4-20
BE1-51/27R - Installation
Neutral Element Back-up Settings
Because the generators are ungrounded, the 51N element of the BE1-51/27R relay has no relays to coordinate
with. An instantaneous element, if used, must be set above the maximum false residual current that can be
developed due to dissimilar CT saturation during an external three-phase fault. In a like manner, the time setting
of the time overcurrent element must ride through this transient resulting from CT saturation.
Ground current contribution from each transformer is 485 amperes. Normal level is 2 × 485
970
A.
Set neutral time element (51/27) for 0.8 amperes pickup.
Set time element (51N) at 0.2 seconds for 970 ampere primary:
970
60 × 0.8
20
Multiples: 08 timedial.
Set instantaneous (50N) pickup at 5 amperes
970
300
3.2 × (
relay pickup).