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Electrical formula sheet
The formulas behind GridCircuits calculators, with symbols as used on each tool page.
| Quantity | Formula |
|---|---|
| Ohm’s law | V = I · R |
| Power (DC / resistive) | P = V · I = I² · R = V² / R |
| Single-phase apparent power | S = V · I |
| Three-phase apparent power | S = √3 · V(LL) · I |
| Real power | P = S · PF |
| Reactive power | Q = S · sin(arccos PF) = √(S² − P²) |
| Transformer full-load current (3φ) | I(FL) = kVA × 1000 / (√3 · V) |
| Infinite-bus fault current | I(SC) = I(FL) × 100 / %Z |
| Voltage drop (1φ / DC) | Vd = 2 · I · R · L |
| Voltage drop (3φ) | Vd = √3 · I · R · L |
| Capacitor kvar for PF correction | Qc = P · [tan(arccos PF1) − tan(arccos PF2)] |
| Resistance vs temperature | R(T) = R(20) · [1 + α (T − 20)] |
| Per-unit value | pu = actual / base; Z(base) = V(base)² / S(base) |
Symbols: V voltage, I current, R resistance, P real power, Q reactive power, S apparent power, PF power factor, L one-way length, %Z transformer percent impedance, α temperature coefficient.