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. These faults cause interruption to electric flows, equipment damages, and even cause the death of humans, birds, and animals. This article discusses an overview of different types of faults and their effects that occurred in electric power systems.

What is an Electrical Fault?

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.

Types of Faults in Electrical Power Systems

In the electrical power system, the faults are mainly two types like open circuit faults and short circuit faults. And further, these types of faults can be classified into symmetrical and unsymmetrical. Let us discuss these types of faults in detail. These faults are classified into two types.

• Symmetrical Fault
• Unsymmetrical Fault

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).

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 on a phased 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.

The symmetrical faults are classified into two types

• Line – Line – Line Fault
• Line – Line – Ground Fault

L – L – L Fault

These kinds of faults are balanced which means the system remains balanced after the fault occurs. So this fault rarely occurs, although it is the harsh kind of fault that holds the largest current. So this current is used to determine the rating of the CB.

L – L – L – G Fault

The 3-phase L – G fault mainly comprises all the 3- phase of the system. This fault mainly occurs among the 3-phases as well as the ground terminal of the system. So, there is a 2 to 3% of probability to occur the fault.

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.

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 occurs 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.

The unsymmetrical faults are classified into two types

• Single L – G (Line-to-Ground) Fault
• L – L (Line-to-Line) Fault
• Double L – G (Line-to-Ground) Fault

Single L – G Fault

This single L – G fault mainly occurs once a single conductor falls toward the ground terminal. So around 70 to 80 % of the fault within the power system is the single L – G fault.

L – L Fault

This L– L fault mainly occurs once two conductors are short-circuited and also due to heavy wind. So the line conductors can be moved because of heavy wind, they may touch with each other and causes short-circuit. So, 15 – 20% of the faults can occur approximately.

Double L – G Fault

In this kind of fault, both the two lines get in touch with each other through the ground. So, there is a 10% probability for faults.

Open Circuit Faults

The open-circuit faults mainly occur because of the malfunction of one otherwise more conductors used in the power system. The open-circuit faults diagram is shown below. This circuit is for 1-phase, 2- phases, and 3-phases open condition.

These faults mainly occur because of common issues like failure of joints in overhead lines, cables, failure in the phase of a circuit breaker, melting of conductor or fuse within one phase or more phases.
These faults are also known as series faults which are unbalanced types otherwise unsymmetrical types apart from 3-phase open fault.

For instance, a transmission line works through a balanced load before an open fault circuit occurs. In the transmission line, if any one of the phases gets dissolved then an alternator’s actual loading can be decreased & increases the acceleration of the alternator, so it works at a speed somewhat higher than the synchronous speed. In other transmission cables, this over speed can cause overvoltages. Therefore, 1-phase & 2-phase open conditions can generate currents and voltages of the power system that causes huge damage to the apparatus.

These faults are categorized into three types like following.

• Open Conductor Fault
• Two conductors Open Fault
• Three Conductors Open Fault.

Causes and Effects of Types of Faults

These faults can be caused because of the circuit malfunctioning as well as broken conductor in 1- phase or more phases. The effects of open circuit faults include the following.

• Electrical power system irregular operation
• These faults may danger to animals as well as human beings
• In particular, a portion of the network, when the voltage is exceeded beyond normal values then it causes insulation failures and develops short circuit faults.
• Even though, these types of circuit faults can be accepted for a long time as compared with short circuit type faults, because these faults must be detached to decrease the high damage.

Short Circuit Faults

Short circuit faults mainly occur because of failure within insulation among phase conductors and earth. An insulation failure can cause a short-circuit path formation that activates short-circuit conditions within the circuit.

The definition of a short circuit is, an abnormal connection of extremely less impedance among two points of dissimilar potential, whether completed by chance or purposely. These faults are the most common types which result in the abnormal high current flow throughout the transmission lines or equipment.

If short circuit faults are allowed to continue even for a small-time, then it leads to wide harm to the apparatus. Short circuit faults are also known as shunt faults because these faults mainly occur because of the failure in insulation among phase conductors otherwise among phase conductors and earth

The different achievable short circuit fault conditions mainly comprise 3-phases to earth, 3-phase clear of the earth, 1- phase to earth, phase to phase, 2- phase to earth, phase to phase and single-phase to earth.

Both the 3-phase fault clear of the earth, as well as the 3-phase fault toward earth, can be symmetrical or balanced while other faults are unsymmetrical faults.

Causes and Effects of Short Circuit Faults

The short circuit faults may occur because of the following reasons.

• These faults may occur because of the internal otherwise external effects
• Internal effects are transmission lines breakdown, equipment damage, insulation aging, corrosion of insulation within the generator, improper installations of electrical devices, transformers, and their inadequate design.
• These faults can be occurred because of outside effects of apparatus, insulation failure because of lighting surges & mechanical damage by the public.

The effects of short circuit faults include the following.

• Arcing faults can cause fire & blast in apparatus like transformers as well as circuit breakers.
• The flow of power can be restricted severely otherwise even totally blocked if the short circuit error persists.
• The system operating voltages can go above or below their acceptance values to make a damaging effect on the service provided through the power system.
• Because of abnormal currents, the apparatus gets heated so that the life span of their insulation can be reduced.

Causes of Types of Faults

The main reasons to cause electrical faults include the following.

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.

Types of Faults & Their Effects

The effects of electrical faults mainly occur because of the following reasons.

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 results 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 disturb 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 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.

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 breakers.

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 the 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.

How to Detect and Locate the Faults?

In transmission lines, the fault is very easy to identify as the crisis is generally noticeable. For instance, once any tree has fallen over the transmission line, otherwise, an electrical pole can be damaged as well as the conductors are lying on the earth.

In a cable system, fault locating can be done when the circuit is not worked otherwise when the circuit works. There are different methods for fault location which can be divided into terminal techniques, which work with currents as well as voltages measured at the cable ends & tracer methods which need inspection through the cable. The normal area of the faults can be located at the terminal techniques to speed up tracing over a transmission cable.

In wiring systems, the location of the fault can be found throughout the verification of the wires. In difficult wiring systems, wherever the wires may be buried, these faults are placed through a Time-domain reflectometer that sends a pulse down the wire & after that examines the reflected signal to recognize faults in the electrical wire.

In a famous underwater telegraph cable, responsive galvanometers were utilized to compute fault currents through testing at fault cable ends. In cables, two methods are used to locate faults like the Varley loop as well as Murray loop.

In a power cable, an insulation fault cannot occur at low voltages. So, a thumper test is used by applying a high voltage pulse, high energy to the cable. The fault location can be done by listening to the discharge sound at the error. When this test donates to harm at the site of cable, it is useful as the faulted location would have to be re- insulate once set up in any case.

In a distribution system with high resistance grounded, a feeder can expand an error to earth however the system maintains in process. The faulted as well as energized feeder can be found in a ring-type current transformer which gathers all the phase wires for the circuit; simply the circuit includes a fault to earth will illustrate a net disturbed current. The grounding resistor is used to make the current of the earth fault easier to notice among two values to beat the fault current.

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