Posted: September 13th, 2017

Computation of Surge Overvoltages on a Typical Power Transmission System using PSCAD/EMTDC Sotfwate

Paper, Order, or Assignment Requirements

Faculty of Computing, Engineering and Technology

 

A transmission system consisting of an overhead line of surge impedance 380 W and travel time 6 µs is connected in series with a Gas Insulated Substation (GIS) of surge impedance 80 W and travel time 0.3 µs. The GIS is terminated at the far end in a transformer of surge impedance 800 W. A  gapless zinc oxide surge arrester is connected across the transformer. A transient surge of V = V_y [e^-αt – e^-βt] and a crest voltage 1200 kV travels along the line towards the GIS. Using PSCAD/EMTDC Software:

 

(a)     Build the system. Show all the system parameters on the circuit diagram.

 

(b)     Compute the voltages at each junction of the system (without and with the surge arrester connected to the transformer) for a lightning impulse of 2/16 µs waveshape and a switching impulse of 100/500 µs waveshape. Also compute the corresponding surge arrester and transformer currents. Use per unit or actual values in your computation.

 

Additional information:

• The values of V_y, α and β corresponding to each waveshape are shown in the table below:

 

 

• The Protective level of the surge arrester, which should not be exceeded when discharging the overvoltage is 640 kV.
• The base values are: V_b = 400 kV; Z_b = 400 W ; t_b = 1 µs
• The surge arrester rating is a function of the maximum power frequency voltage which can occur at the arrester location during fault conditions. For this assignment, the surge arrester rating is 280 kV.
• Use PSCAD/EMTDC default values for the V-I characteristics of the surge arresters.

 

(c)     Plot the V-I characteristics of the surge arrester.

 

(d)     Plot all the results obtained in (b) above.

 

(e)     Assessment requirements

 

(ii)  Individual report                  (70%)

Write an individual formal report (approximately 1500 words of texts) satisfying the technical criteria stated in the assignment front sheet.

 

(i)    Individual oral assessment (30%)

Since building the correct system using PSCAD/EMTDC software gives similar results by all students undertaking this assignment, you are required to present your results using PSCAD/EMTDC software. You will have 10 minutes for your presentation followed by 5 minutes of questions by your tutors. Failure to attend the oral assessment or to demonstrate your work during the oral assessment may result in a zero mark for the entire assignment.

 

PSCAD/EMTDC software is the only solution accepted for this assignment. Any other solution or software will not be accepted and will result in a zero mark.

 

Professor Moofik Al-Tai; 18/09/2014                                      Include this sheet in your report