Innovative Directional Element Polarization
Provide directional stability during phase faults with the positive-sequence, voltage-polarized memory of the phase directional element. Best Choice Ground Directional Element system logic ensures secure ground directional element operation for all types of system grounding practices under varying system conditions.

Frequency Protection
Provide advanced load shedding with six levels of frequency elements and four rate-of-change-of-frequency elements, plus under-/overvoltage protection.

Reclosing Control
Apply four-shot reclosing with sequence coordination, synchronism check, and voltage check.

Fault Locator
Calculate accurate distance-to-fault measurements using the impedance-based fault locator.

Second-Harmonic Blocking
Detect transformer energization with the second-harmonic blocking elements. The output from the harmonic detection elements blocks selected tripping elements until inrush conditions subside.

Fast Dropout Breaker Failure Element
High-speed breaker failure element and native breaker failure logic enhance breaker failure detection.

IEC 61850 Communications Protocol
Apply optional IEC 61850 communications to the SEL-351S Protection System for guaranteed performance of substation automation and control. Streamline configurations of IEC 61850-enabled relays with acSELerator Architect SEL-5032 Software.

Mirrored Bits Communications Technology
Provide fast and reliable relay-to-relay communication for advanced communications-assisted protection, network reconfiguration, pilot protection, and restoration schemes.

Modbus, DNP3, and ASCII Protocols
Easily integrate into new or existing networks with these popular protocols. Supervisory control and data acquisition (SCADA) links, local human-machine interface (HMI), and dial-in modems can access important relay data.

Simple Network Time Protocol (SNTP)
Simplify wiring and installation by receiving a time signal over existing Ethernet networks. SNTP makes a good backup to more accurate IRIG-B time synchronization. The 5 ms accuracy is ideal for basic time synchronization throughout a substation.

Built-In IEEE C37.118 Synchrophasors
Monitor distribution and transmission networks to detect potential cascading voltage collapse before it happens. IEEE C37.118 synchrophasors, at up to 60 messages per second, allow access to system values for wide-area monitoring and control. The IEEE C37.118 standard simplifies communication and data coordination between synchrophasor measurement units.

Parallel Redundancy Protocol (PRP)
Introduce full network redundancy in your system. With PRP, the network can sustain any single-point failure without a packet loss. The relay sends two messages simultaneously using two compatible Ethernet ports; in case one of the packets gets dropped, the message will still arrive to its destination.

Enhanced Breaker Monitoring
Inspect reports for the most recent trip and close operating times and average operating times, or gather trending data for up to 128 previous operations. This information allows timely and economical scheduling of breaker maintenance.

Metering and Power Quality (PQ) Monitoring
With accurate metering, eliminate the need for external meters (MW, MVAR, MWh, MVARh, power factor (PF), root-mean-square (rms), and instantaneous/peak demand). Harmonic metering to the 16th harmonic simplifies PQ analysis. Optional PQ monitoring records voltage sags, swells, and interruptions.

Built-In Web Server
Access basic relay information on a standard Ethernet network with the built-in web server. View relay status, Sequential Events Recorder (SER) data, metering information, and settings for easy access within a local network. Upgrade the firmware through the existing Ethernet connection. Web server access requires a relay password.