Rolling force excitation unit PFVI401

Rolling force excitation unit PFVI401

Rolling force excitation unit PFVI401

The operation of high impedance earthed networks is different compared to solid earthed networks where all major faults have to be cleared very fast. In high impedance earthed networks, some system operators do not clear single phase-toearth faults immediately; they clear the line later when it is more convenient. In case of cross-country faults, many network operators want to selectively clear one of the two earth-faults.

To handle this type phenomena, a separate function called Phase preference logic (PPLPHIZ) is needed, which is not common to be used in transmission applications. In this type of network, it is mostly not possible to use distance protection for detection and clearance of earth-faults. The low magnitude of the earth-fault current might not give start of the zero sequence measurement element or the sensitivity will be too low for acceptance. For this reason a separate high sensitive earth-fault protection is necessary to carry out the fault clearance for single phase-to-earth fault.

Fault infeed from remote end All transmission and most all sub-transmission networks are operated meshed. Typical for this type of network is that fault infeed from remote end will happen when fault occurs on the protected line. The fault current infeed will enlarge the fault impedance seen by the distance protection. This effect is very important to keep in mind when both planning the protection system and making the settings.