brushes move across the insulated segments. Commutating poles or interpoles are used to reduce this sparking. They are in fact electromagnets having a polarity the same as the main pole which follows in the direction of rotation The magnetic field between the poles is produced by what are known as"field coils".These coils are excited or energized by the current produced in the machine. The soft iron core of the field coils retains some magnetism which enables a preliminary current generation to build up eventually to the full machine output. The field windings can be connected to the output current a number of ways-shunt, series or compound. The compound wound arrangement is usual since it provides the best voltage characteristics The compound wound generator has two sets of field coils(Fig 1(a). The shunt coil has many turns of fine wire and the series coil has a few turns, of heavy wire. The shunt field produces full voltage on no-load which falls off as the load current increases ta) Field connections Voltsge from cornpound field wunt field series field Full load currant cbl Characterise curves Fig 1 Compound d.c. generator (a)----Field connections The series field creates an increase in voltage as the load increases. Properly combined or compounded the result is a fairly, constant voltage over a range of load( Fig. 1(b)) alternatin A coil of wire rotating in a magnetic field produces a current, The current can be brought out to two sliprings which are insulated from the shaft Carbon bushes rest on these rings as they otate and collect the current for use in an external circuit. Current collected in this way will be alternating, that is, changing in direction and rising and falling in value. To increase the current produced, additional sets of poles may be introducedbrushes move across the insulated segments. Commutating poles or interpoles are used to reduce this sparking. They are in fact electromagnets having a polarity the same as the main pole which follows in the direction of rotation. The magnetic field between the poles is produced by what are known as “field coils”. These coils are excited or energized by the current produced in the machine. The soft iron core of the field coils retains some magnetism which enables a preliminary current generation to build up eventually to the full machine output. The field windings can be connected to the output current in a number of ways—shunt, series or compound. The compound wound arrangement is usual since it provides the best voltage characteristics. The compound wound generator has two sets of field coils (Fig.1 (a)). The shunt coil has many turns of fine wire and the series coil has a few turns, of heavy wire. The shunt field produces full voltage on no-load which falls off as the load current increases. Fig.1 Compound d.c. generator (a) ----Field connections (b) ---Characteristic cures The series field creates an increase in voltage as the load increases. Properly combined or compounded the result is a fairly, constant voltage over a range of load (Fig. 1(b)). Alternating current generators A coil of wire rotating in a magnetic field produces a current, The current can be brought out to two sliprings which are insulated from the shaft. Carbon bushes rest on these rings as they rotate and collect the current for use in an external circuit. Current collected in this way will be alternating, that is, changing in direction and rising and falling in value. To increase the current produced, additional sets of poles may be introduced