Modelling power transformers at power line carrier frequencies

Many electricity suppliers will be installing smart meters during the next few years. It is likely that these smart meters communicate with the electricity suppliers' control centre using power line carrier (PLC) communications. The CENELEC A frequency band from 9 kHz to 95 kHz is set aside for use by Power Supply Companies. The upper part of this frequency band is very suitable for smart meter reading and smart grid control. In most practical situations, the PLC signals are injected directly onto the LV lines. However it may be desirable to transmit the PLC signals through the MV network and pass them through the LV distribution transformer, as is done in the present ripple control signalling. To design a suitable communication system using this technique, the PLC signal attenuation through the transformer needs to be known. To determine these losses, it is necessary to know how LV distribution transformers behave at these PLC frequencies and what isolation they provide between the LV and the HV distribution networks. ERGON is an Australian Electricity supplier operating in rural Queensland. They have sponsored a project carried out by James Cook University, to develop a communication system for SWER lines, so that smart metering, fault detection and enhanced network control can be applied to SWER lines. In this application the PLC signals are carried on the 19.1 kV SWER lines and the SWER line transformer becomes an integral part of the coupling network, for coupling the communication signals onto the SWER line. As part of this work a high frequency model of a 10 kVA and a 25 kVA power transformer was developed. The paper describes how the transformer parameters of these transformers are measured and shows how those measurements are used to develop the transformer model covering frequencies from 50Hz to 1MHz