The Le-Blanc transformer is a specially connected
transformer that transforms a three-phase power system to a
two-phase or two single-phase powersystems. It is the main
transformer of electric railway in Taiwan to transform69 kV(
three-phase) to 25 kV(single-phase) system. Owing to the
specialwinding connection and different phase transformation,
Le-Blanc transformerscannot use conventional differential
protection directly. Therefore, theovercurrent protection
became the main electrical protection of Le-
Blanctransformers. The purpose of this research is to
design a differential protectivescheme for Le-Blanc
transformers. Three differential protective schemes forLe-
Blanc transformers have been designed based on a current phasor
combination method: (1) Three-relay protective scheme--
Match the secondary current phasors of Le-
Blanc connection to the primary current phasors. (2) Two-
relay protective scheme--Match the primary current phasors to
the secondary current phasors of Le-Blanc
Connection. (3) One-relay protective scheme--Match the
primary and secondary current phasors of Le-
Blanc connection to the same phasor. Results of practical
design examples using the parameters of a Le-Blanc transformer
of Taiwan Railway Bureau(Tairail) are described in this
thesis. The low mismatch sufficiently explains why the
differential protection ofLe-Blanc transformers can be
achieved by these schemes. In addition, laboratory test
results also depict the feasibility of the proposed
protectiveschemes.