Saturday, 16 September 2017

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Design And Construction Of 2kva Pure Sine Wave Inverter



An inverter is a device that changes D.C. voltage into A.C. voltage. A direct current (D.C) is a current that flows in only one direction, while an alternating current (A.C.) is that which flows in both positive and negative directions. Inverters are used to operate electrical equipment from the power produced by a car or boat battery or renewable energy sources, like solar panels or wind turbines. DC power is what batteries store, while AC power is what most electrical appliances need to run. So, an inverter is necessary to convert the power into a usable form.

The output voltage of a sine-wave inverter has a sine wave-form like the sine wave-form of the mains / utility voltage. In a sine wave, the voltage rises and falls smoothly with a smoothly changing phase angle and also changes its polarity instantly when it crosses 0 Volts.

Pure sine wave inverters are used to operate sensitive electronic devices that require high quality waveform with little harmonic distortion. In addition, they have high surge capacity which means they are able to exceed their rated wattage for a limited time. This enables power motors to start easily which can draw up to seven times their rated wattage during start up. Virtually any electronic device will operate with the output from a pure sine wave inverter.

Sine wave inverter has the following characteristics:
  1. High efficiency
  2. Low standby losses
  3. High surge capacity
  4. Low harmonic distortion
All grid tied inverters are pure sine (true sine) inverters, hence the grid, by nature, is a pure sine 
wave electricity source. The importance of pure sine wave inverters may be apparent especially for off grid applications such as RV, boat or cabins. Off grid inverters are used for connecting a battery source or a solar PV system to an AC load such as a home appliance, a laptop charger, a TV.


Pulse Modulated Wave Inverters

The most common generally used inverters available are the “modified square wave or pulse modulated wave inverters” variety, usually available at more moderate prices compared to pure wave models. The modified square wave or PWM output inverters are designed to have somewhat better characteristics than square wave units, while still relatively inexpensive.

Although designed to emulate the pure sine wave output, pulse modulated wave inverters do not offer the same perfect electrical output. As such, a negative by-product of the modified output units is electrical noise (hum) which can prevent these inverters from powering certain loads properly. For example, many televisions and stereos are sensitive to supplied power, use power supply incapable of eliminating common mode noise.
As a result, powering such equipment with a pulse modulated wave inverter may cause a small amount of “snow” on your video picture, or “hum” on your sound system, likewise most appliances with timing devices, battery chargers and variable speed devices may not work well or sometimes may not work at all.

Since the width of the square wave can be adjusted, the rate at which pulse is produced can be controlled using “pulse width control”, and since the pulse in not in ON position at all times (i.e. it has a dead time) the heat produced is almost one quarter that of the square wave inverter. The “dead time” in the pulse width modulator can be said to be the time at which the transistor is not ON thereby reducing the heat produced by the transistor. (Doucet et al, 2007)

Pulse width modulation (PWM) is a powerful technique for controlling analogue with a processor’s digital outputs. . It is also known as pulse duration modulation (PDM). The leading edge of the carrier pulse remains fixed and the occurrence of the trailing of the pulses varies. PWM signals find a wide application in modern electronics. Some of the reasons for this are:

1. Reduced Power Loss – switched circuits tend to have lower power consumption because the switching devices are almost always off (low current means low power) or hard-on (low voltage drop means low power). Common circuits that utilize this feature include switched-mode power supplies, Class D audio power amplifiers, power inverters and motor drivers. Frequently, these circuits use semi-analogue techniques (ramps and comparators) rather than digital techniques, but the advantages still hold.

2. Easy to Generate – PWM signals are quite easy to generate. Many modern microcontrollers include PWM hardware within the chip; using this hardware often takes very little attention from the microprocessor and it can run in the background without interfering with executing code. PWM signals are also quite easy to create directly from a comparator only requiring the carrier and the modulating signals input into the comparator.

3. Digital to Analogue Conversion – pulse width modulation can function effectively, as a digital to analogue converter, particularly combined with appropriate filtering. The fact that the duty cycle of a PWM signal can be accurately controlled by simple counting procedures is one of the reasons why PWM signals can be used to accomplish digital-to-analogue conversion.
The desired PWM technique should have the following characteristics.

  • Good utilization of DC supplies voltage possibly a high voltage gain.  
  • Linearity of voltage control.
  • Low amplitude of low order harmonic of output voltage to minimize the harmonic content of output currents.
  •  Low switching losses in inverter switches.
  •   Sufficient time allowance for proper operation of the inverter switches and control system.

There are many types of PWM techniques used in sine wave inverters. The commonly used techniques are:

Single or 2 level PWM; 

It’s the simplest way of producing the PWM signal. It’s through comparison of a low-power

reference sine wave with a triangle wave as shown in figure 3. Using these two signals as input to a
comparator the output will be a 2-level PWM signal as shown in figure 2.2.1. It is the most common
and popular technique of pulse-width-modulation (PWM).
 A Two-Level PWM

The harmonic content can be reduced significantly by using several pulses in each half- cycle of the output voltage. There exist different levels of multiphase PWM producing an improved output with increase of the level of the PWM used. The most common ones are: 3 levels PWM, 5 levels PWM, 7 levels PWM and 9 levels PWM. The choice of which PWM level to use is determined by the cost of the inverter and the quality of the output. To balance between cost and quality of the inverter, a 3level PWM is commonly used.
A Three level PWM.

Comparing the 3-level PWM to the 2-level PWM, the harmonics plot shows no higher level harmonics of significant magnitude. This represents the 3-Level signal following much more closely the desired sine wave. However, the primary frequency has a much lower voltage magnitude than that of the 2-Level design. The reason for this is the presence of other frequencies which are not harmonics of the 50Hz signal, which are caused by the switching of the signal from one polarity to the other, and back.

In electronic power converters and motors, PWM is used extensively as a means of powering alternating current (AC) devices with an available direct current (DC) source or for advanced DC/AC conversion. Variation of duty cycle in the PWM signal to provide a DC voltage across the load in a specific pattern will appear to the load as an AC signal, or can control the speed of motors that would otherwise run only at full speed or off. The pattern at which the duty cycle of a PWM signal varies can be created through simple analogue components, a digital microcontroller, or specific PWM integrated circuits.

Analogue PWM control requires the generation of both reference and carrier signals that feed into a comparator which creates output signals based on the difference between the signals. The reference signal is sinusoidal and at the frequency of the desired output signal, while the carrier signal is often either a saw tooth or triangular wave at a frequency significantly greater than the reference. When the carrier signal exceeds the reference, the comparator output signal is at one state, and when the reference is at a higher voltage, the output is at its second state. This process is shown in Figure 3 with the triangular carrier wave in black, sinusoidal reference wave in blue, and modulated and unmodulated sine pulses.

A digital microcontroller PWM requires a reference signal, sometimes called a modulating or control signal, which is a sinusoidal in this case; and a carrier signal, which is a triangular wave that controls the switching frequency. Microcontroller modules are used to compare the two to give a PWM signal.

The applications of PWM are wide variety used like ranging from measurement and communications to power control and conversion. In PWM inverter harmonics will be much higher frequencies than for a square wave, making filtering easier.

In PWM, the amplitude of the output voltage can be controlled with the modulating waveforms. Reduced filter requirements to decrease harmonics and the control of the output voltage amplitude are two distinct advantages of PWM. Disadvantages include more complex control circuits for the switches and increased losses due to more frequent switching. (Mburu, 2014)


Square, Modified and Pure Sine Wave Inverters

On the market today are two different types of power inverters, modified sine wave and pure sine wave generators. These inverters differ in their outputs, providing varying levels of efficiency and distortion that can affect electronic devices in different ways.

A modified sine wave is similar to a square wave but instead has a “stepping” look to it that relates more in shape to a sine wave. This can be seen in Figure 2.2.2 below, which displays how a modified sine wave tries to emulate the sine wave itself. The waveform is easy to produce because it is just the product of switching between 3 values at set frequencies, thereby leaving out the more complicated circuitry needed for a pure sine wave. The modified sine wave inverter provides a cheap and easy solution to powering devices that need AC power. It does have some drawbacks as not all devices work properly on a modified sine wave, products such as computers and medical equipment are not resistant to the distortion of the signal and must be run off of a pure sine wave power source. (Doucet et al, 2007)

The sine wave inverters provide electrical power similar to the utility power received. It is highly reliable and does not produce noise interference associated with other types of inverters. With its “perfect” sine wave output, the power produced by the inverter fully assures that sensitive loads will be correctly powered with no interference. Some appliances which are likely to require pure sine wave include computers, battery chargers, variable speed motors, and audio /visual equipments. (Doucet et al, 2007)

Square Modified and Pure sine wave


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Thursday, 10 August 2017

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Revealed: An Overview of Artificial Intelligence

Artificial intelligence

Artificial Intelligence 

Inventing machines that have closer characteristics to human beings have become major goal of scientists till date.

The machines are made using computational  models that act and think in a rational manner. This Inventions are a mere sign of evolution.

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Monday, 7 August 2017

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4 tips for teaching your child science

Teaching your child science

How to get your child interested in science? 

All this points to the manner they grow up and also how their minds are built as they grow older .   In other words, if your children are growing up in an environment that challenges them critically, this would help in their development as an individual. The children at an early age should watch basic science programs, be encouraged to carry out experiments, read and reason. All these would build up the child's interest and even raise their I.Q. 

In choosing the best activities and resources for your kids, always try as much as possible to break things down to the simplest of terms that they can understand or relate to. 

You don't have to know much about science to be able to teach your kids science. The World is changing everyday and so it's advisable for your kids to know exactly what is going on around them. You can do this by controlling what they read at that young age,  get them basic science related books with pictures and read it to them from time to time.

It is also good as a parent to develop some interest in science as well as kids mostly emulate what they see you doing.

Whenever you are at home or you take your children out, instill that curiosity in them. Ask them a lot of questions about the things in their environment and generally what they see everyday. What is that? How do you think that works? Why did that happen? Then let them answer, don't  scold them if they get it wrong, rather correct them in a subtle way. This will help improve their confidence, and help you to determine just what your child has knowledge about.

The only way they would take you seriously is if you take interest in their activities. The aim here is to develop them intellectually, to enable them think and question everything. For example, if your child likes ball sports ask him, why the ball always comes down when he throws it up? or if it's a child that likes to bake ask, why the cake rises? What causes it to rise? etc.

Other tips include..

Choose the Activities

An average child does not think of doing anything productive on their own. That is why it comes down to you as their parent to engage them in simple science activities. You don't what to frustrate them with science by engaging them in hard activities.

Ask the child's opinion

Children learn and accept things better when its within the scope of what they know and love already. So before engaging the children in an activity suggest two or three options that they can choose from. The more it entices their interest, the more they will enjoy the activity.

Visit places

Studies have shown that people assimilate things they see visually compared to what they have heard. It is better to go out on vacation to remote environments to appreciate nature more, to a zoo, a convention or museum. The places a child visits also plays a role on how they develop their minds and their I.Q.

Build on a particular interest

There are different branches of science that exist. After carrying out projects, study your child's response to them. Every child is different and has different interest. Then the books or toys you buy don't have to restrict to a particular age,  because now they will learning at a rate set by their interest.

Just remember to be creative when trying to get your child interested in science. Many great men and women of science have done great things in the world we presently live.
I developed my interest in high school and not from my parents. At the end of the day it depends on the child, but as a parent you should at least try (No harm in that).

If you have any suggestions or additions, kindly comment below.

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Sunday, 30 July 2017

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Physics: static electricity, electric charges and law of charges.

What is electricity?

     The is a form of energy that occurs when electrons flows through a conductor.

Areas Covered

  • Definition of static electricity
  • Nature of atoms of static electricity
  • Electricity charges
  • Law of charges
  • Conductor and insulator

Definition of static electricity

     Static electricity is  produced by the friction between two materials. For example, when rod is rubbed with silk.

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Reservoir Fluid & rocks: Natural gas, crude oil composition and Properties of reservoir rocks

oil distribution
Reservoir fluid distribution.

Reservoir science

 A reservoir science is the science of the study of porous rock and accumulated fluid (Petroleum + water). Reservoirs are formed from the consolidation of permeable sediments moved and deposited by fluid medium on the earth surface from a ‘source rock’.

All reservoirs are of the sedimentary structure and hydrocarbons are trapped within the structure by deformation force upon layers at high temperature (structural trap) or by the depositional environmental changes in lithology.

Reservoir fluids

Composition and properties

   Petroleum: This consists of natural gas, crude oil ,condensate  and constituents (Nitrogen oxide, hydrogen sulfide, carbon (iv) oxide etc). It is referred to as a mixture which is complex, of hydrocarbons (compounds containing hydrogen and oxygen only) and other constituents depending on composition, temperature, pressure etc.

Natural gas:

This is a mixture of individual gas component. Such as;
  • Dry Gas: No liquid just methane.
  • Wet gas: contains liquid droplet with an API gravity of 50-70°API.
  • Acid gas: contains carbon (iv) oxide.
  • Sweet gas: Does not contain hydrogen sulfide.
  • Sour gas: contains hydrogen sulfide.

Properties of Natural gas: 

    Apparent molecular weight, Density, Specific gravity, Specific volume, Gas formation volume factor, Gas isothermal compressibility etc.

Crude oil

  This is a hydrocarbon mixture of individual oil components. The quality is measured in terms of API gravity.
  •     Bitumen: 10°API
  •     Heavy oil: 20 -25°API
  •     Black oil: 30-40°API
  •     Volatile oil: 40-50°API

Properties of crude oil: 

Fluid gravity, Oil density, Oil formation volume factor, Specify gravity, Surface tension, Isothermal compressibility, Total formation volume factor etc.


  Gas condensate are hydrocarbon in which at certain conditions of temperature and pressure has led to the condensation of heavy gas in the reservoir. It occurs at critical temperature and pressure conditions.

Reservoir rocks: 

All reservoir rocks are sedimentary rocks for example sandstone, carbonate, evaporates etc. Other types of rocks like; Igneous and sedimentary rocks cannot form reservoir rock because of their source of formation, structure and properties.

Classification of reservoir rocks includes

             According to Lithology
        Sand stones
          According to Strength
        Partially Consolidated
          According to Pressure
                  -- Normal Pressure
                  -- Abnormal Pressure
                 -- Subnormal
                 -- Geo pressured
          According to Fluid Content
                 -- Gas Reservoir
                 -- Oil Reservoir
                 -- Condensate Reservoir
                 -- Multiphase Reservoir

Properties of reservoir rocks includes

Flow properties
  • Porosity: This refers to the fractional void space within the reservoir rock that is available for storing fluid.

        Porosity = pore volume/bulk volume

  • Permeability (K): this is a property of porous medium which measures capability of rock formation to transmit fluid. It is the interconnection of void spaces to enable transmission or flow of fluids. Its S.I unit is in Darcy.

Elastic properties
   This is related to the strength of rock. It is the reversible deformation by the action of stress under a given external or internal pressure . It includes; stress, strain Poisson Ratio ,Bulk Modulus (Function of Change in Volume) , Shear Modulus (Function of Change in Shape) , Compression Strength etc

Electrical properties
           These properties help to measure the value of Voltage Resistance and measure of ease with which current will pass through. They include; Resistivity, Conductivity.

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Monday, 22 May 2017

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Hazards in chemical process industries - Chemical hazard

Chemical hazard

What are hazards?

 Situations that poses a threat or causes harm to people, the environment, or property.

 What is Industrial hazard? -

Any condition produced by industries that may case injury or death to personnel or loss of property. Hazards may be dormant, armed or active.


 Prioritisation of hazards involves making visible all risks in an operation, the probability of occurrence and the potential damage.

 Then, what is Chemical Hazard: 

     This is a type of occupational hazard caused by exposure to chemicals in the workplace. It is any chemical that can cause illness, injury, or an emergency.

 It can be divided into; Physical and health risk Chemical hazard may be: Toxic, corrosive, irritant, carcinogenic, mutagens, flammable etc.
Physical and health hazard

Many chemical may cause severe burns, if they come in contact with living tissue. Routes to exposure ingestion inhalation from fumes poisoning explosion

    Duration of Exposure of chemicals

Acute - Short Minutes to hours.
Sub acute - Longer up to 90 days
Chronic - Prolonged /Repeated over days, months & years.
    The effect of the chemicals is independent on duration of exposure, but dependent on concentration and type of chemicals exposed.

Safety measures

1) Wear all required PP Es (professional protective equipment) such as: hand gloves, helmets, eye goggles, safety boots and so on, depending if you will be working with a solid, liquid or gaseous form of hazardous chemicals.

2) Identify the hazardous characteristics of a chemicals using a safety data sheet or a pictogram to know how best to handle them.


 Hazardous-waste management is the treatment and disposal of waste that has the ability of causing harm and damage to people, property or environment if it is left untreated or wrong fully disposed.

Characteristics of untreated hazardous waste.

  • Reactivity 
  • Radioactivity 
  • Ignitable 
  • Corrosive 
  • Infectiousness 
  • Toxicity

Watch this self explanatory video

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Wednesday, 17 May 2017

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Cohesive and Adhesive forces: Definition, differences and effects.

Cohesive vs adhesive force

Adhesion and cohesion

Someone emailed me and suggested do a piece on this topic. Well, for easy understanding of the concept of cohesion and adhesion force, i wrote this brief post.

Happy Learning!


  The force of attraction between the molecule of the same substance is called cohesion force.
 The force of attraction between the molecules of different substance is called adhesion force.

     Water has both adhesive and cohesive properties. Adhesion of water to glass is stronger than the cohesion of water. hence, when water is spill ed on a clean glass surface it wets the glass.

On the other hand, the cohesion of mercury is greater than the adhesion to glass. Thus, when mercury is spill ed on glass it forms small spherical droplet or larger flattened droplets and does not wet glass.
Mercury forming a small spherical droplet on glass.

Effects of Cohesion

1) Surface tension: This is a property of liquid that gives it an elastic surface, this is as a result of cohesive forces between adjacent molecules. Here, the molecules at the main body of liquid are pulled equally in allowing directions by neighbouring molecules.
       Water because of this property, heavier objects with less force compared to surface tension to float across it.

2) Meniscus: This is the property of liquid that gives it a curved surface. It has both cohesive and adhesive properties.

Meniscus property at the surface forming a concave and convex curve.

     If the cohesive forces between the liquid molecules is greater than its adhesive force, the surface will form a convex curve.
     If the adhesive forces between the liquid molecules is greater than the cohesive forces, the surface will form a concave curve.

  If  both the adhesive and cohesive forces are equal, the surface is horizontal.

3)  Capillary  action: Here, the cohesive and adhesive forces work together to keep the liquid away from it's natural forces of gravity. The cohesive forces causes the water to form droplets and the adhesive forces keeps the drop in place.
Capillary action
Capillary action on leaves.

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Saturday, 8 April 2017

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Measuring instruments: Micrometre screw gauge vs vernier caliper

Vernier caliper and micrometer screw gauge

Measuring instruments: Micrometre screw gauge vs vernier calliper

What is measurement?

     This is the bedrock of the trade and statistics used for centuries now. It is the ability of one to ascertain the height, size and quantity of something by comparison.
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Sunday, 26 March 2017

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Physics: Introduction to radioactivity,types and properties.



It is a spontaneous emission of radiation from a substance usually an unstable   .This process is also known as nuclear or radioactive decay). In the year 1896, Henri Becquerel a French scientist working with phosphorescent materials discovered that a uranium compound placed on a photographic plate which was covered with light black paper causing the plate to be exposed by blackening the pate itself. This implied that some sort of radiation was coming from the uranium which could pass through. The material was radioactive given-off radiation. Other scientists that researched on radioactivity were;v This radioactivity was spontaneous with the radiation being omitted without anything causing it apparently.

Types of radioactivity

From several experiments that have been carried out, it has shown that there are three different types of radioactive emission called;
 Alpha particles ; whose emission is easily stopped by paper or thick card
 Beta particles ; whose emission is easily stopped by aluminium sheet of different thickness and are negatively charged.
Gamma particles ; whose emission is easily stopped by thick sheet of lead.

types of radioactivity

Properties of alpha particles

      1)  Alpha rays are deflected by magnetic field.  
      2)      The direction of deflection of alpha rays shows that they are positively charged
      3)      They are relatively massive and so have more momentum and tend to continue in their direction of travel.
      4)      Alpha particles are absorbed by paper and air and are easily stopped aluminium thin sheet.
      5)      They have little penetrating power, travelling no more than 5cm. Being large, it is soon stopped by air molecules.
      6)      They are capable of stripping electrons from their atoms because alpha particles have comparatively large mass and momentum.

Properties of beta particles

     1)      There are also deflected by magnetic field but in the opposite direction to alpha particles.
     2)      The direction of deflection of beta rays shows that they are negatively charged with –e .
     3)      They are relatively light and as a result easily deflected.
     4)      They are deflected by different amount showing that they have varying speed..
     5)      They have good penetrating power of about 1 metre.
     6)      They can penetrate a few millimetre of aluminium.
     7)      They produce less ionisation in air than alpha particles.

Properties of gamma rays

    1)      They are electromagnetic waves similar to light wave but of very short wavelength.
    2)      They are electrically uncharged since they are not deflected by a magnetic field.
    3)      They are highly penetrative compared to the other two types and can only be stopped by thick lead blocks.
   4)      They have high penetrating power compared to the other two types.
   5)      They have much less ionisation than alpha rays.
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Saturday, 18 March 2017

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Physical and chemical change; differences and definitions

All explanations are put in the simplest and easiest ways possible for fast comprehension. Enjoy.

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Sunday, 12 March 2017

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Physics: Thermal, linear, area and cubic expansivity

Thermal expansivity


 This is defined as amount a material expands or contracts per unit length, per-degree change in temperature.
The addition of heat will usually cause expansion of the body. during expansion, the dimension of the body increases.

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