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)