3-11
Figure 3-8.—Three-phase alternator connections.
Rather than having six leads coming out of the three-phase alternator, the same leads from each
phase may be connected together to form a wye (Y) connection, as shown in figure 3-8, view B. It is
called a wye connection because, without the neutral, the windings appear as the letter Y, in this case
sideways or upside down.
The neutral connection is brought out to a terminal when a single-phase load must be supplied.
Single-phase voltage is available from neutral to A, neutral to B, and neutral to C.
In a three-phase, Y-connected alternator, the total voltage, or line voltage, across any two of the three
line leads is the vector sum of the individual phase voltages. Each line voltage is 1.73 times one of the
phase voltages. Because the windings form only one path for current flow between phases, the line and
phase currents are the same (equal).
A three-phase stator can also be connected so that the phases are connected end-to-end; it is now
delta connected (fig. 3-8, view C). (Delta because it looks like the Greek letter delta, D.) In the delta
connection, line voltages are equal to phase voltages, but each line current is equal to 1.73 times the phase
current. Both the wye and the delta connections are used in alternators.
The majority of all alternators in use in the Navy today are three-phase machines. They are much
more efficient than either two-phase or single-phase alternators.
Three-Phase Connections
The stator coils of three-phase alternators may be joined together in either wye or delta connections,
as shown in figure 3-9. With these connections only three wires come out of the alternator. This allows
convenient connection to three-phase motors or power distribution transformers. It is necessary to use
three-phase transformers or their electrical equivalent with this type of system.
