Directional earth-fault protections are used when selectivity is required, e.g. due to parallel lines, meshed networks or networks being supplied from a number of directions. They are also normally required in radial fed systems to get selective operation.
RXPG 4 is a transient measuring directional earth-fault relay which determines the direction to an earth fault based on the short-term transient built-up in the beginning of the earth-fault. Thus, no resistance is required in the neutral point of the system. This improves the possibility of discovering high-impedance earth-fault, for example at a broken conductor. RXPG is available in three variants, all with the same measuring features but with logics and outputs adapted for different applications.
The earth-fault protections are available in six different designs. All contain a test switch RTXP 18 and a transient measuring directional relay RXPG 4 of variant A, B or C. Protections containing relays of variant B or C have one or two auxiliary relays RXME 1 respectively. In protections of auxiliary voltages other than 48 and 110 V dc are also a dc-dc converter RXTUG 22H included.
The RXPG 4 relay consists mainly of two input transformers, for the adaptation of current and voltage to the measuring circuits, and of three printed board assemblies.