What are the examples of single and two phase system?

In its simplest form, a single-phase a.c. system comprises two conductors: a line ('hot') conductor and a neutral conductor. In North America, however, it is usual for a single-phase residential supply to have three conductors: the two 'hot' conductors are connected across opposite ends of a single-phase transformer winding, while the neutral conductor is connected to the centre (tap) of that winding. This provides a combination of 240 V and 120 V, and is known as a 'split phase' single-phase system.

A two-phase a.c. system is very rare, these days, and you are unlikely to come across one. It is an archaic system that has long since been replaced by the three-phase system. Essentially, this system was provided by an a.c. generator whose armature windings were physically displaced from each other by 90 degrees, thus providing two phase voltages that are 90 electrical degrees apart. Usually, a two-phase system was a three-wire system, providing two line conductors and a neutral. The resulting line voltage (measured between the two lines) would then be 1.42 times either of the phase voltages (measured between one of the lines and the neutral).