Consider three transformers in Δ - Δ, supplying their rated load. If one transformer is removed, then each of the remaining two transformers is overloaded. The overload on each transformer is given as

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BPSC AE Paper 6 (Electrical) 25 Mar 2022 Official Paper

Answer 1

Open Delta Connection:

The kVA rating of 3ϕ, Δ - Δ transformer is given by:

(kVA)d = \(\sqrt{3}\)V_LI_L

In delta connection: V_L = V_P and I_L = \(\sqrt{3}\)I_P

(kVA)d = \(\sqrt{3}\)V_P(\(\sqrt{3}\)I_P)

(kVA)_d = 3V_pI_p

where, V_p = Phase voltage

I_p = Phase current

(kVA)d = kVA rating of delta connected transformer

The kVA rating of the V-V connected transformer is given by:

(kVA)_v = \(\sqrt{3}\)V_LI_L

If one transformer is removed, then VL = VP and IL = Ip

(kVA)v = \(\sqrt{3}\)V_pI_p

\( {(kVA)_d \over (kVA)_v}= {3V_pI_p \over \sqrt{3}V_pI_p}\)

\( {(kVA)_d \over (kVA)_v}= { \sqrt{3}}\)

\( {(kVA)_d \over (kVA)_v}= 1.732\)