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To solve this problem and write a computer program for calculating the three-phase fault current at point F in the given figure, the following steps are involved:

### Approach:
1. **Impedance Data and Fault Location**: Use the provided positive-sequence impedance data to build the network model for calculating the fault current.
2. **Assumptions**: 
   - Pre-fault resistance values: \(1.0 + j0.0\) pu.
   - Neglect all resistance values.
   - Calculate for both cases: 
     - **Case 1**: Circuit Breaker \( B_2 \) closed.
     - **Case 2**: Circuit Breaker \( B_2 \) open (stub-end fault).
3. **Fault Analysis**:
   - Use the **Z-bus method** or **Thevenin equivalent circuit** to calculate the equivalent impedance seen from the fault point.
   - Calculate the **fault current** using the formula:
     \[
     I_{fault} = \frac{V_{prefault}}{Z_{th}}
     \]
     Where \(Z_{th}\) is the Thevenin equivalent impedance as seen from the fault point, and \(V_{prefault}\) is typically assumed to be 1.0 pu.
4. **Line Removal**: For each scenario (normal, and one line removed at a time), recalculate the fault current.

### Computer Program:
You can develop a Python-based program or use any programming language to implement this. Here's a pseudocode outline for the program:

```python
# Input data
impedances = {
    (1, 2): complex(0.0, 0.1),
    (2, 6): complex(0.05, 0.15),
    (5, 4): complex(0.04, 0.2),
    (2, 4): complex(0.01, 0.1),
    (3, 5): complex(0.015, 0.15),
    (3, 6): complex(0.01, 0.19),
    (4, 5): complex(0.01, 0.19),
    (6, 7): complex(0.03, 0.1),
    (0, 7): complex(0.0, 0.08),
}

def calculate_zth(fault_bus, breaker_status):
    # Calculate Zth (Thevenin impedance) for the network with the given breaker status
    # Use matrix or nodal analysis for the network to calculate Zth
    pass

def calculate_fault_current(v_prefault, zth):
    return v_prefault / zth

# Case 1: CB B2 Closed
zth_closed = calculate_zth(fault_bus='F', breaker_status='closed')
i_fault_closed = calculate_fault_current(v_prefault=1.0, zth=zth_closed)

# Case 2: CB B2 Open
zth_open = calculate_zth(fault_bus='F', breaker_status='open')
i_fault_open = calculate_fault_current(v_prefault=1.0, zth=zth_open)

print("Fault current with B2 closed:", i_fault_closed)
print("Fault current with B2 open (stub-end):", i_fault_open)
```

This program would compute the equivalent impedance for the network configuration, both with the circuit breaker \( B_2 \) open and closed, and then calculate the fault current.

### Questions:
1. How can the fault current be calculated for a more complex network involving multiple buses?
2. What impact does the removal of individual lines have on the Thevenin equivalent impedance?
3. How does the open condition of \( B_2 \) affect the voltage at the fault bus?
4. What numerical methods can be used to solve for the Thevenin impedance in large power networks?
5. How would the inclusion of resistances in the impedance data change the result?

### Tip:
When developing power system models, always start with a per-unit system to simplify the calculations and ensure that values are on a consistent basis.

Write a computer program to calculate the three-phase fault current for a fault at F in Figure 1.16, with the network normal, and with one line at a time removed.

This problem involves calculating the three-phase fault current at point F in a power system network using the Z-bus method and Thevenin equivalent circuit. The solution considers two cases: CB B2 closed and CB B2 open (stub-end fault). This is suitable for electrical engineering students focusing on power system analysis.

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