The Numerical Differential Protective Relay is a power-utility grade, numerical protective relay (Siemens SIPROTEC 5 series) mounted in a table-top enclosure. The relay can perform the protection functions listed below.

• Transformer differential (87T) protection

• Instantaneous phase overcurrent (50) protection

• Instantaneous ground overcurrent (50N) protection

• Phase overcurrent (51) protection

• Ground overcurrent (51N) protection

• Machine or transformer thermal (49) protection

The Numerical Differential Protective Relay can also perform several other standard protection functions (ANSI 37, 38, 46, 74, 86, 87N, and 87M).

The front panel of the relay features a display that can provide information about the relay protection functions, indicate currently measured values of the transformer winding currents, and show information about trip events that have been recorded. A keypad, also on the front panel of the relay, allows users to select the information displayed. The front panel of the relay also features a set of 16 LEDs that allows quick monitoring of the status of various relay functions.

Relay programming (e.g., protection function selection, function settings) is achieved via the Siemens DIGSI 5 software. This software is designed to be run from a personal computer with a Microsoft® Windows™ operating system. Communication between the computer and the relay is through a USB port or an Ethernet port. Relay function settings can also be performed using the keypad and display located on the front panel of the relay. Once programmed, the Numerical Differential Protective Relay can be tested using a built-in relay testing unit to ensure it is programmed to operate as expected. This eliminates the need for users to purchase a costly external relay tester to perform relay testing. The built-in relay testing unit is operated using the DIGSI 5 software.