Instrument transformer bridges with inductively coupled ratio arms

The paper presents an extension of the ratio transformer bridges techniques denoted “instrument transformer bridge with inductively coupled ratio arms” (IBI) which uses two ratio transformers, an instrument transformer (IT) and a decade ratio transformer (the inductively coupled ratio arms (ICRA)). The IT allows to supply the reference standard at its secondary low rating and extends the bridges´ range without extending the dynamic range of both the reference standard and ICRA. The basic block diagram of the IBI is illustrated. Moreover two structures of the IBI: the “HV admittance potential transformer bridge with current comparator” (HPBC); and the “four-terminal impedance current transformer bridge with ICRA” (FCBI) are illustrated as well. These bridges adopt as ratio transformer respectively: a potential transformer (PT) with a decade current comparator (CC); and a current transformer (CT) with a decade voltage ratio transformer. The ICRA are supplied through the compared components, by means of the IT with quantities in a well known ratio and detect their ratio value. The most interesting applications of the bridges are also illustrated. The prototypes of the new bridges, which have been developed, are briefly illustrated and the obtained experimental results are discussed; an uncertainty equal to that one of 0.5 ppm of the ICRA is achieved. The inherent advantages of the bridges are also investigated