Dear Mr. Manoj,
Please find the reply
1.) How should i design my own core dimensions.
Ans: Up on your experience !!!!!!!!!!!!. There is no essay formula for designing core dimension, you can select E shape geometry lamination and select dimension for total length, total width, center leg width side leg width window width and window length.Keep in mind the center leg width should be double to each side leg width.
Magnetic path length,cross sectional area,window area are major design parameter for transformer design.
2.) I have only Power Rating (VA/ Kva ), Insatead of selecting the core dimentions ( width , height ,length ,A,B,C,D...etc) from data sheet i want to design the EI Laminations of my own
Ans: Design lamination core as per above method(#1) and calculate turns and other parameters, if your core loss and copper loss are almost same then you can say that your core design is ok otherwise change the each dimension of the core and recalculate losses repeat the exercise.....
3.) I have to draw the core dimensions by myself without the core size selection chart.
Ans: You can draw your own core dimension as per #1 & #2 Keep in mid that the magnetic flux should travel through the core as per image on post #8.