  When simulating resistive-capacitive circuits or electroquasistatic problems
where conductors and insulators coexist, one observes that large time steps or
low frequencies lead to numerical instabilities, which are related to the
condition number of the system matrix. Here, we propose several stable
formulations by scaling the equation systems. This enables a reliable
calculation of solutions for very low frequencies (even for the static case),
or large time steps. Numerical experiments underline the findings.
