The Numerical Distance 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.

• Phase distance (21) protection

• Ground distance (21N) protection

• Directional phase overcurrent (67) protection

• Directional ground overcurrent (67N) protection

• Directional power (32) 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 Distance Relay can also perform several other standard protection functions (ANSI 27, 37, 38, 46, 59, 68, 74, 81, 86, and 87N).

The front panel of the relay features a display that can provide information about the relay protection functions, indicate numerous currently measured values such as the line voltages, line currents, phase power, three-phase power, and power factor, 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 Distance 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.

Access to the voltage and current inputs of the Numerical Distance Relay is through a removable panel located at the back of the relay enclosure. Access to the relay Ethernet port, binary inputs, and binary outputs (e.g., trip contacts) is also through this removable panel. The Numerical Distance Relay is powered via an ac power inlet mounted on the front of the relay enclosure. A variant of the Numerical Distance Relay with safety jacks and connectors mounted on the front panel to provide access to all relay inputs, outputs, and ports is also available. See the Numerical Distance Relay, Model 3813-A.