Example of Transformer Design Procedure with Core Selection Cross-checking and Calcultion of Losses

Design Procedure:

The design of transformer procedure is given here.

• Step-1: Inputs required for starting the design of transformer are: primary and secondary voltages, power rating, transformer efficiency and switching frequency.
  • Primary Voltage, E_p=400 V
  • Secondary Voltage, E_s=800 V
  • Output Power, P_o=10 kW
  • Frequency, f_s=100 kHz
  • Transformer efficiency, η=97%

• Step-2: Calculate the VA rating of transformer with power rating and its efficiency.

Step-3: Calculate the area product (AP) for the selction of core using the equation. It is a product of window (A_W) and cross-sectional (A_E) areas of core.

• Step-4: Choose a core and calculate the ‘AP’ using A_W and A_E values from datasheet.
  • choose a core https://www.tdk-electronics.tdk.com/inf/80/db/fer/e_55_28_25.pdf

From core data sheet, A_E is directly available

A_E = 420 mm²

Window area can be calculated using core dimensions

A_W = (37.5 – 17.2) * 18.5 = 375.5 mm²

AP = A_E * A_W = 420 * 375.5 = 1,57,731 mm²

• Step-5: The selected core area product should be greater than the calculated area product.

AP of core (1,57,731 mm²) > calculated AP (1,54,650 mm²)

• Step-6: Calculate the primary side number of turns those required to wind on the core.

• Step-7: Calculate the secondary side number of turns using voltage relation

• Step-8: Calcluate the cros-sectional area that required to choose the wire 
  • The primary and secondary currents can be calculated using power and voltages respectively,

The crosssectional areas of wire required in primary and secondary can be calculated,

• Step-9: Choose a wire such that its cross-sectional should be more than the calculated cross-sectional area from previous step.

From AWG sheet,

a_wp = 10.5 mm² @ 30 A

a_ws = 5.26 mm² @ 15 A

primary wire a_wp (10.5 mm²) > calculated a_wp (8.56 mm²) &

secondary wire a_ws (5.26 mm²) > calculated a_ws (4.26 mm²)

Cross Checking Selected Core:

• Step-10: Cross-check the selcted core is suitable to wind the selected wire for calaculated number of truns. If not, choose the another core with next highest AP value and repeate the process from step-4
  • Available core window area, K_W . A_W = 0.4*375.5 mm² = 150.2 mm²
  • Actual required window area, N₁.a_wp+N₂.a_ws = 9*10.5+18*5.26 = 189.18 mm²

The available window area (150.2 mm²) < actual (189.18 mm²)

Therefore, the selected core is not suitable, select a core with more dimensions which has AP slightly more than the currrent one.