New transductor-type d.c. transformer particularly applicable to h.v. d.c. systems

The paper reviews briefly the transductor-type d.c. transformers which are at present in use, including the type using two sets of cores and 90° phase displacement between their auxiliary a.c. supplies. It is shown in the paper that a transductor-type d.c. transformer can be constructed without core duplication, but which nevertheless avoids the production of commutation pulses or notches in its output, this being necessary for the successful operation of fast protective and control equipment in h.v. d.c. systems. Notchless operation is attained by the use of auxiliary circuits associated with the core windings of the measuring transductor. Furthermore, by providing a simple additional circuit, a high degree of transformation accuracy can be obtained throughout the range of measurement. The design parameters of the new d.c. transformer are discussed, together with the particular design of one for experimental purposes. The performance of this transformer is given in the paper, by comparison with a conventional d.c. current transformer constructed on the same size and type of core and with the same winding specification. It is shown that, for the same transient performance, the new d.c. transformer is always more economical than those of conventional pattern; this is true even when it is necessary to include a switching arrangement to provide for d.c. measurement of either polarity.