Design and Development of Superimposed Directional Comparison Protection Scheme

To achieve the UK Net Zero future by 2050, National Grid needs to integrate significantly more renewable generation into
the power grid. This increases the level of harmonics, reduces system inertia and adversely affects the fault level and the
performance of existing protection relays. One solution to the protection problem is the use of new types of protection that use
the change in the voltage and current caused by the fault, often referred to as a superimposed or incremental based protection
technique. This paper describes how a superimposed directional comparison protection scheme performed when applied to a
reduced section of the full UK National Grid network and relates this to the operating performance of traditional protection.
Tests are performed using the simulators DIgSILENT and RelaySimTest configured with different source levels, fault types,
fault locations and fault resistances. Results show the superimposed based protection scheme achieves faster fault detection
and tripping than conventional protection and is capable of detecting higher resistive faults on networks where the source
capacities vary from strong to weak.