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elec4617mid.pdf
elec4617mid.pdf
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elec4617mid.pdf-ELEC4617 Mid-Term Yihuan Liao September 20,
Page 1
ELEC4617 Mid-Term
Yihuan Liao
September 20, 2016
Abstract
These summary notes are for ELEC4617 Mid-session revision in semester
2, 2016.
If you find any mistakes, please contact me via email yihuan-
liao1994@gmail.com. Note that all the figure numbers, page numbers and
the table of contents are clickable hyperlinks.
1
Page 2
Contents
1
Introduction
3
1.1
Configuration of a basic protection system
.............
3
1.2
Terminology used in system protection
...............
3
2
Fault Analysis
5
2.1
Fault Types
..............................
5
2.2
Thevenin Equivalent Circuits
....................
5
2.3
Unsymmetrical Fault Solution
....................
6
3
Relay
7
3.1
Introduction to Relay
........................
7
3.2
Amplitude and Phase Comparator
.................
8
3.3
Digital Relay
.............................
9
3.3.1
Structure of Digital Relay
..................
9
3.3.2
Performance of Digital Protection
.............
9
4
Instrument Transformer, Circuit Breakers and Fuses
11
4.1
Instrument Transformer
.......................
11
4.1.1
Current Transformer
.....................
11
4.1.2
Voltage Transformer
.....................
12
4.2
Circuit Breaker
............................
12
4.3
Fuses
..................................
14
List of Figures
1
Fault Types
..............................
5
2
Single Line-to-Ground Fault
.....................
5
3
Double Line Fault
..........................
6
4
Double Line-to-Ground Fault
....................
6
5
Plain Impedance Relay V.S Conventional MHO Relay
......
8
6
Summary of circuit breaker interruption procedure
........
13
2
Page 3
1
Introduction
1.1
Configuration of a basic protection system
•
Sensingdevices:
–
Current Transformer (CT): Provide current signal for a protection
system.
–
Voltage or potential transformer(VT or PT): Provide voltage signal
for a protection system.
•
Signal Conditioning Network:
–
Process signals from CTs and VTs and transfer the accurate voltage
and current of the power system to relay circuit.
•
Relay Circuit:
–
Detect abnormal conditions through measuring changes of currents,
voltages, impedances and frequency etc.
–
Initiate actions to trip the circuit breakers.
•
Switching Device(Circuit Breaker CB)
–
Isolate the fault through opening circuits.
•
Auxiliary Power Source (Battery)
–
Privide back-up power for relay and circuit breaker.
1.2
Terminology used in system protection
•
Reliability
(Security) of a protective system is defined as the probability
that the system will function correctly when required to act.
This reliability has two aspects:
1. The system must operate in the presence of a fault that is within its
zone of protection.
2. It must refrain from operating unnecessarily for faults outside its
protective zone or in the absence of a fault.
•
Sensitivity
in a protective system is its ability toidentify an abnormal
condition that exceeds a nominal ”pickup” or detection threshold value,
and to initiate protective action when the sensed quantities exceed that
threshold.
•
Selectivity
in a protective system refers to the overall design of protec-
tive strategy wherein only those protective devices closest to a fault will
operate to remove the faulted component.
•
Protection Zones
(primary protection zones) are regions of primary
sensitivity.
3
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