Exams › GATE › Technical

A single-phase 50 kVA, 250 V/500 V two-winding transformer has an efficiency of 95% at full load, unity power factor. If it is reconfigured as a 500 V/750 V autotransformer, its efficiency at its new rated load at unity power factor will be

1. 95.752%
2. 97.851%
3. 98.276%
4. 99.241%

Correct answer: 98.276%

Solution

From 95% efficiency at 50 kVA and unity power factor, the transformer losses can be found. When reconfigured as a 500 V/750 V autotransformer, the power rating increases, while the losses remain approximately the same, leading to a higher efficiency of 98.276%.

Related GATE Technical questions

• The following arrangement consists of an ideal transformer and an attenuator that attenuates by a factor of 0.8. An AC voltage $V_{WX}=100$ V is applied across $WX$ to get an open-circuit voltage $V_{YZ}$ across $YZ$. Next, an AC voltage $V_{YZ}=100$ V is applied across $YZ$ to get an open-circuit voltage $V_{WX}$ across $WX$. Then, $V_{YZ}/V_{WX}$ and $V'_{WX}/V'_{YZ}$ are respectively.
• In a transformer, zero voltage regulation at full load is
• The DC motor that can provide zero speed regulation at full load without any controller is
• A voltage-source inverter is used to control the speed of a three-phase, 50 Hz squirrel-cage induction motor. Its slip for rated torque is 4%. The flux is maintained at the rated value. If the stator resistance and rotational losses are neglected, then the frequency of the impressed voltage required to obtain twice the rated torque at starting should be:
• A three-phase synchronous motor connected to AC mains is running at full load and unity power factor. If its shaft load is reduced by half, with field current held constant, its new power factor will be
• A three-phase, three-stack variable reluctance step motor has 20 poles on each rotor and stator stack. The step angle of this step motor is

⚔️ Practice GATE Technical free + battle 1v1 →