a.c.

a.c.

1. inductive reactance

   • XL = 2*3.142fL
     • XL= inductive reactance
       • f = frequency (Hz)
         • L = inductance (H)
   • V = LXL

2. capacitive reactance

   • Xc = 1/2*3.142fc
   • Xc = capacitive reactance
     • c = capacitance
     • V = LXc

3. power factor

   • 0 - 1 unity

4. basic machenics

   • acceleration = distance / time * (M/Sz)
   • work done = force * distance (Nm)
     • force = mass * 9.81 newtons
       • efficency = output energy or power / input energy or power * 100%

5. leavers

   • effort = load * load to fulcrum distance / effort to fulcrum distance

6. force on current-carring conductor

   • F = BIL
     • F = mechanical force exerted on the condutor mesured in newtons (N)
       • B = flux density of main magnetic field mesured in Wb/m2 - teslas (T)
         • I = current flowing in conductor mesured in amperes (I)
           • L = length of magnetic field mesured in meters (m)
   • flemings left hand motor rule
     • thumb = direction of motion
       • first finger = field
         • second finger = current

7. electrical equipment - three phase a.c. motors

   • stator = stays statatory (squirrel cage)
     • rotor = spins
   • three phase = 120 apart
   • N(rps) = F/P
     • N(rpm) = F*60/P
   • per unit slip = (ns - nr) / ns
     • % slip (ns -nr) / ns * 100

8. transformers

   • induced EMF = L (I2 - I1 / t * volts
     • I2 - I1 = values of current
   • Vp / Vs = Np /Ns or V1 / V2 = N1 / N2
     • V1 / V2 = I2 / I1 = N1 / N2