The electrical transmission infrastructure, in the US has witnessed severe environmental hazards, accidents and in countries like Columbia, Pakistan, and India malicious attacks leading to the sabotage of transmission towers. The physical security of the national electric grid has largely been evaluated through examination of the effect of the physical disruption on the associated electrical quantities. To ensure safe and reliable operation of the power system, detection of tower tilt and its effect on the sag and tension at the initial stage of the disruption is indispensable. The use of the concept of geometric transformation for each phase of a tilted tension section of a high voltage transmission line to evaluate line sag-tension is proposed. The accuracy of the method is compared with the more complex, nonlinear finite element method used in PLS-CADD software. Different combinations of tangent towers tilt in a tension section are studied for sag-tension calculation including conductor temperature effect. Appropriate warning alarms are generated in case of considerable changes in the sag-tension values or violations of limits, enabling operators to take designated actions in initial stages of the physical disruption.