The power transformer, a central node of power grids ensuring electrical energy flows, can experience thermal, electric, ambient or mechanical (TEAM) stresses during manufacturing, transportation, installation and operation. Such stresses in time can deteriorate its insulation ecosystem. On-line systems designed and engineered to provide continuous monitoring of Partial Discharge (PD) are being discussed herein. The content of this paper allows decision makers to take note of required PD monitoring capabilities leading to defects being promptly revealed, understood, and therefore removed. This article discusses the need for on-line monitoring and provides an overview of key functionalities, features and options for PD diagnostics and its relationship to insulation condition. The advantages of on-line PD monitors are outlined via condition-based maintenance examples where PD information played a key role.
