PURPOSE AND SCOPE

This document defines National Grid's policy for the protection arrangements and settings to be applied on its 400kV and 275kV transmission network and lower network voltages at 132kV, 66kV, 33kV and 13kV. Additionally the principles of this document shall be applied to other system voltages where National Grid owns assets.

Protection application and settings policy for the most commonly occurring transmission arrangements for feeders, bus connectors, transformers, series reactors, shunt reactors, quadrature boosters (QBs), static var compensators (SVCs), busbars and switchgear at 400kV, 275kV and 132kV is now included. For protection application and setting guidance on primary arrangements not covered by this document refer to Asset Policy, Electricity Transmission Asset Management (ETAM) and/or Technical Assurance, Capital Delivery Directorate for further advice.

The protection arrangements and settings for the new technologies such as High Voltage Direct Current (HVDC), Series Compensation and Static Compensators are not covered in this document. The document is split into four parts. National Grid protection application policy is specified in Part 1 and Part 2 provides guidance notes, where applicable. The protection settings policy is outlined in Part 3 and associated guidance is provided in Part 4.

Specific protection bay requirements are referenced in this document to the applicable TS 3.24 series specifications which are covered by the high-level specification TS 2.24.

The application and settings for synchronising, delayed auto reclose (DAR), automatic equipment isolation and ferro-resonance quenching are given in National Grid PS(T) 055 and accompanying guidance in TGN(E) 205.

The protection application, settings and guidance for 25 kV phase-phase connected Railway Supply Points is covered in PS(T) 063 and TGN(E) 212.