Effects of sensor technology on differential protection

Developments in substation secondary systems in the future will include more and more the process bus as means to exchange data between sensor and actuators, and control and protection devices, known as Intelligent Electronic Devices (IEDs). Secondary systems will use data coming from different sensors, such as conventional current transformers (CTs) and voltage transformers (VTs) directly attached to IED devices or via merging units (MUs), non-conventional instrument transformers (NCIT) such as fibre optical current sensors (FOCS) and voltage sensor (FOVS). This paper presents results of the performance of differential protection schemes such as line differential protection or bus differential protection in conjunction with those protection schemes receiving data from CTs and MUs as well as FOCS sensor devices. The impact both for line differential protection and bus differential protection caused by saturation of conventional CTs, unsynchronized data outputs from MUs and the use of FOCS sensors is investigated.