The delta-connected winding uses smaller wire than the wye connection. Multiple internal circuits also use smaller wire than a single circuit. (Smaller wire is easier to form and insert into the slots.)
The delta connection is usually found in 5-horsepower motors (and larger), but any size three-phase motor can be delta connected. The same is true of multiple-circuit connections. Internally, a winding can have many parallel circuits (Fig. 6.10).
The dual-voltage (nine-lead) delta connection, with more than one internal delta circuit, is shown in Fig. 6.11. Each half circuit (for example, Tl to T4) has two parallel circuits.
The following list refers to the schematic in Fig. 6.12:
• Leads Tl and T4 are the first half of the phase A circuit. Lead T7 starts the remaining half of the A-phase circuit and ends at line 2 (T2).
• Leads T2 and T5 are the first half of the phase C circuit. Lead T8 starts the remaining half of the C-phase circuit and ends at line 3 (T3).
FIGURE 6.10 A four-circuit or four-delta connection.
FIGURE 6.11 The nine-lead delta schematic with parallel internal connections.
• Leads T3 and T6 are the first half of the phase B circuit. Lead T9 starts the remaining half of the B-phase circuit and ends at line 1 (T1).
• Data between Tl and T4 are exactly the same as those between Tl and T9.
• Data between T2 and T5 are exactly the same as those between T2 and T7.
• Data between T3 and T6 are exactly the same as those between T3 and T8.
With the low-voltage (parallel) connection (Fig. 6.13), line I connects to T], T7, and T6; line 2 to T2, T8, and T4; and line 3 to T3, T9, and T5.
FIGURE 6.12 The nine-lead one- and two-delta connection.
FIGURE 6.13 The nine-lead one- and two-delta connection for low voltage.
In the high-voltage connection (Fig. 6.14), line 1 connects to Tl, line 2 to T2, and line 3 to T3. Lead T4 connects to T7; T5 to T8; T6 to T9; the three connections are insulated separately.
The number combination for high voltage is the same for both wye (Fig. 6.15) and delta. The data between line 1 and line 2, line 2 and line 3, and line 3 and line 1 are exactly the same in both high- and low-voltage connections.
Most of the current that flows from line 1 to line 2 (in a delta connection) will pass through one complete phase winding (Fig. 6.16). Some current will flow through the other two phases.
FIGURE 6.14 The nine-lead one- and two-delta connection for high voltage.
FIGURE 6.15 The nine-lead one- and two-wye connection for high voltage.
FIGURE 6.16 Current flow from Ll to 1.2 in the nine-lead delta-connected motor.