A transformer rated for 500 KVA, 1 KV/0.4 KV has an impedance of 10% and is connected to an infinite bus. The

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A transformer rated for 500 KVA, 1 KV/0.4 KV has an impedance of 10% and is connected to an infinite bus. The fault level of the transformer is

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Option B: 5000 KVA

Explanation & Concepts:
Given: Transformer rating S = 500 KVA, Per-unit Impedance Z_pu = 10% = 0.1, Infinite bus supply

Formula Used: $$Fault\ Level = \frac{Rated\ S}{Z_{pu}}$$

Steps: Identify the Given Parameters: The transformer capacity is $S_{rated} = 500 	ext{ KVA}$ and the percentage impedance is given as $Z\% = 10\%$.. Apply Fault Level Formula: When a transformer is connected to an infinite bus, the short circuit MVA (or KVA) is determined by its own impedance as the supply impedance is negligible.. Calculate the Result: Substitute the values $S_{rated} = 500 	ext{ KVA}$ and $Z_{pu} = 0.1$ into the formula to find the fault level.

Answer: B is correct because the fault level is calculated by dividing the rated KVA by the per-unit impedance, resulting in 5000 KVA.

Exam Tip: The concept of Short Circuit MVA (or KVA) is vital for selecting circuit breakers; a higher impedance limits the fault current, effectively reducing the fault level.

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Option A: 500 KVA

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Option C: $\sqrt{3} 	imes 500 	ext{ KVA}$

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Option D: None of the above

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