html{display:none} SEL-321-5 Phase and Ground Distance Relay | Schweitzer Engineering Laboratories


Phase and Ground Distance Relay

SEL recommends selecting the SEL-311C Transmission Protection System in place of the SEL-321-5. 

Replacement product: SEL-311C

No Longer in Production

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50 Hz EHV and HV applications.

Designed to meet stringent single-pole tripping requirements.

Contains all the protective elements and control logic necessary to protect, monitor, and control any noncompensated overhead line.

The unique adaptive directional element chooses between negative- and zero sequence quantities based on signals generated by a disturbance.

Power-swing blocking is provided during the single-pole-open period immediately following a single-pole trip.

Use acSELerator QuickSet SEL-5030 Software to manage your relay settings.

Use acSELerator Team SEL-5045 Software to automatically gather relay event reports on your PC and manage them with a database.

Use synchroWAVe Event Software to display oscillograms and vector diagrams to analyze event reports.



  • Four zones of phase and ground distance protection.
  • Quadrilateral (and/or mho) characteristic for ground distance protection.
  • Adaptable directional element selects best measurement technique (negative-sequence or zero-sequence impedance).
  • Independent timers for phase and ground distance time-delayed trips.
  • Any zone may be set forward or reverse.
  • Patented Mirrored Bits technology for communications-aided tripping schemes (eight independent channels in each relay).
  • Flexible communications and RTU features including three independent ports; ASCII, multidrop, and binary protocols; compressed ASCII commands; Fast Meter/Fast Operate support; Remote control bits for SCADA/RTU functions.

Minimum Software Version

Latest Firmware Versions

There are no firmware versions available for this product.

Product Revision Firmware ID Date Available Serial Number

The Firmware IDs for older versions of the firmware can typically be found in Appendix A of the instruction manual.

Minimum Software Version

Product Certifications