SEL-751

Feeder Protection Relay

The SEL-751 is the right solution for industrial and utility feeder protection, with conventional/low-energy analog (LEA) current and voltage input support, flexible I/O options, easy mounting, and fast settings.

The SEL-751 provides complete protection for radial and looped distribution circuits. It offers arc-flash mitigation, fault location, high-impedance fault detection, intermittent ground fault (IGF) detection, broken conductor detection, event analysis, and more. You can quickly integrate the relay into serial- or Ethernet-based communications with IEC 61850 Edition 2.1, IEC 60870-5-103, the IEC 62439 Parallel Redundancy Protocol (PRP), High-Availability Seamless Redundancy (HSR), EtherNet/IP, the Rapid Spanning Tree Protocol (RSTP), the IEEE 1588 Precision Time Protocol (PTP), Modbus, DNP3, and other protocols.

Overview

Complete Feeder Protection
Maximize control scheme flexibility using time- and instantaneous-overcurrent, overvoltage, undervoltage, directional power, and frequency elements, with breaker failure protection for one three-pole breaker. Second- and fifth-harmonic blocking improves protection security during magnetizing inrush conditions caused by line re-energization, or by voltage recovery after an out-of-zone fault.

Optional Directional Control
Use overcurrent elements with directional control, and optimize radial and looped network protection for lines and equipment. Best Choice Ground Directional Element logic optimizes directional element performance and eliminates the need for many directional settings. The relay also supports high-impedance grounded, ungrounded, and Petersen coil-grounded systems in relays with the 200 mA neutral current transformer option. The 200 mA CT option can also be used for nondirectional SEF protection.

Optional Protection Features
Use the SEL-751 with the voltage inputs and arc-flash detection options to provide synchronism check, dc station battery monitoring, and arc-flash detection. The SEL-751 supports an option card that includes the Vsync/Vbat with 7 digital inputs or 4 arc-flash inputs. LEA currents and voltage input card supports voltage sensor inputs and Rogowski coil or low-power current transformer inputs for small enclosure installations.

Incipient Fault Detection
Identify potential cable failures to extend asset life and minimize unexpected downtime. The SEL-751 checks for self-extinguishing half-cycle faults, which provides an indication of imminent cable failures.

Fault Location—Find faults faster and restore service more quickly with fault location algorithms. Communicate fault location information automatically to a control center by using serial or Ethernet communications and SCADA protocols.

Cold-Load Pickup Element
Cold-load pickup is the phenomenon that takes place when a distribution circuit is reenergized following an extended outage of that circuit. It can result in current levels that are significantly higher than normal peak load levels. This excess amount of current draw could be falsely identified as an overcurrent condition by the relay. The cold-load pickup element identifies possible cold-load pickup events per the settings in a distribution line after an outage.

Thermal Element
Protect cables and cable insulation against thermal damage using the IEC line/cable thermal (49) element.

Optional Vector Shift
Detect islanding conditions and prevent damage to local generation by detecting voltage angle shifts upon loss of bulk generation.

Open-Conductor Detection
Apply the SEL-751 to detect and isolate open conductors. The SEL-751 incorporates phase discontinuity detection and optional broken conductor detection to provide a reliable solution for open-conductor faults that convert to high-impedance faults.

Optional High-Impedance Fault Detection
Apply the SEL-751 with AST to detect many high-impedance faults, a common result of a downed conductor. Alarm or trip for faults that produce low fault current and are undetectable with conventional relays.

Optional Touchscreen Display
The easy-to-use touchscreen interface provides a one-line mimic display for bay control and monitoring. View metered quantities, phasor diagrams, relay settings, event summaries, target statuses, Sequential Events Recorder (SER) data, and more. Extensive testing shows that the robust capacitive touchscreen display meets or exceeds industry standards as well as SEL quality and reliability requirements.

Harmonic Metering and Total Harmonic Distortion (THD)
Harmonic metering and a THD element allow greater control and monitoring of systems that see significant harmonic disturbances, such as industrial systems and systems with inverter-based resources.

Easy Communications
Choose from Ethernet or serial communications and several protocols, including IEC 60870-5-103, Mirrored Bits communications, EtherNet/IP, IEEE 1588 PTP, and IEC 61850. Pick multiple sessions of Modbus TCP, Modbus RTU, DNP3 LAN/WAN, or DNP3 serial for custom configuration of your applications. When dual-Ethernet ports are selected, the relay also supports RSTP, IEC 62439 PRP, HSR, and Fast Failover Switching.

IEC 61850 Edition 2.1 Communications Protocol
Combine IEC 61850, an Ethernet network, and the SEL-751 for the fastest overall performance for substation automation and control. Streamline configuration of IEC 61850-enabled relays with acSELerator Architect SEL-5032 Software. Improve security using the password authentication and session time-out features. Transfer event files in COMTRADE and CEV formats as well as CID files, settings, and reports.

IEC 61850 Test Mode
Use the IEC 61850 Test Mode to test system components in energized substations without fear of operating control output contacts.

Web Server Access
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.

Accelerate Firmware Downloads
Simplify maintenance by downloading relay firmware via the Ethernet port. This also enables you to access and update all of your network relays simultaneously.

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 1 ms accuracy is ideal for basic time synchronization throughout a substation.

Built-In IEEE C37.118 Synchrophasors
Monitor distribution networks to detect a 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.

Expanded SELogic Control Equations
Use math and logic combinations of analog and digital values for customized applications. Adapt system control based on prefault conditions. Scale analog values and latch momentary inputs for SCADA retrieval.

Enhanced Security on Heavily Loaded Feeders
Employ load-encroachment logic to set phase overcurrent elements independently of load levels.

Flexible Design
Choose from many installation and integration options given the small form factor of the relay and its slide-in expansion card options.

Rugged Design
Trust the industry’s widest ambient operating temperature range, –40° to +85°C (–40° to +185°F). The SEL-751 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. In addition, the SEL-751 is ATEX-certified and Underwriters Laboratories (UL) Class I, Division 2-certified for use in hazardous and potentially explosive environments.

751#11

• Standard firmware
• English language support
• Power supply: 110–250 Vdc, 110–240 Vac, 50/60 Hz, two 125 Vdc/Vac digital inputs (DIs), three digital outputs (DOs)
• 5-inch color touchscreen display with eight pushbuttons
• Dual 10/100BASE-T Ethernet, EIA-232, and single multimode ST fiber-optic serial ports
• Four DIs and four DOs; 125 Vdc/Vac DI, fast high-current-interrupting DO
• Eight arc-flash detection inputs
• Protocols: SEL ASCII, Compressed ASCII, Fast Meter, Fast Operate, Fast Message, Fast SER, Mirrored Bits communications, and Modbus RTU
• Three-phase ac current inputs, neutral ac current input, three-phase ac voltage (300 Vac) inputs