Introduction: A condition assessment and report on the condition of global positioning system (GPS) installations at 3 National Grid substations which will help determine how vulnerable a typical GPS installation is to GPS signal blocking/imitation/interference which can all have detrimental effects on National Grid protection systems. Note: interference can be introduced by adjacent National Grid equipment, this was found during field tests at Ninfield substation. The aforementioned threats can have short term consequences to National Grid (Olympics) and long term consequences (transmission system stability) by potentially in the worst case causing mal-operations on the system.

Objectives: The main objective which will be determined by the assessment of the installation of “24/7” GPS signal blocking/imitation/interference detector at 3 National Grid substations which will assess whether National Grid should be concerned about its extensive amount of equipment utilising GPS which is already installed on the system.

The selection of the 3 National Grid substations will be based on criticality, i.e. next to busy motorways and/or where there are known problems which may be commonly occurring or infrequent but prolonged.