Moisture assessment by FDS & PDC

A large population of aged equipment is apparently contaminated with moisture. Effects on life of Power transformer due to moisture in the solid insulation are:


  • Accelerated rate of aging for cellulosic materials such as paper and press board
  • Reduction of the dielectric strength of paper and press board materials
  • Risk of bubble evolution at high temperatures and limited Overloading capacity


Now a days two approaches are applied; the measurement of charging and discharging currents in time domain (Polarization and Depolarization Currents PDC) and the dielectric spectroscopy in frequency domain (Frequency Domain Spectroscopy FDS) known as DIRANA & provides an indication of the insulation condition such as:


• Moisture content in the oil/paper insulation

• Faults in OIP, RBP and RIP high voltage bushings & CT.

• Faults in the generator, motor and cable insulation

• Monitoring of moisture content in solid insulation during maintenance actions such as On- site drying will be very effective and should be considered as an important application.