Modeling of CT/VT Methods in Substations in Dynamic Simulations using Signal Matrix

In substations, the protection system uses currents from Circuit Breakers (CBs) and Current Transformers (CTs) and voltage from Voltage Transformers (VTs) as an input to IEDs or relays. The CBs in a substation are located according to station configuration and the CTs/VTs are arranged based on CT/VT method used for that station configuration. Considering these practical arrangements are important for analysing substation specific protection. Modeling of these practical methods is ignored in operational studies as it requires Node-breaker (NB) models of power system. Mostly the operational studies are performed using Bus-Branch (BB) models which fail to capture CB currents let alone the CT methods. In this paper, we focus on these aspects of protection that require NB modeling of the system. We show that the Sparse Tableau Approach (STA) based NB modeling of substations can be used to inherently provide the CB and CT currents and VT voltages. We propose a Signal Matrix formulation to model the CT and VT methods in substations for dynamic simulations. This enables seamless integration of practical protection schemes into stability studies without any reduction to BB models and provides an opportunity to study disturbance scenarios that arise within substations. Test cases on WECC 3 generator 9 bus system for breaker failure protection (BFP) and teed protection is used to demonstrate the proposed approach for dynamic simulations. The results show that CB currents can be directly used for BFP and different CT/VT method in a substation may result in varied protection for faults inside substation.