Unmesh I have read your posts again and also those of others some with experience in high power control and some without. this problem should be separated into two parts. First obtain the requisit signal through properly isolated methods. Do not cut corners here. for example if you power an intermediate supply through a transformer be certain that it can withstand the dc potential without leakage as this can upset the fault protection not to mention the possible hazard while servicing it. Remember that all components that contact these voltages must be in a proper protective cage and must be marked as to the danger involved. you may also want to indicate prroper proceedures for safing the area for servicing. Second after you have a safe isolated signal process it as required. but remember that errors in that part of your your design attached to the high power circuits, or your not understanding the existing system design correctly can lead to expensive downtime or worse injury to a person. These large power systems do not forgive mistakes so work very carefuly. Enjoy Terry