ABB RET615 Transformer Protection and Control Relay

Overview

The ABB RET615 is a dedicated transformer protection and control relay for power transformers, unit and step-up transformers, including power generator-transformer blocks, in utility and industrial power systems. It belongs to ABB’s Relion product family and the 615 protection and control series, which ABB characterises by a compact, withdrawable-unit design and a platform engineered around the IEC 61850 standard. Once a standard configuration has been given its application-specific settings, the relay can be put directly into service, which shortens engineering time on substation and switchgear projects.

Seven Star LLC supplies the ABB RET615 to utilities, oil and gas operators, independent power producers and industrial plants in the Sultanate of Oman and across the GCC. Our engineers in Muscat help you choose the standard configuration, analogue inputs, communication module and auxiliary supply before ordering, so the relay matches the protection study and the transformer neutral earthing arrangement on your site.

Protection Principle of the ABB RET615

At the core of the ABB RET615 is three-phase, multi-slope stabilized (biased) transformer differential protection with an instantaneous stage. The relay compares the currents entering and leaving the protected transformer, so phase-to-phase short circuits, winding interturn faults and bushing flashovers inside the zone are cleared quickly and selectively. Second harmonic restraint and an advanced waveform-based blocking algorithm keep the differential function stable during transformer energisation and inrush, while fifth harmonic restraint maintains stability at moderate overexcitation.

Sensitive restricted earth-fault (REF) protection completes the differential scheme and detects even single phase-to-earth faults close to the neutral earthing point. Either a conventional high-impedance scheme or a numerical low-impedance scheme can be selected. With low-impedance REF no stabilising resistors or varistors are needed, and the neutral CT ratio may differ from the phase CT ratio. Thermal overload protection supervises winding stress to prevent premature insulation ageing, and multiple stages of phase overcurrent, negative-sequence and earth-fault backup protection are available separately for both sides of the transformer, together with circuit breaker failure protection.

Engineering Design of the ABB RET615

The ABB RET615 is offered in eight standard configurations. Configurations A, C, E and G suit transformers with an earthed HV-side neutral, with A and E using low-impedance REF and C and G using high-impedance REF. Configurations B, D, F and H fit transformers with a solidly earthed LV-side neutral or an LV neutral earthing resistor, including schemes with a separate earthing transformer inside the protected zone. Configurations E to H add phase-voltage protection and measurement for two-stage overvoltage and undervoltage protection. The signal configuration can be adapted in PCM600 with the signal matrix or graphical application configuration, including multi-layer logic with timers and flip-flops.

Mechanically the relay uses the 615 series case: a 177 x 177 mm (4U) frame, 201 mm depth and 4.1 kg complete weight, with the plug-in unit weighing 2.1 kg. For safety, the case short-circuits CT secondary circuits automatically when the plug-in unit is withdrawn, and a mechanical coding system prevents a current-measuring unit from being inserted into a voltage-measuring case. Flush, semi-flush, wall, rack and 19-inch frame mounting are supported, and RTXP 18 test switches can be fitted alongside for routine secondary injection testing.

Key Features of the ABB RET615

The points below summarise the main capabilities listed in the ABB RET615 product guide.

• Multi-slope stabilized differential protection with an instantaneous stage for two-winding transformers and generator-transformer blocks.
• Second harmonic, fifth harmonic and waveform-based blocking to keep the relay stable during inrush and overexcitation.
• Low-impedance or high-impedance restricted earth-fault protection selected by standard configuration.
• Optional RTD/mA module for oil, ambient and dry-type winding temperatures and for on-load tap changer position indication.
• Optional three-channel arc fault protection for the breaker, busbar and cable compartments of metal-enclosed switchgear.
• Disturbance recorder with up to 12 analogue and 64 binary channels, 1024 time-stamped events and COMTRADE record export.
• IEC 61850 Edition 1 and Edition 2, IEC 61850-9-2 LE process bus, GOOSE, Modbus, DNP3 and IEC 60870-5-103.
• Ethernet redundancy through HSR, PRP or RSTP self-healing rings, with role-based access control and TLS-protected Web HMI.

Industrial Applications

In Oman the ABB RET615 suits 33/11 kV and 11/0.433 kV substation transformers on utility networks, on plant-owned primary substations at refineries, petrochemical complexes and fertiliser plants in Sohar and Duqm, and on generator step-up transformers at captive power plants. Because the RTD and mA inputs can measure top and bottom oil temperature and tap changer position, a single ABB RET615 can combine differential protection with practical transformer condition data that operations teams can read on the local HMI, the Web HMI or the SCADA system.

The relay also fits packaged substations and compact switchgear on desalination plants, district cooling plants and mining operations in Salalah and the interior, where space is limited and IEC 61850 station buses are now the norm. Seven Star LLC supplies the ABB RET615 with engineering support in Muscat, and we can quote matching feeder and motor relays from the same 615 series so the whole switchboard shares one engineering tool and one spare plug-in unit philosophy.

Technical Specifications

The values below come from the ABB RET615 product guide 1MRS756891 Rev. M (product version 5.0 FP1); the final order code defines the exact hardware.

How to Order

To order the ABB RET615, send Seven Star LLC the transformer rating, vector group, neutral earthing method, CT ratios, auxiliary supply and the communication protocol your substation automation system uses. We will propose the matching standard configuration and order code, advise on stock and lead time for Oman and the GCC, and help with setting files and commissioning; the ABB product guide can be downloaded from this page. For the same switchboard we can also quote the ABB REF615 feeder protection relay, the ABB SPAD34 stabilized differential relay for legacy panels and the ABB VD4/P 12.12.25 vacuum circuit breaker.

For motor feeders on the same bus, see the ABB REM615 motor protection relay.