A Power System is a network composed of passive and active electrical components which are used to supply and transmit electric power. In these systems, faults are considered to be abnormal electric current parameter. Numbers of factors are responsible for the fault occurrence a system. Thus, systems are designed for the power system analysis in order to detect and interrupt different types of faults in power system. To fulfil this requirement is the main objective of power system protection. A variety of methods of detecting & locating faults in a power systems exist. Here we have tried to made a short review of some of the common methods of Power System Analysis for Different types of faults in power system and their consequences in brief.
Detection and Types of Faults in Power System
The flow of current to the undesired path and abnormal stoppage of current are termed as fault.
TYPES OF FAULT:
The faults are classified as:
1. Three phase fault
2. Three phase to ground fault
3. Single phase to ground fault
4. Phase to Phase fault
5. Double Phase to earth fault
6. Simultaneous fault
Basically the faults are divided into two type:
- Symmetrical fault
- Asymmetrical fault
1. Symmetrical fault: Symmetrical faults are those type of faults in which all the three phases gets involved simultaneously. For example: triple line fault (L-L-L), triple line to ground fault (L-L-L-G).
2. Asymmetrical fault: In this type of faults, the fault occur mainly in one or two phases and are categorizes as unbalanced fault. For example: single line to ground (L-G), double line to ground (L-L-G).
DETECTION OF FAULT:
If the fault occur then it should be removed or cured as soon as possible, otherwise it can damage and even burn the equipment’s.
1. Faults in the electrical equipment’s can be detected by using sensors which sense the fault.
2. Now a days the faults can also be detected automatically by using automatic fault detection and diagnostic software. Researches are still going on related to the use of this software. CSIRO researchers are still working on this software.
EFFECTS OF FAULT:
Generally the fault occur either within the devices or in the cables which is being used for the supply purpose.
· The cable used for supplying the power become worn because of long or prolonged rubbing against other objects like branches of trees, with another wires etc.
· In the similar way the motor also get burn out and causing short circuit.
· Electrical fault may cause the risk of fire, damage the equipment, and may cause potential electric shock to the people.
· If some equipment’s are placed near the main cables and the fault occur then it may damage that equipment, the short circuit that occur in the main windings or cables if not removed then it also damages the walls as well as the floor.
BUS BAR PROTECTION:
The bus bar protection comes under the apparatus protection scheme.
If the fault occur in the bus bar then it causes enormous damage.so for protecting it the large concentration should be given to the short-circuit capacity of the bus bar.
The bus bar protection mainly includes the apparatus like circuit breakers, disconnecting switches, instrumental transformers etc. Bus bar protections are highly desirable in large and important substations.
We have three types of protections which is generally used for the protection purpose of bus bar, they are:
1. Non-unit protection by backup relays
2. Differential scheme of bus bar protection
3. Frame earth protection
Clearing of bus fault requires the opening of all circuit branching from the faulted bus or bus section.
1. Non-unit protection by backup relays:
Fault cleared by back-up over current, earth fault, and distance protection are usually found to be non-discriminative and slow in operation.
Due to this error, when this is applied for bus bar protection it causes unnecessary tripping of the coil and the relays superficially trips causing discontinuous supply of power.so it is economically unreliable to implement this type of protection.
2. Differential scheme of bus bar protection: It is working on the principle that during normal load conditions or external fault conditions, the sum of the currents entering the bus equals the sum of currents leaving the current.
3. Frame earth protection: In this type of protection as the name indicate, the whole frame work of switchgear is earthed or cemented to the ground through the primary of the current transformer. The ohmic value of the ground resistor must be above 10 ohm. This design of earthing scheme incorporates the frame work protection for the bus bar.
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