Main cause of momentary excessive voltages and current are 1. Lightning 2. Switching 3. Short circuit 4. Resonance Out of these the most common and most severe causes are

Option B: 1 and 2 Explanation & Concepts: Lightning strikes and switching operations are the most common and severe sources of power system transients. Lightning produces high-magnitude external surges, while switching operations cause internal transients due to sudden changes in circuit conditions involving stored electromagnetic energy. Working Principle: Transients occur due to the rapid change in energy state of inductive ($L$) and capacitive ($C$) elements. When a breaker operates (switching), the stored energy $\frac{1}{2}Li^2$ cannot dissipate instantly, causing a voltage spike $v = L \frac{di}{dt}$. Lightning causes high-current surges through atmospheric discharge, creating traveling waves that exceed standard insulation levels. Key Formulas: $v = L \frac{di}{dt}$ — Voltage induced across an inductor due to rapid current change.; $i = C \frac{dv}{dt}$ — Current in a capacitor due to rapid voltage change. Key Points: Lightning transients are external and characterized by very high voltage peaks.; Switching transients are internal and occur during normal operation, faults, or restoration.; Short circuits cause current surges, but voltage transients are primarily associated with the initiation/clearing of the fault.; Resonance can lead to high voltage amplification but is generally less frequent than switching. Advantages: Identification of transient sources helps in insulation coordination.; Enables proper design of Surge Protection Devices (SPDs). Disadvantages: Transients can cause insulation failure in transformers and switchgear.; May lead to nuisance tripping of sensitive electronic equipment. Applications: Power system protection design.; Insulation coordination studies.; Surge arrestor placement optimization. Additional Info: Lightning surges typically have a rise time in microseconds.. Switching transients are often oscillatory in nature.. Option A is incorrect because short circuits are not the primary cause of severe voltage surges compared to switching.. Option C is incorrect as resonance requires specific frequency conditions not as common as switching. Answer: B is correct — Lightning and switching are the most frequent and severe causes of electrical transients in power systems. Exam Tip: Always distinguish between external transients (Lightning - atmospheric) and internal transients (Switching - operational) for competitive exams.

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Main cause of momentary excessive voltages and current are

Lightning
Switching
Short circuit
Resonance

Out of these the most common and most severe causes are

1 and 3

1 and 2

4 and 2

3 and 4

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalPower System

Option B

1 and 2

Quick Summary:

Lightning strikes and switching operations are the most common and severe sources of power system transients. Lightning produces high-magnitude external surges, while switching operations cause internal transients due to sudden changes in circuit conditions involving stored electromagnetic energy.

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$v = L \frac{di}{dt}$ — Voltage induced across an inductor due to rapid current change.

$i = C \frac{dv}{dt}$ — Current in a capacitor due to rapid voltage change.

⚙️ Working Principle

Transients occur due to the rapid change in energy state of inductive ( $L$ ) and capacitive ( $C$ ) elements. When a breaker operates (switching), the stored energy $\frac{1}{2}Li^2$ cannot dissipate instantly, causing a voltage spike $v = L \frac{di}{dt}$ . Lightning causes high-current surges through atmospheric discharge, creating traveling waves that exceed standard insulation levels.

📌 Key Points

▸
Lightning transients are external and characterized by very high voltage peaks.
▸
Switching transients are internal and occur during normal operation, faults, or restoration.
▸
Short circuits cause current surges, but voltage transients are primarily associated with the initiation/clearing of the fault.
▸
Resonance can lead to high voltage amplification but is generally less frequent than switching.

✅ Advantages

▸
Identification of transient sources helps in insulation coordination.
▸
Enables proper design of Surge Protection Devices (SPDs).

❌ Disadvantages / Limitations

▸
Transients can cause insulation failure in transformers and switchgear.
▸
May lead to nuisance tripping of sensitive electronic equipment.

🛠️ Applications / Uses

▸
Power system protection design.
▸
Insulation coordination studies.
▸
Surge arrestor placement optimization.

📄 Additional Information

▸
Lightning surges typically have a rise time in microseconds.
▸
Switching transients are often oscillatory in nature.
▸
Option A is incorrect because short circuits are not the primary cause of severe voltage surges compared to switching.
▸
Option C is incorrect as resonance requires specific frequency conditions not as common as switching.

📊 Diagram / Illustration

✅

B is correct — Lightning and switching are the most frequent and severe causes of electrical transients in power systems.

Core Concepts Used

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Power System Transients Insulation Coordination Surge Phenomena

💡 EXAM TIP

Always distinguish between external transients (Lightning - atmospheric) and internal transients (Switching - operational) for competitive exams.

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