Research of controlled switching strategy to restrain inrush current during the energisation of converter transformer

Abstract

When an unloaded converter transformer is being energised, large inrush current may flow in the voltage jump side depending upon the residual flux in the core and the closing voltage angle of the power grid due to the hysteresis characteristics of the core, causing false operation of protective relays and bringing many adverse effects to the grid and primary electrical devices. Based on the analysis of the elimination of inrush current using controlled switching, the phase-to-phase electromagnetic coupling relationship which would be influenced by the core structure and winding connection mode was taken into account when considering the controlled switching strategy of three-phase transformer. With the analysis of core residual flux after de-energisation and the dynamic magnetisation of core during the energisation, a controlled switching strategy for inrush current restraining when energising converter transformer is presented in this study. Only the current arc quenching sequence during circuit breaker opening and the voltage extinguishing phase angle are asked for this strategy, and the simulation by electromagnetic transients programme and the experiment results indicate that this strategy could restrain the inrush transient efficiently.

Keywords

• transients
• circuit breakers
• power system protection
• relay protection
• power transformers
• power transformer protection
• magnetisation
• EMTP
• electromagnetic coupling
• power grids
• power system control
• controlled switching strategy
• voltage jump side
• power grid
• phase-to-phase electromagnetic coupling relationship
• core structure
• winding connection mode
• three-phase transformer
• core residual flux
• inrush current restraining
• current arc quenching sequence
• voltage extinguishing phase angle
• inrush transient
• converter transformer energising
• electromagnetic transients programme