A research o f utilizing directional protective device f or improving t he sensitivity o f digital relay i n Vietnam coal mines grid

Abstract

As mining activities and productivity escalate, the 6kV power grid infrastructure of open-pit mines has become increasingly diverse in load types and structurally complex. Consequently, the demands placed on relay protection systems are progressively intensifying. Beyond merely ensuring operational safety, these systems are n ow required to enhance power supply reliability, thereby minimizing interruptions that could severely disrupt the production cycle. Notably, none of Vietnam's open-pit mines currently utilize directional Over-current relay (DORC) in their 6kV feeders. Beca use of including electric excavators, the power running to the fault point in 6kV PCC node could come from two direction causing the wrong operating of over-current relays Thus, the utilizing the directional protector is critically important for bolstering the reliability and efficiency of the power supply system in these mining operations. The devices automatically detect not only fauls current value but also their direction, then isolate the fault point after predefined delay. This mechanism significantly reduces the wrong tripping in 6kV grids from earthing as well as one-phase short-circuited, which account for over 80% of total faults MV grids of mines. This paper, through a study of the characteristics of medium-voltage grids with electric excavators a s distributed loads, proposes an effective directional relay application. The synchronization of setting parameters of multi-level DOCR (3levels) is also proposed, supported by thorough simulation and verified utilizing ETA and NEPLAN software, to prevent premature relay operations (false trips), which could lead to unnecessary power outages and prolonged supply interruptions. The integration of directional protector within the framework of overcurrent protection, combined with well-calibrated adjustments, will be validated with a specific 6kV power grid of a coal mine to demonstrate the feasibility and effectiveness of the proposal. The outcome setting values are customized with grids’ internal parameter to perform a discriminative tripping. These ones are also used to recommend their application across all medium-voltage grids in Vietnam's coal mines .