The design of small solenoids without/with-partial insulation (PI) among turns or layers has been proven to grant higher thermal stability than for standard insulated cases. This technology also implies higher safety standards, by e.g. reducing the coil voltages. At the same time, a passive/simpler quench protection systems (QPS) becomes a concrete opportunity. Besides, this approach did not guarantee yet the same advantages on large-scale magnets, as the redistribution of currents and heat after quench is not yet fully understood. The possibility for full internal energy dissipation of the Nb $_{3}$ Sn EUROfusion DEMO toroidal field (TF) coil is here firstly discussed analytically and by means of circuital simulations, highlighting the possible final temperatures for internal dump and resistance ranges for the desired bridge resistors of such a PI coil. This study presents a new 3-D MATLAB numerical model, developed for simulating in a fast fashion charge and quench of PI-DEMO TF coils, by coupling both electrical and thermal physics. The code structure is explained as well as its first benchmarks. A parametric study-where only turn-turn localized bridges are considered-is presented, showing 1-100 V highest coil voltage and very high final temperatures after quenches. Consequences and possible improvements are finally discussed.