Short-Circuit Tests

Test institute:	Forschungsgemeinschaft für Hochspannungs- und Hochstromtechnik e.V. Hallenweg 68219 Mannheim Germany
Date of test:	29th June 1979
Parts tested:	Cable Clamp Type K 36/52 Fastening of individual single-core cables Cable Clamp Type KP 39/53 Joint fastening of trefoil of single-core cables
Test:	Experiments were meant to define the behaviour of cable clamps under dynamic strain applied by maximum short-circuit currents up to 110 kA.

The following figures were assumed as admissible strain on cable clamps:

Type K 36/52	maximum admissible strain	= 10.000 N
Type KP 39/53	maximum admissible strain	= 25.000 N

The forces applied to the cable clamps were computed by the following formula for maximum three-phase short circuits.

whereby:

F	: force applied by short circuit in Newtons
l	: distance between clamps in meters
a	: center-to-center distance between cables in centimeters
I _s	: maximum short circuit in kA

Besides the fact that the tested cable clamps meet the requirements placed on them, these experiments show that

When using single-core cable, we recommend that the dynamic forces of the short-circuit current be considered as well, not only its thermic effects.
In order to prevent excessive bending of cables between clamps, the latter may have to be spaced closer together for high short-circuit currents than their maximum admissible strain would normally dictate.
With high short-circuit currents, simply arranging the cables in trefoil and laying them on racks, for instance, is not enough. As Photographs 3 to 6 show, the bundled cables can be damaged during jumps, or they may damage other system parts.
In such cases, it appears expedient to connect the trefoil to the rack at appropriate intervals, bearing in mind that the rack itself must be able to withstand a certain amount of strain. However, these tests do not allow us to state how high such strain may be.