Question

In load flow studies, PV bus is treated as a PQ bus, when :

• A. Reactive power goes beyond limits
• B. Phase angle becomes high
• C. Voltage limit is violated
• D. Active power limit is violated

Hint:

PV Bus changes to PQ Bus when: \[ Q \text{ violates generator reactive power limits} \]

Answer 1

The Correct Option is A

Concept: In power system load flow analysis:
• PV bus is also called generator bus,
• real power \(P\) and voltage magnitude \(|V|\) are specified,
• reactive power \(Q\) is calculated. However, generators cannot supply unlimited reactive power. When reactive power exceeds generator limits, the PV bus is converted into a PQ bus.

Step 1: Understanding PV bus. For a PV bus: \[ P = \text{specified} \] \[ |V| = \text{specified} \] Unknown quantities are: \[ Q \text{ and } \delta \] Generator excitation system controls voltage magnitude.

Step 2: Understanding reactive power limits. Generators have limits: \[ Q_{min} \le Q \le Q_{max} \] These limits are due to:
• rotor heating,
• stator current limitations,
• stability restrictions.

Step 3: What happens when limits are violated? If calculated reactive power becomes: \[ Q > Q_{max} \] or \[ Q < Q_{min} \] then generator can no longer maintain specified voltage magnitude. Hence:
• voltage control is lost,
• bus can no longer behave as PV bus.

Step 4: Conversion of bus type. Under reactive power limit violation: \[ \text{PV Bus} \rightarrow \text{PQ Bus} \] Now: \[ P \text{ and } Q \] are fixed quantities and voltage magnitude is computed.

Step 5: Selecting the correct answer. Thus PV bus is treated as PQ bus when: \[ \text{Reactive power goes beyond limits} \] Hence correct option is: \[ \boxed{(1)} \]