Formulas: Electrical engineering

DC circuits

• I = U / R

• P = UI = I²R = U² / R

• I = ε / (R + r)

• Q = I²Rt

• Rseries = R1 + R2, 1 / Rparallel = 1 / R1 + 1 / R2


AC circuits

• U = Um / √2, I = Im / √2

• XL = ωL, XC = 1 / (ωC)

• Z = √(R² + (XL − XC)²)

• tan φ = (XL − XC) / R

• P = UI cos φ, S = UI, Q = UI sin φ


Three-phase systems and transformers

• UL = √3 Uph, IL = √3 Iph for delta current relations

• P = √3 ULIL cos φ

• U1 / U2 = N1 / N2

• I1 / I2 = N2 / N1


Machines and measurements

• ns = 60f / p

• s = (ns − n) / ns

• P = Mω

• η = Pout / Pin · 100%