A measuring unit for simultaneous measurement of two current values and two voltage values of a power line with three high-voltage conductors includes: three two-pole electrical interconnections, each interconnection being configured to be connected between two separated ends a high-voltage conductors; a first and second current sensor, configured and arranged to measure a current through the first interconnection and through the third interconnection respectively; and a first and second voltage sensor, configured and arranged to measure a voltage between the first and second interconnection and between the second and third interconnection. The measurement of the two current values and the two voltage values is at a floating potential. This measuring unit may be installed directly on all three phases, of a substation for example, with its own internal power source and with no ground connection. Such features are important for power systems with high penetration of variable renewable energy resources such as solar PV or wind.