Faults in Power System

• October 5, 2025
• Gaurav Joshi

Power systems are designed to handle heavy stress and operate reliably. However, certain faults in power system can still bring even the strongest network to a halt. Generally, these faults are divided into two main types: open circuit faults and short circuit faults. Among these, short circuits can further be classified as symmetrical or asymmetrical. While some of these faults are minor and easy to manage, others can become the most dangerous conditions a system can face.

In this article, we will explore the different faults in power system, discuss their types in detail, understand their severity, and finally, look at the possible consequences they cause.

Table of Contents

1. What Do We Mean by a Fault?
2. Types of Faults in Power System
3. Open Circuit Fault in Power System
4. Short Circuit Fault in Power System
5. Symmetrical Fault in Power System
6. Asymmetrical Fault in Power System
7. Summary of Faults in Power System
8. Consequences of Faults in Power System
9. Conclusion

What Do We Mean by a Fault?

Imagine a light bulb connected to a power source. The current flows from the source to the bulb and back. This is the intended path, and the system is normal.

Now suppose one phase wire touches the ground. A new path forms. This new path offers less impedance, so the current diverts through it. Since the impedance is very low, the current rises sharply. In power systems, this current can reach thousands of amperes.

Whenever current leaves its intended path, a fault occurs. Even if a conductor breaks and current stops, it is still a fault condition.

In simple words, a fault is a condition where the current in a closed circuit diverts from its intended path.

Types of Faults in Power System

There are two broad types of faults in power system:

• Open circuit fault
  
• Short circuit fault
  

Let us study each in detail.

Open Circuit Fault in Power System

In an open circuit fault, one or more conductors break. This stops the flow of current.

Types of Open Circuit Faults

1. Single conductor open fault – One conductor breaks, while others continue to work.

2. Two conductor open fault – Two conductors fail, leaving one conductor in use.

3. Three conductor open fault – All three conductors break. No current flows.

Consequences of Open Circuit Faults

These faults are not very severe. Yet, they put stress on healthy phases.

• In a three conductor open fault, supply stops completely. This does not cause major damage.
  
• In a one or two conductor open fault, a three-phase load puts extra stress on the remaining conductor. This may cause overheating, insulation failure, or breakdown.
  

Though open circuit faults do not create serious risks, they can still disturb system balance.

Short Circuit Fault in Power System

The second category is the short circuit fault. This happens when conductors touch each other or when a conductor touches the ground.

Short circuit faults fall into two categories:

• Symmetrical fault
  
• Asymmetrical fault

One of these is the most dangerous type of faults in power system.

Symmetrical Fault in Power System

In a symmetrical fault, the fault current is equal in all three phases. The currents in R, Y, and B phases remain balanced, separated by 120 degrees.

Even though the system stays balanced, this fault is very severe. The waveform shows perfect symmetry. The positive and negative half-cycles are identical.

Types of Symmetrical Faults

1. Triple line fault – All three phases short together.

2. Triple line to ground fault – All three phases short together and connect to the ground.

Consequences of Symmetrical Faults

Symmetrical faults are rare but the most severe type of faults in power system. Their occurrence is less than 5% of all faults. Yet, their impact is high.

• They generate very large short circuit currents.
  
• These currents produce intense heat, which can cause fire.
  
• The high currents create electromagnetic forces that damage equipment.
  
• Generators and transformers may suffer winding damage.
  
• If not cleared quickly, the fault can spread and destabilize the system.
  
• Workers near the fault face risks from arcs, gases, and flashovers.
  

Because of these reasons, circuit breakers must be chosen based on symmetrical fault calculations.

Asymmetrical Fault in Power System

In an asymmetrical fault, the system becomes unbalanced. The currents are not equal. One phase may carry normal current, while others carry high currents. The waveforms are not symmetrical.

Types of Asymmetrical Faults

1. Line to ground fault (LG fault) – One phase touches the ground. This is the most common fault.

2. Line-to-line fault – Two phases short together.

3. Double line to ground fault – Two phases short together and connect to the ground.

Consequences of Asymmetrical Faults

Asymmetrical faults are very common. About 90–95% of faults are of this type. Out of these, line to ground faults form nearly 70–80%.

• They generate short circuit currents, but not as high as symmetrical faults.
  
• Protective systems like circuit breakers can handle these faults effectively.
  
• They occur more frequently but are less dangerous compared to symmetrical faults.
  

Summary of Faults in Power System

Let us recap the discussion:

• Open circuit faults include single, double, or triple conductor open faults. They are not very severe.
  
• Short circuit faults include symmetrical and asymmetrical types.
  
• Asymmetrical faults are the most common, with line to ground faults leading. They form 90–95% of all cases.
  
• Symmetrical faults are the most severe, though rare. They form less than 5% of faults.
  

Consequences of Faults in Power System

The impact of faults in power system depends on the type.

• Open circuit faults create imbalance but do not cause high current.
  
• Asymmetrical faults are frequent but less damaging.
  
• Symmetrical faults are rare but most severe. They can destabilize the entire power network.
  

This is why protective devices must be designed with symmetrical fault levels in mind.

Conclusion

Faults in power system disturb the intended current path. Open circuits stop current flow. Short circuits divert it, creating dangerous situations.

Asymmetrical faults are most common, while symmetrical faults are most severe. Even though rare, symmetrical faults can damage equipment, cause fire, and threaten stability.

For a better visual understanding of these concepts, watch the original video. It explains with clear diagrams and simple examples.