laxman289

yeah thats right...breaks cause a problem..but here in india two rails are joined by large thick metallic plate.so i assume that the change in flux will be much lower in case of breaks than cracks...if we r adding a suitable resistance then gate current can b made lower than min gate current required to trigger but there isnt any other closed path through which flux can pass

working-in the normal state(no cracks) no emf is induced in secondary coil.when crack is there the magnetic flux changes hence emf is induced in the secondary which turns on the thyristor and hence buzzer.will this circuit work as intended