The ratio of the operating capacity to the available capacity of an Open-Delta connection is ___________

Open Delta Connection:

• When one of the windings of a delta-connected transformer gets open, it starts working as an open delta connection.
• An open delta connection transformer uses two single-phase transformers to provide a three-phase supply to the load. 
• An open delta connection system is also called a V-V system.
   

Calculation:

The operating capacity of the V-V system is given by:

(kVA)_Δ-Δ  = \( \sqrt{3} V_LI_L\)

When one of the windings gets open, the V-V system has only two windings left.

(kVA)_V-V = 2V_LI_L

\( {(kVA)_{\Delta-\Delta} \over (kVA)_{V-V}} = {\sqrt{3}V_LI_L \over 2V_LI_L} \)

\( {(kVA)_{\Delta-\Delta} \over (kVA)_{V-V}} = {\sqrt{3}\over 2} = 0.866\)