--- title: "Need for protection and causes of faults" subject: "Switchgear and Protection" chapter: 1 key: "semester_6/switchgear_and_protection:need-protection-fault-causes" source: https://www.bctengineer.com/q/semester_6/switchgear_and_protection/need-protection-fault-causes site: BCT Engineering --- # Need for protection and causes of faults Switchgear and Protection · Chapter 1: Principle of Power System Protection - Asked in: 2070 Bhadra, 4 marks - Video: [Causes of Faults in Power Systems Reasons of faults in Power Systems Power System Protection VTU EEE](https://www.youtube.com/watch?v=KC7Gyayx19A) — Simplified EEE Studies - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/switchgear_and_protection/need-protection-fault-causes - Whole chapter: https://www.bctengineer.com/md/semester_6/switchgear_and_protection/chapter-1 ## Question Why protection system is needed in electrical power system? State and explain various causes of electrical faults. ## Short answer Protection is needed to quickly isolate faulty parts, preventing equipment damage, maintaining supply continuity, and preserving stability. Fault causes include insulation failure from ageing or overheating, lightning, switching surges, mechanical contact from trees or animals, pollution, human error, equipment defects, and sustained overload. ## Answer #### Need for a protection system A power system cannot be designed to be fault-free. When a fault occurs, very high current flows and voltage collapses. Protection is required to: - Disconnect the faulty part quickly, so that equipment (generators, transformers, cables) is not damaged by heating and mechanical forces. - Maintain continuity of supply to healthy parts of the system. - Preserve system stability (keep generators in synchronism). - Prevent fire, explosion and danger to human life. - Detect abnormal conditions like overload, under/over voltage and unbalance before they become faults. #### Causes of electrical faults 1. **Insulation failure:** ageing, overheating, moisture, contamination and over-stress break down insulation of cables, transformers and machines. 2. **Lightning:** direct strokes or induced surges cause flashover of line insulators (the most common cause of overhead line faults). 3. **Switching surges:** over-voltages during switching of lines and capacitor banks can flash over weak insulation. 4. **Mechanical causes:** falling trees, birds, animals and kites bridging conductors; conductor breakage by wind or ice; excavation damage to cables. 5. **Environmental pollution:** salt or industrial dust deposits on insulators cause flashover in wet conditions. 6. **Human error:** wrong switching operations, closing on earthed equipment, poor maintenance. 7. **Equipment failure:** defects in breakers, CTs, joints and terminations. 8. **Overloading:** sustained overload overheats conductors and insulation, leading to breakdown. Most faults (about 70–80 % on overhead lines) are single line-to-ground faults; three-phase symmetrical faults are rare (about 5 %) but are the most severe. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is protection needed? A. To quickly disconnect the faulty part, protect equipment and maintain supply and stability B. Because faults never occur in properly designed systems C. To increase the fault current D. To keep faulty equipment energised Answer: A. Systems cannot be fault-free; protection limits damage and keeps the rest running. (Key point: Need of protection) 2. Which cause is the most common for overhead line faults per the answer? A. Overloading of transformers B. Lightning flashover of insulators C. Human error in switching D. Defective CT joints Answer: B. Lightning is stated as the most common cause of overhead line faults. (Key point: Lightning) 3. Which fault type is most frequent but which is the most severe? A. SLG is most frequent; three-phase symmetrical is rare but most severe B. Three-phase is most frequent and least severe C. SLG is both rarest and most severe D. Line-to-line is most frequent (70-80%) Answer: A. About 70-80% are single line-to-ground; 3-phase (about 5%) is most severe. (Key point: Fault types) 4. How does environmental pollution cause faults? A. It increases conductor temperature directly B. It lowers CT ratio C. Salt or dust on insulators causes flashover in wet conditions D. It increases breaker speed Answer: C. Contaminated insulators flash over when wet. (Key point: Pollution) ## Related in Switchgear and Protection - [Causes and protection against overvoltage](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Aovervoltage-protection-methods) — Switchgear and Protection, chapter 5, asked 2× - [Differential protection of power transformer](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Atransformer-differential-protection) — Switchgear and Protection, chapter 7 - [Protection requirements; protective system vs scheme](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Aprotective-system-vs-scheme) — Switchgear and Protection, chapter 1 - [Buchholz relay for internal faults](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Abuchholz-internal-faults) — Switchgear and Protection, chapter 7 - [Overvoltage causes; solid grounding merits](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Aovervoltage-causes-solid-grounding) — Switchgear and Protection, chapter 5, asked 2× - [Need of capacitive voltage transformer](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Aneed-of-cvt) — Switchgear and Protection, chapter 2 ## Related in other subjects - [Causes of poor power factor and improvement](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Apoor-pf-causes-improvement) — Industrial Power Distribution and Illumination, chapter 10 - [Low power factor causes, disadvantages](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Alow-power-factor-causes-disadvantages) — Basic Electrical Engineering, chapter 7 - [T/F: protection ratio vs system voltage](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-protection-ratio-system-voltage) — Transmission and Distribution System Design, chapter 3 - [Electrification system and fire protection](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aelectrification-fire) — Building Technology, chapter 12