In the ongoing expansion of HV power grids, new power sources from renewables, wind, solar and battery power have been introduced. These sources use converters/inverters for interfacing to the grid, which pollutes it with harmonics. Harmonics will inevitably lead to increased losses in power transformers, especially in the older types, as well as in both overhead power lines and underground cables in the HV grid. HV grid operation needs new reference instrumentation both for the calibration of instrumentation in substations and for the monitoring of harmonics, to ensure stability and reliability. HV grid condition monitoring is crucial to ensure the reliability of the electricity grid. There is a strong industrial need for applying new partial discharge (PD) detection and is in particular relevant for monitoring HVDC systems.