The single line diagram (SLD) is the most basic of the set of diagrams that are used to document the electrical functionality of the substation. Its emphasis is on communicating the functions of the power equipment and the associated protection and control system. The SLD is also a critical link between the schematic diagrams and the relay settings documents in troubleshooting protection and control circuits.

Devices and description of this sample SLD

  • RED 670: Main-1 Differential / Distance Protection
  • 7SD522: Main-2 Differential / Distance Protection
  • 7VK87: CB Fail Protection Relay with Backup DOC/DEF Protection for OHL bays1
  • 7KE85: Disturbance Recorder
  • 7SD82: Main-1/2 Cable Differential Protection
  • 7UT82: Low Impedance Restricted Earth Fault Protection
  • 7SJ82: CB Fail Protection Relay with Backup OC/EF Protection
  • 7SS85: Main-1/2 Centralized busbar Protection
  • MFM: Multifunction Meter with transducer outputs for NCC measurements and display for indication of measured values.
  • 6MD85: Bay Controller Unit (BCU)
  • 85X, 85R1, 85R2: 7PA27, Intertrip Receive Relay
  • F85: SWT3000, Intertrip Unit for OHL & UGC Bays

Following shows the ANSI code and functional

  • 21: Distance protection
  • 25: Synchrocheck
  • 50: Definite time overcurrent protection
  • 50N: Definite time earth fault protection
  • 50BF: Circuit-breaker failure protection
  • 51: Inverse time overcurrent protection
  • 51N: Inverse time earth fault protection
  • 64: Sensitive ground-fault protection
  • 67: Directional overcurrent protection
  • 67N: Directional earth fault protection
  • 68: Power swing blocking
  • 79: Automatic reclosing
  • 87: Differential protection
  • 87B: Busbar differential protection
  • FL: Fault locator