systems are divided into thefollowing three categories.
This category comprises those systems in which any phase conductor that comes into contactwith earth or an earth conductor is automatically disconnected from the system.
This category comprises those systems that,under fault conditions,are operated for a shorttime, not exceeding 8 h on any occasion,with one phase earthed.
For example, for a 13,8 kV system of Category A or B, the cable should have a rated voltagenot less than 8,7/15 kV.
ln a system where an earth fault is not automatically and promptly eliminated, the increasedstresses on the insulation of cables during the earth fault are likely to affect the life of thecables to a certain degree. If the system is expected to be operated fairly often with asustained earth fault, it may be preferable to use cables suitable for Category C. In any case,for classification as Category B, the expected total duration of earth faults in any year shouldnot exceed 125 h.
This category comprises all systems that do not fall into Categories A and B.
The nominal system voltages from 3,3 kV to 30 kV shown in Table 1 are generally inaccordance with lEC 60038:2009, series l.For nominal system voltages intermediate betweenthese standard voltages and also between 0,6/1 kV and 1,8/3,3 kV, the cables should beselected with a rated voltage not less than the next higher standard value.For example: a firstearth fault with one phase earthed causes a √3 higher voltage between the phases and earthduring the fault. lf the duration of this earth fault exceeds the times given for Category B, thenaccording to Table 1, for a 17,5 kV system, the cable is to have a rated voltage not less than12/20 kv.
A DC voltage to earth of up to a maximum of 1,5 times the AC U,voltage may be used.However, consideration should be given to the peak value when determining the voltage ofDC systems derived from rectifiers, bearing in mind that smoothing does not modify the peakvalue when the semiconductors are operating on an open circuit.IEC 61892-4 pdf download.