mprovement has been made on solving problems of the basic instantaneous protection based feeder automation

such as the long restoring time for temporary faults and the enlargement of faulty zone isolation due to over load. First

the source switches are designed to be capable of re-losing twice. The duration of temporary fault restoration is considerably reduced by adding a time delay mechanism to the tripping procedure of sectionalizing switches in case of out-of-voltage. The drawback of enlarging the outage zone due to overload is then avoided by introducing an out-of-voltage lock mechanism into the sectionalizing switches and loop switches

respectively. It is pointed out that the reclosing time delay of sectionalizing switches

i.e.

X-time values

can be set at the same value. Moreover

a hierarchical model of distribution network is proposed，on the basis of which the principles of setting the closing time delay of tie switches

i.e.XL-time

are detailed. A linear planning approach is proposed for setting the XL-time values of loop switches. Finally

a complicated meshed grid with six sources and sixty-six feeder switches is given as an example showing the feasibility of the proposed methods.