Fault current direction, Star- Delta starter faults checking, Return path of electrical circuit

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Fundamentals of Electrical Engineering – Key Rules to Remember

1. Direction of Electricity Flow

  • Electricity always flows from source to load.

  • It never flows “backward” from load to source.



2. Condition for Current Flow

  • A potential difference (voltage) must exist for current to flow.

  • Current always flows from high potential to low potential.

3. Single-Phase Current Return Path

  • In a single-phase system, whatever current the load draws will return through the Neutral.

  • Neutral ensures circuit completion.

4. Nature of Capacitor Bank Current

  • Current drawn by capacitor banks is reactive current (kVAR).

  • It is not active (real) power, so do not confuse reactive compensation with actual energy supply.

5. Behavior of Fault Current

  • Fault current always flows backwards from the fault point toward the source.

  • Example: If a motor develops a fault, its overload (O/L) relay trips first, not the transformer.

  • Reason: During fault, the load’s resistance drops very low, allowing very high current flow.

  • System is designed so faults are cleared locally first.

6. Motor Connected in Delta – Why No Short Circuit?

  • In a delta-connected motor with 6 leads, two supply phases meet in one winding.

  • Still, no short-circuit occurs because of the winding resistance and impedance.

  • If only one phase is connected to the winding, full voltage appears at the other end, but current won’t flow unless a return path exists.

7. Return Path is Essential

  • Current flows only when a complete path (closed circuit) is available.

  • Why must a circuit be completed? Because potential difference alone is not enough—a return path enables charge flow.

  • In a motor, when two different phases are applied to one winding:

    • They are never at the same potential due to their phase angle difference.

    • This potential difference across winding causes current flow and rotation.

✅ Key Takeaway:

  • Electricity follows strict rules of potential difference and return path.

  • Load currents, fault currents, and reactive currents all behave differently but are always governed by these fundamentals.


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