A1.3
Assignment 1 Protection Problems
In Chapter 2 of the textbook Fundamentals of Power System Protection, there is a discussion on the application of IDMT relay on a radial distribution feeder for the following system:
The first step in the protection design is to decide CT ratios and plug settings for relays A and B. Then the second step is to determine the time multiplier
settings for the two relays by the following criterion:
Q1. For the system given above, please prove mathematically that the TMS of relay A determined above will be able to maintain selectivity between relays A and B for any possible fault current at bus B.
Q2. As commented in the above textbook, the above design principle can be extended to an n bus system with the aid of a computer algorithm. Consider a radial
feeder consists of n buses and (n-1) IDMT relays shown as below:
Power Systems Operation and Protection Spring 2018
A1.4
Please write a computer program to do the corresponding IDMT relay designs
following steps given in the textbook. The following requirements must be met.
i) Use Matlab m file to write your code.
ii) Input to your program will include at least: minimum and maximum fault currents at each of the buses; available CT ratios.
iii) Output of your program must be the CT ratios, plug settings, and time multiplier settings for each of the n-1 relays.
iv) You must test your program by the example on the textbook (i.e. the system in Q1), and test it further by an example of a 4 bus radial system (use assumed input parameters). Testing details (e.g. input) and results (i.e. output) must be presented in the report.
v) The computer code (m file) must be enclosed in the report, and necessary
comments are needed to make the code readable.
Power Systems Operation and Protection Spring 2018