Q3 A Phase Are In The Diagram Presented In Figure Q3a A Three Phase Star Connected Load Is Supplied From A Balanced 1 (91.89 KiB) Viewed 24 times
Q3. (a) phase are: In the diagram presented in Figure Q3a a three-phase star connected load is supplied from a balanced 415V three-phase supply. The impedances of the load ZA = ZB = ZC = (5-j2) 2. Answer the following questions: (i) What are the values of voltage and current measured by the voltmeter and ammeter shown in Figure Q3a? 2 marks (ii) Taking voltage of phase A as a reference, draw a phasor diagram of the phase voltages and currents of the load. 2 marks (iii) What is the real power measured by the wattmeter W1 considering its specific, unconventional connection as shown in Figure Q3a? The phasor diagram drawn in (ii) should provide helpful guidance. Note: * indicates the beginning of the current and voltage coil of the wattmeter. 3 marks Assume that the impedances of the measuring instruments are negligible, i.e. zero for ammeter and infinite for voltmeter. ZA W, Z₂ Zo Figure Q3a: Three-phase load A small part of a three-phase network supplying a number of loads is shown in Figure Q3b. The grid infeed fault level is 850 MVA. (i) Using a common base of 50 MVA, determine the resulting per unit values for the network components shown in Figure Q3b. Show these on a sketch of the single line diagram. 5 marks A Bo O N (b)
(ii) Calculate the steady state fault level at busbar B in the network shown in Figure Q3b. Based on your result, choose appropriate breaking capacity of a circuit breaker for this busbar, and justify your choice. Select from the following values: 150 MVA, 200 MVA, 250 MVA, 300 MVA, 350 MVA. 8 marks A TR₁: 40 MVA, 132 kV/33 kV, X = 0.11 pu 15 MVA, 33 kV, X₂= 0.2 pu X = 40 S2/ph TR₂: 20 MVA, C 11 kV/33 kV, X = 0.11 pu Grid infeed 132 kV Fault Level 850 MVA (G₁) 8 MVA, 11 KV. X= 0.1 pu Load B | X = 5 S/ph X = 10 n/ph X = 10 $2/ph Figure Q3b: Power network (M₁) Load D 6 MVA, 11 KV, X= 0.1 pu (G₂) Load
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