How is transformer load ratio calculated?
Transformer loading, It is the ratio of the apparent power drawn (S_load = P/cosφ) to the rated power.: %loading = S_load / S_rated × 100. For example, if 620 kW (cosφ 0.9) is drawn from a 1000 kVA transformer, the apparent load is ≈ 689 kVA, i.e., ≈ loading. The typical suitable range for continuous operation is –80.
%Yurning = (P/cosφ) / S_rated × 100 · I = S_load/(√3·U)
Example calculation: 1000 kVA transformer, 620 kW load, cosφ 0.9 → apparent load 620/0.9 ≈ 689 kVA → loading ≈ (suitable range); secondary current ≈ 994 A.
Transformer Load Ratio (%)
Calculate the transformer's percentage load and secondary current based on its rated power; identify over/under loads.
Load rate
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Apparent load S
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Secondary current
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Notes: Loading = (P/cosφ) / S_rated · Secondary current = S_load/(√3·U). The appropriate continuity range is typically –80 (in terms of efficiency and reserve margin); >0 is overload. The precise assessment is made according to the load profile and ambient temperature.
How is it calculated?
- Enter the transformer power (kVA) and secondary voltage.
- Enter the active power drawn (kW) and cosφ.
- Press Calculate; the load %, apparent load, and secondary current will be displayed.
Frequently Asked Questions
What percentage load should the transformer be subjected to?
In continuous operation, a range of –80 is typically suitable in terms of yield and reserve margin; anything above 0 is considered overloading.
What happens if the transformer is overloaded?
Winding temperature and aging increase, lifespan shortens, and protection may trip. Load reduction or capacity increase is required.
Why is low load inefficient?
At very low loads, iron (no-load) loss becomes dominant and efficiency decreases; the transformer operates below its optimum point.
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