A Novel Approach For Measurements And Analysis Engineering Essay

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Our technological world has become deeply dependent upon the continuous availability of electrical power. In most countries, commercial power is made available via nationwide grids, interconnecting numerous generating stations to the loads. The grid must supply basic national needs of residential, lighting, heating, refrigeration, air conditioning, and transportation as well as critical supply to governmental, industrial, financial, commercial, and medical and communications communities. Commercial power literally enables today's modern world to function at its busy pace. Sophisticated technology has reached deeply into our homes and careers, and with the advent of e-commerce is continually changing the way we interact with the rest of the world.

Many power problems originate in the commercial power grid, which, with its thousands of miles of transmission lines, is subject to weather conditions such as hurricanes, lightning storms, snow, ice, and flooding along with equipment failure, traffic accidents and major switching operations. Also, power problems affecting today's technological equipment are often generated locally within a facility from any number of situations, such as local construction, heavy startup loads, faulty distribution components, and even typical background electrical noise.



Widespread use of electronics in everything from home electronics to the control of massive and costly industrial processes has raised the awareness of power quality. Power quality, or more specifically, a power quality disturbance, is generally defined as any change in power (voltage, current, or frequency) that interferes with the normal operation of electrical equipment.

The study of power quality, and ways to control it, is a concern for electric utilities, large industrial companies, businesses, and even home users. The study has intensified as equipment has become increasingly sensitive to even minute changes in the power supply voltage, current, and frequency. Unfortunately, different terminology has been used to describe many of the existing power disturbances, which creates confusion and makes it more difficult to effectively discuss, study, and make changes to today's power quality problems. The Institute of Electrical and Electronics Engineers (IEEE) has attempted to address this problem by developing a standard that includes definitions of power disturbances. The standard (IEEE Standard 1159-1995, "IEEE Recommended Practice for Monitoring Electrical Power Quality") [1] describes many power quality problems, of which this paper will discuss the most common.

1.2 Ways to Look the Power

Electricity at the wall outlet is an electromagnetic phenomenon. Commercial power is provided as alternating current (AC), a silent, seemingly limitless source of energy that can be generated at power stations, boosted by transformers, and delivered over hundreds of miles to any location in the region. Seeing what this energy is doing in small slices of time can provide an understanding of how important simple, smooth ac power is to reliable operation of the sophisticated systems that we are dependent upon. An oscilloscope allows us to see what this energy looks like. In a perfect world, commercial ac power appears as a smooth, symmetrical sine wave, varying at either 50 or 60 cycles every second (Hertz - Hz) depending on which part of the world we're in. what an average AC sine wave would

The sinusoidal wave shape shown above represents a voltage changing from a positive value to a negative value, 60 times per second. When this flowing wave shape changes size, shape, symmetry, frequency, or develops notches, impulses, ringing, or drops to zero (however briefly), there is a power disturbance. Simple drawings representative of changes in the above ideal sine wave shape will be shown throughout this paper for the seven categories of power quality disturbances that will be discussed.


Being able to talk effectively about power, such as knowing the difference between an interruption, and an oscillatory transient, could make a huge difference when making purchase decisions for power correction devices. A communication mistake can have expensive consequences when the wrong power correction device is purchased for our needs, which includes downtime, lost wages, or even equipment damage [2].

This IEEE defined power quality disturbances shown in this paper have been organized into seven categories based on wave shape:

This paper will conform to these categories and include graphics, which should clarify the differences between individual power quality disturbances.

2.1. Transients

Potentially the most damaging type of power disturbance, transients fall into two subcategories:

1. Impulsive

Impulsive transients are sudden high peak events that raise the voltage and/or current levels in either a positive or a negative direction. These types of events can be categorized further by the speed at which they occur (fast, medium, and slow). Impulsive transients can be very fast events (5 nanoseconds [ns] rise time from steady state to the peak of the impulse) of short-term duration (less than 50 ns).

One example of a positive impulsive transient caused by electrostatic discharge (ESD) event.

Figure 1 Impulsive Transient

The impulsive transient is what most people are referring to when they say they have experienced a surge or a spike. Many different terms, such as bump, glitch, power surge, and spike have been used to describe impulsive transients.

Causes of impulsive transients include lightning, poor grounding, the switching of inductive loads, utility fault clearing, and Electrostatic Discharge (ESD). The results can range from the loss (or corruption) of data, to physical damage of equipment. Of these causes, lightning is probably the most damaging.

The problem with lightning is easily recognized after witnessing an electrical storm. The amount of energy that it takes to light up the night sky can certainly destroy sensitive equipment. Moreover, it doesn't take a direct lightning strike to cause damage. The electro- magnetic fields, created by lightning can cause much of the potential damage by inducing current onto nearby conductive structures.

Figure 2.1.2 Magnetic Field Created By Lightning Strike

Two of the most viable protection methods when it comes to impulsive transients pertain to the elimination of potential ESD, and the use of surge suppression devices (popularly referred to as transient voltage surge suppressors: TVSS, or surge protective device: SPD).

While ESD can arc off of our finger with no damage to us, beyond a slight surprise, it is more than enough to cause an entire computer motherboard to stop dead and to never function again. In data centers, printed circuit board manufacturing facilities or any similar environment where PCBs are exposed to human handling, it is important to dissipate the potential for ESD. For example, almost any proper data center environment involves conditioning of the air in the room. Conditioning the air does not just cool the air to help remove heat from data center equipment, but also adjusts the amount of moisture in the air. Keeping the humidity in the air between 40 - 55% humidity will decrease the potential for ESD to occur. We've probably experienced how humidity affects ESD potential if we've ever been through a winter (when the air is very dry) when a few drags of our socks across the carpet cause a tremendous arc to jump from our finger unexpectedly to the doorknob we were reaching for, or expectedly if we were aiming for someone's ear. Another thing we will see in PCB environments, such as we would see in any small computer repair business, is equipment to keep the human body grounded. This equipment includes wrist straps, antistatic mats and desktops, and antistatic footwear. Most of this equipment is connected to a wire, which leads to the ground of the facility, which keeps people safe from electric shock and also dissipates possible ESD to ground.

In some cases SPD circuits are built into the electrical devices themselves, such as computer power supplies with built in suppression abilities. More commonly, they are used in stand- alone surge suppression devices, or included with UPSs to provide surge suppression and emergency battery power should in interruption occur (or when power levels are outside the boundaries of nominal, or safe, power conditions).

2. Oscillatory

An oscillatory transient is a sudden change in the steady-state condition of a signal's voltage, current, or both, at both the positive and negative signal limits, oscillating at the natural system frequency. In simple terms, the transient causes the power signal to alternately swell and then shrink, very rapidly. Oscillatory transients usually decay to zero within a cycle (a decaying oscillation).

These transients occur when we turn off an inductive or capacitive load, such as a motor or capacitor bank. An oscillatory transient results because the load resists the change. This is similar to what happens when we suddenly turn off a rapidly flowing faucet and hear a hammering noise in the pipes. The flowing water resists the change, and the fluid equivalent of an oscillatory transient occurs.

When oscillatory transients appear on an energized circuit, usually because of utility switching operations (especially when capacitor banks are automatically switched into the system), they can be quite disruptive to electronic equipment. Oscillatory Transient attributable to capacitor banks being energized.

Figure 2. Oscillatory transient

The most recognized problem associated with capacitor switching and its oscillatory transient is the tripping of adjustable speed drives (ASDs). The relatively slow transient causes a rise in the dc link voltage (the voltage that controls the activation of the ASD), which causes the drive to trip off-line with an indication of overvoltage.

A common solution to capacitor tripping is the installation of line reactors or chokes that dampen the oscillatory transient to a manageable level. These reactors can be installed ahead of the drive or on the dc link and are available as a standard feature or as an option on most ASDs.

Another rising solution to capacitor switching transient problems is the zero crossing switches. When a sine wave's arc descends and reaches the zero level (before it becomes negative), this is known as the zero crossing. A transient caused by capacitor switching will have a greater magnitude the farther the switching occurs away from the zero crossing timing of the sine wave. A zero crossing switch solves this problem by monitoring the sine wave to make sure that capacitor switching occurs as close as possible to the zero crossing timing of the sine wave.

Figure 3. Zero crossing

Of course UPS and SPD systems are also very effective at reducing the harm that oscillatory transients can do, especially between common data processing equipment such as computers in a network. However, SPD and UPS devices can sometimes not prevent the intersystem occurrences of oscillatory transients that a zero crossing switch and/or choke type device can prevent on specialized equipment, such as manufacturing floor machinery and there control systems.

2.2 Interruptions

An interruption [3] is defined as the complete loss of supply voltage or load current. Depending on its duration, an interruption is categorized as instantaneous, momentary, temporary, or sustained. Duration range for interruption types are as follows:

Instantaneous 0.5 to 30 cycles

Momentary 30 cycles to 2 seconds

Temporary 2 seconds to 2 minutes

Sustained Greater than 2 minutes

Figure 4. Momentary interruption

The causes of interruptions can vary, but are usually the result of some type of electrical supply grid damage, such as lightning strikes, animals, trees, vehicle accidents, destructive weather (high winds, heavy snow or ice on lines, etc.), equipment failure, or a basic circuit breaker tripping. While the utility infrastructure is designed to automatically compensate for many of these problems, it is not infallible.

We probably experienced an interruption if we have ever seen all the power in our house go out (all lights and electronics), just to have everything come back on a few minutes later while we're breaking out the candles. Of course, having the power go out in our house, even if it lasts all night, may be only an inconvenience, but for businesses it can also cause great expense.

Solutions to help against interruptions vary, both in effectiveness and cost. The first effort should go into eliminating or reducing the likelihood of potential problems. Good design and maintenance of utility systems are, of course, essential. This also applies to the industrial customer's system design, which is often as extensive and vulnerable as the utility system.

It's probably safe to say that we are experiencing a sustained interruption if the power has been off for more than two minutes, and we see utility trucks appear shortly after to repair utility lines outside.

3.1. Sag /Undervoltage

Sag is a reduction of AC voltage at a given frequency for the duration of 0.5 cycles to 1 minute's time. Sags are usually caused by system faults, and are also often the result of switching on loads with heavy startup currents.

Figure 5. Sag

Common causes of sags include starting large loads (such as one might see when they first start up a large air conditioning unit) and remote fault clearing performed by utility equipment. Similarly, the starting of large motors inside an industrial facility can result in significant voltage drop (sag). A motor can draw six times its normal running current, or more, while starting. Creating a large and sudden electrical load such as this will likely cause a significant voltage drop to the rest of the circuit it resides on. Imagine someone turning on all the water in our house while we're in the shower. The water would probably run cold and the water pressure would drop. Of course, to solve this problem, we might have a second water heater that is dedicated to the shower. The same holds true for circuits with large startup loads that create a large inrush current draw.

3.2 Swell /overvoltage

While it may be the most effective solution, adding a dedicated circuit for large startup loads may not always be practical or economical, especially if a whole facility has a myriad of large startup loads. Other solutions to large starting loads include alternative power starting sources that do not load the rest of the electrical infrastructure at motor startup such as, reduced-voltage starters, with either autotransformers, or star-delta configurations. A solid- state type of soft starter is also available and is effective at reducing the voltage sag at motor start-up. Most recently, adjustable speed drives (ASDs), which vary the speed of a motor in accordance with the load (along with other uses), have been used to control the industrial process more efficiently and economically, and as an additional benefit, addresses the problem of large motor starting.

As mentioned in the Interruptions section, the attempt of the utility infrastructure to clear remote faults can cause problems for end users. When this problem is more evident it is seen as an interruption. However, it can also manifest itself as sag for problems that are cleared more quickly or that are momentarily recurring. Some of the same techniques that were used to address interruptions can be utilized to address voltage sags: UPS equipment, motor generators, and system design techniques. However, sometimes the damage being caused by sags is not apparent until the results are seen over time (damaged equipment, data corruption, errors in industrial processing).

3.3. Undervoltage

Under voltages are the results of long-term problems that create sags. The term "brownout" has been commonly used to describe this problem, and has been superseded by the term Undervoltage. Brownout is ambiguous in that it also refers to commercial power delivery strategy during periods of extended high demand [4]. Undervoltage can create overheating in motors, and can lead to the failure of non-linear loads such as computer power supplies. The solution for sags also applies to Undervoltage. However, a UPS with the ability to adjust voltage using an inverter first before using battery power will prevent the need to replace UPS batteries as often. More importantly, if an Undervoltage remains constant, it may be a sign of a serious equipment fault, configuration problem, or that the utility supply needs to be addressed.

Figure 6. Undervoltage

A swell is the reverse form of sag, having an increase in AC voltage for duration of 0.5 cycles to 1 minute's time. For swells, high-impedance neutral connections, sudden (especially large) load reductions, and a single-phase fault on a three-phase system are common sources.

Figure 7. Swell

The result can be data errors, flickering of lights, degradation of electrical contacts, semiconductor damage in electronics, and insulation degradation. Power line conditioners, UPS systems, and ferroresonant "control" transformers are common solutions.

Much like sags, swells may not be apparent until their results are seen. Having UPS and/or power conditioning devices that also monitor and log incoming power events will help to measure when, and how often, these events occur.

3.4. Overvoltage

Overvoltages can be the result of long-term problems that create swells. An overvoltage can be thought of as an extended swell. Overvoltages are also common in areas where supply transformer tap settings are set incorrectly and loads have been reduced. This is common in seasonal regions where communities reduce in power usage during off-season and the output set for the high usage part of the season is still being supplied even though the power need is much smaller. It's like putting our thumb over the end of a garden hose. The pressure increases because the hole where the water comes out has been made smaller, even though the amount of water coming out of the hose remains the same. Overvoltage conditions can create high current draw and cause the unnecessary tripping of downstream circuit breakers, as well as overheating and putting stress on equipment.

Figure 8. Overvoltage

3.5. Waveform distortion

Since an overvoltage is really just a constant swell, the same UPS or conditioning equipment that works for swells will work for overvoltages. However, if the incoming power is constantly in an overvoltage condition, then the utility power to our facility may need correction as well. The same symptoms for swells also apply to overvoltages. Since overvoltages can be more constant, excess heat may be an outward indication of an overvoltage. Equipment (under normal environmental conditions and usage), which normally produces a certain amount of heat, may suddenly increase in heat output because of the stress caused by an overvoltage. This may be detrimental in a tightly packed data center environment. Heat and its effect on today's data centers, with their many tightly packed blade server type environments, is of great concern to the IT community.

There are five primary types of waveform distortion:

1. DC offset

Direct current (DC) can be induced into an AC distribution system, often due to failure of rectifiers within the many AC to DC conversion technologies that have proliferated modern equipment. DC can traverse the ac power system and add unwanted current to devices already operating at their rated level. Overheating and saturation of transformers can be the result of circulating DC currents. When a transformer saturates, it not only gets hot, but also is unable to deliver full power to the load, and the subsequent waveform distortion can create further instability in electronic load equipment.

Figure 9. DC offset

The solution to DC offset problems is to replace the faulty equipment that is the source of the problem. Having very modular, user replaceable, equipment can greatly increase the ease to resolve DC offset problems caused by faulty equipment, with less costs than may usually be needed for specialized repair labor.

2. Harmonics

Harmonic distortion [5] is the corruption of the fundamental sine wave at frequencies that are multiples of the fundamental. (e.g., 180 Hz is the third harmonic of a 60 Hz fundamental frequency; 3 X 60 = 180).

Symptoms of harmonic problems include overheated transformers, neutral conductors, and other electrical distribution equipment, as well as the tripping of circuit breakers and loss of synchronization on timing circuits that are dependent upon a clean sine wave trigger at the zero crossover point.

Harmonic distortion has been a significant problem with IT equipment in the past, due to the nature of switch-mode power supplies (SMPS). These non-linear loads, and many other capacitive designs, instead of drawing current over each full half cycle, "sip" power at each positive and negative peak of the voltage wave. The return current, because it is only short- term, (approximately 1/3 of a cycle) combines on the neutral with all other returns from SMPS using each of the three phases in the typical distribution system. Instead of subtracting, the pulsed neutral currents add together, creating very high neutral currents, at a theoretical maximum of 1.73 times the maximum phase current. An overloaded neutral can lead to extremely high voltages on the legs of the distribution power, leading to heavy damage to attached equipment. At the same time, the load for these multiple SMPS is drawn at the very peaks of each voltage half-cycle, which has often led to transformer saturation and consequent overheating.

Figure 10. Harmonic Waveform Distortions

3. Interharmonics

Interharmonics are a type of waveform distortion that are usually the result of a signal imposed on the supply voltage by electrical equipment such as static frequency converters, induction motors and arcing devices. Cycloconverters (which control large linear motors used in rolling mill, cement, and mining equipment), create some of the most significant Interharmonics supply power problems. These devices transform the supply voltage into an AC voltage of a frequency lower or higher than that of the supply frequency.

The most noticeable effect of Interharmonics is visual flickering of displays and incandescent lights, as well as causing possible heat and communication interference.

Figure 11.

Interharmonics waveform distortion

Solutions to Interharmonics include filters, UPS systems, and line conditioners.

4. Notching

Notching is a periodic voltage disturbance caused by electronic devices, such as variable speed drives, light dimmers and arc welders under normal operation. This problem could be described as a transient impulse problem, but because the notches are periodic over each ½ cycle, notching is considered a waveform distortion problem. The usual consequences of notching are system halts, data loss, and data transmission problems.

One solution to notching is to move the load away from the equipment causing the problem (if possible). UPSs and filter equipment are also viable solutions to notching if equipment cannot be relocated.

5. Noise

Noise is unwanted voltage or current superimposed on the power system voltage or current waveform. Noise can be generated by power electronic devices, control circuits, arc welders, switching power supplies, radio transmitters and so on. Poorly grounded sites make the system more susceptible to noise. Noise can cause technical equipment problems such as data errors, equipment malfunction, long-term component failure, hard disk failure, and distorted video displays.

Figure 12. Noise

There are many different approaches to controlling noise and sometimes it is necessary to use several different techniques together to achieve the required result.

Data corruption is one of the most common results of noise. EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) can create inductance (induced current and voltage) on systems that carry data. Since the data is traveling in digital format (ones and zeros that are represented by a voltage, or lack of voltage), excess voltage above data operating levels can make the appearance of data that does not belong or the opposite.

The solution to this particular problem involves moving data carrying devices and/or cabling away from the source of EMI/RFI, or to provide additional shielding for the data devices and/or their cabling to reduce, or nullify, the effects of the EMI/RFI.

3.6. Voltage fluctuations

Since voltage fluctuations are fundamentally different from the rest of the waveform anomalies, they are placed in their own category. A voltage fluctuation is a systematic variation of the voltage waveform or a series of random voltage changes, of small dimensions, namely 95 to 105% of nominal at a low frequency, generally below 25 Hz.

Figure 13. Voltage fluctuations

Any load exhibiting significant current variations can cause voltage fluctuations. Arc furnaces are the most common cause of voltage fluctuation on the transmission and distribution system. One symptom of this problem is flickering of incandescent lamps. Removing the offending load, relocating the sensitive equipment, or installing power line conditioning or UPS devices, are methods to resolve this problem.

3.7. Frequency variations

Frequency variation [6] is extremely rare in stable utility power systems, especially systems interconnected via a power grid. Where sites have dedicated standby generators or poor power infrastructure, frequency variation is more common especially if the generator is heavily loaded. IT equipment is frequency tolerant, and generally not affected by minor shifts in local generator frequency. What would be affected would be any motor device or sensitive device that relies on steady regular cycling of power over time. Frequency variations may cause a motor to run faster or slower to match the frequency of the input power. This would cause the motor to run inefficiently and/or lead to added heat and degradation of the motor through increased motor speed and/or additional current draw.

Figure 14. Frequency variations


The average value of the output voltage is obtained as follows. Let the supply voltage be   VS = E x Sin (α), where α varies from 0 to 2ω radians. Since the output waveform repeats itself for every half-cycle, the average output voltage is expressed as a function of ω, the firing angle, as shown in equation (1).  The R.M.S. value of output voltage is obtained as shown in equation (2). The ripple factor in output voltage can be defined in two ways. The definition followed in this text as illustrated in equation (3). The maximum average output voltage occurs at a firing angle of 0o. Let it be Vom. Then the ripple factor RF (α) is defined as shown in equation (3).


The alternate definition uses Vo, avg (α) as the denominator instead of Vom. If Vo, avg (α) is used as the denominator, then RF (α) can tend to infinity. It is more logical to express the ripple content as a fraction of the maximum average voltage. The variation of average output voltage, R.M.S output voltage and ripple factor with the firing angle have been shown below. The plots shown below have been normalized with respect to Vom. For example, when the firing angle is 90o, the average output is shown to be 0.5. It means that the actual average output voltage is 0.5Vom. It can also be seen that when the firing angle is 0o, the R.M.S. output voltage is about 1.1Vom and the ripple factor is about 0.48. The ripple factor increases as the firing angle increases. It increases to 0.658 at a firing angle of 65o and then it falls as the firing angle increases further. At the firing angle of 65o, the R.M.S. ripple voltage in the output is 0.658Vom. For a sinusoidal source of 240 V R.M.S., the maximum R.M.S. ripple voltage works out to be 142 V.

4.1. Performance Parameters

As it contains some fundamental component and harmonics. For the output voltage, its ripple content is the performance criterion. It would be desirable to obtain the amplitude frequency spectrum of the output in order to design a suitable filter circuit. 

As far as the ac source is concerned, the distortion in the source current is the performance criterion. The total harmonic distortion (THD) or the harmonic factor, the amplitude frequency spectrum of the source current, the apparent power factor and the displacement power factor have also to be computed.

Given a periodic function f (t) with a period of T, f (t) can be described by a trigonometric Fourier series, as shown in equation (4).   The coefficients are defined as shown in equations (5), (6) and (7).

The source frequency, f, is taken as the fundamental frequency and hence ω o = 2 ω f. It is preferable to express the above equation in terms of angle α, where α = ω o t. If T is the cycle period, ω o T = 2 ω f T = 2 ω, since f = 1/T. Then the equations for the Fourier coefficients can be expressed as shown in equations (8), (9) and (10).

In the case of the full-wave, the period of the output is only half that of the input sinusoidal source and hence the output contains a dc component and even harmonics only. The source current has half-wave symmetry. A waveform defined as f (t) over a cycle is said to have half-wave symmetry if it satisfies equation (11).  A waveform with half-wave symmetry contains a fundamental component and odd harmonics only.

Let the Fourier coefficients for the output voltage be av0 (α), av2n (α) and bv2n (α), where α is the firing angle and these coefficients are evaluated as shown in equations (12), (13) and (14). Since the output repeats itself twice for every cycle of source voltage, it contains only even harmonics.   Then we obtain the amplitude of the harmonic as shown in equation (16).

Let the Fourier coefficients for the source current be acur0 (α), acur2n (α) and bcur2n (α). The line current waveform has half-wave symmetry and contains only odd harmonics. Then, load current iLine (α) is defined by equation (17).

The R.M.S. source current can be computed from the value obtained for the output voltage, as shown in equation (22).  Then the total harmonic distortion is defined by equation (23). Let the R.M.S current when the firing angle is 0o be IR.M.S, max. Since the waveform of the source current is purely sinusoidal when the firing angle is 0o, the crest factor can be taken to be square root of 2. The program that simulates the operation of this circuit computes the various values for a given firing angle and displays them in a suitable manner.

The displacement power factor, DPF, is the cosine of the angle by which the fundamental component of the line current lags the source voltage. Then apparent power factor can be estimated as shown in equation (24).

4.2. Simulation

The firing angle has to be keyed-in. Then click on Compute button. The plots for voltage have been normalized with respect to Vom and the currents with respect to IR.M.S, max. The statistical details related to the output voltage have been normalized with respect to Vom and those related to the source current with respect to IR.M.S,max. The amplitude of each harmonic in the output voltage has been normalized with respect to E which is the amplitude of the source voltage, whereas the amplitude of each harmonics in the source current has been normalized with respect to E/R.

The circuit used for Pspice simulation is shown below.  All the nodes other than the datum node are connected to the datum node through a 1 MΩ resistor.  A floating node or a node that tends to float can be a problem for Pspice simulation.

Figure 15. Full wave bridge rectifier

The program is presented below.

  * Full-wave Bridge Rectifier

VIN 1 0 SIN (0 340V 50Hz)

XT1 1 2 5 2 SCR

XT2 0 2 6 2 SCR

XT3 3 0 7 0 SCR

XT4 3 1 8 1 SCR

VP1 5 2 PULSE (0 10 1667U 1N 1N 100U 20M)

VP2 6 2 PULSE (0 10 11667U 1N 1N 100U 20M)

VP3 7 0 PULSE (0 10 1667U 1N 1N 100U 20M)

VP4 8 1 PULSE (0 10 1167U 1N 1N 100U 20M)

R1 2 3 10

R2 1 0 1MEG

R3 2 0 1MEG

R4 3 0 1MEG

* Sub circuit for SCR

.SUBCKT SCR 101 102 103 102

S1 101 105 106 102 SMOD

RG 103 104 50

VX 104 102 DC 0

VY 105 107 DC 0

DT 107 102 DMOD

RT 106 102 1

CT 106 102 10U

F1 102 106 POLY (2) VX VY 0 50 11


.MODEL DMOD D ((IS=2.2E-15 BV=1200 TT=0 CJO=0)


.TRAN 10US 60.0MS 20.0MS 10US

.FOUR 50 V (2, 3) I (VIN)





The waveforms obtained are presented below.

 Figure 16. Voltage waveform across the load resistor

Figure 17. Voltage Waveform across SCR1

Figure 18. Average Load Current

Figure 19.Frequency spectrum of line current

Figure 20.Frequency spectrum of output voltage


The widespread use of electronics has raised the awareness of power quality and its affect on the critical electrical equipment that businesses use. Our world is increasingly run by small microprocessors that are sensitive to even small electrical fluctuations. These micro- processors can control blazingly fast automated robotic assembly and packaging line systems that cannot afford downtime. Economical solutions are available to limit, or eliminate, the affects of power quality disturbances. However, in order for the industry to communicate and understand power disturbances and how to prevent them, common terms and definitions are needed to describe the different phenomena.

Reducing equipment downtime and production expense, therefore increasing profit is the goal of any size business. Communicating by understanding the electrical environment, and equipment's susceptibility to power quality disturbances, will help in the discovery of better methods to achieve business goals and dreams.

Systematic procedures for evaluating power quality concerns can be developed but they must include all levels of the system, form the transmission system to the end user facilities. Power quality problems show up as impacts within the end user facility but may involve interaction between all levels of the system.

A consistent set of definitions for different types of power quality variations is the starting point for developing evaluation procedures. The definitions permit standardized measurements and evaluations across different systems. A data analysis system for power quality measurements should be able to process data from a variety of instruments and support a range of applications for processing data. With continuous power quality monitoring, it is very important to be able to summarize variations with time trends and statistics, in addition to characterizing individual events.


The authors wish to thank the Principal of S.S.G.B.C.O.E.T. Bhusawal and H.O.D. of Electronics & Communication Engineering Dept also, thanks to all teaching staff and non teaching staff for supporting this work.