A. 50 %
B. 60 %
C. 80 %
D. 95 %
Answer: D. 95 %
Explanation:
The efficiency of the transformer is obtained from various experiments conducted on different loads. The efficiency of power transformer is always greater than 90%. Thus, it can be said highly efficient device.
Power transformers are operated on full load hence power transformers are designed to have maximum efficiency at full load.
The efficiency of a power transformer under short-circuit test conditions is approximately zero % because during short circuit test output power of transformer is zero.
When load is not connected across secondary of transformer, the output power of transformer is zero. As, efficiency is ratio of output power by input power, the efficiency will be zero at no load condition.
Note:
Transformer efficiency is defined as the ratio of its output power to input power
At light load, hysteresis losses (magnetization and demagnetization of the core of the transformer) and eddy current losses are high compared to output power; Hence, the efficiency is low at this condition.
When the load on the transformer is further increased, its efficiency increases At heavy loads, copper losses are high compared to the output power; Hence the efficiency is low at this condition
Efficiency is maximum at both copper losses are equal to iron losses
Transformer efficiency is the ratio of its output power to input power and it depends on both load power factor and load magnitude
At low load, a transformer has low efficiency as hysteresis losses (magnetization and demagnetization of a core of transformer) and eddy current losses dominate over output power