Can you also evaluate the Duty/Cycle status while determining the resistor wattage ?

[stuncer]

As you know, when 30v voltage drops on a 390r resistor, 2.3W power is generated and this resistance is min. need to choose 3W

But if this voltage occurs for a short time like 50nS in a 50mS period, can 1/4W or even 1/8W be used?

I also have one more question, I wanted to ask here in order not to make the Forum busy.
As you know, in the snubber part, a film type capacitor is used. But film type capacitors occupy a lot of space on the pcb in terms of the area they cover.
Moreover, if we are talking about the control of 4 three-phase motors, it is necessary to allocate a min.10cmX10cm area on the pcb to capacitors.
I couldn't find any clear information in my research, can I use a Multilayer (Ceramic) capacitor instead of a film type capacitor in the snubber part?
The dimensions of the 10nF 1000VDC multilayer capacitor are almost 1/20 smaller than the film type capacitor

 

[dick_freebird]

You can duty-cycle-average for bulk temp rise but you must also
look at short-pulse effects, adiabatic heating at points of current
crowding / voltage drop can be extreme. In my world of IC
interconnect reliability I will use a 10X steady state current density,
which is a conservative rule of thumb.

You might have similar concerns with thin film resistors and less
(or higher peak/average ratio) with thick film or bulk resistor
bodies, as heat is shed in the film and travels slower (us to ms)
to "spread" to uniformity (before the next pulse?). The more
concentrated thermal dissipation is, the more to worry about
the short-pulse particulars (look for research on this if you get
no "blessed" guidance from the mfr's or same-tech competitors'
apps / reliability collateral.