Electrical Engineering Exam Formula Sheet

Principles of Electrical Engineering Formula Sheet Star/Delta - Delta/Star conversions: R1 R2 + R2 R3 + R1R3 R2

Ra =

Rb =

R1

R1R2 + R2 R3 + R1 R3 R1 Rc

R2

Rc =

Ra

R1R2 + R2 R3 + R1 R3 R3

Rb

R3

R1 =

Ra Rc Ra + Rb + Rc

R2 =

Rb Rc Ra + Rb + Rc

R3 =

Voltage divider: V1=V{(R1)/(R1+R2)}

Ra Rb Ra + Rb + Rc

Current divider: I1=I{(R2)/(R1+R2)}

Power Formulas: DC

P=I2R

P=VI,

AC (1 phase)

P=V2/R

P=VIcos(Φ),


= √3VLILcos(Φ)

AC (3 phase)  = √3VLIL

 = √3VLILsin(Φ) 3 phase formulas:  = √3VPh

IL = Iph

Star connection:

Delta connection:

 = √3IPh

VL = Vph

Resonance Circuits: Series:

Parallel:

fO =

Transient Analysis:

ω L Q= o

2π LC

fo = 1

Alternative parallel:

Charging:

1

Q= R

1 ω o CR

BW =

fo

2π LC ωO =

1 2π

R2 1 − 2 LC L

ZD = L

RL Circuits T=L/R I L = I O (1 − e ( − t / T ) )

CR

RC Circuits T=RC VC = Vo(1- e(-t/T)) IC = IOe(-t/T)

Discharging:

Q

IL = IOe(-t/T)

VC = VOe(-t/T) IC = -IOe(-t/T)