2101L Lab6

Analyse several voltage and current situations in different loading scenarios in a simplified radial (transformer to consumption) medium-voltage power system example. There are only 2 nodes in the 35 kV line – node 0 from the 110/35 kV and node 1 with one consumer. Briefly reflect on the complexity of the calculations for known input or output voltage, as well as for fixed or voltage-dependent consumption in this simple power system model.  Analyse and discuss the sensitivity of the voltage drop [in % of amplitude and the degrees of phase] with respect to the current level [in %] and to the power factor.

What does the term FACTS mean in the use of power electronics in Smart Networks using appropriate diagrams and giving an example of a typical FACTS controller. Smart Grids use wireless and wired communication techniques – explain the operation of each with the use of appropriate diagrams and the advantages/disadvantages of each.

Which of the following statements is/are true? (A In purely inductive circuit, the current leads voltage. (B) In purely resistive circuit, the current lags voltage. C In purely resistive circuit, the current is in phase with voltage. D In purely capacitive circuit, the voltage lags current.

Explore the concept of smart grids and their impact on modern power system management.

Consider a 40MVA, 132/11kV transformer with a reactance of 15% on its rating, shown in Figure Q2. It is equipped with an on-load tap-changer that is used to maintain constant voltage at the 11kV busbar by compensating for variations in the voltage of the 132kV network, and for the voltage drop across the transformer. The variation of the network voltage at 132kV transformer busbar for heavy loading conditions is shown in the table below. Active power losses in the transformer are ignored, and it is assumed that the value of the reactance of the transformer is not influenced by the change in the turn ratio. Calculate t, the tap ratio, and the actual voltage at bus 2 in this case. (Note: For instance, a nominal ratio of the transformer is 132/11, when tapped to give 144/11 ratio, therefore t is 144/132=1.09). Load Power factor Voltage at 132kV Desired voltage at busbar (Bus 1) 11KV busbar (Bus 2) 5MVA 0.9 185kV 11kV Bus 2 Bus 1 X=15% t:1 Figure Q2

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4. A CT with an excitation curve given in the figure has a rated current ratio of 500:5 A and a secondary leakage impedance of 0.1 +j0.5 ohms. Calculate the CT secondary output current and the CT error for the following cases: a.) The impedance of the terminating device is 4.9 +j 0.5 ohms and the primary CT load current is 400 A. b.) The impedance of the terminating device is 4.9 +j0.5 ohms and the primary CT load current is 1200A c.) The impedance of the terminating device is 14.9 + j 1.5 ohms and the primary CT fault current is 400 A. d.) The impedance of the terminating device is 14.9 + j 1.5 ohms and the primary CT fault current is 1200 A w 100 80 60 40 20 2 4 6 10 Secondary exciting amps-, Secondary exciting volts-E'

Discuss the concept of smart grids and their potential advantages in modern power systems.