Inductive and Capacitive Reactances

Inductive Reactance:

It is the opposition to the current flow in an AC circuit that contain only inductance element and we refer to it by the symbol (XL). If the circuit contains resistance and reactance, the total opposition to the current flow called impedance and we refer to it by the symbol (Z).

When an AC current passes throw an inductance, counter EMF is generated and trying to oppose changes in the current. This opposition is called inductive reactance (XL).

Inductive reactance is measured in ohm and proportional to the value of inductance and the value of the applied frequency according to the following formula:

XL = 2 π F L where π = 3.14, L =value of inductor in henry.

Z = √ (R²+XL² )

Phase relationship between applied voltage and current:

In pure resistive load, current and voltage are in phase (angle = 0) and in pure inductive load, the current lag the voltage by an angle equal to 90 degree and it said to be out of phase. In a circuit contain inductive reactance and resistance the current will lag the voltage by an angle in between (0) degree and (90) degree depending on the ratio between the amount of inductive reactance components to resistive components, as the more resistive component the more in phase relationship and vice versa.

Capacitive Reactance:

It is the opposition to the current flow in an AC circuit that contain only capacitive element and we refer to it by the symbol (XC). If the circuit contains resistance and capacitance, the total opposition to the current flow called impedance and we refer to it by the symbol (Z).

Capacitive reactance is measured in ohm and it increases when the value of capacitor capacitance decreased according to the following formula:

XC =1 / (2π F C)          where π = 3.14,   C = value of capacitance in farad.

Z = √ (R²+XC² )

Phase relationship between applied voltage and current:

In pure capacitive load, current lead voltage by an angle equal to 90 degree and it said to be out of phase. In a circuit contain capacitive reactance and resistance, the current will lead the voltage by an angle in between (0) degree and (90) degree depending on the ratio between the amount of capacitive reactance components to resistive components as the more resistive component the more in phase relationship and vice versa.

Electrical Resistance

It simply defines as the opposition to the current flow in an electric circuit .There are five factors that affect conductor resistance; "conductor length, conductor diameter, temperature, physical condition and conductor material type" let us know about each factor:

Conductor length:

When we apply a voltage on a conductor connected to a load, electrons will be pushed in the conductor to operate the load and the longer the conductor the more resistance of it and the more voltage drop on it. Conductors manufacturers commonly provide the buyer with ohms per km to realize the overall conductor resistance so if you need to replace a conductor, you should take in account the conductor length.

Conductor Diameter:

The more the conductor diameter, the less the conductor resistance and the more the current flow in the conductor. So if you need to install a conductor in an electrical circuit you must choose the proper size that fits circuit current flow.

Conductor Material Type:

The more free electrons in the conductor material, the less the conductor resistance and the more current carrying capability of the conductor like "copper, gold, silver and aluminum" materials which consider as less resistance materials and in the other hand, materials like rubber, glass, ceramic and plastics consider as a high resistance material due to the no presence of free electrons.

Temperature:

In the conductors when the wire temperature increase the electrons move faster but not in the correct direction and hence the resistance increase. But in insulators when the temperature increase the resistance decrease and in semiconductor devices when the temperature increase, the resistance decrease.

Physical Conditions:

This conditions are like, when we have partially cut on the conductor or when we have bad connection between conductors ….etc. All of this increases the resistance so you should take care of conditions like this. 

Electric Car

Now a day's large amount of petroleum fuels are consumed by cars, buses and other transportation means, so more interest has been given to reduce the consumed petroleum fuel or to use another type of renewable energy sources.

The scientists find that electricity is the most effective alternative fuel that can be used instead of the petroleum fuel to use in the transportation sector, in what they called "plug in hybrid car".

Electric car are now available for any one in the open market and it is expected that by the year 2016, most of car manufacturer will produce the plug in hybrid car in many models.

How can electric car work?

Electric cars store electricity in large batteries when we connect them to a wall outlet of standard 120 volt or standard 240 volt for anumber of hours.

These batteries operate an electric motor that power the wheels and when car driver uses the brake the electric motor work as a generator and recharge these batteries.

Advantages and disadvantages of electric car

Electric can has many benefits over the conventional car as it reduce the pollution resulting from the combustion engine and it reduces the dependence on the imported oil fuel which consider for many countries as a big problem that face their economic growth because of oil fuel high prices and its varying cost .

On the other hand electric car faces many limitations as it is more expensive than conventional car due to the additional cost of the batteries used in it. Also about the battery recharging process, it is rarely to found the private or public companies that will do that.

So governments should put the politics and economic incentives to encourage people to use electric cars instead of conventional cars and that already now done by some countries like, united stat and china governments.

Magnets Produce Electricity

Magnetic fields produced by magnets can move the free electrons for some metals like copper. When these free electrons move from their level in the atom, electrical current flow will be produced.

How can magnets produce electricity?

Electricity and magnetism are strongly linked to each other as electricity can generate magnetic fields and magnetic fields can generate electricity, when electricity is changed with respect to time, a magnetic field will produced and when magnetic field is changed with respect to time, electricity will be produced. This is called electromagnetism.

Electricity is generated at power plants which use huge turbine generators, these turbines use various types of fuels to move, they can use oil, natural gas or coal to generate steam flow power. Turbines can use uranium atoms split to heat water converting it also to steam which rotate them or they can get kinetic energy from water fall at dam or from wind.

What happened inside the generator to produce electricity?

The turbine is connected to a shaft in the generator and inside the generator; a magnets and coils of copper wires are present. In some designs the turbine move the magnets inside the coil and in another design the turbine moves the coil inside the magnets, in two cases the result is a varying magnetic field with a time that cut the copper wires and hence the free electrons in the copper conductors will move from one atom to another and electrical current will flow in the load connected to the generator.

In most cases the turbine shaft moves the copper wires inside the two big magnets as the first magnet has north pole to the front on one side and the second magnet on the other side has south pole to the front, the magnetic fields between these magnets pull and push the electrons in the copper conductors making them flow, these moving electrons are the electricity that flow into the loads connected to the generator.

Types of Electricity

We have two types of electricity, the first one called static electricity and the second called dynamic electricity.

Dynamic electricity may be direct current electricity (DC) or alternating current electricity (AC) …. Let us know more about the two types:

Static electricity:

This type of electricity is generated when two non conducting material are rubbed together, such as a glass material and a silk cloth material, in this case the two material become electrically charged as one material will suffer from lacking of electrons (+ charged material) and the other material will have extra electrons (- charged material) and these charges remains fixed on the material surfaces until the two material are in touch or connected to a conductor to form a closed circuit  , in this case the electrons will flow otherwise there will no flow of electrons so we called it as static electricity.

Dynamic electricity:

This is the common type of electricity which we use in our homes or factories , where this type of electricity results from motion of free electrons from one atom to another, if the these free electrons flow in one direction, we call this type as direct current electricity (DC) and if these free electrons change its direction from positive to negative periodically (in the same time interval), we call this type as alternating current electricity (AC).

As an example, DC current is produced by the car battery and AC current is produced by car alternator.

In our life we use DC current to operate certain application while we use AC current to operate other application and we have the ability to convert AC to DC throw abridge called " rectifier "  and to convert DC to AC throw a device called "inverter " all of this depending on our application and need.

As a brief difference between AC and DC current, we can say that AC current is safe to flow for long distance and provide more power and the frequency of it is 50 HZ or 60 HZ according to the country while DC voltage cannot flow for along distance as it begins to loss power and the frequency of it is zero.

Electrical Current Flow Effects

When the electrical current flow in a load circuit the result will be light, heat generation, electromagnetism and chemical reaction, let us clear these effects:

Heat generation:

As an example when electrical current flows throw incandescent lamp, heat will be generated throw the conversion of electrical energy to thermal energy inside the lamp components. Also when electrical current exceeds the rated value of the fuse, fuse link will be melted due to excessive heat.

Electromagnetism:

In fact electricity may be used to produce magnetism and also magnetism can be used to produce electricity. When any conductor carries electrical current, magnetic field will be produced around this conductor where magnetic field strength will proportional to the amount of current flow in the conductor. Magnetic fields will take various forms with a variable strength according to the conductor shape as following:

When the electrical current passes throw a straight conductor the magnetic field will form circular lines around the conductor.

When the electrical current passes throw a loop conductor, the magnetic field lines will be concentrated to make a strong magnetic field, in this case magnetic field strength will proportional to the current value and the number of turns .If we put an iron core inside these coils we can get strong electromagnetic field as the iron material increase the magnetic filed strength.

Chemical reactions: 

When a battery is connected to an external electrical load, electrical current will flow throw it, the question is how the current is generated from a battery?

The answer is, each battery consists of two different metals and acid mixture with water, when a chemical reaction between these components is done, voltage difference will appear between the two battery terminals and the current will flow across the load until the two metals become the same and the acid reduced to nearly zero. On the other hand when we charge a battery by an alternator the reaction will reversed as the chemical reaction will produced by the current flow consequently  the current will make electrochemical reaction that restore again the metal and the acid with water mixture until the battery will be full charged again .

Electrical Current Flow Theory

How can you catch electricity?

Electricity is a form of energy that we cannot live without it. Sometimes it called the unseen force as we cannot see, touch and smell or hear it.But on the other hand we see the effect of electricity when the lamp give the light or when the motor rotates …etc. and we can hear the effect of electricity when a fuse blow out also we can smell the effect of electricity when some insulated wire are over heated due to the excessive amount of current pass throw it so the insulation is burned.

Theory of the electrical current flow:

We have two theories that describe how the current flow throw any load,the first one called conventional theory and the second called electrons theory, let us know the difference:

Conventional theory:

It says that the electrical current flow throw any load from the positive to the negative side of the power supply as it see that the free electrons flow from the high potential side to the low potential side. This theory is usually used for automotive systems.

Electrons theory:

It says that the electrical current flow throw any load from the negative to the positive side of the power supply as it see that the free electrons flow from the high number of electrons side to the low number of electrons side to balance the charges inside the power supply. This theory is usually used for electronics systems.

About the effect of the current direction, in fact some devices like diode are affected by the current direction and other devices don't affect as resistive loads.

Electrons flow and electrical current formation:

There are a number of electrons in the inner and outer orbit of the atom, the electrons present in the outer orbit are away from the nucleus and less attracted to it, so we call them "free electrons" as the are so easy to move . Electrical current is formed when these free electrons move from one atom to the next one. These electrons become free due to a certain force like heat, friction, pressure, chemical reaction or magnetic action.

Electricity from Generators to Loads

Electricity makes our life comfortable and easier. We use electricity more and more every year and off course we need it in places far from the generation power plants places. So in most cases electricity must move for along distances from one place to another before it will be used and the same time there are a standards present in the loads places that describe the electricity specifications that will operate our machines and appliances. 

Let’s trace the path of electricity from a generation power plant to the load (a lamp or other appliance) present in your house:

First, the electricity is generated at power generation plants and then it moves through conductors to power transformers that will steps up the electricity voltage (called step up transformers) to a standard known level and then the electricity is transmitted throw of transmission lines network which called "electric grid" .These transmission lines consist of huge tower lines that you can see along the highway and all transmission lines are connected together.

The reason that makes us step up the voltage before transmission is to reduce electricity losses in the conductors.

Second, near to cities that comprise the electrical loads there will be a step down transformers located in substations (contain transformers + switches + another electrical equipment's) at the end of the transmission lines referred above, this step down transformers reduce the voltage value to another standard level.

Third, this reduced voltage electricity is then carried by distribution lines that deliver the electricity to another step down transformers, present in the center of the cities and villages at the vicinity of the customers electrical loads and usually these step down transformers are called distribution transformers and they sound as a large gray metal box mounted on an electric pole. Distribution lines can be overhead lines or underground cables.

Finally, this reduced voltage electricity out from the distribution transformers feed your electrical loads in your house like lamps and other equipment's as the generated reduced voltage is suitable to operate them according to the standards and to your local regulation.

The electricity enters your house through a three-wire cable, controlled by

a circuit breaker or a fuse to feed your outlets and wall switches in your house and off course the utility company puts an electric meter beside this circuit breaker or fuse to measure how much electricity you will use every month.

Electricity Generation Fuels

Electricity generation fuels type is differ from one country to another, Let us take United States as an example; there are "four " kinds of power plants fuels that produce most of the electricity in united state:  Coal, Nuclear, Natural Gas and Hydropower as coal plants generate almost half of the electricity in United State and on other hand the renewable energy source " geothermal, wind, and solar power plants ", generate three percent of the produced electricity .In other countries, we will see another types of fuels and another percentage for each fuel. Let us know about the (4) type's power stations that mainly united state depends on:

(1) Fossil Fuel Power Plants:

Fossil fuel power plants burn fuels like natural gas, coal or oil to produce electricity. These energy sources are called fossil fuels because they are formed from the remains and residuals of an ancient sea plants and animals. Most of our electricity is generated from these fossil fuel power plants.

Power plants burn the fossil fuels and use the heat generated to boil the water into a steam, this steam is channeled through a number of pipes at high pressure to move a turbine generator providing the electricity. Fossil fuel power plants have many disadvantages as they produce emissions that pollute the air, contribute to global climate change and also they are considered as less efficiency type of power plants. Sometimes we call fossil fuel power plants as a thermal power plants because they use heat energy to make electricity (note that "Thermeis" is the Greek word for heat).Most fossil power plants in the United States use coal because it is cheap and abundant to extent that almost 92 % of the coal in the United States is sent to power plants to generate electricity.

(2) Nuclear Power Plants:

Nuclear power plants are called also thermal power plants as they generate electricity in the same way as fossil fuel plants referred above, except that they use uranium as a fuel which isn’t burned.

Uranium is a material found in the rocks underground. A nuclear power plant splits uranium atoms into small atoms in a process called "fission"and the result is a huge amount of heat. This heat is used to convert water into steam, which drives a turbine generator and finally electricity is generated.

Nuclear power plants don’t produce carbon emissions, but their waste is radioactive. Nuclear waste must becarefully stored to avoid contamination of people and the environment.

(3) Hydropower Plants:

Hydropower plants use the kinetic energy resulting from the moving of the water to generate electricity as this Fast moving water spin the blades of a turbine generator. Hydropower is considers as a renewable energy source because it is generated from rainfall.

Not only United states but all countries all over the world aims to increase the usage percentage of renewable energy such as wind, solar, ..etc. to avoid the many disadvantages resulting from using the fossil fuels.

Electricity Cost

The cost of electricity with respect to electricity supply authorities depends on several factors. If these factors cost increased, the cost of the customers consumed electricity "kwh bill" would increase. So electricity supply authorities should be more interested in reducing these factors cost.

What are the factors that affect electricity cost?

Mainly there are three factors:-

(1) Fuel Cost:

It considered as the most effective factor that affect the cost of electricity generation, in fact many energy sources (fuels) can be used to generate electricity but with a variable cost for example, the cheapest fuel cost is the falling water power used in hydropower station and the most expensive is the sun rays used by solar cells in solar power station.

(2) Building Cost:

The second factor affect the electricity cost is the cost of the power plant building itself and also its components for example nuclear power plants are very expensive to build, but on the other hand their fuel (uranium) is inexpensive. Also Coal-fired plants are cheaper to build, but their fuel (coal) is more expensive so electricity supply authorities commonly do a number of technical studies in indicate the most cheaper and effective power plant type.

(3) Efficiency:

One of the most important factors that figure electricity cost, as supply authorities must also consider the plant’s efficiency. Efficiency is the amount of useful energy you get out of a system compared to the input energy. The most efficient machine is the machine that converts all the energy input into useful work with fewer amounts of losses. So in power plant, the more the plant efficiency the less the cost of electricity generated.

In general, today’s power plants use (3) units of fuel to produce one unit of electricity (kwh), as a typical coal power plant burns about 8100 tons of coal each day and about two-thirds of the chemical energy in the coal (5,300 tons) is lost as it is converted first to heat energy and then to kinetic energy, and finally into electrical energy.

Most of the lost energy in power plants is the heat. You can notice this wasted heat in the big clouds of steam pouring out of the towers on some power plants

Over Voltage and Voltage Swell

They are considered as a sever power quality problems present in electrical distribution network that have damage effects on the electrical equipments.

What do over voltage and voltage swell mean?

Over Voltage: is the increase in AC RMS voltage at power frequency to greater than 110% of the network nominal voltage and for duration longer than one minute. According to IEEE 1159/1995, increased voltage will range from 110% to 120% of the nominal voltage and for duration longer than one minute.

Voltage Swell: is the increase in AC RMS voltage at power frequency to the rang between 110% to 180% of the network nominal voltage and for duration rang from 0.5 cycle (10 ms) to one minute. According to IEEE 1159/1995, increased voltage will range from 110% to 120% of the nominal voltage and for duration rang from 3 sec to one minute.

What are the causes of over voltage and voltage swell?

Over Voltage Causes:

(1) Load switched off and power factor correction capacitors switched on.

(2) Poor system voltage regulation.

Voltage swell causes:

(1) Single line to ground fault .  

(2) "Start – Stop" of heavy loads.

(3) Bad dimensioned power supply and bad regulated transformer mainly at off-peak hours.

What are the impacts of over voltage and voltage swell?

These two problems have more dangerous effects on electrical equipment's and electrical distribution network components than under voltage and voltage sag as following:

Over Voltage Impacts:

Over  voltage causes many problems with the equipments that required steady state voltage especially modern load so it causes malfunction, miss operation and in some times full operation stoppage.

Voltage Swell Impacts:

Voltage swell causes many problems like:

(1) Data loss and flickering of lighting and screens.

(2) Stoppage or damage of sensitive electrical equipments especially if the voltage values are too high.

Under Voltage and Voltage Sag

They are two popular and important power quality problems present in electrical distribution network that strongly affect the proper functioning of the loads in modern society.

What do under voltage and voltage sag (dip) mean?

Under Voltage: is the decrease in AC RMS voltage at power frequency to less than 90% of the network nominal voltage and for duration longer than one minute. According to IEEE 1159/1995, decreased voltage will range from 80% to 90% of the nominal voltage and for duration longer than one minute.

Voltage Sag: is the decrease in AC RMS voltage at power frequency to the rang between 10% to 90% of the network nominal voltage and for duration rang from 0.5 cycle (10 ms) to one minute. According to IEEE 1159/1995, decreased voltage will range from 10% to 90% of the nominal voltage and for duration rang from 3 sec to one minute.

What are the causes of under voltage and voltage sag?

Under Voltage Causes:

(1) Load switched on and power factor correction capacitors switched off.

(2) Poor system voltage regulation.

Voltage Sag Causes:

(1) Local and remote faults that happen in transmission and distribution especially faults in parallel feeders and customers installation.

(2) Connection of heavy loads and starts up of large motors.

What are the impacts of under voltage and voltage sag?

These two problems have dangerous effects on electrical equipments and electrical distribution network components as following:

Under Voltage Impacts:

Under voltage causes many problems with the equipments that required steady state voltage especially modern load so it causes malfunction, miss operation and in some times full operation stoppage.

Voltage Sag Impacts:

Voltage sag causes many problems like:

(1) Malfunction of information technology equipments which called microprocessor based control systems (PLC, ASD, PCs……etc) that may lead to process stoppage.

(2) Tripping of contactors and electromagnetic relays.

(3) Disconnection and less efficiency in rotating machines.

How Natural Gas Affect Electricity Bill?

Natural gas considers as one of the most important sources of electricity generation as it is cleaner than other types of fossil fuel so it is good for environment than other types of fossil fuels.

How does natural gas affect your electricity bill?

Most of power generation plant burn natural gas to generate electricity and off course electric companies have various ways of incorporating natural gas cost in your bill. As they pay for natural gas seller, you also should pay to them.

So as the natural gas price change from a month to another, the cost of kilowatt hour you used will also change, this is what happens in cities like New York and Texas. Utilities in these cities pass the cost of fuel to the consumer electricity bill and this is because deregulation and retail competition selected by them.

In fact natural gas price not only the factor that determine your electricity bill but also there are another factors that affect like seasonal demand changes, any way you should search for electricity retailer that sell electricity to you in low price and good quality.

How can you eliminate your electricity bill?

Some electricity consumers searching for alternating way to eliminate electricity bill, one of the most effective ways is to generate electricity locally by using sources of renewable energy at your premises like, installing solar panel in the roof and in this case you will not see electricity bill again.

Solar panels become so popular in many countries due the high cost of electricity bill and although you pay for initial investment, you will not also pay for the electricity bill again. Other electricity consumers use another renewable energy source like wind power to locally generate electricity, any way you should do feasibility study before installing solar panel or using wind turbine to generate electricity.

50HZ Appliance & 60HZ Power Supply and vice versa

A 50 HZ power supply is common used in Europe while a 60 HZ power supply is common used in USA, Typically most of the electrical loads have a frequency range they are compatible with and it is common to see that the range span is from 50 HZ to 60 Hz

?What is the difference between 50 HZ and 60 HZ power transformer

Transformer which made for 60 HZ  is smaller than transformer made for 50 HZ , but in some cases they are in the same size and in this case the 60 HZ version will use lower grade steel laminations which mean it will  be cheaper than the other

?Can we connect 60 HZ power transformer to 50 HZ power supply

If you make this the transformer will get much hotter than normal and easily reach to a dangerous temperature that will cause transformer failure, this is because the transformer primary number of turns is designed according to input voltage to input frequency ratio (V/F) so if the frequency is reduced then (V/F) ratio will increase and there will not be sufficient number of turns to prevent transformer from reaching core saturation, So transformer will draw more much current from the main getting more hotter leading to failure

?Can we connect 50 HZ power transformer to 60 HZ power supply

Yes, you can and you will rarely have a problem as operating a 50 HZ transformer on 60 HZ power supply reduces the drawn current and hence the transformer will run a little cooler  

?Can we connect 50HZ induction motor to 60HZ Power Supply or vice versa

If I connect a 60 HZ induction motor to a 50 HZ power supply, the motor will draw more current and run at lower speed and if I connect a 50 HZ induction motor to a 60 HZ power supply the motor will draw lower current and run at high speed and in the two cases the result will be excessive heat buildup inside the motor that strongly shortened motor operating life

?How can you safely operate a 60 Hz appliance at a 50 HZ power supply or vice versa

:You should follow the following steps

First: contact the appliance manufacturer as it may be possible to safely 

.operate your appliance with the manufacturer approval

Second: some manufacturers sell the same appliance in 50 HZ and 60 HZ 

.countries, so try to connect manufacturer as he may have a solution
Third: you can purchase 60 HZ sine wave power supply but this solution is generally very expensive and it will be more cost effective to replace the appliance than to buy the 60 HZ power supply