631 / 2019-04-10 00:52:55

Modelling Transformer Open Phase and DC Bias on a Real Time Digital Simulator for Close-Loop Protection and Control Testing of Power Transformers

DC Bias, Geomagnetically Induced Current (GIC), Transformer Model, Real Time Digital Simulators (RTDS), Open-Phase Conditions

Transformer open phase conditions and DC Bias (e.g. caused by Geomagnetically Induced Current) are two important scenarios in protection and control testing of power systems. It is challenging to model these two scenarios in EMT simulation programs, because precise modelling of the core structure along with the saturation effects are required. The conventional three-phase transformer models used in EMT-Type simulation programs assume that a three-phase transformer is made up of three magnetically identical single-phase transformers. In reality, the saturation of the iron in three-phase transformers is not uniform in various parts of the core magnetic path. This can be observed in both 3-limb and 5-limb transformer cores, even under normal operating conditions. This paper reports our experiences in simulating the above two complicated scenarios with UMEC (Unified Magnetic Equivalent Circuit Circuit) transformer model using RTDS® real time simulator. The paper firstly provides a background knowledge of protection and control testing using Real Time Digital Simulators, and continues with an introduction to transformer open phase and DC Bias conditions in power system operation. Then the UMEC transformer model with the capability of modelling internal faults is proposed, which is followed by the validation and accuracy comparison. Finally the case studies are presented and the results are analyzed. The paper demonstrates that transformer models based on UMEC theory can correctly represent the actual characteristics of 3-limb and 5-limb transformers in both open phase conditions and DC Bias for the purpose of protection and control HIL (Hardware-in-the-Loop) testing of power systems equipment.