GE Multilin 845 Transformer Protection Relay

Overview

The GE Multilin 845 is a transformer protection system from the Multilin 8 Series, now offered by GE Vernova, designed for the protection, control and management of 2- and 3-winding power and distribution transformers in utility and industrial networks. It delivers fast differential protection with CT saturation and directional supervision, a full set of backup overcurrent, voltage and frequency elements, and transformer health functions such as hottest-spot temperature, aging factor and loss of life. GE Vernova also highlights integrated connectivity with its Kelman dissolved gas analysis devices, so one relay can combine electrical protection with chemical condition data from the transformer oil.

Seven Star LLC supplies the GE Multilin 845 to substations, power plants and industrial facilities throughout Oman and the GCC. From our base in Muscat we help protection engineers specify the number of CT banks, voltage inputs, RTD and analog I/O, arc flash sensors and communication options so that the GE Multilin 845 matches the transformer and switchgear it will protect.

Differential Protection Principle

Transformers are under constant thermal and electrodynamic stress, and the aim of the relay is to clear internal faults as fast as possible while ignoring external events. The GE Multilin 845 compares the compensated currents entering and leaving each winding. All CTs are connected in wye and the relay performs phase shift, magnitude and zero-sequence compensation automatically from a library of more than 100 transformer types. The percent differential element follows a configurable dual-breakpoint, dual-slope characteristic with a cubic spline transition between the breakpoints, and an unrestrained differential element trips heavy internal faults without waiting for restraint logic.

Magnetising inrush during energisation is handled by second harmonic restraint with four programmable methods (per phase, average, 2-out-of-3 and 1-out-of-3), and a fifth harmonic inhibit blocks operation during overexcitation caused by high volts per hertz. When the relay reads tap position from the on-load tap changer it adjusts magnitude compensation to the new ratio, keeping differential current near zero. Restricted ground fault protection, also called zero-sequence differential, covers faults close to the neutral of impedance-earthed star windings where phase differential lacks sensitivity.

Engineering Design of the GE Multilin 845

The GE Multilin 845 uses the 8 Series draw-out chassis with a field swappable power supply, harsh-environment conformal coating, no electrolytic capacitors and an IP54 front rating, with an optional IP20 rear cover. The rear panel carries CT and VT inputs, digital I/O, dc mA inputs and outputs, RTD inputs, arc flash sensor connections, the standard serial and RJ45 module and an advanced fibre communications module. GE Vernova quotes front panel dimensions of about 9.90 by 8.42 inches in the brochure dimension drawing.

Backup protection includes phase, neutral and ground instantaneous and time overcurrent with up to six time overcurrent elements per winding, directional elements with voltage memory, negative sequence overcurrent, volts per hertz, synchrocheck, directional power and frequency elements. Integrated arc flash protection with a 2 ms protection pass uses up to four light sensors supervised by overcurrent to reduce incident energy in switchgear. Twenty virtual pushbuttons and a configurable single line diagram with up to six pages support local switchgear control.

Key Features

Key capabilities of the GE Multilin 845 for transformer protection and asset management include:

• Dual-slope, dual-breakpoint percent differential with unrestrained differential, CT saturation detection and directional supervision.
• Second and fifth harmonic restraint with four selectable inrush restraint methods for secure energisation.
• Restricted ground fault protection for impedance-earthed star windings.
• Hottest-spot temperature, aging factor, loss of life and harmonic derating functions for insulation life management.
• Tap position input by BCD, dc mA or resistance, with tap changer failure detection and automatic ratio compensation.
• Integration with Kelman Transfix, DGA500, Minitrans and Hydran M2 devices for dissolved gas monitoring.
• Integrated arc flash detection using light sensors supervised by overcurrent.
• IEC 61850 Ed2, PRP, DNP3.0, IEC 60870-5-103/104 and Modbus, with two independent network ports and cyber security tools.

Industrial Applications

The GE Multilin 845 suits generator step-up and auxiliary transformers in power stations, grid and primary substation transformers in transmission and distribution networks, and the large unit and process transformers found in refineries, aluminium and steel plants, cement works and desalination facilities. In Oman this covers utility substations, independent water and power plants along the Batinah coast, and industrial estates in Sohar, Sur, Duqm and Salalah where transformer outages carry a high production cost. Protection engineers reviewing alternatives often look at the SEL-787 transformer protection relay and the ABB RET615 transformer protection and control relay in the same evaluation.

Seven Star LLC supports these users with model selection and sourcing support from Muscat, including legacy replacement work where an older electromechanical or static differential relay such as the ABB SPAD34 stabilized differential protection relay is being modernised with a numerical scheme like the GE Multilin 845 for sites across Oman and the GCC.

Technical Specifications

The GE Multilin 845 information below is taken from the GE Vernova brochure GEA-12875E. Detailed ratings and the order code should be confirmed against current GE Vernova documentation.

How to Order

Send your formal RFQ for the GE Multilin 845 to Seven Star LLC with the transformer vector group, winding count, CT and VT ratios and required I/O, or quote the GE Vernova order code directly. Our instrumentation and power division in Muscat will confirm the configuration, coordinate delivery across Oman and the GCC, and share the GE Vernova brochure available for download on this page. Contact our engineering team to plan your GE Multilin 845 transformer protection scheme.