Q: Given P₀ and Pₖ from tests, how do I calculate efficiency at different load levels?
A: Efficiency η = P_out / (P_out + P₀ + β² × Pₖ) × 100%, where β = load factor.
Example: 10 MVA transformer, P₀ = 12 kW, Pₖ = 85 kW:
|
Load |
β |
Output (kW) |
P₀ (kW) |
β²×Pₖ (kW) |
η (%) |
|
25% |
0.25 |
2,500 |
12 |
5.3 |
99.31 |
|
50% |
0.50 |
5,000 |
12 |
21.3 |
99.34 |
|
75% |
0.75 |
7,500 |
12 |
47.8 |
99.21 |
|
100% |
1.00 |
10,000 |
12 |
85.0 |
99.04 |
|
120% |
1.20 |
12,000 |
12 |
122.4 |
98.89 |
Maximum efficiency at β = √(P₀ / Pₖ) = 0.376 → ~37.6% load.
Energy efficiency standards:
• IEC 60076-20: EEI classes A (highest) → D.
• EU Ecodesign 2019/1783: Tier 2 (2021), Tier 3 (2025–27).
• DOE 10 CFR Part 431: new rule effective June 2026.
• GB 20052-2020 (China): Grade 1 (highest) → 3.
• IS 1180 (India): BEE Star Rating 1–5.
TCO approach: TCO = Price + A × P₀ + B × Pₖ
A ≈ $3,000–8,000/kW (no-load capitalized cost).
B ≈ $500–2,000/kW (load capitalized cost).