What is a function of a transformer in a line interactive UPS?

Question

Options

• ATo increase the power factor as the load increases
• BTo increase harmonics by stepping down the output
• CTo regulate output voltage as the input voltage varies
• DTo provide low impedance for switched mode power supplies

• A
  2% (1)
• B
  11% (7)
• C
  83% (53)
• D
  5% (3)

Explanation

In a line interactive UPS, the transformer (typically an autotransformer) actively adjusts its tap positions to boost or reduce the incoming AC voltage, keeping the output stable when the utility supply fluctuates - this is precisely what makes the design "line interactive." Option A is wrong because transformers do not improve power factor as a function of load; power factor correction requires separate components such as capacitors or active correction circuits. Option B is wrong on two counts: transformers do not generate harmonics by design, and "stepping down" describes a voltage reduction, not a harmonic increase. Option D is wrong because providing low impedance for switched-mode power supplies is a characteristic of output filtering components, not the regulatory transformer.

Memory tip: The word "interactive" in "line interactive" tells you the UPS is continuously interacting with the incoming line voltage - that interaction is voltage regulation via the transformer, without switching to battery for every small fluctuation.

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