Page 633 - Basic Electrical Engineering

draw excessive current which is not desirable. The coil of the OLR will
remain energized when the motor is running on normal load and its armature
will remain in the position shown. When the motor is drawing more current

than its rated current the armature gets lifted and the contacts cc of the NVR
get short-circuited thereby demagnetizing the NVR electromagnet. The

starter arm will eventually return to OFF position stopping the motor.
Protecting devices like no-volt-release (NVR) and over-load-release (OLR)

mechanisms have been added while designing a dc motor starter. The starter
shown in Fig. 7.19 (a) is called a three-point starter. The three points or

connection points are designated as L, A, and F. The connection of the starter
terminals to the motor armature and field terminals and the supply terminals
are as follows. Connect one supply line to L. Connect one armature terminal

A to point A and connect starter terminal F to field terminal F as has been
shown in Fig. 7.19 (a). The other ends of armature and field, i.e., AA and FF

are joined together and are connected to the supply line L .
2