High-voltage alternating current switch-fuse combinations acc. to IEC 62 271-105
In order to increase the utilization range of a switch, it is combined with current limiting HV fuse-links. This combination unit offers short-circuit protection in addition to load switching capacity. HV fuse-links provide short-circuit protection, while the switch interrupts the currents below the transfer current of the combination unit.
In addition to the inrush current, short-circuit current on secondary terminal short-circuits and low voltage selectivity, the following switch characteristics should be taken into account:
– Rated transfer current (ltransfer)
– Fuse-initiated opening time of the switch (t0)
Selection of HV fuse-links acc. to IEC 62 271-105 graphic shows the rated transfer current (ltransfer) as a vertical line. The fuse-initiated opening time (t0) must be multiplied by 0,9 (procedure according to IEC 62 271-105) and a horizontal line be drawn. This results in an intersection that is characteristic to the switch and must be established for each switch individually.
|Selection of HV fuse-links acc. to IEC 62 271-105 graphic|
This switch intersection divides the sheet into four quadrants (see Selection of HV fuse-links acc. to IEC 62 271-105 graphic).
Suitable for the switch-fuse combination are HV fuse-links only with a time-current characteristic that does not pass through quadrant IV (“forbidden area”). Generally suitable for use in switch-fuse combinations according to IEC 62 271-105 are all HV fuse-links with striker which meet this criterion. EFEN has assigned HV fuse-links to the switch-fuse combination and the transformers of all major manufactures. These documents are available on request.