The contact surface condition directly affects the breaking performance and operational reliability of vacuum circuit breakers. Since vacuum interrupters are typically sealed within solid insulating materials

existing contact assessment methods mostly rely on disassembly procedures

making it difficult to achieve non-destructive measurement on-site in engineering. To address this issue

this paper proposes a non-destructive measurement method based on field emission current during the closing process under DC voltage

enabling quantitative evaluation of contact surface microtopography without disassembling the vacuum interrupter. First

this paper systematically analyzes thermionic-field emission theory

establishes mathematical models suitable for different measurement scenarios

and compares the applicability and measurement accuracy of two methods

namely

AC static contact gap and DC dynamic contact gap measurements. Subsequently

by integrating Fowler-Nordheim and Murphy-Good theories

characteristic field emission current profiles are constructed

and corresponding extraction methods for the field enhancement factor and effective emission area of contacts are proposed. In capacitive switching experiments

the proposed measurement system is integrated with a comprehensive test platform. By sequentially applying high-frequency inrush currents and monitoring field emission characteristics

quantitative tracking of contact surface erosion is achieved. The experimental results demonstrate that this method not only simplifies the measurement process and significantly improves engineering applicability

but also exhibits strong data consistency and theoretical interpretability. The method can provide effective support for online condition assessment and lifespan prediction of vacuum circuit breakers.