How are Transformers Protected in the Field?

For maintaining a power grid in continuous working order, power transformers play a critical part. As repair and/or replacement of components in a power grid typically has a long lead time, protection from faults has to limit the damage to a faulted transformer. Moreover, transformer faults need quick prevention, and certain protection features identify operating conditions that could cause a failure of the transformer. This includes over-excitation protection and temperature-based protection.

Classification of transformer failure is as follows:

  • Failure in windings due to short circuits—this includes turn-to-turn shorts, phase-to-phase shorts, phase-to-ground shorts, and open windings
  • Faults in the Core—this includes failure of core insulation, and lamination shorts
  • Failure of Terminals—this includes open leads, short circuits, and loose connections
  • Failures of On-Load Tap Changer—this includes electrical and mechanical failures, short circuits, and overheating

Utility and industry power distribution networks utilizing power transformers typically install protection relays for the supervision, protection, control, and measurement of different parameters of power transformers, step-up and unit transformers, and power generator-transformers as well.

Transformer relays provide a flexible protection scheme for power transformers with two windings. They limit the damage to a transformer that has a fault and may identify operating conditions that could cause a devastating transformer or grid failure. Relay protection features include thermal overload protection, differential protection, voltage protection, and automatic voltage regulation. Some relays also have configurable functionality for meeting specific requirements of various applications.

For instance, the transformer protection and control relay, RET615 from ABB, conforms to IEC standards and offers a compact and versatile solution for industrial and utility power distribution systems.

A dedicated protection and control relay, the RET615 offers supervision, protection, control, and measurement of power transformers. It offers several benefits such as a compact and versatile solution, while integrating supervision, monitoring, control, and protection is one single unit.

RET615 offers an extended range of control and protection functionality for power transformers with two windings. It provides the transformer high inrush stability, while offering fast and advanced differential protection.

Setting up and tailoring the RET615 protection and control relay is simple and easy because it has ready-made configurations that match the most commonly used vector groups. This includes swift installation and testing, thanks to its withdrawable plug-in unit.

The RET615 has a large graphical display that shows the customizable SLDs. Users have the choice of accessing the SLDs directly on the display or via a web browser human machine interface that is simple and easy to use.

Along with measurement facility, RET615 also offers voltage and differential protection. It supports several neutral earthing options, including the restricted earth-fault principles of numerical low-impedance or high-impedance. The relay offers high-speed outputs for optional arc protection.

RET615 conforms to IEC 61850 Editions 1 & 2 standards, which include PRP and HSR, and GOOSE messaging. It follows IEC 61850-9-2 LE standard for supervised communication and less wiring.

Time synchronization is highly accurate as the RET615 conforms to IEEE 1588 V2, offering maximum benefit of Ethernet communication at substation level. In addition, RET615 supports DNP3, Modbus, and IEC60870-5-103 protocols for communication.