ENG4104 Power Systems 4

Section A – Answer All Questions [75 marks]

Q1 Power System Analysis [58]

(a)         Load Flow Analysis

(i)          A transmission line of impedance ZL  = 0.01 +j 0.05 pu links bus  1 to

bus 2. The voltage supplied to bus  1 is  1.0上0。pu and the load S2  at bus

2 is 1.1 +j 0.6 pu. Using the iterative method (calculate for three iterations: n = 0, 1, 2), determine the per unit voltage at bus 2. [8]

(ii)         For the power system illustrated in Figure Q1a, the voltages at both ends of the power system are given as:

V1  = 1.05上δ。pu , V2   = 1上0。pu

The line reactance is given as j 0.05 pu. The real power at both ends of the line are P1  = P2  = 5pu. The complex power outputs SL1  and SL2  at the two buses are given as:

SL1  = 6 + j3pu, SL2  = 5 − j2pu

If the  load  SL3  at bus 2 is  the  same as the  generator power at bus  1 (SL3=SG1), determine the generator power SG2 connected to bus 2 (using the formulae provided).  [8]

Useful formulae:

(b)       Per Unit Analysis                                                                                               [10]

For the power system shown in Figure Q1b, calculate the per unit impedances of all components with given zone  1 voltage base 22kV and power base  100 MVA (for the system).

(Zone voltage bases 2 marks,  per unit impedance calculation for each component 2 marks.)

(c)       Fault Level Analysis                                                                                          [14]

A simple electrical network is shown in Figure Q1c. All reactance values are shown in per-unit form to a common base voltage. Working to a base capacity of  100  MVA,  estimate  the  short circuit capacity and fault current should a symmetrical three-phase fault occur on the 132 kV busbar at the position shown.

[per unit reactance calculations 6 marks, equivalent circuit and simplification 6 marks, capacity and current calculations 2 marks]

(d)         Compare the load flow, per unit, and fault level analysis from aspects of: main purposes  (6  marks),  mathematical problems   (6  marks),   solving  procedures (6 marks).                                  [18]

Q2 Net-Zero Carbon Emission Context (Open-ended) [17]

(a)         The  Scottish Government has committed to  100% reduction in carbon dioxide emissions  by  2045  (so-called  ‘net-zero’,  compared to 1990s  level). In  your opinion, by 2035 what percentage of electricity in Scotland should be derived from renewable resources and why?                                     [5]

(b)         Apart from Solar energy, describe another two main forms of renewable energy currently  in  use  in the UK and for that indicate and explain three of  their technical  limitations with regards to  the  integration  to power  systems.  (each form of energy 6 marks)                                                                                    [12]