The analysis of the power system under faulty condition is one of the most important and complex task in power engineering. The main aim of the power system is just provide the continuity of power supply to the consumers and that should be present in the power system anyhow. Hence, Analysis of the different faults is necessary to ensure maximum continuity of electrical supply with minimum damage to equipment life and properties. While designing the protective schemes, one has to understand the fault characteristics of the individual power system elements and according to that we have to implement different conventional methods and devices for it. This project will conduct a research and analyze the behaviors of a system under faulty conditions and try to utilize different methods of limiting the fault current. Hence, we can achieve reliable, flexible and stable power system.
1.1 PROBLEM SUMMARY.
Power system is not static but changes during operation (switching on or off of generators and transmission lines) and during planning (addition of generators &transmission lines). Thus fault studies need to be routinely performed by utility engineers (GEB). The problem of the Fault current in the Power system increases day by day.
Faults usually occur in a power system due to the insulation failure, flashover(Lightning strokes), physical damage and human error. Due to that power system affected and many problems occurs like unstable power system, discontinuity in power supply, Blackout, etc. Hence, it becomes one of the most serious problem in the power system.
Therefore, the analysis of the power system under faulty condition is one of the most important and complex task in power engineering. For limiting this fault current we studied various conventional methods and devices for it and try to reduce it as possible.
In this project we tried to understand the fault current, how much it will flow in faulty condition, and try to compensate it with different limiting techniques and devices. So, that we made our power system smooth and stable.
1.2 AIM AND OBJECTIVES OF THE PROJECT.
The main aim of this project is to analyze the Fault current and try to give different limiting techniques for it.
The objective of fault analysis is that Fault analysis aims to determine the causes that gave rises to certain failures (especially repetitive breakdowns and those with a high cost) to take appropriate steps. It is important to emphasize this dual function of fault analysis. From this analysis we can also select our power equipments like circuit breaker, isolators, etc. and make our system more reliable.
1.3 PROJECT DETAILS AND PROBLEM SPECIFICATIONS
First, we have to understand the whole detail about the fault. What are the causes behind it, its impact on the power system, etc.
1.3.1 What is fault??
An electrical power system consists of generators, transformers, transmission lines, distribution line etc. Normally, a power system operates under balanced conditions. Under abnormal conditions, the system may become unbalanced.
A Fault is an abnormal condition which affects the power continuity. We can also say that The fault in a circuit is any failure that interferes with the normal system operation. A fault usually results in high current flowing through the lines and if proper protection is not used, it may damages the power system equipments. Thus, the analysis of fault level is necessary.
1.3.2 Causes of fault occurrence.
Figure 1.3.2(a) Lightning stroke. Figure 1.3.2(b) Ice loading on conductor.
Figure 1.3.2(c) Birds shorting the line. Figure 1.3.2(d) Tree along a line.
The fault may occur on a power system due to a number of reasons. Some of the reasons are:-
1) Falling of a tree along a line.
2) Vehicles colliding with supporting structures.
3) Insulation failure of the system.
4) Birds shorting the transmission line.
5) Wind and ice loading on the transmission lines.
6) Over loading of undergrounding cables.
Figure 1.3.2(e) Percentage wise possible causes.
In fault analysis it is very important how faults are distributed in the various sections of a power system. There are many statistics on that which are available in the literature and internet as well. However, typically, the distribution is as follows:
Table 1. Distribution of fault in equipment.
SR.NO. AREA FAULT DISTRIBUTION
1. Overhead lines 50%
2. Cables 10%
3. Switchgear 15%
4 Transformers 12%
5. CTs and PTs 2%
6. Control Equipment 3%
7. Miscellaneous 8%
The probability of the failure or occurrence of abnormal condition is more on overhead power lines. This is so due to their:
â€¢ Greater length
â€¢ Exposure to the atmosphere.
1.3.3 Effect on the power system.
The fault current affect the system like damage of power equipment, short circuit of winding, Fire in substation as shown in the below figure. They reduce the Reliabilty, stability and flexibility of the power system. Due to this condition voltage fluctuation will be occurred and system will be affected.
A Fault implies any abnormal conditions there is an impact on the strength of the conductor as given below:
â€¢ phase conductors or
â€¢ phase conductors and earth, or any earthed screens surrounding the conductors.
Figure 1.3.3(a) Fire in substation.
Figure 1.3.3(b) 30-31st July 2012 power blackout in India
1.3.4 Types of Fault
If one, or two, or all three phases break or if insulators break due to fatigue weather, this fault is called a â€œpermanent faultâ€.it will remain after a quick power removing.
Faults which are involving ionized current paths are called transient faults. They usually clear if power is removed from the line for a short time and then restored. Approximately 75% of all faults are having transient nature.
There are mainly two types of fault present in the power system network.
1) Symmetrical Fault:-
When this type of fault occurs in the power system then system remains balanced, these faults are relatively rare, but are the easiest to analyze so weâ€™ll consider them first.
In this there are two types of fault
1) L-L-L Fault.
2) L-L-L-G Fault.
This fault can be with ground or without involving ground.
Figure 1.3.4(a) L-L-L Fault.
Figure 1.3.4 (b) L-L-L-G Fault.
2) Unsymmetrical Fault:-
This type of system is no longer balanced during this fault condition. It is very common, but more difficult to analyze.
a) Shunt Fault:- occurs due to overvoltage.
â€¢ L-G fault
â€¢ L-L fault
â€¢ L-L-G fault
b) Series fault:-occurs due to over-current.
â€¢ Open conductor Fault.
Figure 1.3.4(c) Shunt Fault.
Figure 1.3.4(d) Open circuit Fault.
Table 2 : percentage of the different fault in system.
SR.NO TYPE OF FAULT OCCURRENCE
1. Symmetrical fault 5%
2. L-L-G Fault 10%
3. L-L Fault 15%
4. L-G Fault 70%
Mostly, in the power system L-G fault occurs due to the tree falling on line, vehicle accident with line pole etc. symmetrical fault occurs rarely.
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