scope:

PURPOSE AND SCOPE

This TGN presents the seasonal pre-fault and post-fault continuous thermal ratings, together with the short-term overload ratings, applicable to National Grid's standard conductor sizes and resistivities, as specified in National Grid Technical Specification NGTS 3.4.37: 'Conductors for Overhead Lines'. In addition, the ratings are provided for the special conductors used on the Thames, Severn and Usk river crossings. Thus, this issue of the TGN covers all of the conductors currently in use on National Grid's system.

The ratings are tabulated in amperes and in MVA, based on National Grid's standard 132 kV, 275 kV and 400 kV overhead line circuits operating at a nominal frequency of 50 Hz and nominal system voltage, as specified in NGTS 1. For ACSR, the standard rated temperatures are 50ºC, 65ºC and 75ºC; for AAAC, 50ºC, 65ºC, 75ºC and 90ºC; for ACAR, 75ºC; for GZTACSR, 170ºC, for ACCC, 150ºC, for ACCR, 190ºC. In order to minimise the amount of data presented, only those combinations of rated temperature, voltage, conductor size, type and bundle which are currently in use - or are likely to be used - are included. To cater for the special case of L66/2 construction (2x300 mm² Upas AAAC), a 55ºC rating is provided. Where necessary conductors can be profiled for temperatures other than those presented in this document. Further details are given in Section 6.

Appendices A and B contain rating data per conductor and per circuit, respectively, in concise form. Appendices C to H contain detailed overload current and MVA capabilities for each circuit type; Appendix I provides this data for the river-crossing sections of the respective circuits.

Note:This document applies to the overhead line portion of a circuit only and must not be assumed to apply to associated equipment or to be a requirement to be met, in general, by associated equipment.