Hi everyone,
We are using EE65 for 3.3kw power. Output should be 420v 8A. Currently we are facing issues issue with transformer temperature. We run 5mins means temperature reaches 70deg, but not stable.In this case peak to peak voltage 900v and current 15 ripple. Any suggestions please?

 

420 VAC(rms) * 8 A = 3.36 kw, which exceeds the rating. You should lower the output voltage to maintain a lower temperature. Nobody that I know ever runs a product up to its maximum rating and slightly beyond, that is the road to perdition. Didn't anybody ever clue you in that some safety margin is required if you want a reliable system.

 

EE65 is a high frequency ferrite transformer.
What type of drive circuit are you using?
What peak flux density are you using?

 

Yes, a lot of information is missing. You are taking more that the rated power out of your transformer, If you are using it with 50 0r 60 Hz the efficiency will be very poor.
So tell us about the application and what is the input power to the transformer. Voltage, current, and frequency. AND let us know if it is an inverter application or a mains powered application.