Bushings are strategically important compo-nents for the transmission of electrical energy. They are exposed to high thermal and electrical stresses. There-fore monitoring becomes more and more important. A new solution for an advanced on-line monitoring of capacitance C and dissipation factor tan δ is presented: It is able to continuously monitor the dielectric quanti-ties C and tan δ at power frequency, service voltage and service temperature. A reference signal is necessary to determine possible changes of C and tan δ. It is pro-posed to take the reference from existing three-or sin-gle-phase air capacities. Before the input signals can be evaluated, they are digitized and filtered. The phase difference between object signal and reference signal enables the determination of the change of dissipation factor. Excellent accuracy in comparison with Schering bridge measurements is achieved, both in single-and three-phase environment, even with strong harmonic distortions.