Permissive underreach transfer-trip interface

What it represents

Identifies the documented use of an underreaching local detection and remote permissive path. A protection scheme combines measurements, decision elements and communication or trip outputs to protect a defined part of the network. A function number names a job; the scheme interface shows how that job connects to other equipment.

In a substation feeder bay, local current and voltage measurements may combine with a remote-end signal before the protection issues the assigned trip request. Backup actions use their own defined initiations and supervision. For this reference, the drawing identifies “Underreaching detection and channel” at the input and “Assigned permissive output” at the output. Scheme naming does not define every terminal behavior.

Keep each protected zone, initiating quantity, blocking signal and trip destination distinct. Settings, communication performance and coordination require the approved protection study and selected relay documentation. The functional block is an independent explanation of this named application. Equipment-specific ratings, terminal connections and operating conditions must be established in the project documentation.

How to read it

• Start at the named input: Underreaching detection and channel. Identify its source device or document and the state represented on the drawing.
• Follow the named output: Assigned permissive output. Cross-reference its destination and separate the command from confirmation that the equipment responded.
• Scheme naming does not define every terminal behavior.
• Keep each protected zone, initiating quantity, blocking signal and trip destination distinct. Settings, communication performance and coordination require the approved protection study and selected relay documentation.

Information to show or reference

• Label the source and connection reference for underreaching detection and channel.
• Identify the destination and defined state of assigned permissive output.
• Record the equipment or control-document revision supporting this functional block.
• Check this application limit in the project design: Scheme naming does not define every terminal behavior.

Sources you can follow

These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.

About this graphic

This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.

SVG and DXF downloads contain this original artwork. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.