This document discusses faults in electrical power systems. It defines a fault as any abnormal electric current, such as a short circuit. There are two main types of faults: symmetrical faults, which are severe but rare, including line-to-line-to-ground and line-to-line faults; and unsymmetrical faults, which are more common and less severe, including line-to-ground, line-to-line, and double line-to-ground faults. Faults can be caused by weather conditions, equipment failures, human errors, or fires. Effects of faults include overcurrent, danger to personnel, equipment loss, and electrical fires. Fault limiting devices like fuses, circuit breakers, and relays are

1. SNS COLLEGE OF TECHNOLOGY
(An Autonomous Institution)
COIMBATORE-35
Accredited by NBA-AICTE and Accredited by NAAC – UGC with A+ Grade
Approved by AICTE, New Delhi & Affiliated to Anna University, Chennai
DEPARTMENT OF ELECTRICALAND ELECTRONICS ENGINEERING
COURSE NAME: 16EE402 PROTECTION AND SWITCHGEAR
IV YEAR / VII SEMESTER
Unit 1 – PROTECTION SCHEMES
Topic 3: NATURE AND CAUSES OF FAULTS

2. TOPIC OUTLINE
Here we going to see Faults, Reasons for faults, Types of Faults
1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 2 / 1 4

3. 1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 3 / 1 4
In an electric power system, a fault or fault current is any abnormal
electric current. For example, a short circuit is a fault in which current
bypasses the normal load. An open-circuit fault occurs if a circuit is
interrupted by some failure
Definition for Fault

4. 1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 4 / 1 4
Fault detection and analysis are necessary to select or design suitable
switchgear equipment, electromechanical relays, circuit breakers, and
other protection devices.

5. 1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 5 / 1 4
There are mainly two types of faults in the electrical power system.
Symmetrical faults
These are very severe faults and occur infrequently in the power systems. These are also
called balanced faults
• Line To Line To Ground (L-L-L-G)
• Line To Line (L-L-L)
TYPES OF FAULTS
ONLY 2 – 5 % OF TOTAL FAULTS,
SEVERE DAMAGE TO POWER
SYSTEM EQUIPMENT

6. 1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 6 / 1 4
SYMMETRICAL FAULTS

7. 1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 7 / 1 4
ZONES OF PROTECTION

8. 1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 8 / 1 4
Unsymmetrical faults
These are very common and less severe than symmetrical faults. There are mainly three types namely
• Line to Ground (L-G)
• Line to Line (L-L)
• Double Line to Ground (LL-G) faults
65 to 70 line to ground fault (L-G)
15 to 20 - double line to ground
5 to 10 - line to line
• These are also called unbalanced faults since their occurrence causes unbalance in the system.
• The Unbalance of the system means that that impedance values are different in each phase causing
unbalance current to flow in the phases.
• These are more difficult to analyze and are carried by per phase basis similar to three-phase balanced
faults.
TYPES OF FAULTS

9. 1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 9 / 1 4
CAUSES OF ELECTRICAL FAULTS
• WEATHER CONDITIONS
• EQUIPMENT FAILURES
• HUMAN ERRORS
• SMOKE OF FIRES

10. 1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 1 0 / 1 4
EFFECTS OF ELECTRICAL FAULTS
• Over current flow
• Danger to operating personnel
• Loss of equipment
• Disturbs interconnected active circuits
•Electrical fires

11. 1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 1 1 / 1 4
FAULT LIMITING DEVICES
• Fuse
• Circuit breaker
• Relay
• Lighting power protection devices

12. FROM THEORY TO PRACTICE
Practical
Applications
1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 1 2 / 1 4

13. RECALL TIME
ASSESSMENT
TIME
1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 1 3 / 1 4

14. THANK YOU
1 8 . 0 9 . 2 0 2 0 1 6 E E 4 0 2 / P S G / R . S A T H E E S H K U M A R / A P / E E E 1 4 / 1 4