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EE454 – Power System Analysis

Midterm Examination – November 2, 2021

Question 1 (20 points)

Dealt with material that we did not cover in EE454 this autumn.

Question 2 (25 points)

Dealt with material that we did not cover in EE454 this autumn.

Question 3 (30 points)

A three-phase generator operating at its nominal voltage injects 0.5 p.u. of active power and 0.2 p.u. of reactive power into the grid. The synchronous reactance Xs  of this generator is 0.7 p.u.

a)   Calculate the magnitude and angle of the current supplied by this generator

b)   Calculate the internal e.m.f. of this generator under these conditions

c)   Calculate the power factor at which this generator operates

d)   Calculate the power angle at which this generator operates

e)   If this generator is at the sending end of a line of impedance 0.02 + j0.15 p.u., how much active and reactive power are delivered at the receiving end of this line?

f)    What would be the magnitude and angle of the internal e.m.f. if this generator were to supply the same amount of active power at unity power factor?

g)   What would be the magnitude and angle of the current supplied by this generator if it were to supply the same amount of active power at unity power factor?

h)   Given that the base power SB  is 100 MVA and the base voltage is 30 kV, convert the current calculate in (a) to SI units.

Question 4 (10 points)

Explain briefly why the DC side of a voltage source converter often cannot be modeled as an ideal DC voltage source and how such converters are controlled in this case.

Question 5 (15 points)

A 60- HZ generator rated at 50 kW supplies a load of 40 kW at a frequency of 57.6 Hz. Consider only primary frequency control in parts a) and b).

a)   What is the droop coefficient of this generator?

b)   If a second generator, rated at 40 kW and with the same droop coefficient, is               synchronized with the previous one to share the load, how much power does each of these generator provide? At what frequency would they operate?

c)   Briefly explain the differences between primary and secondary frequency control.