Question 4 A generator transformer unit (G and GT₁) with its associated station transformer (ST2) is connected via a 400kV busbar and double circuit supergrid feeder - transformers (STG3 and STG4) to 132kV and 33kV busbars via T5 as shown in Fig 3. VAR compensating reactors (X and X4) and static load impedances (L1 and L2) are also connected (note that L₁ is not earthed). The 400kV overhead lines have self impedances ZA1, ZAO and ZB1, ZBO and the mutual zero sequence impedance between them is ZMO (both circuits share the same towers). (a) Draw the positive, negative and zero phase sequence networks for the whole system. (b) Show how the phase sequence networks are interconnected is a single phase-earth fault occurs on the 132kV busbar at FA. (c) List the power transformer neutrals which carry fault current under single phase-earth fault conditions for the fault at FA- (d) A residual current relay is fitted in the 132kV neutral of T5. Explain briefly whether or not this relay will operate for a single-phase-to-earth fault at the following fault points: (i) the 132kV busbar, FA (ii) the 400kV busbar at FB, or (iii) the 33 kV busbar at Fc? R2 GT1 400KV ST 2 ₂₁ ZA ZB ZMO SGT3 SGT4 132 kV TS 33 W Fc BET OL2 GRET

Solved: Question 4 A generator transformer unit (G and GT₁) with its associate

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question 4 a generator transformer unit g and gt with its associated s

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Question 4 A generator transformer unit (G and GT₁) with its associated station transformer (ST2) is connected via a 400kV busbar and double circuit supergrid feeder - transformers (STG3 and STG4) to 132kV and 33kV busbars via T5 as shown in Fig 3. VAR compensating reactors (X and X4) and static load impedances (L1 and