GE Multilin 345 Transformer Protection Relay

Overview

The GE Multilin 345 is a transformer protection system from the Multilin 3 Series, designed as a microprocessor-based relay for primary and backup protection of small and medium size distribution transformers. It brings biased differential protection with a dual-slope, dual-breakpoint characteristic, inrush and overexcitation inhibits, restricted ground fault elements and a basic thermal model into a compact relay that also provides phase, neutral, ground and negative sequence overcurrent backup. Two identical setting groups allow automatic changes of protection settings when operating conditions change.

Seven Star LLC supplies the GE Multilin 345 to utilities, switchgear builders and industrial plants across Oman and the GCC. Distribution transformers feeding compounds, pumping stations and process plants are often protected only by fuses or overcurrent relays, and our engineers in Muscat help customers decide where a dedicated differential relay such as the GE Multilin 345 adds worthwhile protection.

Differential Protection Principle

Differential protection compares the currents on both sides of the transformer after correcting for ratio and vector group. The GE Multilin 345 performs automatic magnitude and phase compensation for more than twenty types of two-winding transformers, so the differential current is close to zero during normal load and through faults. The restraint characteristic is defined by the minimum pickup differential current, slope 1 and slope 2 joined by a cubic spline curve, and breakpoints 1 and 2. The maximum winding current is used as the restraining signal, improving through-fault stability when CTs saturate, and an instantaneous differential element trips heavy internal faults directly.

When a transformer is energised, magnetising inrush can look like an internal fault. The second harmonic inrush inhibit can be set to per-phase, 2-out-of-3 or average mode to suit different transformer designs. Overexcitation from high voltage or low frequency is handled by fifth harmonic inhibiting integrated into the percent differential element. Restricted ground fault elements protect the neutral end of wye-connected windings, where phase differential has limited sensitivity, detecting ground faults down to 5% of the winding while using phase currents as restraint to avoid false operation during external faults with CT saturation.

Engineering Design of the GE Multilin 345

Hardware follows the 3 Series format used across GE compact relays: a withdrawable unit in a small case that allows several relays to be mounted side by side. In draw-out form the GE Multilin 345 is removed without rewiring and without disconnecting communication cables, and it keeps its communication status after withdrawal. Assignable CT inputs allow the timed and instantaneous overcurrent elements to be applied to either winding, and a pluggable RS485 and IRIG-B connector makes field troubleshooting easier.

The relay provides ten contact inputs with programmable thresholds, two Form A trip outputs with coil monitoring and five Form C outputs, plus sixteen logic elements for simple user logic. A four-line, twenty-character display and twelve LED indicators show targets and measurements, with a front USB port for local access. Recording includes an event recorder with 256 events time stamped to one millisecond and oscillography at 32 samples per cycle with digital states. GE tests the design through highly accelerated life testing for extreme operating conditions.

Key Features

The GE Multilin 345 provides a practical set of transformer protection features in a compact relay.

• Dual-slope, dual-breakpoint restrained differential with cubic spline transition and instantaneous differential.
• Automatic magnitude and phase compensation for more than twenty two-winding transformer types.
• Second harmonic inrush inhibit (per phase, 2-out-of-3 or average) and fifth harmonic overexcitation inhibit.
• Restricted ground fault protection sensitive to faults down to 5% of the winding.
• Thermal model based on winding heating and cooling constants, with alarm or trip.
• Phase, neutral, ground and negative sequence overcurrent assignable to either winding, plus breaker failure.
• Ten inputs, seven outputs, sixteen logic elements and two setting groups.
• USB, RS485, copper and fibre Ethernet with IEC 61850, GOOSE, Modbus, DNP3.0 and IEC 60870-5-103/104.

Industrial Applications

GE lists low and medium voltage two-winding power transformers, reactors and autotransformers, applications that need fast and secure communications, and harsh environments that call for protection against corrosion and humidity. In Oman this includes distribution transformers in utility primary and secondary substations, unit transformers feeding pump stations on water transmission schemes, transformers in desalination and district cooling plants, and process transformers in Sohar, Duqm and Salalah industrial areas where heat, dust and coastal humidity are part of everyday operation. Protection engineers often compare the GE Multilin 345 with the ABB RET615 transformer protection and control relay and the SEL-787 transformer protection relay.

Seven Star LLC supports these users with model selection and sourcing support from Muscat. For older substations still running static or electromechanical differential relays such as the ABB SPAD34, we help customers in Oman and the GCC plan a migration to the GE Multilin 345 with settings and wiring reviewed against the GE documentation.

Technical Specifications

The GE Multilin 345 data below comes from the GE brochure GEA-12778K; confirm the final order code with current GE documentation.

How to Order

Send your formal RFQ for the GE Multilin 345 to Seven Star LLC with the GE order code, or with the transformer rating, vector group, CT ratios and preferred communications. Our instrumentation and power division in Muscat will confirm the configuration, coordinate delivery across Oman and the GCC, and share the GE brochure available for download on this page. Contact our engineering team for help applying the GE Multilin 345 to your distribution transformers.