This question was asked inSupervisor Instructor Electrical Part B Technical Paper 2026Question 86 of 120 published · Gujarat Subordinate Service Selection BoardOpen paper
Q86ModerateThree-Phase Circuits

In a three-phase delta connection, if one phase becomes open, what is its effect on the system?

Answer & step-by-step solution
Correct answer: B. The load keeps working but becomes unbalanced.
Quick explanation

B — The load keeps working but becomes unbalanced. A delta has alternative paths between line terminals, so with one phase open it runs as open-delta (V-V) with reduced, unbalanced capacity.

Detailed solution (in the paper’s original language)

સમજૂતી

Delta-connected system માં line terminals વચ્ચે alternative electrical paths હોય છે.

એક phase/branch open થાય તો બાકી જોડાયેલા ભાગોમાં current ચાલુ રહી શકે છે; તેથી load સંપૂર્ણપણે બંધ થતું નથી, પરંતુ currents અને loading unbalanced બને છે.

મુખ્ય ખ્યાલ

Delta માં open phase → operation ચાલુ રહી શકે, પરંતુ unbalanced બને.

પરીક્ષા મુદ્દો

Open-phase પ્રશ્નમાં connection delta છે કે star તે પહેલા જુઓ.

ઝડપી ટ્રિક

Delta માં alternate paths હોય છે; open phase imbalance બનાવે છે, total shutdown જરૂરી નથી.

બીજા વિકલ્પો ખોટા કેમ છે

Symmetry ગુમાય એટલે normal balanced operation શક્ય નથી; પરંતુ complete shutdown પણ સામાન્ય પરિણામ નથી.

સામાન્ય ભૂલ

કોઈપણ open phase થાય એટલે તમામ load disconnect થાય એવું માનવું.

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