Abstract: This paper presents an experimental investigation of
transformer dielectric response and solid insulation water content.
The dielectric response was carried out on the base of Hybrid
Frequency Dielectric Spectroscopy and Polarization Current
measurements method (FDS &PC). The calculation of the water
content in paper is based on the water content in oil and the obtained
equilibrium curves. A reference measurements were performed at
equilibrium conditions for water content in oil and paper of
transformer at different stable temperatures (25, 50, 60 and 70°C) to
prepare references to evaluate the insulation behavior at the not
equilibrium conditions. Some measurements performed at the
different simulated normal working modes of transformer operation
at the same temperature where the equilibrium conditions. The
obtained results show that when transformer temperature is mach
more than the its ambient temperature, the transformer temperature
decreases immediately after disconnecting the transformer from the
network and this temperature reduction influences the transformer
insulation condition in the measuring process. In addition to the oil
temperature at the near places to the sensors, the temperature
uniformity in transformer which can be changed by a big change in
the load of transformer before the measuring time will influence the
result. The investigations have shown that the extremely influence of
the time between disconnecting the transformer and beginning the
measurements on the results. And the online monitoring for water
content in paper measurements, on the basis of the oil water content
on line monitoring and the obtained equilibrium curves. The
measurements where performed continuously and for about 50 days
without any disconnection in the prepared the adiabatic room.