# A load-flow program is run twice, in the second run, the previous reference bus gets changed to a PQ bus. Which one of the following statements is true?

A load-flow program is run twice, in the second run, the previous reference bus gets changed to a PQ bus. Which one of the following statements is true?

### Right Answer is: The system losses will be unchanged but the complex bus voltages will change.

#### SOLUTION

• In load flow analysis is the steady-state analysis of the power system network. It determines the operating state of the power system for a given loading.
• Load flow solves a set of simultaneous non-linear algebraic power equations for the two unknown variables |V| and ∠δ at each node in a system.
• The output of the load flow analysis is the voltage and phase angle, real and reactive power at both sides in each line, line losses, and slack bus power.
• The system losses are a function of system properties that are independent of choosing a type of bus.
Whereas the complex bus voltage is a function of parameters that are being calculated.
• In load flow analysis the system losses are the function of system properties which is independent of the selection of the type of bus as reference bus. That is, system losses are constant and will remain unchanged on changing the type of reference bus.
• While complex bus voltages are the function of system parameters and one such parameter is a selection of reference bus. That is, complex bus voltages are dependent on the reference bus parameter and any change in it will change the complex bus voltages.
• When a load-flow program is run twice, in the second run, the previous reference bus gets changed to PQ bus then the losses in the system remain unchanged.
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