联系我们： 手动添加方式: 微信>添加朋友>企业微信联系人>13262280223 或者 QQ: 1483266981

DEPARTMENT OF ELECTRONIC, ELECTRICAL AND
SYSTEMS ENGINEERING
MSc in Electrical Power Systems
Power System Stability Control and Protection
2nd Assignment
Introduction: This assignment aims to help student develop practical skills in designing
differential protection scheme for transmission network. The assignment deadline is available
on Canvas.
Consider the following single-phase transmission network consisting of two equivalent sources
(A and B both at 60Hz), two transmission lines (Line 1 and Line 2), and three buses (Bus 1,
Bus 2 and Bus 3).The two equivalent sources are supplying three loads (Load1, Load2 and
Load3). Two percentage differential relays (DR-1 and DR-2) are installed to protect the two
transmission lines. The restraining current is designed as the sum of the current at both
terminals of a protected line. The currents at both ends of a protected line are measured via the
Current Transformers (CTs). The relays are sending trip signals to the Circuit Breakers (CBs)
at both ends.
The system parameters are detailed as follows;
Source A voltage: 158 kV (peak), 00
Source A impedance: 1+j10 Ω
Source B voltage: 157 kV (peak), -150
.
Source B impedance: 1+j10 Ω
Line 1 impedance: 2+j20 Ω
Line 2 impedance: 2+j20 Ω
Load 1: 138 kV (rated RMS voltage), 100 MW, 30 MVAr
Load 2: 138 kV(rated RMS voltage), 100 MW, 30 MVAr
Load 3: 138 kV (rated RMS voltage), 100 MW, 30 MVAr
Fault: 0 Ω, inception time 20 ms.
CB1 operating time: 15 ms
CB2 operating time: 25 ms
CB3 operating time: 18 ms
CB4 operating time: 21 ms
CT-2: 2000/1 A
CT-1, CT-3, CT-4: 2000/5 A
DR-1: pick-up=0.2A (secondary), bias=0.3
DR-2: pick-up=0.2A (secondary), bias=0.3
Task 1: Please construct the above transmission network in SIMULINK using the provided
parameters. Show and explain how the differential relays are modelled in SIMULINK.
Run the simulation of the system without fault (set the simulation time duration to be 0.10s).
What are the values of primary and secondary currents in CT1, CT2, CT3 and CT4 Read and
explain the values of differential and restraining currents measured by DR-1 and DR-2. Do the
relays behave correctly Explain your answers.
Task 2: Repeat Task 1 but with a 10% error rate from CT-1 by changing its rated secondary
current from 5A to 4.5A. Explain the values of differential and restraining currents measured
by the DR-1. Does the relay behave correctly Explain your answers.
Task 3: Keep the CT-1 error from Task 2. Simulate the fault at 20% away from Bus 2 with
zero fault resistance and 20ms inception time. Disconnect the trip signal of DR-2 in order to
model a permanent fault. Explain the values of differential and restraining currents measured
by DR-1 and DR-2. Do the relays behave correctly Explain your answers.
Task 4: Keep the CT-1 error from Task 2. Repeat Task 3 but with the trip signal of DR-2
connected to the CBs. Observe the operation of the relays. Do the relays behave correctly
Task 5: Keep the CT-1 error from Task 2. Place the fault in the middle of the line 1 (there is
no fault on line 2). Observe the operation of the relays. Do the relays behave correctly Explain
your answers.
Task 6: Repeat Task 5 with different values of fault resistances and find the maximum
resistance under which the DR-1 operates. Explain your answers.
Report Structure: Based on the above assignment, you are asked to prepare a report of around
20 pages including the following sections:
1. Cover page (Please use the cover page template available on Canvas and complete all
sections on the cover page. The cover page should be limited within 1 page)
2. Table of content
3. Introduction
4. Simulation results from SIMULINK with detailed explanations (calculations) and
discussions.
5. Conclusions
6. References (IEEE format should be used)
Report Layout: Page numbers should be inserted at the bottom centre of each page except the
cover page. Report should be typed on A4 paper, spaced 1.5 with margins as follows: Top-
2.54cm, bottom-2.54cm, left-2.54cm, right-2.54cm. Font size of 11 or 12 can be used.
Report Writing: The style of writing should be formal and precise with no more words than
needed to make the meaning clear. Every statement must be justified, and nothing that is written
should be vague. Tables and diagrams should be used wherever appropriate. A specific point
that must be made is that the report should be written in the third person. For example, ‘this
was carried out’ should be used rather than ‘I did this’. This is the traditional method of
expression used in scientific and technical writing.
Marking Criteria: The following is the marking criteria for this assignment:
(1) Introduction – a general description of the problem to be solved (10%).
(2) Methodology – how the problems are solved and related theories (20%).
(3) Results and discussion (40%).
(4) Conclusions (10%).
(5) Use of references (5%)
(6) Overall report quality and structure (15%)
Plagiarism: Plagiarism will not be tolerated. It is the act of a Student claiming as their own,
intentionally or by omission, work which was not done by that Student. Plagiarism also
includes a Student deliberately claiming to have done work submitted by the Student for
assessment which was never undertaken by that Student, including self-plagiarism and the
other breaches. Sanctions of a plagiarism include the Student failing the Programme of study.
The report as well as the SIMULINK file will need to be submitted via the Canvas. Please do
not submit .zip files. Submit .pdf or word file for the report, and .m file or .mdl file/.slx file for
MATLAB codes/SIMULINK models.