Question

Just need help with questions 5 & 6 please. Thanks in advance.

A4-1: Zone 1 Zone 2 Zone 3 Xine 40 ohms @90 Zload 40 j30 ohms Vs 34.2kV0 T1 та Wye-Delta Delta-Wye 20MVA 30MVA 180kV/17.8kV 34.6kV/200kV X-0.10 pu X-0.25 pu A4-2: Zone 2 Zone 3 Zone 1 Xline 80 ohms 90 Sload (3ph) 18MVA pf 0.90 lagging VL 27.5kV @O Vs T1 Т2 Delta-Wye 20MVA Wye-Delta 25MVA 220KV/27.6k 6.9kV/225kV X-0.10 pu X-025 pu Zone 2 A4-3: Zone 1 Zone 3 Sload (3ph)-24MVA pf 0.90 lagging Vu 30.0kV @O 120 ohms@ 90 Xline Vs T- та Wye-Wye Wye-Delta 25MVA 20MVA 15.0kV/200KV 220KV/32KV X-0.20 pu X-0.40 pu 5) Determine the base voltages, currents, impedances, and apparent power for the three-phase system in figure A4-3 below. Use the T2 ratings as base values (10 marks) For the three-phase system in figure A4-3 determine the source voltage in per-unit, current in each zone in per-unit, and the load current in Amps. (10 marks) 6) 7) Draw the per-unit circuit for the three-phase system in figure A4-3. Include all bases, currents in each zone, source voltage, and all impedances in per-unit form, and phase-shifts across transformers. (5 marks)

Answer 1

A4-3 Baa MVA= 2SMVA Baa KV in Zone 2 - 220ku 32KV Bar kv in Zone 3 6.Skv 1S κυ 220 KV x 200KV KVb 2one i) baa Zone 2) = KVbas (Zone 3)- 2 20 v 32ky MVAbaa 2S MUA Zone 2SHVA MVA Zone 2) MVA (Zon 3) 25HUA 2 16.5 o 89 (KV) MVAb Baos impedand (Zon e ) 25 Bese impedanee (Zone 2) 2 20 25 322 40.96s Bass impedanes (Zone 3) 874-773 A Baa Current zone ) 2S x 1o Zone 2) 2S x 10 Bane Current 6S.608 A Bx 220x103 Base uent (2one 3)- 25 X 10 451 0S9 A U3 x32 x 10

XT, (old)xHVAne XTi (new) (kvoeld MVAatd 2 (K Ubnw) 2 . . XT (nw)= 0 2x 25 O 20 66 pu X Xiine (pu)j120 ja61a83p 36 Sinu T Хтр arre baa Valua henu no chang (muprduų j Stodd 24MVA at 0.19 V-L 30KV 24 x1o V3 x30x10 4 61 86 02 A at - (6.0),s ILDAR 461 8E02 -2s BY°A (load Cured in 25.8y Pomps IDAD (Pu) 4 61 8602 024 pu af 0.9 4S1 oS9 Tionopu) guivalent cruut jo J.0242-2. 84° pu jo 06/983 LOAD pu for aach zone ,'s urent in Sina cirut is in svno Same and egul to load Cuwent - 25-4 pu Zpu (each Zone ) /02 42-

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VLOAD (ru) O.9315 30Ku 32K VLDAD (pu) O 0-937S LO pu Applying KVL Ve VLO AD C o o61983 024 -25.84)o 668583) . Vs= 0 375L0+ m Vs 381226 5