Maximum Possible Efficiency of a Single Phase Transformer

Given Data:
- Transformer Rating: 10 KVA
- Primary Voltage: 400V
- Secondary Voltage: 200V
- Pu. Equivalent Resistance: 0.02
- Pu. Equivalent Reactance: 0.1
- Core Losses: 1.31%

Pu. Equivalent Resistance and Reactance
The pu. equivalent resistance and reactance of a transformer are calculated using the following formulas:

Pu. Equivalent Resistance = (R / V1^2) * S
Pu. Equivalent Reactance = (X / V1^2) * S

Where,
R = Resistance of the transformer
X = Reactance of the transformer
V1 = Primary Voltage of the transformer
S = Transformer Rating in KVA

Using the given values, we can calculate the pu. equivalent resistance and reactance as follows:

Pu. Equivalent Resistance = (R / V1^2) * S
Pu. Equivalent Resistance = (0.02 / 400^2) * 10
Pu. Equivalent Resistance = 0.0000005

Pu. Equivalent Reactance = (X / V1^2) * S
Pu. Equivalent Reactance = (0.1 / 400^2) * 10
Pu. Equivalent Reactance = 0.0000025

Maximum Efficiency at UPF
The maximum efficiency of a transformer is obtained when the copper losses are equal to the core losses. At unity power factor (UPF), the copper losses are equal to the load losses. Therefore, the maximum efficiency at UPF can be calculated as follows:

Efficiency = (Output Power - Core Losses) / Input Power
Efficiency = (10,000 - (1.31/100)*10,000) / 10,000
Efficiency = 0.9869

Therefore, the maximum possible efficiency of the transformer at UPF is 98.69%.

Explanation
The pu. equivalent resistance and reactance of a transformer are used to analyze its performance under varying conditions. The equivalent circuit of a transformer is used to calculate the pu. equivalent resistance and reactance. The maximum efficiency of a transformer can be obtained when the copper losses are equal to the core losses. At UPF, the copper losses are equal to the load losses. The efficiency of a transformer can be improved by reducing its copper losses and core losses.