A3RW-4.0/1/S/IP21 is a digital relay produced by the Swedish company Breve Tufvassons. It is a multifunctional digital protection and control relay intended for protection, supervision, measurement and control applications in power industry for medium as well as for high voltage networks. It is designed for installations in different environments, up to -25°C to +60°C, and is available in various sizes from 96x96x136mm to 96x192x136mm depending on the customer's needs. The A3RW-4.0/1/S/IP21 is a three-phase device and features a number of protection functions such as overcurrent, earth fault, negative-sequence and ground fault protection, as well as different modes of operation such as auto-reclose, synchronisation and automatic voltage regulation. Communication capabilities are enabled by either an RS485 interface or an Ethernet connection, allowing for remote access, monitoring and control.