SEL-387-The first multi-winding current differential and overcurrent relay with dual slope characteristics, harmonic restraint, and user programmable logic was released in 1997. Later, in 1998 - SEL-321 - the first relay to also include high-speed peer-to-peer serial protocol for teleportation applications (Figure 23) was available. Generator protection SEL-300G (Figures 21 and 25) with 100 % stator earth fault protection is available since 1998. SEL offers the first protective relays to also include synchronized phasor measurements (Synchrophasors) as a standard feature since 1999. Reyrolle (UK) started the ARGUS line in 1994 (Figure20).
These relays used microprocessor technology which enabled more features, such as communications, data storage and alphanumerical display to be provided. The relay incorporated an event recorder that time and date stamped the last 100 events and as a consequence was named Argus- a mythical creature with 100 eyes. The Argus family developed into six variants and in the latest versions the event log could hold up to 500 events. Digital overcurrent protection ARGUS 1 with IDMTL-, DTL-, NI-, VI-, EI- and LTI-functionality was produced since 1997 (Figure 24).