1. The one-line diagram of an unloaded power system is shown below. Reactance of the transmission line is shown on the diagram. The generators and transformers are rated as follows:

Generator 1: 20 MVA, 13.8 kV, X" =0.20 per unit

Generator 2: 30 MVA, 18 kV, X" =0.20 per unit

Transformer T] : 25 MVA, 220Y/13.8 ~ kV, X=10%

Transformer T2 : 30 MVA, 220Y/18 ~ kV, X=10%

Draw the impedance diagram with all reactances marked in per unit and with letters to indicate points corresponding to the one-line diagram. Choose a base of 50 MVA, 13.8 kV in the circuit of generatorl.

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old r $B/'UAJl [VB' ~J LGflPv L,," B PkiJ Ve.~"" 20 MVA ~ t

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2. A 100 MVA 33 kV 3-phase generator has a subtransient reactance of 15%. The generator is connected to the motors through a transmission line and transformers as shown in fig below. The motors have rated inputs of 30/MVA, 20 MVA and 50 MVA at 30 kV with 20% subtransient reactance. The 3-phase transformers are rated at 110 MVA, 32 kV ~ /110 kV Y with leakage reactance 8%. The line has reactance of 50 ohms. Selecting the generator rating as the base quantities in the generator circuit, determine the base in other parts of the system and evaluate the corresponding p.u. values.

110 MvA- p lluM~~,1" M' -f' '\., 30 MV4 j 3o/c:.V ) QJ-..PI132./1 \0 ;, \eX;:. 8' (. II 0/3-i. M 1.8-i ~ j50n ~ >---+---l" "\.. 2.0 M VA J ~o Ie.v : (). 1

M ~ 7t.";::100 MVA. 33 kV 15 % .",-, so /III. V~ ~ ;okY' ; " . Lpv

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3. Three zones of a single-phase circuit are identified in Figure below. The zones are connected by transformers T I and T2, whose ratings are also shown. Using base values of30 kVA and 240 volts in zone 1, draw the per-unit circuit and determine the per-unit impedances and the per-unit source voltage. Then calculate the load current both in per-unit and in amperes. Transformer winding resistances and shunt admittance branches are neglected.

loneZ 10fl93ZOI'IB 1 I I

V, ~ 220/0" volts : ~El-.........:;;:::==~3~'1

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4. A simple power system consisting of one synchronous generator and one load connected by two transformers and a transmission line is shown in the following figure. Draw the impedance diagram with all impedances marked in per unit. Choose a base of 100 MVA, 13.8 kV in the circuit of generator.

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G1 rating: T1 ratings: T1 ratings: IOOMVA lOOMVA SOMVA

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