Evaluation of Behavior of Q(t) Measurement and Noise Effects

DC power equipment is increasingly being integrated into our society, necessitating reliable diagnostic methods for insulation materials under high DC electric fields. The current integration method (Q(t) measurement) is considered one of the applicable methods for measuring Q(t) data. However, the mathematical and physical analysis of Q(t) measurements is not yet fully developed, resulting in partially analyzed data, especially concerning variance handling. By introducing a circuit model and solving differential equations numerically, this study investigates the causes of variance in the delay properties at the early stages of Q(t). Average Q(t) data for polyimide sample sheets with pseudo-noise in initial conditions were generated, and the numerical changes were evaluated. The findings suggested that variances in delay properties were mainly due to initial offsets in the first and second time derivatives of Q(t), rather than offsets in Q(t) itself. Therefore, it is revealed that the user of Q(t) measurement should be more attentive to the stability and control of inrush current when applying it to actual insulation materials to make diagnoses more reliable.