PURPOSE AND SCOPE

The purpose of this Technical Guidance Note (TGN) is to provide the background and necessary guidance on the application of policy PS(T) 055. This policy states the application and setting of systems that provide specific auto switching and delayed auto reclose functionality.

The information provided in the tables in this TGN support and should be read in conjunction with the policy PS(T) 055.

This information states the functional and setting requirements for equipment that is designed to perform the following tasks:-

a) (Re)closure of Circuit Breakers under dead or live power system conditions.

b) Delayed Automatic Reclosure (DAR) of Circuit Breakers.

c) Automatic Switching of Disconnectors to perform plant isolation operations.

d) Automatic Switching of Disconnectors or Earth Switches to perform ferroresonance quenching.

The purpose of these functions and settings shall be to enable: -

e) Automated operation of plant following the tripping of a circuit due to the detection of a fault that will :-

(i) automatically isolate faulted plant or circuits from the system

(ii) restore healthy plant or circuits to service

f) Automated Closure of a circuit breaker initiated by a manual command from the SCS g) Automated removal of abnormal system conditions - ferroresonance

For a given plant configuration the required DAR, Plant Isolation, Ferroresonance Suppression and Synchronising operating characteristics shall be achieved by applying appropriate settings.

The location of each section within this document and the associated section title has been designed to correlate with the layout of sections and section titles in the Policy.

The information stated in the following tables will contain sections that will indicate:-

h) A section title for a function that will directly correlate to a section in the policy

i) The purpose of the function that the setting is applicable to i.e. DAR, SAS or both.

The information stated in the following tables will optionally contain sections that will indicate :-

j) A setting Name

k) A Setting Range

l) A preferred Normal Value for the setting

m) An application note to indicate

(i) How the normal value is calculated

(ii) if the Normal Setting can be recalculated

(iii) the circumstances under which recalculation is permitted.

When the functions or settings specified in this document cannot be achieved or are considered inappropriate, reference should be made to National Grid Asset Policy.