A delta-connected power source provides greater fault tolerance than a wye-connected source. If one of the windings in a delta-connected source fails open, the line voltage remains 120V and only the current in the remaining functioning windings increases. However, if a winding in a wye-connected source fails open, it halves the voltage supplied to two of the loads.

1. !

2. Blue Red White Blue
Red White

3. pen failures in the load elements.
e greatest advantage of the ∆-connected source is its fault toler
f the windings in a ∆-connected three-phase source to fail open
ng load voltage or current!
120 V ! 0o 120 V
+ -
+
winding 120 V 120 V 120 V
failed open! ! 120o
-
Even with a source winding failure, the line voltage is still 120 V,
120 V. The only difference is extra current in the remaining fu

4. nsequence of a source winding failing open for a ∆-connected sour
in the remaining windings. Compare this fault tolerance with
ng an open source winding in Figure 10.38.
208 V
+ +
120 V 120 V
!0 o - - ! 120 o
104 V 104 V
winding
failed open!
Open “Y” source winding halves the voltage on two loads of a ∆ co
onnected load, two of the resistances suffer reduced voltage whil

5. nsequence of a source winding failing open for a ∆-connected sour
in the remaining windings. Compare this fault tolerance with
ng an open source winding in Figure 10.38.
208 V
+ +
120 V 120 V
!0 o - - ! 120 o
104 V 104 V
winding
failed open!
Open “Y” source winding halves the voltage on two loads of a ∆ co
onnected load, two of the resistances suffer reduced voltage whil

6. nsequence of a source winding failing open for a ∆-connected sour
in the remaining windings. Compare this fault tolerance with
ng an open source winding in Figure 10.38.
208V
0 V
+ +
120 V 120 V
!0 o - - ! 120 o
104 V 104 V
winding
failed open!
Open “Y” source winding halves the voltage on two loads of a ∆ co
onnected load, two of the resistances suffer reduced voltage whil