It has already been pointed out that for transmission of electric power, 3-phase, 3-wire a.c. system is universally adopted. The different possible systems of transmission are :
The electric power can be transmitted either by means of d.c. or a.c. Each system has its own merits and demerits.
1. D.C. transmission.
For some years past, the transmission of electric power by d.c. has been receiving the active consideration of engineers due to its numerous advantages.
There are several types of insulators but the most commonly used are pin type, suspension type, strain insulator and shackle insulator.
1 Pin type Insulators