Polarisation - Depolarisation (PDC) and Retuen Voltage Measurement (RVM)

Hello .....

Could you inform me what is the standard references to interpretation of PDC and RVM in relation to water content in the solid insulation for Oil Filled Transformer and how to calculate S/M (Siemens per meter) to % water content during PDC or RVM test..

Thank you for all

Rgds

Siswanto