OLTC transformer model connecting 3-wire MV with 4-wire multigrounded LV networks

•A new OLTC transformer modeling technique is proposed.•Taps are modelled as equivalent current sources.•Power flow analysis is significantly accelerated.•Applicable to 3-wire medium voltage and 4-wire multigrounded low voltage networks. This short communication presents a comprehensive model of on-load tap-changer (OLTC) transformers that connects 3-wire medium voltage (MV) with 4-wire multigrounded low voltage (LV) networks. The proposed model enables the inclusion of the 3-wire MV network and the 4-wire multigrounded LV network into a single YBUS matrix without any assumption or simplification. Its distinct feature is that the tap changer of the transformer is simulated outside the YBUS matrix, thus a refactorization of the YBUS matrix is not required in every tap change. The proposed transformer model has been validated in a 4-Bus network, while its performance has been tested in the IEEE 8500-Node and IEEE 906-Bus test networks.