  Many optimization problems in electrical engineering consider a large number
of design parameters. A sensitivity analysis identifies the design parameters
with the strongest influence on the problem of interest. This paper introduces
the adjoint variable method as an efficient approach to study sensitivities of
nonlinear electroquasistatic problems in time domain. In contrast to the more
common direct sensitivity method, the adjoint variable method has a
computational cost nearly independent of the number of parameters. The method
is applied to study the sensitivity of the field grading material parameters on
the performance of a 320 kV cable joint specimen, which is modeled as a Finite
Element nonlinear transient electroquasistatic problem. Special attention is
paid to the treatment of quantities of interest, which are evaluated at
specific points in time or space. It is shown that shown that the method is a
valuable tool to study this strongly nonlinear and highly transient technical
example.
