Question

If the reference bus is changed in two load flow runs with same system data and power obtained for reference bus taken as specified P and Q in the later run: _______.

• A. The system losses will be unchanged but complex bus voltages will change
• B. The system losses will change but complex bus voltages remain unchanged
• C. The system losses as well as complex bus voltage will change
• D. The system losses as well as complex bus voltage will be unchanged

Hint:

Changing reference bus? → Same power losses, but voltages (angles) shift.

Answer 1

The Correct Option is A

Step 1: Understanding Reference (Slack) Bus
The slack/reference bus balances system losses by adjusting its generation. It also provides angle reference (usually 0°) for all other buses.
Step 2: Changing Reference Bus
When the reference bus is changed:
- The power losses in the system remain constant, because the system data (loads, lines, generation) are unchanged.
- However, complex bus voltages will shift due to new angle references.
Step 3: Important Insight
While real and reactive power flows stay the same, phase angles shift, which changes the complex representation of voltages.
Conclusion:
Only voltages (angle values) shift; losses remain unaffected.