A Project On Short Circuit Calculation Of The Nigerian Eastern Grid Network

Project and Seminar Material For Electrical Electronics Engineering EEE

Project and Seminar Material For Electrical Electronics Engineering EEE


Abstract


This project is based on the short circuit calculation of eastern grid network.

Short circuit occurs when two or more conductors that normally operate with a potential difference (P.D) come in contact with each other. Short circuiting results in danger to operating personnel, danger of igniting combustible gas such as methane in hazardous areas giving rise to a disaster of horrendous proportions. Also it greatly increased damage at the fault location (fault energy = I2 x Rf x t, where t is the time).

Constraint to grid operation in Nigeria due to short circuit was treated and the solution to adjust the problem.
The simulation of this project was done with engineering calculation software NEPLAN which was developed by B.C.P (Bursarello + Cott + partner) from Switzerland for system modeling and analysis.

This project was done to provide a proper analysis on the selection of switch gear, setting of relays and stability of system operation


Table Of Contents


Preliminary Page(s)

  • Title page
  • Certification
  • Dedication
  • Acknowledgement
  • Abstract
  • Table of contents

Chapter One

  • 1.0 Introduction to fault
  • 1.1 Types of fault
  • 1.2 Classification of fault
  • 1.3 Meaning of short circuit
  • 1.4 Consequences of short circuiting

Chapter Two

  • 2.0 Literature review on short circuit calculation
  • 2.1 Introduction of grid network
  • 2.2 Constraint to grid operation in Nigeria
    • Communication constraint
    • Generation constraint
    • Transmission constraint

Chapter Three

  • 3.0 Transmission line modeling
    • Medium line transmission
    • Nominal-T representation
    • Nominal- representation-
  • 3.1 Transformer modeling
    • Tap changing transformer
    • Phase-shifting transformer
  • 3.2 Formation of YBus

Chapter Four

  • 4.0 Introduction to NEPLAN
  • 4.1 Introduction to Nigerian grid
  • 4.2 Nigerian 330kv transmission grid network
  • 4.3 Bus identification of Nigerian 330kv grid network
  • 4.4 Eastern part of Nigerian grid network
  • 4.4.1 Eastern transmission line description
  • 4.4.2 The Eastern lines parameter of double and single circuit
  • 4.5 Single phase short circuit calculation using NEPLAN
  • 4.6 Result analysis (using NEPLAN)
  • 4.7 Current at fault location
  • 4.7.1 Generator data for eastern grid
  • 4.7.2 Types of conductor used in the transmission line
  • 4.7.3 Types of tower
  • 4.8 Component that make up the project
  • 4.9 A typical calculation on 3-Ø short circuit fault

Chapter Five

  • 5.0 Recommendation and conclusion
  • 5.1 Reference

Chapter One


1.0 Introduction Of Fault

It is not practical to design and build electrical equipment or network so as to completely eliminate the possibility of failure in service.

It is therefore an everyday fact of life that different types of faults occur on electrical systems, however infrequently, and at random location.

Fault can be broadly classified into two main areas which have been designated “Active” and “Passive”.


1.1 Types Of Fault

  1. Active fault
  2. Passive fault
  3. Types of faults on a three-phase system
  4. Transient and permanent fault

1. Active fault:

The “active” fault is when actual current flows from one phase conductor to another (phase-to-phase) or alternatively from one phase conductor to earth (phase –to-earth). This type of fault can further be classified into two areas, namely the “Solid” fault and “Incipient” fault.

The solid fault occurs as a result of an immediate complete breakdown of insulation as would happen if say, a pick struck an underground cable, bridging conductors etc.

The incipient fault on the other hand, is a fault that starts from very small beginnings from say some partial discharge (excessive electronic activity often referred to as Corona) in a void in the insulation, increasing and developing over an extended period, until such time as it burns away adjacent insulation, eventually running away and developing into a “solid” fault.

Other causes can typically be a high-resistance joint or contact, alternatively pollution of insulators causing tracking across their surface. Once tracking occurs, any surrounding air will ionize which then behaves like a solid conductor consequently creating a “solid” fault.

2. Passive fault:

This are not real faults in the true sense of the word but are conditions that are stressing the system beyond its design capacity, so that ultimately active faults will occur.
Typical examples are

Overloading:

leading to overheating of insulation(deteriorating quality, reduced life and ultimate failure)

Overvoltage:

stressing the insulation beyond its limits.

Under Frequency:

causing plant to behave incorrectly

Power Swings:

generators going out –of-step or synchronism with each other.

3. Three-phase system fault

These are types of fault on a 3-ф system

Phase –to-earth fault:

This is cause as a result of the breakdown of insulation of one phase and earth. It occurrence is about 70%.

There is a circuit diagram in the complete material that shows an example (scroll down to the end of this project to get the complete material)

Phase –to-phase fault:

this is a type of short circuit fault that due to breakdown of insulation between either of the two phases. It occurrence is 15%.

There is a circuit diagram in the complete material that shows an example (scroll down to the end of this project to get the complete material)

Phase –to-phase –to -earth fault:

this is the breakdown of insulation of two phases and earth. It occurrence in power network is 10%.

There is a circuit diagram in the complete material that shows an example (scroll down to the end of this project to get the complete material)

Three- phase fault:

This type of fault result due to breakdown of insulation between all the three phases or when there is a bridge involving all the three phase at a time. Its occurrence is 2 to 3 percent.

There is a circuit diagram in the complete material that shows an example (scroll down to the end of this project to get the complete material)

It will be noted that for a phase –to –phase fault, the current will be high, because the fault current is only limited by the inherent (neutral) series impedance of the power system up to the point of fault.

By design, this inherent series impedance in power system is purposely chosen to be as low as possible in order to get maximum power to the consumer and limit unnecessary losses in the network itself in the interests of efficiency.

4. Transient and permanent faults:

these are faults which do not damage the insulation permanently and allow the circuit to be safely re-energized after a short period of time.

Permanent fault as the name implies are the result of permanent damage to the insulation. In this case, the equipment has to be repaired and reclosing must not be entertained.


1.2 Classification Of Fault

Symmetrical fault (balanced):

This is a kind of fault that gives rise to symmetrical fault current. In this type of fault, current in the three phases are equal and have 120° displacement.

Example, when all the three phase of conductors of a three phase line are brought together simultaneously into a short-circuit condition.

Unbalanced Or Unsymmetrical Fault

This is also another type of fault in a power system that gives rise to unsymmetrical fault current. In this case, the line current is unequal and the displacement is unequal.

Here, IR ≠ IY ≠ IB

Examples of unsymmetrical fault are;

  • Single line- to- line –ground fault (L-G)
  • Line- to- line fault (L-L)
  • Double line-to- ground fault (D-L-G)

1.3 Meaning Of Short Circuit

A short circuit occurs when two or more conductors that normally operate with potential difference come in contact with each other. Electric power systems consist of generator, transformer, transmission lines and consumer unit (load). The system must be protected against flow of heavy short circuit current (which can cause permanent damage to major equipment) by disconnecting the faulty section of the system by means of circuit breakers and protective relaying


1.4 Consequence Is Short-Circuiting:

The consequence is variable depending on the type and duration of the fault, the point in the installation where the fault occurs and the short-circuit power. Consequence includes:

1. At the fault location, the presence of electrical arcs, resulting in

  • Damage to insulation
  • Welding of conductor
  • Fire and danger of life

2. On the faulty circuit

  • Deformation of the busbars
  • Disconnection of cable
  • Excessive temperature rise due to an increase in joule losses
  • Shutdown of a part of the network
  • Dynamic instability or the loss of machine synchronization
  • Disturbances in control/monitoring circuit.

Chapter Five


5.0 Recommendation And Conclusion

It is important and necessary to know the maximum short circuit current that can occur in a power system in order to select circuit breaker that are adequate to withstand the current and operate successful to cut off faulty section and also in order to select the protective relay for circuit operations.

Short circuit analysis is important in power system for planning, selection of circuit breakers and setting of relays.
It is also necessary to be able to calculate approximately at least, the size of protective reactors, circuit current to a value in which a circuit breaker can handle.

Fault current can be reduced by insertion of reactors in series with power system and also by using super conducting fault current limiters. NEPLAN is power system software that is use for the short circuit calculation in this project. It can also be used for load flow studies, transient stability, voltage stability and motor starting. It helps to have a better fault level calculation.


A Project On Short Circuit Calculation Of The Nigerian Eastern Grid Network


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