GE 745-W3-P5-G5-HI-A-L-R-E-H Draw-Out Numerical Transformer Protection Relay with Conformal Coating

Technical Specifications

Main Features and Advantages

Adaptive harmonic restraint for secure energisation: The GE Multilin 745-W3-P5-G5-HI-A-L-R-E-H​ implements dual-slope percentage differential protection with three user-selectable restraint methods, combining conventional and adaptive second-harmonic blocking with fifth-harmonic inhibition. This lets the relay distinguish magnetising inrush and overexcitation from genuine internal winding faults, so the transformer can be energised confidently without desensitising the differential element. Pickup is adjustable from 0.05 to 1.00 × CT with independent slope-1 (15–100%) and slope-2 (50–100%) settings and a programmable knee point, and restraint is derived from maximum winding current for exceptional through-fault stability under CT saturation.Three-winding coverage in one chassis: Because the 745-W3-P5-G5-HI-A-L-R-E-H​ is configured for three windings per phase with 5 A CT inputs on every winding and both ground inputs, a single relay protects three-winding transformers and autotransformers that would otherwise need two or more differential relays plus interposing CTs. Dynamic CT ratio mismatch correction works hand in hand with the tap-position input to keep the differential balance accurate as the on-load tap changer moves through up to 50 positions.Restricted ground fault and loss-of-life in one unit: The R option gives the 745-W3-P5-G5-HI-A-L-R-E-H​ sensitive restricted ground fault detection for winding-to-ground faults near the neutral, while the L option continuously computes hottest-spot temperature, ageing factor and loss-of-life percentage. Maintenance teams gain a live view of insulation consumption rather than a guess, which directly supports condition-based maintenance and deferral of capital replacement.Built for the field, not just the panel: The H conformal coating protects internal boards against humidity and chemical contamination, the draw-out case allows relay replacement without disturbing CT and VT wiring, and FlexLogic lets engineers build interlocks, breaker-failure schemes and custom alarm matrices without external auxiliary relays. Sixteen logic inputs accept dry or wet contacts, seven isolated analog outputs feed DCS and SCADA trends, and IRIG-B time synchronisation aligns event records across the substation so post-fault analysis is unambiguous.

Application Field

Utility transmission and distribution substations: The GE Multilin 745-W3-P5-G5-HI-A-L-R-E-H​ is most often specified as the main differential protection for HV/MV power transformers from roughly 11 kV through transmission class, including three-winding units and autotransformers with a tertiary winding. Its three-winding differential zones replace legacy electromechanical or static relays during substation refurbishment, and the draw-out case keeps replacement time to minutes during outages.Heavy industry and process plants: Steel mills, cement works, chemical complexes, refineries and mining operations deploy the 745-W3-P5-G5-HI-A-L-R-E-H​ on incoming and unit transformers feeding large drives, furnace transformers and rectifier transformers. Here the conformal-coated variant matters: sulphur-rich, humid or dusty atmospheres that destroy standard electronics are tolerated, while harmonics analysis to the 21st helps engineers quantify the distortion produced by variable-speed drives and rectifiers before it overheats the transformer.Generation, renewables and grid interconnection: Power-plant unit and station-service transformers, wind-farm collector transformers and solar PV step-up transformers all benefit from the sensitive differential element with inrush blocking, plus overexcitation (V/Hz) protection that guards the core during load rejection or weak-grid voltage excursions. The GE 745-W3-P5-G5-HI-A-L-R-E-H​ also integrates easily into digital substation architectures, feeding measurements, alarms and oscillography to SCADA, DCS and plant asset-management systems over Modbus, DNP 3.0 or Ethernet, which removes the separate transducer and meter layer.Critical infrastructure: Data centres, hospitals, rail traction substations and water-treatment facilities use the 745-W3-P5-G5-HI-A-L-R-E-H​ where an unprotected transformer failure is unacceptable. In these settings the loss-of-life and hottest-spot monitoring functions are as valuable as the tripping functions, because they let operators load the transformer closer to its true thermal limit with evidence rather than conservatism.