**Faults in a 3-Phase System**

A fault in a 3-phase system refers to an abnormal condition that occurs when there is a failure or malfunction in the electrical network. These faults can be caused by various factors such as short circuits, ground faults, insulation breakdown, or equipment failure. Regardless of the causes, faults in a 3-phase system can be categorized into two types: symmetrical faults and unsymmetrical faults.

**Symmetrical Faults**

Symmetrical faults occur when all three phases of the system experience a fault of the same magnitude and at the same time. This can happen due to a short circuit between all three phases or a fault to ground that affects all three phases equally. Symmetrical faults are characterized by balanced voltages and currents, and they can cause severe damage to the equipment and electrical network. However, they are relatively easy to detect and analyze, as the fault currents and voltages are symmetrical.

**Unsymmetrical Faults**

Unsymmetrical faults, on the other hand, occur when the fault affects one or two phases of the system, while the remaining phases remain unaffected. This can happen due to a short circuit between two phases, a fault to ground on one phase, or a combination of faults. Unsymmetrical faults are characterized by unbalanced voltages and currents, and they can be more challenging to detect and analyze compared to symmetrical faults. The severity and impact of unsymmetrical faults depend on the type and location of the fault.

**The Fault in a 3-Phase System**

The fault in a 3-phase system refers to any abnormal condition that disrupts the normal operation of the electrical network. Regardless of the causes, both symmetrical faults and unsymmetrical faults can cause faults in a 3-phase system. Therefore, the correct answer to the question is option 'B' - Both symmetrical faults and unsymmetrical faults.

It is important to note that external faults, such as faults occurring in the power supply or in connected equipment, can also cause faults in a 3-phase system. These external faults can be either symmetrical or unsymmetrical, depending on the nature of the fault. Therefore, option 'D' - External faults, cannot be considered as the only fault in a 3-phase system.

In conclusion, faults in a 3-phase system can be both symmetrical and unsymmetrical in nature, and they can be caused by various factors. It is important for electrical engineers and technicians to be able to detect, analyze, and mitigate these faults to ensure the safety and reliability of the electrical network.