Electric power transmission lines send electric
power to demanded area, and distribution lines distribute it to consumers.
There are a few ways of electric power distribution, network a single-phase
two-wire type, a single-phase three-wire type, a three-phase four-wire
type, beside a three-phase three-wire type.
1. Single-phase two-wire type: Electric power is sent with two
wires from a single-phase electric power source. Residential power
system (100V, 120V ac) and midnight supply system (200V) adopt this
method. It is easy to install the single-phase two-wires because of
less number of wire, but its distribution effectiveness is low.
2. Single-phase three-wire type: The single-phase three-wire
system is formed by adding the neutral wire to a single-phase electric
power source. See the figure below. It is widely adopted for general
lighting (100V ac/200V ac). Electric current in neutral wire becomes
small if the load is balanced, distribution effectiveness is better
than the single-phase two-wire system.
3. Three-phase four-wire type: A neutral wire is drawn from the neutral
point of three-phase electric power source. It is often adopted for
large buildings and factories. |
 |
|
Why
is a three-phase alternating current used often for electric devices?
In
a three-phase three-wire type distribution system electric current is sent
with three wires from a three-phase electric power source. Electric power
transmission lines and high voltage distribution systems adopted it, because
of that effectiveness of electric power transmission per a wire. Event at
such low voltage as 200V, three-phase induction motors are widely used.