Figure 3 Impedance Method Example
Figure 3 Impedance Method Example

From Figure 3, given the parameters below, calculate the 3-phase fault and X/R ratio at Fault 1, Fault 2 and Fault 3:

  1. Utility
    Available Fault = 436 MVA
    X/R = 15
  2. Cable 1
    Length = 1300 m
    Unit Resistance = 0.39 ohms/km
    Unit Reactance = 0.039 ohms/km
    Number of parallel conductors / phase = 1
  3. Transformer
    Primary Voltage = 13.8 kV
    Secondary Voltage = 0.48 kV
    Capacity = 2 MVA
    %Z = 5.75%
    X/R = 5.662
  4. Cable 2
    Length = 500 m
    Unit Resistance = 0.048 ohms/km
    Unit Reactance = 0.029 ohms/km
    Number of parallel conductors / phase = 2