GE Multilin 745 Series Transformer Protection Relays

Technical Dossier

Product Details And Specifications

GE Multilin 745 Series: Comprehensive Module Range and Technical Overview

The GE Multilin 745 Transformer Management Relay (TMR) is a purpose-built protection, control, and monitoring platform for power transformers deployed across heavy industrial sectors including petrochemical plants, nuclear power stations, oil refineries, pulp and paper mills, and large-scale utility substations. First introduced in the mid-1990s, the 745 series established a benchmark for multi-function transformer protection by consolidating differential protection, overcurrent, overflux, thermal modeling, and fault recording into a single 19-inch rack-mountable unit. Its installed base spans North America, Europe, and Asia-Pacific, with units still in active service at facilities operating on 20–30 year maintenance cycles. The 745-W3-P511-G51-HI-R-E variant specifically designates a configuration with three-winding capability, standard I/O complement, high-impedance restricted earth fault input, and RS-485 communications — a specification commonly found in refinery main transformer bays and nuclear auxiliary transformer panels.

The Evolution of 745 Series Architecture

The 745 platform was developed by GE Multilin (formerly Multilin Inc., acquired by GE in 1994) as a successor to discrete electromechanical and early solid-state transformer protection schemes. The original 745 firmware (v1.x–v2.x) supported two-winding differential protection with basic harmonic restraint. Version 3.x introduced three-winding differential capability, expanded the CT input range, and added DNP 3.0 serial communications alongside the existing Modbus RTU protocol — directly addressing the integration requirements of SCADA systems prevalent in 1990s utility and industrial environments.

Version 4.x and later releases added IEC 61850 GOOSE messaging support (on equipped hardware variants), enhanced oscillography with 64 samples per cycle, and expanded thermal model parameters for ONAN/ONAF/OFAF cooling modes. The hardware platform itself evolved from a single-board architecture to a modular backplane design, allowing field replacement of the power supply, CPU, and I/O boards independently — a critical serviceability feature for installations where relay replacement requires outage coordination.

The 745 series reached end-of-active-production status, with GE Multilin positioning the T60 Transformer Protection System (part of the Universal Relay platform) as the primary modern replacement. However, the T60 uses a fundamentally different hardware and firmware architecture, making direct swap-in replacement non-trivial. Panel cutout dimensions, CT wiring schemes, and SCADA communication configurations all require engineering review during migration. As a result, the 745 remains in active procurement for brownfield maintenance, with demand concentrated on spare relay units, replacement I/O boards, and power supply modules.

745 Series Full Catalog & Functionalities (SKU List)

The following SKUs represent verified models within the GE Multilin 745 Transformer Management Relay family, organized by functional configuration. Each model number encodes winding count, I/O complement, communication options, and mounting style.

Three-Winding Differential Protection Variants

• 745-W3-P511-G51-HI-R-E: Three-winding TMR, standard I/O, high-impedance REF input, RS-485 Modbus/DNP3, panel-mount, English display — the subject SKU of this listing.
• 745-W3-P511-G51-HI-R-F: Three-winding TMR, standard I/O, high-impedance REF input, RS-485, French display variant.
• 745-W3-P511-G51-HI-E: Three-winding TMR, standard I/O, high-impedance REF, Ethernet (10Base-T) communications port, English display.
• 745-W3-P511-G51-HI-E-F: Three-winding TMR, Ethernet comms, French display.
• 745-W3-P511-G51-LO-R-E: Three-winding TMR, low-impedance REF input configuration, RS-485, English display.

Two-Winding Differential Protection Variants

• 745-W2-P511-G51-HI-R-E: Two-winding TMR, standard I/O, high-impedance REF, RS-485, English display — the most common two-winding variant in North American utility applications.
• 745-W2-P511-G51-HI-E: Two-winding TMR, Ethernet communications, high-impedance REF, English display.
• 745-W2-P511-G51-LO-R-E: Two-winding TMR, low-impedance REF input, RS-485, English display.
• 745-W2-P511-G51-HI-R-F: Two-winding TMR, high-impedance REF, RS-485, French display — common in Canadian utility installations.

Enhanced I/O and Special Function Variants

• 745-W3-P511-G51-HI-R-E-H: Three-winding TMR with enhanced harmonic restraint firmware, RS-485, English display — specified for transformers with high inrush current profiles.
• 745-W3-P511-G51-HI-E-H: Three-winding TMR, enhanced harmonic restraint, Ethernet comms, English display.
• 745-W2-P511-G51-HI-R-E-H: Two-winding TMR, enhanced harmonic restraint, RS-485, English display.

Replacement and Sub-Assembly Modules

• 745-POWER-SUPPLY-A: Standard AC/DC power supply module for 745 series chassis — 100–240 VAC / 125 VDC input range.
• 745-POWER-SUPPLY-B: Wide-range DC input power supply module — 24–250 VDC, for substation battery bus applications.
• 745-CPU-MODULE: Central processing and firmware board for 745 series; required for firmware version upgrades and CPU board failures.
• 745-IO-MODULE-A: Standard analog input/output expansion board; provides additional CT/VT input channels for complex winding configurations.
• 745-DISPLAY-MODULE: Front-panel LCD display and keypad assembly; field-replaceable without relay de-energization in most configurations.

Sourcing Hard-to-Find & Obsolete 745 Series Parts

The GE Multilin 745 series is classified as a mature/end-of-life product line. GE Grid Solutions (the successor entity to GE Multilin) has transitioned active support to the T60 platform. This creates a well-defined procurement challenge: facilities operating 745 relays under long-term maintenance agreements or within regulated industries (nuclear, utility) cannot execute unplanned platform migrations and require continued access to like-for-like spare units and sub-assemblies.

DriveKNMS maintains a dedicated inventory program for 745 series components sourced through authorized surplus channels, decommissioned utility equipment, and tested pull units. All units are subject to functional verification prior to dispatch. For obsolete variants where new-old-stock is unavailable, DriveKNMS can facilitate repair-and-return service for CPU boards, power supply modules, and I/O assemblies. Customers operating under IEC 61511 or NERC CIP maintenance frameworks are advised to document the provenance and test records of any replacement relay — DriveKNMS provides full test documentation upon request.

Lead times for common variants such as the 745-W3-P511-G51-HI-R-E and 745-W2-P511-G51-HI-R-E are typically 3–10 business days from confirmed stock. Rare configurations and sub-assembly modules are quoted on a case-by-case basis with a standard 5-business-day sourcing assessment.

Quality Control for the 745 Series Range

The 745 relay's internal architecture presents specific test requirements that differ from standard PLC I/O modules. Key verification procedures applied by DriveKNMS to all 745 series units include:

• Differential element pickup and slope characteristic test: CT inputs are injected with calibrated secondary currents to verify operate/restraint region boundaries against the relay's configured slope settings (Slope 1 and Slope 2). Results are compared against the factory calibration record where available.
• Harmonic restraint verification: Second and fifth harmonic blocking thresholds are tested by injecting composite waveforms to confirm the relay correctly inhibits tripping during transformer energization inrush conditions.
• Overcurrent element timing test: Phase and ground overcurrent elements (51, 51N, 50, 50N) are tested for pickup accuracy and time-dial curve conformance per IEEE C37.112.
• Communications port integrity check: RS-485 (Modbus RTU and DNP 3.0) and Ethernet ports are verified for correct register mapping and response to standard poll sequences using a protocol analyzer.
• Power supply output verification: Internal DC bus voltages are measured under load to confirm regulation within ±2% of nominal across the specified input voltage range.
• Output contact resistance and insulation test: Trip and alarm output contacts are tested for contact resistance (100 MΩ at 500 VDC) to confirm relay output circuit integrity.
• Firmware version audit: Installed firmware version is recorded and reported. Customers requiring a specific firmware version for compatibility with existing SCADA configurations are advised at the time of quotation.

For sourcing inquiries, technical specifications, or repair assessments on GE Multilin 745 Series relays:

• Email: [email protected]
• WhatsApp: +86 18359293191
• Web: driveknms.com