A DC monitoring system is configured to measure and analyze VFD (Variable Frequency Drive) operational characteristics. The VFD is configured to receive three-phase input power from a standardized source and to provide variable frequency three-phase output power to a three-phase motor. In some applications, the VFD and motor operate at a medium voltage. The VFD can include multiple inverter modules consisting of a DC section and switching section, also referred to as a multiple bus configuration. The DC monitoring system includes a measurement module coupled to each DC bus of the VFD, a data communication network, and a PQube monitoring device for transmitting data signals corresponding to voltage values of the VFD DC bus obtained in a medium voltage compartment to a low voltage compartment for processing and analysis. Processing of the data signals enables comparative and predictive analysis to determine early warning for possible capacitance failure in the VFD.