Specifications
66
+
-
1 8 3 10 5 12
6 11 4 9 2 7
I
A
I
A
I
A
2
Fig. 5.2 - Commutator ring diagram
Find the current direction by applying Fleming’s right hand rule, when the mode of operation
is a generator and Fleming’s left hand rule, when the mode of operation is a motor. Or the
current direction to all coil sides can be arbitrarily assumed. Mark downward current direction
for the coil sides under the north pole regions and upward current direction under south pole
regions, as shown in Fig. 5.1.
To fix the brush arm positions and to find the number of parallel paths offered by the armature
winding, commutator ring diagram is used, as shown in Fig. 5.2.
Draw the vertical solid lines equal to number of coil sides and join them with reference to
Table 5.1, as shown in Fig. 5.2. Also mark the current direction through the coil sides with
reference to main winding diagram in Fig. 5.2.
Look for adjacent pair of coil sides having the same current direction. For coil sides 12 and
7 carry which carry upward currents, mark negative brush arm, and for coil sides 6 and 1 carry
downward currents, mark positive brush arm, as shown in Fig. 5.2. Brush arms should be
equal to the number of poles.
Now, transfer the brush arms to the main winding diagram in Fig 5.1. Mark positive brush
arm below the commutator segment 1, where the coil sides 1 and 6 meet. Similarily, mark
negative brush arm below the commutator segment 4, where the coil sides 2 and 12 meet. Tap
out two leads and mark A for positive brush arm and AA for negative brush arms. These two
leads now indicate the armature terminals of a dc machine.
To decide the number of parallel paths offered by the lap winding, redraw Fig. 5.2 as shown
in Fig. 5.3.
Fig. 5.3 - Paralled paths for 2 pole 6 slot simplex lap winding
1
3
5
7
911
1
810
12 2
46
- +
A AA