Types of Faults and Effects in Electrical Power Systems

The electrical power system is growing in size and complexity in all sectors such as generation, transmission, distribution, and load systems. Types of faults like short circuit conditions in the power system network result in severe economic losses and reduce the reliability of the electrical system.

An electrical fault is an abnormal condition, caused by equipment failures such as transformers and rotating machines, human errors, and environmental conditions. Theses faults cause interruption to electric flows, equipment damages, and even cause the death of humans, birds, and animals.

Faults in Electrical Power System

Types of Faults

An electrical fault is the deviation of voltages and currents from nominal values or states. Under normal operating conditions, power system equipment or lines carry normal voltages and currents which results in safer operation of the system.

But when a fault occurs, it causes excessively high currents to flow which causes damage to equipment and devices. Fault detection and analysis are necessary to select or design suitable switchgear equipment, electromechanical relays, circuit breakers, and other protection devices.

There are mainly two types of faults in the electrical power system. Those are symmetrical and unsymmetrical faults.

1.Symmetrical faults


These are very severe faults and occur infrequently in the power systems. These are also called balanced faults and are of two types namely line to line to ground (L-L-L-G) and line to line (L-L-L).

Symmetrical faults
Symmetrical faults

Only 2-5 percent of system faults are symmetrical faults. If these faults occur, the system remains balanced but results in severe damage to the electrical power system equipment.

The above figure shows two types of three-phase symmetrical faults. Analysis of this fault is easy and usually carried by per phase basis. Three-phase fault analysis or information is required for selecting set-phase relays, rupturing capacity of the circuit breakers, and rating of the protective switchgear.

2.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), and double line to ground (LL-G) faults.

Unsymmetrical faults
Unsymmetrical faults

The line to ground fault (L-G) is the most common fault and 65-70 percent of faults are of this type.

It causes the conductor to make contact with the earth or ground. 15 to 20 percent of faults are double line to ground and causes the two conductors to make contact with the ground. The line to line faults occur when two conductors make contact with each other mainly while swinging of lines due to winds and 5- 10 percent of the faults are of this type.

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.

Causes of Electrical Faults 

Weather conditions: It includes lighting strikes, heavy rains, heavy winds, salt deposition on overhead lines and conductors, snow and ice accumulation on transmission lines, etc. These environmental conditions interrupt the power supply and also damage electrical installations.

Equipment failures: Various electrical equipment like generators, motors, transformers, reactors, switching devices, etc causes short circuit faults due to malfunctioning, aging, insulation failure of cables, and winding. These failures result in high current to flow through the devices or equipment which further damages it.

Human errors: Electrical faults are also caused due to human errors such as selecting improper rating of equipment or devices, forgetting metallic or electrical conducting parts after servicing or maintenance, switching the circuit while it is under servicing, etc.

Smoke of fires: Ionization of air, due to smoke particles, surrounding the overhead lines results in spark between the lines or between conductors to the insulator. This flashover causes insulators to lose their insulating capacity due to high voltages.

Effects of electrical faults 

Over current flow: When the fault occurs it creates a very low impedance path for the current flow. This results in a very high current being drawn from the supply, causing the tripping of relays, damaging insulation and components of the equipment.

Danger to operating personnel: Fault occurrence can also cause shocks to individuals. The severity of the shock depends on the current and voltage at the fault location and even may lead to death.

Loss of equipment: Heavy current due to short circuit faults result in the components being burnt completely which leads to improper working of equipment or device. Sometimes heavy fire causes complete burnout of the equipment.

Disturbs interconnected active circuits: Faults not only affect the location at which they occur but also disturbs the active interconnected circuits to the faulted line.

Electrical fires: Short circuit causes flashovers and sparks due to the ionization of air between two conducting paths which further leads to fire as we often observe in news such as building and shopping complex fires.

Fault limiting devices 

It is possible to minimize causes like human errors, but not environmental changes. Fault clearing is a crucial task in the power system network. If we manage to disrupt or break the circuit when a fault arises, it reduces the considerable damage to the equipment and also property.

Some of these fault limiting devices include fuses, circuit breakers, relays, etc. and are discussed below.

Fuse: It is the primary protection device. It is a thin wire enclosed in a casing or glass which connects two metal parts. This wire melts when excessive current flows in the circuit. The type of fuse depends on the voltage at which it is to operate. Manual replacement of wire is necessary once it a blowout.

Protecting devices
Protecting devices

Circuit breaker: It makes the circuit at normal as well as breaks at abnormal conditions. It causes automatic tripping of the circuit when a fault occurs. It can be electromechanical circuit breakers like vacuum/oil circuit breakers etc, or ultrafast electronic circuit breaker.

Relay: It is a condition-based operating switch. It consists of a magnetic coil and normally open and closed contacts. Fault occurrence raises the current which energizes relay coil, resulting in the contacts to operate so the circuit is interrupted from flowing of current. Protective relays are of different types like impedance relays, mho relays, etc.

Lighting power protection devices: These include lighting arrestors and grounding devices to protect the system against lightning and surge voltages.

Application-based three-phase fault analysis

We can analyze three-phase faults by using a simple circuit as shown below. In this temporary and permanent faults are created by fault switches. If we press the button once as a temporary fault, the timer’s arrangement trips the load and also restores the power supply back to the load. If we press ON this button for a particular time as a permanent fault, this system completely shutdowns the load by relay arrangement.

Three phase fault analysis
Three-phase fault analysis

I hope that you got a basic idea about three-phase faults. Thanks for your valuable time spending with the article. Furthermore any queries regarding electrical and electronic projects, please write your feedback in the comment section below.

Photo Credits

Fires due to electrical faults by 3.bp.blogspot
Unsymmetrical faults by pdfonline
Protecting devices by inspectapedia


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  2. layaiq ahmed says:

    its quite best info about electrical

  3. chinedu umeh says:

    What is the solution for relay tripping

  4. Sunil dewasi says:

    Understandable explanation … NYC sir I want study relays in details so if you help me sir ….

  5. Daimon e konyani says:

    Good explanation

  6. sandeep pandey says:

    Thanks a lot sir
    Sir next articles send also in my email .

  7. Thank you for this great article … I hope you can attach me fault analysis problems and exampĺes

  8. Kavya Shree says:

    Can u please tell the frequency of occurrence for various types of fault and with examples .please reply your answer in my email

  9. Kassim kobina Toffic says:

    the information is indeed a greet important n helpful .

  10. Dev Yadav says:

    which Electric fault is most dangerous & why ? plz reply me in my Email i am waiting four your answer
    thank you

    1. Bai Kargbo says:

      Our house bulb [Filament type of bulb] kept blowing off when ever we fix it, breakers keep tripping after some hours

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