What Dspark is referring to is an increase in Skin Effect with larger conductors at higher frequencies [Dspark, I'm just amplifying on your message, not being arrogant!].
What types of calcualtions are you intending to modify with different Hz?? I'm still trying to figure out how to do Voltage drop calcs [X and R figures] at 400 Hz and make them + 99.99% accurate!!
Anyhow, here's the deal:
If you lower the frequency, Inductive Reactance [XL] becomes the "dominate" type of Reactance.
If you increase the frequency, Capacitive Reactance [XC] becomes the "dominate" type of Reactance.
25 Hz has low skin effect problems on large conductors, but requires very large cores and coils for Inductive devices [AC motors, Transformers, Ballasts, etc.]. Line charging is much lower at 25 Hz than at 60 Hz, so there's less charge Capacitance between circuit conductors [a GFCI could be trip rated at maybe 1 or 2 milliamps without nuiscance trips].
25 Hz would have a totally different X vs R calculation for voltage drops.
The change in Hz would effect the overall KVA of a certain motor during many points along the HP output curves, and also non-loaded.
25 Hz would run a typical 2 pole Induction motor at maximum speed of 1500 RPMs unloaded [slip would bring it to 1425 RPMs for a 5% slip off synch Hz].
400 Hz would be exactly the opposite!
Skin effect will be dramatically increased on large conductors.
Cores and coils for Induction machines [motors, transformers, ballasts, etc.] can be made smaller, but primary / secondary separation increases [so does coupled RFI/EMI]. Inductive machine become more efficient with higher Hz.
Line charging increases big time as Hz increases, so GFCI [and the like] would need higher trip ratings [+20 milliamps and such].
Capacitive Reactance will become a factor at some points on a motor's power curves - especially at no-load [idle]. That would throw power factors into the Leading type areas, rather than the more familiar lagging type.
AC Induction motors would have a great max speed at 400 Hz! The same 2 pole AC Induction motor [let's use a Squirrel cage rotor type motor] that peaked at 1500 RPMs idle / 1425 RPMs full load at 25 Hz, would be 24000 RPMs idle / 22800 RPMs full load [5% slip].
Drawn amperage per KVA as regarding to KW will be common on all Hz. If you have a 1 KVA load connected to 100 VAC, it's going to draw the same 10 amps as it would at any other frequency.
The key is how much KVAR per KW is bouncing around the circuit.
Lower Hz, higher XL KVARs [normally],
Higher Hz, higher XC KVARs [normally],
All still delivering the same amount of KW [Horsepower, if driving motors].
If you are trying to adjust a voltage drop calculation - one which uses Reactance [X] and Resistance [R] instead of straight Resistance - you will need to adjust "Q" according to the Hz.
If I can somehow stumble across an existing formula, I'll add it to this thread.
Hope this make sense!!