Transformer thermal-model calculator — top-oil and hot-spot temperature rise to IEC 60076-7
Give the cooling method, the rated no-load and load losses, a load curve and the ambient temperature, and the engine returns the top-oil rise, the hot-spot rise and the hot-spot temperature for every operating point, with the hot-spot limit drawn in. Values the engine cannot produce are shown as not available, never as zero.
Sample case pre-filled: 1000 kVA transformer, P0 = 1700 W, Pk = 14500 W, cooling ONAN, load curve 50/75/100/125/150 % and 40 °C ambient. Overwrite the fields with your own values - every number below is computed by the engine.
RequiredRecommendedLeft bar: blue = required, gold = recommended. Optional and advanced fields are collapsed by default.
Not calculated yet - fill in the input data and press the button.
This page does not give a conclusion on whether the temperature-rise test can be waived or replaced. The requirements and exemptions for the temperature-rise test are set by IEC 60076-2 (liquid-immersed, = GB/T 1094.2) and IEC 60076-11 (dry-type) and by the technical agreement between buyer and seller; they are outside the scope of this platform.
This page is a steady-state exponential engineering model, not a finite-element thermal simulation: it does not resolve the temperature gradient inside the winding, the oil-flow distribution or local oil-duct blockages.
This page does not cover dry-type transformers (their temperature rise and insulation classes follow IEC 60076-11).
The relative ageing rate and daily life loss, where shown, are equivalent estimates for operating comparison and do not constitute a life guarantee or a test judgement.
Any parameter not supplied by you is shown as not available, or explicitly labelled as an engine existing default. Missing values are never replaced by zero.
Results are for selection and operation reference only; the manufacturer temperature-rise calculation and the type-test report prevail.
Thermal model: IEC 60076-7:2018 section 7.3 (steady-state exponential solution): d_oil = d_or*[(1+R*K^2)/(1+R)]^x, d_hs = d_oil + d_hr*K^y, theta_h = theta_a + d_hs; R = Pk/P0, K = S/Sn. The temperature-rise algebra is the platform single source engines/params.js::tempRiseAt - this page adds no new formula.
Cooling method -> exponents and constants taken from the IEC 60076-7 exponent-and-constants table (table number to be verified; values reproduced from DOI 10.1002/etep.1631 and consistent with the Amperis loading / hot-spot calculator).
The rated top-oil rise and the rated hot-spot-to-oil gradient are nameplate / manufacturer data-sheet values, not standard constants; the defaults here (55 K / 25 K) are the engine existing defaults and can be overridden.
Sample case: P0 = 1.0 kW, Pk = 9.0 kW (R = 9), ONAN. At K = 1.0: top-oil rise 55.0 K, hot-spot rise 80.0 K, hot-spot temperature 120.0 °C at 40 °C ambient. At K = 1.3: 80.9 K / 118.9 K / 158.9 °C.
Scope: oil-immersed transformers only. Dry-type units follow IEC 60076-11 and are out of scope. The hot-spot and ageing quantities are engineering estimates, not test results.
This page is a running check with the IEC 60076-7 thermal model. It is not a temperature-rise test and cannot replace one.