An analytical method for calculation of critical energies of uncooled composite superconductors is presented based on the transient model for heat conduction. In the model, the dependence of the ohmic heat generation on temperature as well as the finite duration and the finite length of thermal disturbances are taken into account while the thermophysical parameters of the conductor are assumed to be constant. Critical energies, determined on the basis of analysis of the time dependent maximum temperature in the normal zone, are used to formulate a simple explicit expression for the critical energy by the method of non-linear regression.