What are the two standard tests used to determine a synchronous generator’s impedance characteristics?

• A. Open-circuit (no-load) test and short-circuit test.
• B. No-load test and load test.
• C. Electrical continuity test and insulation test.
• D. Thermal test and vibration test.

Answer: (A)

When you want to determine a synchronous generator’s impedance characteristics, you use two standard tests: the open-circuit (no-load) test and the short-circuit test. In the open-circuit test, you excite the field and raise the terminal voltage with no load connected, so essentially no current flows. This lets you observe the internal generated emf and how it relates to excitation without voltage drop from load currents, giving a clear view of the machine’s emf behavior and the portion of the impedance that shows up under no-load conditions. In the short-circuit test, you short the terminals and apply voltage to drive current, so the current is limited mainly by the machine’s internal impedance. The voltage required to push a given current under short-circuit conditions reveals the synchronous impedance (the combination of armature resistance and the synchronous reactance). Together, these two tests define the generator’s impedance characteristics and its equivalent circuit for analysis, such as stability and fault studies.