Alstom VDC

The VDC is the DC voltage supervision relay module for Alstom MiCOM / Midos protection racks, used for substation station DC battery bus monitoring. This VDC continuously monitors the 24V, 48V, 110V or 220V DC control supply, detects undervoltage, overvoltage and DC supply loss, and outputs alarm contact signals to SCADA and local alarm annunciator. It is widely called VDC voltage relay in spare part lists.

This VDC adopts plug-in withdrawable design, compatible with Midos rack base shared with MCGG, MVAJ, MVAX protection relays. It has built-in delay circuit to avoid false alarm caused by transient voltage dip during breaker switching. Gold-plated changeover contacts are used for alarm signal transmission. Front window and indicator lamp show normal / fault status. It does not have protection tripping logic, only for DC power quality supervision of relay cabinet.

The VDC is widely deployed in power grid substations, power plant relay protection panels, fed by station backup DC battery system. This legacy Alstom (AREVA) Midos series relay is discontinued. Most available units are tested surplus spare parts for protection cabinet overhaul and emergency replacement. Voltage rating must be confirmed before spare replacement.