Short circuit test

Test Institute: Forschungsgemeinschaft für Hochspannungs- und Hochstromtechnik e.V.
68219 Mannheim
Date of Test: June 29, 1979
Parts tested: Cable Clamp Type K   36/52 Fastening of individual single-core cables
Cable Clamp Type KP 39/53 Joint fastening of trefoils 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:

Typ K 36/52
       maximum admissable strain = 10,000 N

Typ KP 39/53     maximum admissable strain = 25,000 N

The resulting forces on the Cable Clamps were calculated according to the following formula for a three-pole short circuit.

Herein are:
F  : force applied by short circuit [N]
l   : distance between clamps [m]
a  : center-to-center distance between cables [cm]
I s: maximum short circuit [kA]


Result of the tests:

Besides the fact that the tested Cable Clamps meet the requirements placed on them, these experiments show that:

  1. 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.
  2. 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.
  3. With high short-circuit currents, simply arranging the cables in trefoil and laying them on racks, for instance, is not enough. As photographs 3, 4, 5, 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.