Abstract
On AC electric railway, when a trouble happens in AC feeding circuit, protection is done by distance relay and AC ΔI type fault selective device to act an enormous change happens in the feeding current. Recently, with an increase in the transport capacity, feeding currents from substations increase and AC re-generative rolling stocks are increasingly adopted for rapid transportation.
Under these circumstances, loads covered by distance relays have come to be closer to the protective zone, so the protective zone has now to be reduced.
We developed a new distance relay that can cover wide zone for fault currents and narrow zone for loads of electric rolling stocks.
Protective zones are switched by detection of higher harmonics because load currents have higher harmonics but fault currents have hardly any such harmonics.
This distance relay has been introduced on narrow gauge lines after its expected ability was confirmed both in an experiment of this device alone and in its field test.
