Protective relays measure current in each branch of a 3-phase circuit testing for anomalies. The selection and applications of protective relays and their associated schemes shall achieve reliability, security, speed and properly coordinated. The rectangular devices are test connection blocks, used for testing and isolation of instrument transformer circuits. A protection scheme – for example, a differential protection scheme – is. A protection relay is a crucial component of electrical systems that safeguard infrastructure, employees, and equipment from electric problems and malfunctions.