Standards Development

Scope

This document provides guidance for UHV AC substation maintenance considering system-oriented
maintenance issues of UHV AC transmission systems.

This document is based on the maintenance technology development and on-site practices that have
been involved in UHV AC transmission systems. It can be used by power system planners, equipment
suppliers, engineering contractors, maintenance staffs and power grid operators.

Purpose

UHV AC transmission system features large capacity and high voltage, which draws high requirements for the reliability and safety of its equipment and transmission lines. In order to obtain the operation condition and maintain the transmission system soundness during its service life, necessary maintenance is required. Until now, several UHV AC test bases and transmission projects have been constructed in several countries. Maintenance for UHV AC equipment and transmission lines is needed.

UHV AC transmission system requires high availability and reliability. The impact on UHV AC power grid caused by unplanned power supply interruption is much greater than that on lower voltage grids. Planned maintenance interruptions need longer preparation time before part of the UHV system is de- energized. This requires more detailed system oriented maintenance for planning and executing of maintenance activities. Moreover the size, weight and structure of equipment and transmission lines in UHV AC system are different from those of EHV AC system.

For example, some UHV transformers have two separate parts, a main transformer and a regulating transformer, which are not common in EHV transformers. The weight of the main transformer is more than 500 t and the height is more than 17 m, which makes the maintenance of UHV transformers more complex. These UHV transformers have a large workload in maintenance test, overhaul, and spare equipment replacement and so on. Also, compared with EHV AC transmission lines, UHV AC transmission lines have a larger structure size and a longer transmission distance. Therefore, in order to facilitate field application, more portable and more convenient live working tools and equipment are needed.

Generally, the maintenance of UHV AC transmission systems is very different from other voltage level systems in terms of methods, requirements, tools and so on. Guidelines of maintenance on UHV AC transmission systems should be developed.