Before your Start

•   Ensure   you  read   the   instruction   document   ‘DIgSILENT   PowerFactory   Modelling Instruction’  and  DIgSILENT  tutorial  documents  ‘DIgSILENT   Tutorial_Introduction’, ‘DIgSILENT Tutorial_Project’, ‘DIgSILENT Tutorial_LoadFlow’ in the ELE page;

•   DIgSILENT PowerFactory provides Student Licence (PF4S); you are encouraged to make direct contact with DIgSILENT to acquire one licence so you can install in your own computer and can access to and practice the simulation study remotely.

Requirements on Report

•   A report needs to be produced to answer each question in the lab sheet.

•   Assessment: The lab report has a total of 100 marks. The lab report counts for 10% of your final mark.

•   The report should be written in a concise manner to both summarising and discussing the results.

•   The report  should be  submitted as PDF file online through ELE2 system by noon,  1st December 2023.

•  Avoid any form of plagiarism.

•   Format to be used for the results:

Preparation

Open the project file ‘Power System Analysis_Lab  1_P1.pfd’. Ensure the library contains generator type G1, tower type L6, conductor types 1Z×275 kV_ASCR Zebra 400 mm2  and 4Z×275 kV_ASCR Zebra 400 mm2  (300×300).

Problem formation:

A load centre is supplied by hydro-generator (11 kV terminal voltage) through a 11/275 kV step-up transformer, a 200 km long double-circuit transmission line operating at 275 kV, and a 275/33 kV step-down transformer. The configuration of the transmission system is given in the Figure Q1. The load level varies from 40 MW to 340 MW.

The parameters of the components are given in the following tables:

Transmission Line

Note: tower, conductor and earth conductor types are included in the library in the project file.

Transformer

Question 1.1: Network conditions with loads at unity power factor [15 marks]

•    Run power flow calculation for loads of 40, 80, 120, 160, 240 and 280 MW

•    Record the active and reactive powers as well as voltage magnitudes and phases of

the generator bus and load bus. Present your recordings in the form of table/figure in   your report;              [10 marks]

•    Discuss your findings;                                                                                       [5 marks]

•    Note:

o To change the setting of active power for the load, go into the ‘power flow’ tab in the load model;

o To run a power flow calculation, click on the ‘Load Flow Calculation’ button

Question 1.2: Network conditions with loads at 0.9 inductive power factor [15 marks]

•    Change the load power factor to 0.9 inductive by introducing appropriate MVAr values

•    Run power flow calculation for loads of 40, 80, 120 and 160 MW. And record the

new active and reactive powers as well as voltage magnitudes and phases of the generator bus and load bus. Present your recordings in the form of table/figure in your report;           [10 marks]

•    Discuss your findings and specify the loads at which the voltage drops below 0.9 p.u.; [5  marks]

•    Note:

o To change the setting of reactive power for the load, go into the ‘power flow’ tab in the load model;

Question 1.3: Network conditions with loads at 0.9 inductive power factor with reactive power compensation [20 marks]

•    One approach to keep the load voltage as close to 1.0 p.u. as possible is to connect a source of reactive power near the load bus. In this case, a shunt capacitor or a shunt inductor is added to the load bus. It will produce or absorb reactive power to support and maintain the voltage.

•    Connect a shunt capacitor/inductor model to the load bus and change its rated voltage and adjust the rated reactive power setting. Repeat the calculations in Question 1.2.

•    Find the most suitable values of the reactive power generation/absorption of the shunt capacitor/inductor to maintain the load bus voltage as close as possible to 1.0 p.u. for each load level. And record the reactive power values, new active and reactive powers as well as voltage magnitudes and phases of the generator bus and load bus. Present your recordings in the form of table/figure in your report; [15  marks]

•    Discuss your findings;                                                                                       [5 marks]

•    Note:

o To set the reactive power rating, goto the ‘shunt RLC’ model, choose capacitor or inductor type, and adjust the rated reactive power value

o Keep the number of step in the ‘shunt capacitor’ as 1.

4.  Problem 2 _ N-R Iterative Power Flow Calculation [50 marks]

Preparation

Open the project file ‘Power System Analysis_Lab  1_P2.pfd’. Ensure the library contains generator type G1.

Problem formation:

The three-bus system is given in Figure Q2. System voltage level is 400 kV. Voltages and line impedances are in per unit. The chosen system power base is 100 MVA.

For transmission line, create a ‘line type’ for all three lines. For the ‘line type’:

•    Rated voltage: 400 kV

•    Rated current: 2 kA

•    Type: overheadline

•    1,2- Sequence reactance X’: 10 Ohm/km

•    Note: you need to go back to the line model to change the length of line to match the given impedance value in p.u.

For generator, select the provided generator type ‘G1’ in the library. However, change the generator ratings in the type to:

•    Rated apparent power: 200 MVA

•    Rated voltage: 400 kV

•    Rated power factor: 1.0