What are the types of faults in a power system?

What is a fault in the electrical system?

A fault in a power system can be described as an abnormal condition that interrupts the normal flow of current. Due to the fault, a huge amount of current would flow through the conductors or the cables and this flow would take place mostly through the inappropriate paths in the circuit. During the normal operating conditions of the power system, the electrical current through the circuit would have magnitude and it will be dependent upon the value of the generator voltage and also the impedance of the transmission and the distribution system.

What are the major reasons for the power system faults?

The complexity of the electric power system is really huge, the electric power system is composed of generators, transformers, transmission lines, etc. Due to this complexity and also because of the environmental conditions the chances for the fault in a power system is really high.

Major reasons for the fault in a power system is because of

• Insulation failure of the equipment
• Flashover
• Physical damage
• It could also happen because of the human error
• Permanent faults could be caused in case if the line is being in the ground, breaking of the insulator string, and also due to the equipment failure.
• Faults can happen due to short circuits to earth or between live conductors and it can also happen because of the broken conductors in one or more phases

So due to this the power system must be protected from heavy short circuit currents because it would damage the equipment. We can use circuit breakers and protective relays to protect the power system. The power system faults can also happen due to thermal or mechanical failures. Thermal faults could happen due to high ambient temperature, coolant loss, overvoltage, and over current. Mechanical faults could happen because of the earthquake, heavy wind, snow, or ice, it can also happen because of the forces created by the overcurrent.

What is a short circuit?

In case if the system insulation is damaged at a certain point, or in case if any conducting object comes in contact with a bare power conductor then it is called a short circuit or a fault.

What is the effect of faults in a power system?

The effect of the fault in a power system is depended upon the type of fault, fault duration, fault location, and also the short circuit capacity of the source.

• Excessive current flow
• Huge damage
• Dangerous to the operation personal
• Due to excessive heating, there could be an explosion
• Bus-bar deformation
• Damaged cables
• Insulation damage
• In case if there is high mechanical and thermal stress then most of the equipment in the plant would carry the fault current
• In case if the fault is not cleared quickly then there will be instability in the interconnected systems.

What is the voltage collapse in a power system?

Voltage collapse would occur due to a sequence of voltage instability events and due to this, there would be unacceptable voltage levels in certain parts of the power system. There should be a proper voltage level in a power system otherwise it would affect the power system operation. The voltage instability is caused due to the heavily stressed system and also because of the reactive power demand. We can determine the stability of the voltage in a power system by examining the production, transmission, and conception of reactive power. In case if the load is increased beyond the voltage collapse point then it would lead to the loss of equilibrium, due to this the power system operation is affected.

Major reasons for the voltage collapse

• Characteristics of the load, voltage, and frequency
• The action of tap load changing transformers
• It is also caused due to the characteristics of the reactive power compensating devices
• Transmission network strength and power transfer loss
• It could cause when the load on the transmission line is really high
• If the voltage source is really far from the load centers
• Very low source voltage

Factors affecting the voltage stability

• The reactive power transfer is really difficult because of high reactive power loss and due to this the reactive power that is needed for the voltage control is created and consumed at the control area
• While responding to a disturbance, the power consumed by the load can be restored by the motor slip adjustment, voltage regulators, and thermostats
• The restored loads would apply stress on the HV lines and this would create a reduction in voltage.
• The instability in the voltage occurs if the load dynamics try to restore the power consumption beyond the transmission network capability

What are the temporary and permanent faults?

Temporary faults

The temporary faults are faults that would only occur for a certain period of time and can be cleared without interrupting operation. A lightning strike is the major type of temporary fault because it won’t create any permanent damage.

Permanent faults

These faults would interrupt the operation of the power system, so in order to clear the faults, there should be the involvement of the protection engineers. The permanent faults are created by the wind, thermal heating, and sag.

What are the active and passive faults?

Active fault

This type of fault is caused if the active current flows from one phase conductor to the other or it can also happen from one phase conductor to earth. There are two types of active faults and they are solid faults and incipient faults.

Passive fault

The passive faults can’t be considered as real faults, it can be described as a condition that would make the system stress beyond its design capacity.

What are the different types of faults in a power system?

Symmetrical faults

The symmetrical faults are also known as balanced faults, the three-phase system can be considered as a single phase system in normal operating conditions and during this condition, the load, voltage, and current will be balanced. The symmetrical fault would affect each of the three phases equally. A very small percent of the power system faults are symmetrical faults the rest of the faults are unsymmetrical faults. The symmetrical faults are in balanced condition so we can determine the faults by checking the positive sequence network. The symmetrical faults are caused due to the system energization with maintenance earthing clamp connected to it.

Unsymmetrical faults

The major type of power system fault is caused because of this, unlike the symmetrical fault, this fault won’t affect each of the three phases equally. Shunt faults and series faults are the major two types of unsymmetrical faults. In an unsymmetrical fault, we can determine the fault current through a sequence circuit or a sequence network.

Major reasons for the unbalanced faults

• Insulation breaks down
• Over-voltage and lightning discharge
• Mechanical damage

Common types of unsymmetrical fault

The line to line fault

This fault is caused due to the short circuit between the lines and this is caused due to the ionization of the air, or in case if the bare line conductors make contact due to the broken insulator. During this fault, there will be an increase in current in the faulted phase and also there will be a one-eighty degree phase shift between the faulted phase current. During this fault, there will be a reduction in voltage in the faulted phase.

Line to ground fault

This fault is due to the short circuit between the line and the ground and this is caused due to physical contact, this could be caused due to the lightning. So during this fault, there will be a drop in faulted phase voltage and also high faulted phase current. There will be the negative and zero sequence current.

Double line to ground fault

This type of fault is caused when two lines would come into contact with the ground. In the faulted phase there will be a rise in current and also a drop in voltage.