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Feeder Protection Relay


The SEL-851 provides powerful feeder protection, monitoring, and control for utility and industrial applications in a compact device. It includes arc-flash protection that significantly reduces incident energy by sending a trip signal to a breaker in as fast as 1 ms. With high-resolution currents and voltages sampled at 10 kHz, the SEL-851 allows you to gain better visibility of your system. It also comes with SEL Grid Configurator software to help you quickly create, manage, and deploy device settings.

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Powerful Feeder Protection—The SEL-851 includes four current inputs and three optional voltage inputs for comprehensive current, voltage, and frequency protection. Protect low- and medium-voltage three-phase feeders with breaker/contactor failure, negative-sequence, and neutral instantaneous elements. The voltage input option provides voltage, frequency, directional power, loss-of-potential, and power factor elements.

Arc-Flash Mitigation—Improve safety and prevent equipment damage with the relay’s four arc-flash detection (AFD) inputs. The SEL-851 combines light-sensing technology and high-speed overcurrent protection to detect arc-flash events in as fast as 1 ms without false tripping.

Improved System Visibility—With high-resolution currents and voltages sampled at 10 kHz, system visibility is improved. This allows you to identify problems, such as harmonics produced by switching or damaged cables, before they cause a significant interruption.

Increased System Reliability—Improve your system reliability by coordinating the SEL-851 and its reclosing control functionality with downstream reclosers for a complete restoration scheme.

Reduced Commissioning Time—You can configure SEL-851 settings using the relay HMI or using SEL Grid Configurator software, which is a new tool that increases efficiency and improves settings insights. It features a spreadsheet-style editor, powerful protection visualization, comprehensive reporting, custom filters, and multiple-device settings management.

Easy Communications—Choose from Ethernet or serial communications ports and several protocols, including Mirrored Bits communications and IEC 61850 Edition 2. Pick multiple sessions of Modbus TCP, Modbus serial, DNP3 LAN/WAN, or DNP3 serial for custom configuration of your applications.


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      Large LCD display for navigation, relay control, and diagnostics

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      Context-adjusted navigation keys

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      USB port

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      Two fixed and eight programmable tricolor LEDs

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      Fundamental feeder controls

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      4 digital inputs

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      5 digital outputs (1 Form C, 2 Form A Standard, 2 Form A Hybrid)

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      Universal power supply (24–250 Vdc, 110–240 Vac)

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      EIA-232/EIA-485 serial port

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      Single or dual 10/100BASE-T Ethernet port(s)

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      6 additional digital inputs

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      Current inputs

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      Three-phase ac voltage inputs (300 Vac)

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      4 arc-flash inputs



Simplified Design

The SEL-851 is built with high-reliability hardware and comes with software-selectable binary inputs, a universal power supply, and universal current inputs. Its simplified design helps reduce expenses.

Integrated Web Server

The built-in web server enables secure, remote access to the relay with password protection. You can download status reports or view metering and relay information remotely. This helps minimize trips to the relay location, saving time and money. The web server also enables firmware upgrades.

Operator Controls

Increase operator safety during commissioning and testing using the LOCAL/REMOTE pushbutton control on the relay’s front panel. Perform breaker control using the TRIP and CLOSE pushbutton controls.

Metering and Monitoring

The SEL-851 relay’s built-in metering function allows you to eliminate separately mounted metering devices. Analyze Sequential Events Recorder (SER) reports and oscillographic event reports for rapid commissioning, testing, and post-fault diagnostics.

Load Profiling

Load profile monitoring provides a periodic snapshot (selectable rate of every 5, 10, 15, 30, or 60 minutes) of as many as 16 selectable analog quantities. The relay maintains load profile information in nonvolatile buffer memory, which can hold as many as 4,000 time-stamped entries.

Rugged Hardware

Trust the industry’s widest ambient operating temperature range, –40° to +85°C (–40° to +185°F). The plastic chassis SEL-851 withstands vibration, electrical surges, fast transients, and extreme temperatures, meeting stringent industry standards. A conformal-coating option for the printed circuit boards provides an additional barrier to airborne contaminants, such as hydrogen sulfide, chlorine, salt, and moisture.

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