Cable cleats are needed to restrain high voltage cables during short circuit events. Current levels in these events can range upwards of 200,000 amps. In the worst case of a 3-phase short, magnetic field induced repulsive forces between the cables can range upwards of 10,000 pounds and develop within 1/100th of a second. Substantial damage can occur before circuit breakers can react to the short. Cable restraint is critical to protecting infrastructure and personnel as well as reducing downtime.
The expense and time required to design, build and test cable cleat designs that meet the globally accepted test protocol and repeat that process for an entirely new product line seemed prohibitive given the target time frame. A reasonably accurate and economical (in terms of solve time) simulation methodology had to be a critical component of the development process. The simulation would have to be able to model this highly dynamic, multibody contact, 3-phase alternating current short circuit test event that occurs in 1/10th second, can develop component velocities of more than 2,000 inches/second, and results in high material deformation and catastrophic failure.
ANSYS LS-DYNA explicit dynamics integrated with an electromagnetic simulation engine is well suited to this kind of simulation. Significant simulation development milestones included (1) adjusting the stiffness, yield strength, and mass of solid copper conductors to behave like stranded conductors at the prevailing temperatures; (2) developing high strain-rate material models for each component; (3) integrating the electromagnetic solution capability into the simulation; (4) development of a 30-variable mathematical model to exactly match the short circuit test current pattern and using a genetic algorithm to find the variable coefficients; (5) developing element erosion criteria to enable simulation of physical failure; and (6) successful verification in early testing.
The new cable cleat product lines were originally certified in testing very near the peak short circuit current levels predicted by the simulation. Repeated simulations to verify design changes and predict peak current certification levels in testing resulted in a substantial reduction in the prototype-and-test cycle. The estimated savings attributed to simulation versus prototype-and-test was a very high percentage of the total product line development cost.