Analysis of Online Monitoring Error and Equivalent Circuit Model for Dielectric Loss Angle of Capacitive Equipment

The tangent value of the dielectric loss angle, tan $\delta $ , is a crucial electrical parameter that indicates the insulation status of capacitive equipment. The accurate measurement of tan $\delta $ is critical for detecting both overall defects and localized large defects in the insulation medium. The equipment voltage and its insulation leakage current serve as the electrical parameters for tan $\delta $ calculation. This article examines the factors influencing online monitoring of voltage and current measurements, proposes an equivalent circuit model affecting voltage and current measurements, and conducts an error analysis of tan $\delta $ . The study identifies current sensors, insulation of signal cable, spatial electromagnetic field coupling, cable parameters, and signal conditioning unit characteristics as the main factors affecting insulation leakage current measurements. Additionally, the insulation and temperature characteristics of capacitor units in capacitive voltage transformers (CVTs) are identified as the primary factors influencing voltage measurement. By establishing multifactor equivalent circuit models for current and voltage measurement channels, this article theoretically and experimentally analyzes the effects of various factors on tan $\delta $ . This work not only provides a detailed explanation of the various sources of errors in online monitoring of the dielectric loss angle but also offers valuable theoretical guidance for the online measurement of tan $\delta $ under complex operating conditions.