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Advanced Generator Protection System


The SEL-400G offers primary and backup protection for generators of all sizes and types, including hydro, pumped-storage hydro, steam turbine, and combustion gas turbine generators. It combines generator, generator bus, and generator step-up transformer protection in one package, making the relay an economical solution for an entire plant.

Advanced protection functions, like transverse differential protection, provide turn-to-turn fault detection, allowing you to detect faults earlier, limit damage to your generator, and return to service faster. Adaptive differential protection and a wide frequency tracking range (5–120 Hz) improve your protection security. Dual frequency zones and autosynchronization offer smooth synchronization to the grid.

You can quickly integrate the SEL-400G into serial- or Ethernet-based communications with IEC 61850, the IEC 62439 Parallel Redundancy Protocol (PRP), Mirrored Bits communications, Modbus, DNP3, and other protocols. SEL Grid Configurator software allows you to quickly and confidently create, manage, and deploy device settings.

Starting At

$12,000 USD

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Advanced Generator Protection—Two independent universal differential elements provide protection for the generator and GSU transformer in a single relay. The SEL-400G also offers 18 current inputs, 6 voltage inputs, wide-range frequency tracking (5–120 Hz), advanced antimotoring protection, loss-of-field protection, and more.

Pumped Storage Logic—This feature enables pumped storage hydropower protection without the need for external relays to switch CT wiring, which lowers costs and improves reliability.

Stator Ground Fault Protection—Achieve passive and active ground fault detection across 100 percent of the stator winding without sacrificing security. The stator winding ground fault protection elements include integrating timers that detect intermittent ground faults and isolate the generator before the fault evolves into a permanent fault.

Rotor/Field Winding Protection—Applying the SEL-2664 Field Ground Module and the SEL-2664S Stator Ground Protection Relay with the SEL-400G allows you to protect your system against rotor/field winding short circuits. With the field ground protection element, the first fault will trigger an alarm and a second fault results in a trip signal.

Simplified Settings Management—SEL Grid Configurator is a new configuration software tool that delivers a modern user experience, helps increase efficiency, and improves settings insights. It features a spreadsheet-style editor, powerful protection visualization, comprehensive reporting, custom filters, and multiple-device settings management.

Communication and Integration—Quickly integrate the SEL-400G into serial- or Ethernet-based communications with IEC 61850, the IEC 62439 PRP, Mirrored Bits communications, Modbus, DNP3, and other protocols.


400G Front Callouts400G Back Callouts

Advanced Generator and Unit Protection

The 18 current and 6 voltage inputs on the SEL-400G enable complex application support or protection of other equipment, such as transformers. This allows you to increase machine life by detecting faults and abnormal conditions before they cause permanent damage.

Wide-Range Frequency Tracking

The wide-range frequency tracking (5 to 120 Hz) ensures that all protection functions are secure and dependable across a wide range of system frequencies or generator speeds. This provides protection during events such as unit overspeed or inverter-driven startup.

100 Percent Stator Ground Detection

The SEL-400G detects stator ground faults on high-impedance grounded generators using a conventional neutral-overvoltage element with a third-harmonic voltage differential detection scheme for 100 percent stator winding coverage. You can apply the frequency injection and neutral overvoltage in the SEL-2664S to protect high-impedance grounded generators from ground faults at standstill, during startup, or while running.


The built-in automatic synchronizer function eliminates the need for expensive external synchronizer equipment. The SEL-400G automatically synchronizes frequency, voltage, and phase control and connects the generator to the power system.

Easy Communications

Quickly integrate the SEL-400G into serial- or Ethernet-based communications with IEC 61850, IEC 62439 PRP, Mirrored Bits communications, Modbus, DNP3, and other protocols.

RTD-Based Thermal Protection

Use an external SEL-2600 RTD Module to acquire thermal data for alarm, monitoring, and trip functions in the SEL-400G.

Metering and Reporting

View generator autosynchronizer, Sequential Events Recorder (SER), and 180-cycle oscillographic event reports in COMTRADE and CEV formats to analyze generator startup, shutdown, or system faults. You can measure electrical, thermal, and generator run-time quantities and can retrieve COMTRADE files via Ethernet FTP or IEC 61850 MMS.

Synchrophasor Data

Apply SEL synchrophasors (IEEE C37.118) to turn state estimation into state measurement and to provide early warning of potential system instability. The SEL-400G phasor measurement accuracy meets the IEEE C37.118-2005 Level 1 requirement.

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