Life of fault currents. The maximum fault levels

Life in the modern
society without electricity is hard to imagine. Electric power is a driver of
the today’s economy, and has shaped the contemporary world. We depend on it to
provide light and temperature regulation, run our appliances and power our
gadgets. Power blackouts suspend the proceedings of normal life.

The use of
electricity has increased since its advent in late nineteenth century. The
growth in population, urban development and industrialization has seen growth
in electricity demand over the past years. Electricity demand is predicted to
increase in the future especially with the popularity of electric vehicles 1. Furthermore, the
share of renewable energy sources is expected to increase threefold by 2030
most of which is in the form of distributed generation (DG) 2.

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Figure 1:
Electricity generation mix worldwide 2


To cater for the high
demand, new electricity sources that can provide bulk power are being added to
the existing grid. Simultaneously, there has been a great increase in distributed
generation (DG) which is the generation of electricity at the point of
consumption. People are increasingly connecting renewable sources like solar,
wind and biomass with the grid to export the surplus electricity.

However, the
expensive grid infrastructure is not subjected to corresponding change required
with inclusion of additional power. The transmission and distribution equipment
of the grid is designed to handle certain magnitudes of fault currents. The
maximum fault levels have increased due to the addition of DG. This has led to a
need of upgradation of transformers, busbars, circuit-breakers and other
equipment to sustain the new levels of fault currents.

Figure 2:
Increase in Fault Level with Connection of New DG 3


Furthermore, many
grids are stretched to their capacity with this increased demand and supply of
power 4. Fault current
levels are rising at the rate of 1-2% per year. As a consequence, grid systems
need to be continually modified by increasing the fault capacity of the components
which is expensive and complex to implement 5. The increase in
fault levels can cause permanent equipment damage, disturb the normal operation
of the grid and therefore can inflict economic losses.

There are several
methods of containing the fault current levels that are discussed in chapter 2,
such as reducing grid interconnections and increasing system’s operating
voltage. However, the Fault Current Limiters (FCLs) provide the most flexible
way to overcome these challenges as discussed later.

Furthermore, “as the deregulation environment takes hold and utilities
seek more efficient and cost-effective methods to couple grids, improve power quality,
and delay expensive upgrades,” 6 fault current
limiters will find increased application in distribution systems. Currently,
researchers have been experimenting with various FCL technologies strictly via
computer simulation that is very specific in nature. Power companies have also
started investing in this technology as they see immense potential in current
limiting technologies.



Goals & Objectives

This thesis aims at
the following objectives:

1.      Literature review of various types of existing FCLs

2.      Modeling of a standard power network (IEEE 30 bus system) in power system
software for FCL testing

3.      Simulation work by using different FCL types and locations on the
test-bench power network.

4.      Using optimization techniques to optimize the number of FCLs, their size,
type and location for a standard power network

5.      Ensure original fault current levels in the system after addition of FCLs

6.      Critical analysis of the results

7.      Suggestions

8.      Perform FCL optimization on a real distribution company’s power network
and produce an economic feasibly for FCL use (subject to the availability of



Literature review
highlighted the most-used FCLs as well as the newly developed technologies. The
principle of working of FCLs were researched to see how they can be modelled on
the softwares Simulink and PSCAD. The advantages and disadvantages of different
types of FCL enabled choosing the most suitable ones for use in the power
system. IEEE 30 bus system was modelled in both Simulink and PSCAD. The
Simulink model was very slow to generate wave forms and therefore PSCAD was
used for the task. Optimization technique of genetic algorithm (GA) was studied
to apply on the power system. Therefore, the line data of IEEE 30 bus system
was obtained to determine load flow analysis.

Thesis Organization

Chapter 2 includes
the existing literature review on existing types of FCLs. Chapter 3 covers the
IEEE 30 bus system simulations performed on PSCAD with a fault current limiter.
Chapter 4 introduces to the optimization techniques used for FCL optimization.