Electrical Formulas & Units

DC or a purely resistive AC element; V in volts, I in amperes, R in ohms.

Ideal inductor; f in Hz and L in H gives XL in Ω.

Ideal capacitor; f in Hz and C in F gives XC in Ω. Capacitive impedance has a negative imaginary sign.

R and X must be at the same frequency and referred to the same electrical circuit; useful for LV impedance and voltage-drop approximation.

Temperature in °C, α20 matched to conductor material near reference temperature; account for AC skin/proximity effects separately.

Balanced sinusoidal three-phase system, R/X per unit length and L in matching units. Neglects higher-order phasor effects.

Same conductor size and temperature in both legs, sinusoidal AC; use matching impedance-length units. DC uses R term only.

Identical length, conductor type, installation and equal current sharing; unequal impedances require explicit current distribution.

Correction factors must match the specific cable construction, installation method, ambient/soil temperature and grouping. Not a universal independent multiplier model.

Temperature coefficient as fractional 1/°C, identical series modules, applicable manufacturer model and conservative minimum design cell temperature. Do not use ambient and cell temperature interchangeably.

Identical string models and matched operating conditions; verify per-input and combined MPPT operating and Isc limits separately. Current-limited MPPT may clip.

DC or resistive sinusoidal AC RMS values. V in volts, I in amperes, P in watts.

RMS voltage across load and RMS current; S in VA, U in V.

Balanced sinusoidal system; S in VA, ULL in V, IL in A.

Fundamental sinusoidal quantities; cos φ is displacement power factor. Harmonics require additional consideration.

Sinusoidal steady state with consistent sign/magnitude conventions. Distortion power not included.

Same active power before/after, sinusoidal, both states lagging; P in kW gives Qc in kvar.

Corrected ampacity must reflect installation method, grouping, conductor temperature, neutral harmonic loading and applicable protection. This alone does not authorize a reduced neutral.

Complex fundamental RMS phasors referenced consistently. Triplen harmonic neutral current may add arithmetically and must be evaluated separately.

Use consistent active-power quantities and defined operating point; efficiency varies with load and temperature. Percent efficiency is 100η.

Sinusoidal waveform, RMS ULL and line current; sign convention for capacitive/inductive Q must be declared.

Same rated module power for the counted group; sum independently if module models differ. STC nameplate does not predict instantaneous in-field output.

Use consistent kW bases. No universal allowable maximum; respect manufacturer voltage, current, PV capacity and thermal limits.

P in kWp, H in kWh/m²/month relative to 1 kW/m², PR dimensionless with consistent loss boundary. Monthly totals cannot establish clipping or battery dispatch.

Consistent AC/DC energy boundary, time step, efficiency convention and SOC limits required. Cannot be simulated reliably from monthly generation/load totals alone.

Use realistic lifecycle maintenance, replacements, degradation, export compensation, tariffs and discount rates; monthly-only dispatch scenarios are preliminary.

Balanced, ideal three-phase capacitors; CΔ is the capacitance of ONE delta branch in farads, voltage in V, Q in var.

Balanced, isolated capacitor-only bank with third line floating, no reactors, bleed resistors affecting measurement or external circuits. Not universal to real equipment.

Sn in VA and side rated line-to-line voltage in V; use nameplate data, no cos φ input.

uk is short-circuit impedance percent on rated base, S in VA, U in V; phase angle and R/X not given by uk alone.

Current in A, time in s, k in A·√s/mm² for actual material and initial/final temperatures; does not verify mechanical withstand or protective clearing.

Use compatible ULL in V and fault current Ik in A for VA. Does not calculate fault current on its own.

Preliminary IEC 60909-oriented screen, not a full fault study; impedances must be referred to one voltage level in ohms. Account separately for motors, corrections, earth faults and minimum fault conditions.

Simplified network-dependent peak screening only; use correct IEC 60909 calculation method and device Icm/peak withstand to verify.

Applicable only to the permitted adiabatic conditions with protective fault current/let-through I²t and k matched to material, insulation and temperatures. Verify mechanical minima and continuity.

Same applicable material and installation assumptions. Sizes in mm². Confirm proper rounding to installed standard section and verify independent thermal/mechanical constraints.

Same rated base and temperature reference; load losses or test data are required to estimate uR.

Approximate at rated voltage/frequency, constant temperature and rated reference copper loss; stray losses and harmonics may require explicit treatment.