The paper describes a new method of on-line monitoring of insulation dissipation factor-harmonic analysis, as well as a discussion on the factors influencing upon accuracy.

Aiming at the shortage of measuring mechanism for electrical equipment fault caused by dielectric in current electrical power system,the authors analyze the measurement theory for dielectric loss,propose an on-line measurement system for dielectric loss based on the single chip,and use LMS adaptive filtering algorithm in the design system.

Cyanate ester resin has lower dielectric loss factor,low and stable dielectric constant.

Then signification and definition of dielectric loss factor-tanδ is analyzed under harmonics exist.

An analysis has been made in this paper on the effect of space disturbance upon capacitive bushing dielectric loss factor tanδ measurement,which appears to be smaller value than the normal,sometimes even to be a negative value,in site test.

At 220 kV CVT of Line Gunan, both capacity and dielectric dissipation factor are valuably measured.

Through theoretical and practical analyses on dielectric dissipation factor measuring methods of capacitive current transformer with positive and negative connecting modes, the authors propose an onsite measuring method, which can diminish the working strength and enhance the working efficiency.

Dielectric dissipation factor (tanδ) is a key parameter in capacitive power equipment insulation on-line monitoring, which can reflect the insulation station of the capacitive equipments such as Bush and CT.