Question

During a power failure, a domestic household uninterruptible power supply (UPS) supplies AC power to a limited number of lights and fans in various rooms. As per a Newton-Raphson load-flow formulation, the UPS would be represented as a:

• A. Slack bus
• B. PV bus
• C. PQ bus
• D. PQV bus

Hint:

In power system analysis, the bus that maintains voltage magnitude and angle and balances system power is modeled as a Slack Bus — just like a standalone UPS during a power outage.

Answer 1

The Correct Option is A

In load-flow studies using the Newton-Raphson method, a Slack Bus (or reference bus) is defined as the bus that:

• Maintains a fixed voltage magnitude and angle.
• Supplies or absorbs the difference in real and reactive power (losses, mismatch) after the power flow solution.

In the given scenario:

• The UPS acts as the sole power provider during a failure.
• It maintains the system voltage and balances the real/reactive power for the connected loads.

Hence, it acts as the Slack Bus in the load-flow formulation.