Construction Of 10KVA Variable Three Phase Static Compensator For Power Quality Improvement

ABSTRACT

A Power quality problem is an occurrence manifested as a nonstandard voltage, current or frequency that results in a failure or a  mis-operation  of end  user  equipments.  Utility distribution networks, sensitive industrial  loads  and  critical commercial operations suffer from various types of outages and service interruptions which can cost significant financial losses. With the restructuring of power systems and with shifting trend towards distributed and dispersed generation, the issue of power quality is going to take  newer  dimensions.  In developing countries like Nigeria,  where  the variation  of power frequency and many such other determinants of power quality are themselves a serious question, it is very vital to take positive steps in this direction. The present work is to identify the prominent concerns in this area and hence the measures that can enhance the quality of the power are recommended.

This  paper  presents  the  enhancement  of  voltage  sags/swell;  harmonic  distortion  and low  power  factor  using Static Compensator (D-STATCOM). The STATCOM injects a current into the system to mitigate the voltage sags/swell.

TABLE OF CONTENTS

 TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

DEFINITION OF TERMS

TABLE OF CONTENT

CHAPTER ONE

• INTRODUCTION
• DEFINITION OF POWER QUALITY
• AIM OF THE PROJECT
• CONTROL OBJECTIVES OF STATCOM
• SIGNIFICANCE OF THE PROJECT
• SCOPE OF THE PTOJECT
• EFFECT OF POWER QUALITY PROBLEMS

CHAPTER TWO

LITERATURE REVIEW

2.0      LITERATURE REVIEW

2.1      OVERVIEW OF THE STUDY

2.2     NEED FOR COMPENSATION

2.3     TYPES OF COMPENSATION

2.4    OVERVIEW OF STATCOM AND ITS USES

2.5     APPLICATIONS OF STATCOMS

2.5    DETERMINING THE BEST FOUNDATION

 

CHAPTER THREE

DESIGN METHODOLOGY

3.1      METHODOLOGY

3.2      DESIGN OF STATCOM

3.3      MODELLING OF STATCOM

3.4      OPERATION OF STAT-COM

CHAPTER FOUR

RESULT ANALYSIS

4.1 RESULT

4.2 POWER FACTOR COMPARISION

CHAPTER FIVE

5.0      CONCLUSION AND REFERENCES

• CONCLUSION

5.2     REFERENCES

 CHAPTER ONE

1.1                                                      INTRODUCTION

An electric distribution system is part of an electric system  between  the bulk  power  source  or sources  and  the  consumer’s  service  switches.  The bulk power sources are located in or near the load area to be served by the distribution system and may be either generating stations or power substations supplied  over   transmission   lines. Distribution systems can, in general, be divided into six parts, namely, sub transmission circuits, distribution substations, distribution or primary feeders, distribution transformers, secondary circuits or secondary’s, and consumer’s service connections and meters or consumer’s services. One of the most common power quality  problems  today  is  voltage  sag/swell.  It  is often set only by two parameters, depth/magnitude and duration. The voltage sag/swell magnitude is ranged  from  10%  to 90% of nominal  voltage and with duration from half a cycle to 1 min. In a three- phase system voltage sag is by nature a three-phase phenomenon, which affects both the phase-to-ground and phase-to-phase voltages. Voltage sag is caused by a fault in the utility system, a fault within  the customer’s facility or  a  large increase of the load current,   like   starting   a   motor   or   transformer energizing.   Typical   faults   are   single-phase   or multiple-phase short circuits, which leads to high currents. The high current results in a voltage drop over the network impedance. At the fault location the voltage in the faulted phases drops close to zero, whereas in the non-faulted phases it remains more or less unchanged.

Voltage  sags  are  one  of  the  most  occurring power quality problems. For an industry voltage sags occur more often and cause severe problems and economical  losses.  Utilities often  focus  on disturbances from end-user  equipment as the main power quality problems.[2]

Harmonic currents in distribution system can cause harmonic distortion, low power factor and additional losses as well as heating in the electrical equipment. It also can cause vibration and noise in machines and malfunction of the sensitive equipment. There are different ways to enhance power quality problems in transmission  and  distribution  systems. Among these, the STATCOM is one of the most effective devices. A new PWM-based control scheme has been implemented to control the electronic valves in the STATCOM. The STATCOM has additional capability to sustain reactive current at low voltage, and can be developed as a voltage and frequency support by replacing capacitors with batteries as energy storage. To enhance the power quality such  as  voltage sags/swell, harmonic distortion   and  low  power   factor   in   distribution system.

1.2                                        DEFINITION OF POWER QUALITY

Power quality is defined as the ability of a system or an equipment to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment. PQ mainly deals with 1. Continuity of the supply. 2.”Quality” of the voltage.

1.3                                               AIM OF THE PROJECT

The factors that are affecting power quality are voltage sag, voltage variation, interruption, swells, brownout, distortions, Harmonic, noise, voltage spikes, voltage flicker etc. This causes some deviations in the power when compared with the normal standards. The above problems may overcome by using compensation devices (custom power devices) either compensate load i.e. correct its power factor, unbalance etc.

However, the objective of this work is to construct compensation devices that can correct this power factor problem using static compensator (STATCOM).

1.4                          CONTROL OBJECTIVES OF  STATCOM

The shunt  connected  converter  has the following control objectives:

• Voltage support and control
• Voltage  Fluctuation      And     Flicker Mitigation
• Unsymmetrical load balancing
• Power factor correction
• Active harmonics cancellation
• Improve transient stability of the power system

 

1.5                                         SIGNIFICANCE OF THE PROJECT

In distribution system the distribution networks and sensitive industrial loads are suffering from different type of outage and interruption which can lead to loss in production and other measurable and non measurable factor. The factors that are affecting power quality are voltage sag, voltage variation, interruption, swells, brownout, distortions, Harmonic, noise, voltage spikes, voltage flicker etc. This causes some deviations in the power when compared with the normal standards. The above problems may overcome by using compensation devices (custom power devices) either compensate load i.e. correct its power factor, unbalance etc. or improve the quality of the supply voltage. These devices include static compensator (STATCOM), Dynamic voltage restorer (DVR), and unified power quality compensator (UPQC) to obtain Better performance. However, in this work we are focusing on the compensation using static compensator (STATCOM).

1.6                                              SCOPE OF THE PTOJECT

For economic operation of a power system, the level of power quality should be properly maintained. PQ is a vast concept concerning optimization. The adverse effects due to over voltages, also the losses incurred due to the under voltages have to be seriously dealt. Also, nonlinear loads introduce harmonics in the system which have their own adverse effects including power factor reduction. Hence, power quality provides a good platform to deal with all these problems.

1.7                                    EFFECT OF POWER QUALITY PROBLEMS

Without the proper power, an electrical device may malfunction, fail prematurely or not operate at all. There are many ways in which electric power can be of poor quality and many more causes of such poor quality power. Some of the most common power supply problems and their likely effect on sensitive equipment:

1. Voltage surges/spikes

Voltage surges/spikes are the opposite of dips – a rise that may be nearly instantaneous (spike) or takes place over a longer duration (surge). A voltage surge takes place when the voltage is 110% or more above normal. The most common cause is heavy electrical equipment being turned off. Under these conditions, computer systems and other high tech equipment can experience flickering lights, equipment shutoff, errors or memory loss. Possible Solutions are surge suppressors, voltage regulators, uninterruptable power supplies, power conditioners[4].

2. Voltage Dips

Short duration under-voltages are called “Voltage Sags” or “Voltage Dips [IEC]”. Voltage sag [5, 6] is a reduction in the supply voltage magnitude followed by a voltage recovery after a short period of time. The major cause of voltage dips on a supply system is a fault on the system, i.e. sufficiently remote electrically that a voltage interruption does not occur. Other sources are the starting of large loads and, occasionally, the supply of large inductive loads [6]. The impact on consumers may range from the annoying (non-periodic light flicker) to the serious (tripping of sensitive loads and stalling of motors.

3. Under voltages

Excessive network loading, loss of generation, incorrectly set transformer taps and voltage regulator malfunctions, causes under voltage. Loads with a poor power factor or a general lack of reactive power support on a network also contribute. Under voltage can also indirectly lead to overloading problems as equipment takes an increased current to maintain power output (e.g. motor loads) [5].

4. High-Voltage Spikes

High-voltage spikes occur when there is a sudden voltage peak of up to 6,000 volts. These spikes are usually the result of nearby lightning strikes, but there can be other causes as well. The effects on vulnerable electronic systems can include loss of data and burned circuit boards. Possible Solutions are using Surge Suppressors, Voltage Regulators, Uninterruptable Power Supplies, Power Conditioners [7].

5. Frequency Variation

A frequency variation involves a change in frequency from the normally stable utility frequency of 50 or 60 Hz, depending on your geographic location. This may be caused by erratic operation of emergency generators or unstable frequency power sources. For sensitive equipment, the results can be data loss, program failure, equipment lock-up or complete shutdown. Possible Solutions are using Voltage Regulators and Power Conditioners [7].

6. Power Sag

Power sags are a common power quality problem. Despite being a short duration (10ms to 1s) event during which a reduction in the RMS voltage magnitude takes place, a small reduction in the system voltage can cause serious consequences. Sages are usually caused by system faults, and often the result of switching on loads with high demand startup currents. For more details about power sags visit our newsletter archives. Possible Solutions are using Voltage Regulators, Uninterruptable Power Supplies, and Power Conditioners [8].

7. Electrical Line Noise

Electrical line noise is defined as Radio Frequency Interference (RFI) and Electromagnetic Interference (EMI) and causes unwanted effects in the circuits of computer systems. Sources of the problems include motors, relays, motor control devices, broadcast transmissions, microwave radiation, and distant electrical storms. RFI, EMI and other frequency problems can cause equipment to lock-up, and data error or loss. Possible Solutions are using Voltage Regulators, Uninterruptable Power Supplies, and Power Conditioners [7].

8. Brownouts

A brownout is a steady lower voltage state. An example of a brownout is what happens during peak electrical demand in the summer, when utilities can’t always meet the requirements and must lower the voltage to limit maximum power. When this happens, systems can experience glitches, data loss and equipment failure. Possible Solutions are using Voltage Regulators, Uninterruptable Power Supplies, and Power Conditioners [9].

9. Blackouts

A power failure or blackout is a zero-voltage condition that lasts for more than two cycles. It may be caused by tripping a circuit breaker, power distribution failure or utility power failure. A blackout can cause data loss or corruption and equipment damage. Possible Solutions is using Generators [10].

10. Very short interruptions

Total interruption of electrical supply for duration from few milliseconds to one or two seconds. Mainly due to the opening and automatic reclosure of protection devices to decommission a faulty section of the network. The main fault causes are insulation failure, lightning and insulator flashover. Consequences of these interruptions are tripping of protection devices, loss of information and malfunction of data processing equipment [11].

11. Long interruptions

Long interruption of electrical supply for duration greater than 1 to 2 seconds. The main fault causes are Equipment failure in the power system network, storms and objects (trees, cars, etc) striking lines or poles, fire, human error, bad coordination or failure of protection devices. A consequence of these interruptions is stoppage of all equipment [1].

12. Voltage swell

Momentary increase of the voltage, at the power frequency, outside the normal tolerances, with duration of more than one cycle and typically less than a few seconds. The main causes are Start/stop of heavy loads, badly dimensioned power sources, badly regulated transformers (mainly during off-peak hours).Consequences is data loss, flickering of lighting and screens, stoppage or damage of sensitive equipment, if the voltage values are too high [11].

13. Harmonic distortion

Voltage or current waveforms assume non-sinusoidal shape. The waveform corresponds to the sum of different sine-waves with different magnitude and phase, having frequencies that are multiples of power-system frequency. Main Causes are Classic sources: electric machines working above the knee of the magnetization curve (magnetic saturation), arc furnaces, welding machines, rectifiers, and DC brush motors. Modern sources: all non-linear loads, such as power electronics equipment including ASDs, switched mode power supplies, data processing equipment, high efficiency lighting [11]. Consequences are increased probability in occurrence of resonance, neutral overload in 3-phase systems, overheating of all cables and equipment, loss of efficiency in electric machines, electromagnetic interference with communication systems, and errors in measures when using average reading meters, nuisance tripping of thermal protections.

14. Voltage fluctuation

Oscillation of voltage value, amplitude modulated by a signal with frequency of 0 to 30 Hz. Causes are arc furnaces, frequent start/stop of electric motors (for instance elevators), oscillating loads. Consequences are most consequences are common to under voltages. The most perceptible consequence is the flickering of lighting and screens, giving the impression of unsteadiness of visual perception [1].

15. Noise

Superimposing of high frequency signals on the waveform of the power-system frequency. Main Causes are Electromagnetic interferences provoked by Hertzian waves such as microwaves, television diffusion, and radiation due to welding machines, arc furnaces, and electronic equipment. Improper grounding may also be a cause. Consequences are disturbances on sensitive electronic equipment, usually not destructive. It may cause data loss and data processing errors [12].

16. Voltage Unbalance

A voltage variation in a three-phase system in which the three voltage magnitudes or the phase angle differences between them are not equal. Causes are large single-phase loads (induction furnaces, traction loads), incorrect distribution of all single-phase loads by the three phases of the system (this may be also due to a fault). Consequences are Unbalanced systems imply the existence of a negative sequence that is harmful to all three phase loads. The most affected loads are three-phase induction machines [13].