The costs of electric power outages to American electric customers are generally called “socio-economic” costs.

 Attempts have been made to quantify these costs but the estimates vary widely.

One source reports that the costs are $26 billion each year and that they have been increasing as the electric power industry is restructured.

A 2001 report1 from the Electric Power Research Institute (EPRI) states that power outages and problems with power quality cost the U.S. economy over $119 billion per year.

Numerous impacts of power outages have been identified. Included among these impacts are:

• Loss of life due to accidents (e.g., no street lights);

• Loss of life of ill and elderly (death rates go up);

• Loss of productivity by industry;

• Loss of sales by business;

• Loss of wages of labor;

• Damage to equipment in industry;

• Fires and explosions;

• Riots and thefts;

• Increased insurance rates.


One common method of measuring resistances ranging 0–1000 MΩ is by using meggers or insulation-resistance testers. This is the usual ohmmeter with a battery used for voltage source.

This instrument is used to measure very high resistances, such as those found in cable insulations, between motor windings, in transformer windings, etc.

Normal multimeters do not provide accurate indications above 10 MΩ because of the low voltage used in the ohmmeter circuit.

Meggers can apply a high voltage to a circuit under test and this voltage causes a current if any electrical leakage exists. This makes it useful as an insulation tester.

Some laboratory test meters have a built-in high-voltage source. The high voltage permits accurate high-resistance measurement, but such meters are usually not portable.

The megger is essentially a portable ohmmeter with a built-in high-voltage source. The built-in high-voltage source may be derived from a magnet-type DC generator or battery.

In a DC generator-type megger, a hand crank is used to turn the armature to produce voltages up to 500, 1000, and 2500 (depending on the model used).

An electronic battery-operated type of instrument is popular because it is light, compact, and can be held and operated in one hand, i.e., there is no generator to turn.

High-testing voltage is produced by an electronic circuit, which uses an internal battery as an energy source.

Resistance is directly displayed on the front panel digital display. A range of voltages can be selected while testing.


While a person is conducting tests with an instrument on live line supply, there is a possibility of a sharp rise in voltage for a short duration.

This may result in an arc or flash between measurement terminals of the testing device. In addition, if a heavy flash occurs, it may critically injure a person handling the instrument.

To safeguard the person using the measuring instrument and to classify the various instruments as per the application they are used in, the IEC has classified instruments in the following categories:

• Category IV: Distribution systems, service connections, and primary overcurrent protection for larger installations

• Category III: Three-phase and single-phase distribution within a premises

• Category II: Appliances, lighting points, socket-outlets

• Category I: Transient-protected electronic equipment.

The IEC Standard 61010 provides guidelines for manufacturers to follow safety norms for testing devices. It is to be noted that irrespective of their maximum voltage rating, a Category IV device provides a greater degree of transient protection than Category III, etc.

The Category III device is suitable for most of the testing undertaken by electricians.


The CRO measuring instrument may sound very familiar, as it is a very useful device. It is used for measurement of voltages (AC/DC) and display of waveforms by providing information on time duration, frequency, and their shapes.

Features of CRO
Below are listed the various features of the CRO:
• It allows voltage (AC/DC) amplitude measurement and time period measurement from the waveform displayed on screen.
• Dual trace CRO allows the user to see two traces at a time on two different channels for comparison.
• Two sets of controls provide the facility to show time period differences, amplitude differences, and shape/distortion comparison.
• Storage oscilloscopes allow storage of waveforms for later analysis.
• Storage facility is very useful since it provides a cursor function, which shows the value of a measured variable at a particular instance.

Operating CRO
To operate the CRO, perform the following procedure:
• The power on switch is provided for on/off control.
• The measurement probe provided consists of two leads – one connected to the signal and the other, ground probe, connected to the ground of circuit.
• Turn on the CRO.
• Check the integrity of leads and the CRO by connecting the I/P probe to a test socket of 5 V square wave signal.
• While checking non-isolated signals (that are earthed) do not connect ground/earth to the CRO, else it may create short-circuit at the input signal.
• Adjust both channels’ vertical axis by placing AC\DC\GND signal in GND position.
• Place the function switch in the suitable signal function as required (AC\DC).
• Check the test probe selection, i.e., divide by 1 or 10 that allows signal attenuation.
• The intensity knob is used to vary the brightness of the trace.
• The focus knob is used to change the sharpness of the trace displayed.
• The Y shift allows you to shift the waveform displayed vertically (up/down).
• The X shift allows you to shift the waveform displayed horizontally left or right.
• The Volts/Div switch is used to vary the magnitude of the voltage variable displayed on the screen. It is calibrated in Volts/Div of the vertical scale.

A control knob is provided in the center to adjust amplitude between calibrated settings.
• To find the amplitude of a signal multiply the Y-axis reading with the Volts/Div setting.
• The Time/Div is used to control the span of the X-axis.
• Physical markings between two points can be used to calculate the time span.

The same time span can be used to measure the frequency of the waveform displayed.
• A control knob is provided at the center for the same purpose as in Volts/Div.
• To find the time duration of a waveform, measure the signal span reading difference. When this is multiplied by Times/Div it will give the time duration of the signal.


A control circuit is for the automatic control of equipment, for safety interlocking, and sequencing the operations of the plant equipment and machines.

Control circuits hardware consists of relay contacts, wires, hardware timers, and counters, relay coils, etc. These consist of input contacts representing various conditions; the output coils are energized or de-energized depending on the input conditions represented by the control circuit.

Input contacts represent the binary state of the condition:
• True or false
• On or off.

There are two types of contacts NO (normally open) and NC (normally closed).
• Input contact: These are contacts of relays, contactors, timers, counter, field instrument switches, pressure switches, limit switches, etc.
• Output coil: These have two states – On or Off. Output coil can be auxiliary contactor or Main contactor coil.

A few simple control circuits are shown in figure below to represent logical AND, OR, and such conditions.

1. ‘AND’ operation circuit
Figure 2.3(a) shows a simple control circuit (AND operation) with two input contacts (NO) representing two conditions that must be true to complete the circuit to switch on the output relay coil and change the state of output from ‘Off’ to ‘On’.

2. ‘OR’ operation circuit
Figure 2.3(b) shows a circuit with three input contacts (NO) representing that at least one of the three conditions should be true to complete the circuit to switch On the relay coil and change output state from ‘Off’ to ‘On’.

3. ‘AND with OR’ operation circuit
Figure 2.3(c) shows a control circuit, consisting of a combination of AND and OR operations.

There are two parallel (OR condition) paths with two input contacts (NO) connected in series in each path representing AND conditions.

The path for coil K3 will be completed when one of the path conditions comes true. The circuit then will switch ‘On’ the relay coil and change the output state from ‘Off’ to ‘On’.


Electrical power is measured with a wattmeter. A wattmeter consists of a current coil connected in series with load, while the other potential coil is connected parallel with load.

Depending on the strength of each magnetic field movement, the pointer gets affected. The true or real power is directly shown in a wattmeter.

In three-phase systems, power can be measured using several methods. For temporary measurements, a single wattmeter can be used.

However, for permanent measurements, a three-phase wattmeter having two elements is used which indicates both balanced and unbalanced loads. For an unbalanced load, two wattmeters must be used as shown in the below.

The total power is calculated by adding the measurement readings given by the two wattmeters. With this method, the power factor can also be obtained.

When using the two-wattmeter method, it is important to note that the reading of one wattmeter should be reversed if the power factor of the system is less than 0.5. In such a case, the leads of one wattmeter may have to be reversed in order to get a positive reading.

In the case of a power factor less than 0.5, the readings must be subtracted instead of being added. The power factor of the three-phase system, using the two wattmeter method (W1 and W2) can be calculated as follows:

Tan φ = (1.732*W1*W2) / (W1 +W2)

Since the sum and subtraction of readings are done to calculate total true power of a three-phase system, methods shown are not used practically in industry. Rather three phase power analyzers are used which are more user-friendly.


Battery Types
Chemical batteries are individual cells filled with a conducting medium-electrolyte that, when connected together, form a battery. Multiple batteries connected together form a battery bank. At present, there are two main types of batteries:

Primary batteries (non-rechargeable)
Secondary batteries (rechargeable).

Secondary batteries are further divided into two categories based on the operating temperature of the electrolyte. Ambient operating temperature batteries have either aqueous (flooded) or nonaqueous electrolytes.

High operating temperature batteries (molten electrodes) have either solid or molten electrolytes. Batteries in EVs are the secondary-rechargeable-type and are in either of the two sub-categories. A battery for an EV must meet certain performance goals.

These goals include quick discharge and recharge capability, long cycle life (the number of discharges before becoming unserviceable), low cost, recyclability, high specific energy (amount of usable energy, measured in watt-hours per pound [lb] or kilogram [kg]), high energy density (amount of energy stored per unit volume), specific power (determines the potential for acceleration), and the ability to work in extreme heat or cold.

No battery currently available meets all these criteria.

Lead–Acid Batteries
Lead–acid starting batteries (shallow-cycle lead–acid secondary batteries) are the most common battery used in vehicles today. This battery is an ambient temperature, aqueous electrolyte battery.

A cousin to this battery is the deep-cycle lead–acid battery, now widely used in golf carts and forklifts. The first electric cars built also used this technology. Although the lead–acid battery is relatively inexpensive, it is very heavy, with a limited usable energy by weight (specific energy).

The battery’s low specific energy and poor energy density make for a very large and heavy battery pack, which cannot power a vehicle as far as an equivalent gas-powered vehicle.

Lead–acid batteries should not be discharged by more than 80% of their rated capacity or depth of discharge (DOD). Exceeding the 80% DOD shortens the life of the battery. Lead–acid batteries are inexpensive, readily available, and are highly recyclable, using the elaborate recycling system already in place.

Nickel Iron and Nickel Cadmium Batteries
Nickel iron (Edison cells) and nickel cadmium (nicad) pocket and sintered plate batteries have been in use for many years. Both of these batteries have a specific energy of around 25 Wh/lb (55 Wh/kg), which is higher than advanced lead–acid batteries.

These batteries also have a long cycle life. Both of these batteries are recyclable. Nickel iron batteries are non-toxic, while nicads are toxic. They can also be discharged to 100% DOD without damage.

The biggest drawback to these batteries is their cost. Depending on the size of battery bank in the vehicle, it may cost between $20,000 and $60,000 for the batteries. The batteries should last at least 100,000 mi (160,900 km) in normal service.

Nickel Metal Hydride Batteries
Nickel metal hydride batteries are offered as the best of the next generation of batteries. They have a high specific energy: around 40.8 Wh/lb (90 Wh/kg).

According to a U.S. DOE report, the batteries are benign to the environment and are recyclable. They also are reported to have a very long cycle life.

Nickel metal hydride batteries have a high self-discharge rate: they lose their charge when stored for long periods of time. They are already commercially available as “AA” and “C” cell batteries, for small consumer appliances and toys.

This battery is a high-temperature battery, with the electrolyte operating at temperatures of 572°F
(300°C). The sodium component of this battery explodes on contact with water, which raises certain
safety concerns.

Lithium Iron and Lithium Polymer Batteries
The USABC considers lithium iron batteries to be the long-term battery solution for EVs. The batteries have a very high specific energy: 68 Wh/lb (150 Wh/kg).

They have a molten-salt electrolyte and share many features of a sealed bipolar battery. Lithium iron batteries are also reported to have a very long cycle life.

These are widely used in laptop computers. These batteries will allow a vehicle to travel distances
and accelerate at a rate comparable to conventional gasoline-powered vehicles.

Lithium polymer batteries eliminate liquid electrolytes. They are thin and flexible, and can be molded into a variety of shapes and sizes.

Zinc and Aluminum Air Batteries
Zinc air batteries are currently being tested in postal trucks in Germany. These batteries use either aluminum or zinc as a sacrificial anode.

As the battery produces electricity, the anode dissolves into the electrolyte. When the anode is completely dissolved, a new anode is placed in the vehicle.

The aluminum or zinc and the electrolyte are removed and sent to a recycling facility. These batteries have a specific energy of over 97 Wh/lb (200 Wh/kg).

The German postal vans currently carry 80 kWh of energy in their battery, giving them about the same range as 13 gallons (49.2 liters) of gasoline. In their tests, the vans have achieved a range of 615 mi (990 km) at 25 miles per hour (40 km/h).


What is commonly defined as electricity is really just the movement of electrons. So, let’s start at that point.

Current (I, Amps)
Current (as the name implies) is the movement or flow of electrons (I) and is measured in units of Amperes. This is usually abbreviated to Amp or, even shorter, A. The flow of electrons in an electrical current can be considered the same as the flow of water molecules in a stream.

To get anything to move requires potential and the same thing happens
to electrons.

Potential (V, Volts)
Potential is the force (called Electromotive Force or EMF) that drives the electrons and has a measurement of voltage. This is abbreviated as a unit of measurement to Volt or even further to V.

Resistance (R, Ohms)
Resistance is the property that resists current flow. It is analogous to friction in mechanical systems. The unit of this is ohm (we have to give some credit to the fellow who first named it). It is sometimes shown with its official ohm mark (Ω) and the short form of the word resistance is always R.

Resistance not only depends on the material used for the conductor but also upon size and temperature. Increase in the cross-sectional area will decrease the resistance Increase in the length will increase the resistance. Increase in the temperature will increase the resistance (for most materials that conduct electricity)

Capacitance (C, Farads)
Any two conductors separated by an insulating material form a capacitor or condenser. Capacitance of a device is its capacity to hold electrons or a charge. The units of measurement are farads. We commonly see it in smaller amounts called microfarads μF and picofarads pF. Capacitance depends on the construction.

Magnetic Flux (Unit of Measurement is Webers)
When current flows in a conductor, a magnetic field is created around that conductor. This field is commonly presented as lines of magnetic force and magnetic flux refers to the term of measurement of the magnetic flow within the field.

This is comparable to the term current and electron flow in an electric field. The following illustration shows the direction of magnetic flux around a conductor and the application of the easily remembered right-hand-rule. Mentally, place your right hand around the conductor with the thumb pointing in the direction of current flow and the fingers will curl in the direction of magnetic flux.

Magnetic Lines of Force (MMF)
Lines of magnetic force (MMF) have an effect on adjacent conductors and even itself. This effect is most pronounced if the conductor overlaps itself as in the shape of a coil.
Magnetic Self-Inductance
Any current-carrying conductor that is coiled in this fashion forms an Inductor, named by the way it induces current flow in itself (selfinductance) or in other conductors.

Inductance (L, Henrys)
Opposition to current flowing through an inductor is inductance. This is a circuit property just as resistance is for a resistor. The inductance is in opposition to any change in the current flow. The unit of inductance is Henry (H) and the symbol is L.

Frequency (f, Hertz)
Any electrical system can be placed in one of two categories direct current (dc) or alternating current (dc). In dc systems the current only flows in one direction.

The source of energy maintains a constant electromotive force, as typical with a battery. The majority of electrical systems are ac.

Frequency is the rate of alternating the direction of current flow. The short form is f and units are cycles per second or Hertz (short-formed to Hz).

Reactance (X, Ohms)
The opposition to alternating current (ac) flow in capacitors and inductors is known as reactance. The symbol for capacitive reactance is XC and for inductive reactance XL.

Although we will not go into the derivation of the values, it can be shown that when f is the frequency of the ac current:
XL= 2 Πf L

Impedance (Z, Ohms)
The total opposition or combined impeding effect of resistance plus reactance to the flow of alternating current is impedance. The word impedance is short formed to Z and the unit is ohms.

Active Power (P Watts)
Instead of working directly with the term electrical energy, it is normal practice to use the rate at which energy is utilized during a certain time period. This is defined as power. There are three components of power: active, reactive and apparent.

Active power or real power is the rate at which energy is consumed resulting in useful work being done. For example, when current flows through a resistance, heat is given off. It is given the symbol P and has the units of Watts.

Reactive Power (Q, Vars)
Reactive power is the power produced by current flowing through reactive elements, whether inductance or capacitance. It is given the representative letter Q and has the units volt-amp-reactive (VAR).

Reactive power can also be considered as the rate of exchange of energy between a capacitor or inductor load and a generator or between capacitors and inductors.

Although it does not produce any real work, it is the necessary force acting in generators, motors and transformers. Examples of this are the charging/discharging of a capacitor or coil. Although this creates a transfer of energy, it does not consume or use power as a resistor would.
Apparent Power (U, Volt Amps)
Apparent power is the total or combined power produced by current flowing through any combination of passive and reactive elements. It is given the representative letter U and has the units’ volt-amps (VA).

Power Factor (PF)
Real power/ apparent power
Power Factor is the comparison of Real power to apparent power.

• For a resistor, there is no reactive power consumed. Thus apparent power used is totally real. The power factor would be 1 or often referred to as unity power factor

• For a pure inductor or capacitor, the apparent power consumed is entirely reactive (real power is nil). The power factor would then be 0.

• For power consumed by impedance consisting of resistance, inductance and capacitance the power factor will of course vary between these two limits. The most efficient use or consumption of power is obtained as we approach unity power factor.


You know semiconductors as transistors, diodes, and chips. Silicon material is used to make devices that will conduct a certain amount of current when needed.

These devices are made for easy use and with low voltages. You will encounter semiconductor chips in memory devices and computers; transistors are used in many types of circuits, and diodes are used as rectifiers and control devices.

Diodes have an anode and a cathode. The cathode end is marked (+) to indicate which polarity it must be connected to in order to work properly.

Diodes have many uses. They are found in circuits that are used to change ac to dc for certain control devices. They may also be used as protective devices in circuits.

The transistor is used for switching and amplification. It consists of three active elements. There are two basic types of transistors, PNP and NPN.

These terms will be discussed later. E stands for emitter, C stands for collector, and B is used to indicate the base connection.

Switches are used to turn on or off a circuit. They can be made as a simple on off device or used to control many functions in a number of circuits. Switches have names that designate what they can do in terms of turning on or off a circuit or circuits.

For instance, there are SPST (single pole, single throw) switches, DPDT (double pole, double throw), DPST (double pole, single throw), single-pole, six-position, and so forth.

Relays are switches that are moved electrically instead of by hand. They can be made in almost any configuration of poles, throws, and construction.

The force that operates a relay is magnetic. The magnetic pull is produced by current passing through a coil of wire. The attraction of an armature causes the switch sections to operate


Delta connection (/_\)
In a balanced circuit, when the generators are connected in delta, the voltage between any two lines is equal to that of a single phase.

 The line voltage and the voltage across any winding are in phase, but the line current is 30° or 150° out of phase with the current in any of the other windings.

In the delta-connected generator, the line current from any one of the windings is found by multiplying the phase current by the square root of 3, which is 1.73.

Wye connection (Y)
In the wye connection, the current in the line is in phase with the current in the winding. The voltage between any two lines is not equal to the voltage of a single phase, but is equal to the vector sum of the two windings between the lines.

The current in line A of is the current flowing through the winding L1; that in line B is the current flowing through the winding L2; and the current flowing in line C is that of the winding L3.

Therefore, the current in any line is in phase with the current in the winding that it feeds. Since the line voltage is the vector sum of the voltages across any two coils, the line voltage EL and the voltage across the winding Ef are 30° out of phase.

The line voltage may be found by multiplying the voltage of any winding Ef by 1.73.

Delta and wye summarized
The properties of delta connections may be summarized as follows: The three windings of the delta connection form a closed loop. The sum of the three equal voltages, which are 120° out of phase, is zero.

Thus, the circulating current in the closed loop formed by the windings is zero. The magnitude of any line current is equal to the square root of 3 (1.73) times the magnitude of any phase current.

Properties of the wye connection do not form a closed loop. The magnitude of the voltage between any two lines equals the magnitude of any phase voltage times the square root of 3, that is, EL-L = sqrt 3 X Ef


Relays are a necessary part of many control and pilot-light circuits. They are similar in design to contactors, but are generally lighter in construction so they carry smaller currents.

Compressors used for household refrigerators, freezers, dehumidifiers, vending machines, and water coolers have the capacitor-start, induction-run type of motor. This type of compressor may have a circuit that resembles below.

When the compressor is turned on by the thermostat demanding action, the relay is closed and the start winding is in the circuit.

Once the motor comes up to about 75% of rated speed, there is enough current flow through the relay coil to cause it to energize, and it pulls the contacts of the relay open, thereby taking the start capacitor and start winding out of the circuit.

This allows the motor to run with one winding as designed.

Below show the current type of relay. This is generally used with small refrigeration compressors up to 3/4 horsepower.

This is generally used with large commercial and air-conditioning compressors up to 5 horsepower.

Protection of the motor against prolonged overload is accomplished by time limit overload relays. They are operative during the starting period and running period.

Relay action is delayed long enough to take care of the heavy starting currents and momentary overloads without tripping.


French physicist and physician, D’ Arsonval was a pioneer in electrotherapy, he studied the medical application of high-frequency currents. Among his inventions were dielectric heating and various measuring devices, including the thermocouple ammeter and moving-coil galvanometer.

These measuring tools helped establish the science of electrical engineering. d’Arsonval’s galvanometer, which he invented in 1882 for measuring weak electric currents, became the basis for almost all panel-type pointer meters. He was also involved in the industrial application of electricity.

Jaques-Arsene d’Arsonval was born on June 8, 1851 at the Pigsty, canton Saint-Germain-les-Belles, in his family house of “Borie” known from 14th century. His family had very old and noble roots. Nine children were born in the family, but only two of them including Arsene survived. Arsene d’Arsonval has studied in the Imperial College of Limoges (now LycEe Gay-Lussac).

After the Franco-Prussian war of 1870 he went to Paris where he met the famous physiologist Claude Bernard (1813-1878) and was drawn to Bernard’s lectures at Sainte-Barbe college in Paris (the College bears d’Arsonval’s name since 1959). d’Arsonval was Bernard’s prEparateur from 1873 to 1878. After Bernard’s death he assisted Charles-Edouard Brown-SEquard (1817-1894), giving the latter’s winter courses, and eventually replaced him at the College de France when Brown-SEquard died in 1894. The picture shows him as a student in 1873.

His invention in 1882 with Étienne-Jules Marey (1830-1904) and Deprez of what is now known as the Deprez-d'Arsonval galvanometer, came after he had studied muscle contractions in frogs using a telephone, which operates on an extremely feeble currents similar to animal electricity. He demonstrated how a human being could conduct an alternating current strong enough to light an electric lamp (1892).

In 1881, Arsène d'Arsonval first suggested harnessing the temperature difference in the tropical seas for the generation of electricity. His idea was given a first test by Georges Claude in Cuba in the 1920's, and this technology is now ready for producing electricity from sea solar power. In 1902 d’Arsonval worked with Georges Claude on industrial methods for the liquefaction of gases.

His contribution to medicine, now overshadowed by the antibiotic era, created a minor revolution in clinical therapeutics. D’Arsonval literally founded the paramedical field of physiotherapy. In 1918 he was elected president of the Institute for Actinology.

The important point here is that we can use electromagnetic energy to make something turn, which brings us to one of the greatest leaps in electronic advancement - the D'ARSONVAL MOVEMENT. The D'Arsonval movement is the basis for all early metering devices, and is still in common use today. There are 5 basic parts to a D'Arsonval movement.


Six general types of capacitors are the most widely used:

1. Air
2. Ceramic
3. Mica
4. Electrolytic
5. Paper
6. Tantalum

The electrolytic capacitor is marked with + and - and has polarity that must be observed when it is connected in a circuit. The other types do not need a polarity marking. Below shows an electrolytic capacitor that may be found in air conditioning, refrigeration, and heating applications. It is used as ac motor run and start capacitors below:

 Air capacitors.
Air capacitors have air for a dielectric. They are usually variable capacitors used in the tuning circuits of radios.

Mica capacitors.
Aluminum foil is used as the plate material in mica capacitors. Between the aluminum foil plates is a thin sheet of mica. Sometimes the mica is sprayed with a conducting paint. The paint then forms the plate on one side of the mica. Mica capacitors are usually sealed in Bakelite or some type of plastic.

Paper capacitors.
Aluminum is also used as the plate material in paper capacitors. However, the plates are separated by a paper dielectric. The materials (paper and aluminum) are rolled into a cylindrical shape. A wire is connected to alternate ends of the foil and it is encased in plastic.

Ceramic capacitors.
Ceramic dielectric materials make high-voltage capacitors. They have very little change in capacitance due to temperature changes. These small capacitors usually consist of a ceramic disc coated on both sides with silver. They are made in values from 1 picofarad up to 0.05 microfarad. Breakdown voltages of ceramic capacitors run as high as 10,000 volts and more.

Oil-filled capacitors.
Oil-filled capacitors are paper capacitors encased in oil. They are sometimes referred to as bathtub capacitors. The main advantages of these capacitors are sturdy construction and high voltage breakdown ratings. They are used in places where grease and oil are likely to be encountered.


The d’Arsonval meter movement has a small, rectangular coil of wire. The coil is suspended in a magnetic field created by a permanent magnet. When current is applied to the coil, it becomes an electromagnet.

The energized coil then lines up with the poles of the permanent magnet. The amount of current applied to the coil controls its movement. An electromagnet that is free to move will align its axis with the magnetic axis of a fixed magnet.

The coil must be free to rotate in order to align itself with the magnetic axis. The coil in the meter is mounted on pivots that permit easy rotation.

Two small springs are mounted on the top and bottom. These springs offer slight resistance to the rotation of the coil. The springs control the position of the coil when there is no current flowing.

When current flows in the coil, it produces a magnetic field around the coil. This magnetic flux overcomes the force of the springs and moves the coil.

A pointer on top of the coil rotates to mark the amount of movement. The greater the current through the coil, the more it turns, and the further the pointer moves. The pointer then stops in front of a marked scale on the face of the meter.

As you look closer at the d’Arsonval meter movement, you will find that it can be extremely sensitive to small currents. For instance, a relatively inexpensive meter can give a full-scale deflection of 10 microamperes (A).

Full-scale deflection is the total range of a meter scale. A microampere is one-millionth (0.000001) of an ampere.

Meter deflection is determined by three factors:
1. The number of turns of wire in the coil and the amount of current flowing in the coil.
2. The strength of the magnetic field produced by the permanent magnet affects the positioning of the coil.

3. The tension of the springs and the friction of the bearings determine the sensitivity of the meter movement. The amount of current flowing through the meter determines its pointer deflection since it is the only variable in the meter movement circuit.

The scale of the meter is calibrated (marked) to show the type of reading (volts, ohms, or amperes).

Before you use a meter, check its instruction manual. Each meter is a little different and you should be aware of any important instructions in the instruction manual.


Electricity is all around us. It moves the entire planet. Most, if not all activities significant to our lives involves electricity. The evolution of our world, corresponded with the advent of electricity.

But how much do we know about electricity. More importantly, how much do we not know about electricity?

Electricity is viewed as productive. Electricity is also viewed with amazement and danger by the others. Especially those who have less understanding.

As electrical engineer, it is one of our responsibilities to educate people about electricity.

This entry is a collection of the best article, and information in the web related to electricity.
Basic information, myths, and misconception busters.

Electricity, phenomenon associated with stationary or moving electric charges. Electric charge is a fundamental property of matter and is borne by elementary particles. In electricity the particle involved is the electron, which carries a charge designated, by convention, as negative. Thus, the various manifestations of electricity are the result of the accumulation or motion of numbers of electrons. Read more...

Main events
600BC: Static electricity
Thales, a Greek, found that when amber was rubbed with silk it attracted feathers and other light objects. He had discovered static electricity. The Greek word for amber is ëelectron', from which we get ëelectricity' and ëelectronics'. Read more...

The developed world is irreversibly dependent on electricity. This addiction is happening  “accidentally,” as an unintended consequence of forces such as population growth, electrification and computerization. Taken separately, those trends did not seem momentous. Taken together, they are the unstoppable drivers behind the coming transformation of our electrical power infrastructure. Read more...

Of the total energy consumed in America, about 39% is used to generate electricity. Therefore, electricity consumption is an important portion of a consumer's environmental footprint. All forms of electricity generation have some level of environmental impact. Most of the electricity in the United States is generated from fossil fuels, such as coal, natural gas, and oil. Read more...

Boosting efficiency in the electricity use in 8 European regions. Electricity consumption is rising, in some areas with alarming speed. There is a strong risk that the increase in electricity consumption will overcompensate the growth in electricity production from renewable energy sources. A considerable lack of awareness about these increases exists, not only among the general public but also in SMEs, in public administrations and in political decision makers on regional and local levels. Read more...

Have you ever wondered how much we depend on electricity? Where does electricity come from? What are those volts, amps and watts anyway? If you have ever thought about any of these questions, then you've come to the right place. This page will tell you the amazing story of electricity. You'll be shocked by how hot it is. If you want to go to any page, look down or glance over to the side bar. We hope that this site helps you learn more about electricity. Read more...

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Written by a highly regarded power industry expert, this comprehensive manual covers in full detail all aspects of electric power distribution systems, both as they exist today and as they are evolving toward the future. A new chapter examines the impact of the emergence of cogeneration and distributed generation on the power distribution network. 

Topics include an overview of the process of electricity transmission and distribution, a thorough discussion of each component of the system - conductor supports, insulators and conductors, line equipment, substations, distribution circuits and more - as well as both overhead and underground construction considerations. 

Improvements in both materials and methods of power distribution are also explored, including the trend toward gradual replacement of heavier porcelain insulators with lighter polymer ones. The complex aspects of electric power distribution are explained in easy-to-understand, non-technical language.

From the Publisher
A training and reference book for electrical utility companies covering utilities power reaching the consumers. Coverage includes all tools, equipment, facilities, between power utility to the consumer, applications, installation and maintenance. 

Theory of electricity and power covered in layman's terms, where applicable.


The following are recommended changes to the existing Over-Current Protection Pickup Guidelines:

1.       The minimum line to ground (LG) fault current will be calculated using a 10 Ohm fault impedance.
2.       The minimum phase fault current will be calculated using a 2 ohm fault impedance and will be the lesser of the phase to phase (LL) and a three phase (3p) fault. (2 ohms is the approximate arc impedance through air for our standard wire spacing)
3.       At a backup device (recloser or circuit breaker) we should strive (i.e. not mandatory) to detect a bolted fault at the end of the next device’s zone. This applies for both ground and phase settings.

Distribution Circuit Breaker
 Time Delay
 Phase Pickup
Minimum              = line ampacity or 2 x (maximum load current) which ever is the lowest
Maximum             = 1 phase (EOZ) 2 ohm (the lesser of the phase to phase and three phase fault, at the End OF ZONE, through a two Ohm impedance)
Max. Backup       = 1-LL (ENZ) (the bolted phase to phase fault, at the END of the Next Zone)

Ground Pickup

Minimum              = 0.3-0.5 x (maximum load current) or 0.3-0.5 x (line ampacity) which ever is the lowest
Maximum             = 1-LG (EOZ) 10 Ohm (the line to ground fault current, at the End Of Zone, through a ten Ohm impedance)
Max. Backup       = 1-LG (ENZ - the bolted line to ground fault, at the End of th Next Zone)

 Phase Pickup
Minimum              = 0.9 x 1-LL (EOZ)
Maximum             = 1.25 x 3phase bus fault

 Ground Pickup

Minimum              = 0.9 x 1-LG (EOZ)
Maximum             = 1.25 x 3phase bus fault

Recloser with Phase and Ground Settings
Phase Pickup
Minimum              = 2 x (maximum load current)
Maximum             = 1 phase (EOZ with 2 Ohm fault impedance)
Max. Backup       = 1-LL (ENZ)

Ground Pickup
Minimum              = 0.5 x (maximum load current)
Maximum             = 1-LG (EOZ with 10 Ohm fault impedance)
Max Backup        = 1-LG (ENZ)

Recloser with only Phase Settings
Phase Pickup
Minimum              = 2 x (maximum load current)
Maximum             = 1-LG (EOZ with 10 Ohm fault impedance)
Max. Backup       = 1-LG (ENZ)

The value of a (10) ten ohm ground fault impedance was initially chosen because it appeared to be the most prevalent in the industry from what could be determined. It is recognized that fault impedance from zero to forty Ohms are in use. The (10) ten ohm value gained legitimacy after reviewing EPRI Report EL-3085, Distribution Fault Current Analysis. This report indicates that 83% of faults involved the neutral or ground. The maximum fault impedance was calculated to be 3 Ohms.

As stated earlier, the value of a (2) two ohm phase fault impedance was chosen because it is the approximate arc impedance through air for our standard wire spacing.


The incandescent lamp is a thermal radiator. The filament wire begins to glow when it is heated to a sufficiently high temperature by an electric current. As the temperature increases the spectrum of the radiated light shifts towards the shorter wavelength range – the red heat of the filament shifts to the warm white light of the incandescent lamp.

Depending on lamp type and wattage the temperature of the filament can reach up to 3000 K, in the case of halogen lamps over 3000 K. Maximum radiation at these temperatures still lies in the infrared range, with the result that in comparison to the visible spectrum there is a high degree of thermal radiation and very little UV radiation.

Lack of a suitable material for the filament means that it is not possible to increase the temperature further, which would increase the luminous efficacy and produce a cool white luminous colour. As is the case with all heated solid bodies – or the highly compressed gas produced by the sun – the incandescent lamp radiates a continuous spectrum.

The spectral distribution curve is therefore continuous and does not consist of a set of individual lines. The heating of the filament wire results from its high electrical resistance – electrical energy is converted into radiant energy, of which one part is visible light.

Although this is basically a simple principle, there are a substantial number of practical problems involved in the construction of an incandescent lamp. There are only a few conducting materials, for example, that have a sufficiently high melting point and at the same time a sufficiently low evaporation rate below melting point that render them suitable for use as filament wires.

Nowadays practically only tungsten is used for the manufacture of filament wires, because it only melts at a temperature of 3653 K and has a low evaporation rate. The tungsten is made into fine wires and is wound to make single or double coiled filaments. In the case of the incandescent lamp the filament is located inside a soft glass bulb, which is relatively large in order to keep light loss, due to deposits of evaporated tungsten (blackening), to a minimum.

To prevent the filament from oxidizing the outer envelope is evacuated for low wattages and filled with nitrogen or a nitrogen-based inert gas mixture for higher wattages. The thermal insulation properties of the gas used to fill the bulb increases the temperature of the wire filament, but at the same time reduces the evaporation rate of the tungsten, which in turn leads to increased luminous efficacy and a longer lamp life.

The inert gases predominantly used are argon and krypton. The krypton permits a higher operating temperature – and greater luminous efficacy. Due to the fact that it is so expensive, krypton is only used in special applications.

A characteristic feature of incandescent lamps is their low colour temperature - the light they produce is warm in comparison to daylight. The continuous colour spectrum of the incandescent lamp provides excellent colour rendition.

As a point source with a high luminance, sparkling effects can be produced on shiny surfaces and the light easily controlled using optical equipment. Incandescent lamps can therefore be applied for both narrow-beam accent lighting and for wide-beam general lighting.

Incandescent lamps can be easily dimmed. No additional control gear is required for their operation and the lamps can be operated in any burning position. In spite of these advantages, there are a number of disadvantages: low luminous efficacy, for example, and a relatively short lamp life, while the lamp life relates significantly to the operating voltage.

Special incandescent lamps are available with a dichroic coating inside the bulb that reflects the infrared component back to the wire filament, which increases the luminous efficacy by up to 40 %


The detailed procedure for insulation co-ordination set out in IEC 60071-1 (European standard EN60071 1 is identical) consists of the selection of a set of standard withstand voltages which characterize the insulation of the equipment of the system. This set of withstands correspond to each of the different stresses to which the system may be subject:

• Continuous power frequency voltage (the highest voltage of the system for the life of the system).
• Slow-front overvoltage (a standard switching impulse).
• Fast-front overvoltage (a standard lightning impulse).
• Very-fast-front overvoltage (depends on the characteristics of the connected apparatus).
• Longitudinal overvoltage (a voltage between terminals combining a power frequency voltage at one end with a switching (or lightning) impulse at the other).

These voltages and overvoltages need to be determined in amplitude, shape and duration by system study. For each class of overvoltage, the analysis then determines a ‘representative overvoltage’, taking account of the characteristics of the insulation.

The representative overvoltage may be characterized by one of:
• an assumed maximum,
• a set of peak values,
• a complete statistical distribution of peak values.

The next step is the determination of ‘co-ordination withstand’ voltages – the lowest values of the withstand voltages of the insulation in use which meet the system or equipment performance criteria when subjected to the ‘representative overvoltages’ under service conditions. Factors are then applied to compensate for:

• the differences in equipment assembly,
• the dispersion of the quality of the products within the system,
• the quality of installation,
• the ageing of installation during its lifetime,
• atmospheric conditions,
• contingency for other factors.

This results in so-called ‘required withstand voltages’ – test voltages that must be withstood in a standard withstand test. 

In specifying equipment the next step is then to specify a standard test withstand voltage (a set of specific test voltages is provided in IEC 60071-1) which is the next above the required withstand voltage, assuming the same shape of test voltage.

 A test conversion factor must be applied to the required withstand voltage if the test voltage is of a different shape to the class of overvoltage in question.


In order to match both the mechanical and electrical characteristics of the overhead line conductor to the environmental conditions climatic details must first be collected and analyzed.

• Temperature
The maximum, minimum and average ambient temperature influences conductor current rating and sag. For temperate conditions typically 20°C with 55°C temperature rise. For tropical conditions 35°C or 40°C with 40°C or 35°C temperature rise. Maximum conductor operating temperature should not exceed 75°C for bare conductors to prevent annealing of aluminium. Conductortemperatures up to 210°C are possible with ‘GAP’ conductor

• Wind velocity
Required for structure and conductor design. Electrical conductor ratings may be based on cross wind speeds of 0.5 m/s or longitudinal wind speeds of 1 m/s.

• Solar radiation
Required for conductor ratings but also for fittings such as composite insulators which may be affected by exposure to high thermal and ultraviolet (UV) radiation. Typical values of 850W/m2 and 1200W/m2 may be assumed for temperate and tropical conditions respectively.

• Rainfall Important in relation to flooding (necessity for extension legs on towers), corona discharge and associated electromagnetic interference, natural washing and insulator performance.

• Humidity
Effect on insulator design.

• Altitude
Effect on insulation and conductor voltage gradient.

• Ice and snow
Required for design of conductor sags and tensions. Build-up can also affect insulation as well as conductor aerodynamic stability.

• Atmospheric
Effect on insulation and choice of conductor pollution material (IEC 60815-1 and -2 – Guide for the selection of insulators in respect of polluted conditions – drafts for public comment).

• Soil
 Electrically affecting grounding requirements (soil characteristics resistivity) and structurally the foundation design (weights, cohesion and angle of repose).

• Lightning
Effect on insulation levels and also earth wire screening arrangements necessary to provide satisfactory outage performance.

• Seismic factor
Effect on tower and foundation design.

• General loadings
Refer also to IEC 60826 (Design criteria for overhead lines), EN50341 (Overhead lines exceeding AC45 kV –supersedes 60826 for European use) and BS8100 (Loading and strength of overhead transmission lines).


The machine is provided with an enclosure to give physical protection from external sources of motor damage. The following standard enclosures have been adopted by NEMA:

• Open enclosure: An enclosure with ventilating openings that permits passage of external cooling air over and around the windings of the machine.

• Drip-proof enclosure: An open enclosure in which ventilating openings are so constructed that successful operating is not interfered with when drops of liquid or solid particles strike or enter the enclosure at any angle from 0° to 15° downward from the vertical.

• Splash-proof enclosure: An open enclosure in which ventilating openings are constructed so that successful operation is not interfered with when drops of liquid or solid particles strike or enter the enclosure at any angle not greater than 100° downward from the vertical.

• Guarded enclosure: An open enclosure in which all openings giving direct access to live metal or rotating parts are limited in size by structural parts or by screens, baffles, grilles, or other means to prevent accidental contact with hazardous parts.

• Externally ventilated enclosure: An open closure that is ventilated by a separate motor-driven blower mounted on the enclosure.

• Pipe-ventilated enclosure: An open enclosure with provision for connecting inlet ducts or pipes. It is called force-ventilated when the air through the enclosure is driven by an external blower.

• Weather-protected type 1 enclosure: An open enclosure with ventilating passages constructed and arranged to minimize the entrance of rain, snow, and airborne particles to the live and rotating parts.

• Weather-protected type 2 enclosure: An open enclosure with ventilating passages at both intake and discharge constructed and arranged to permit high-velocity air and airborne particles to be discharged without entering the internal ventilating passages of the enclosure. Motors and Generators 555

• Totally enclosed enclosure: This enclosure prevents free exchange of air between the inside and outside of the enclosure. This enclosure is not airtight.

• Totally enclosed nonventilated enclosure: An enclosure that is not equipped for cooling by means external to the enclosing parts.

• Totally enclosed fan-cooled enclosure: An enclosure that is equipped for exterior cooling by means of a fan or fans integral with the enclosure but external to the enclosing parts.

• Explosion-proof enclosure: A totally enclosed enclosure designed and constructed to withstand an explosion of a specified gas or vapor that may occur within it and to prevent the ignition of gas or vapor surrounding the machine by sparks.

• Dust-ignition-proof enclosure: A totally enclosed enclosure constructed in a manner to exclude ignitable amounts of dust or amounts that might affect the performance or rating, and which will not permit heat, arcs, or sparks liberated inside the enclosure to cause ignition of exterior accumulations or atmospheric suspensions of a specific dust on or in the vicinity of the enclosure.

• Waterproof enclosure: A totally enclosed enclosure so constructed that it will exclude water coming externally from a hose. Leakage around the shaft is allowed provided it does not enter the oil reservoir. A check valve or drain is provided at the lowest part of the enclosure for drainage.

• Totally enclosed pipe-ventilated enclosure: A totally enclosed enclosure except for openings arranged for inlet and out-ducts or pipes for connection to the enclosed for admission and discharge of ventilating air.

• Totally enclosed water-cooled enclosure: A totally enclosed enclosure cooled by circulating water or water pipes coming in direct contact with the motor parts.

• Totally enclosed water–air-cooled enclosure: A totally enclosed enclosure cooled by circulating air, which in turn is cooled by circulating water, the heat exchanger medium.

• Totally enclosed air–air-cooled enclosure: A totally enclosed enclosure cooled by circulating internal air through heat exchangers, which, in turn, are cooled by circulating external air.


There are many types of 3 phase motors but by far the most common is the induction motor. It is quite useful to be able to test them for serviceability.

Before carrying out electrical tests it is a good idea to ensure that the rotor turns freely. This may involve disconnecting any mechanical loads. The rotor should rotate easily and you should not be able to hear any rumbling from the motor bearings.

Next, if the motor has a fan on the outside of it, check that it is clear of any debris which may have been sucked in to it. Also check that any air vents into the motor are not blocked.

Generally, if the motor windings are burnt out there will be an unmistakable smell of burnt varnish. However, it is still a good idea to test the windings as the smell could be from the motor being overloaded.

Three phase motors are made up of three separate windings – in the terminal box there will be six terminals as each motor winding will have two ends. The ends of the motor windings will usually be identified as W1, W2; U1, U2; or V1, V2.

The first part of the test is carried out using a low resistance ohm meter. Test each winding end to end (W1 to W2, U1 to U2 and V1 to V2). The resistance of each winding should be approximately the same and the resistance value will depend on the size of the motor.

If the resistance values are different, then the motor will not be electrically balanced and it should be sent for rewinding. If resistance values are the same, then the next test is carried out using an insulation resistance tester.

Join W1 and W2 together, U1 and U2 together and V1 and V2 together. Carry out an insulation resistance test between the joined ends, i.e. W to U then W to V and then between U and V. Then repeat the test between joined ends and the case, or the earthing terminal of the motor (these tests can be in any order to suit you).

Providing the insulation resistance is 2MΩ or greater then the motor is fine. If the insulation resistance is above 0.5MΩ this could be due to dampness and it is often a good idea to run the motor for a while before carrying out the insulation test again as the motor may dry out with use.

To reconnect the motor windings in star, join W2, U2 and V2 together and connect the 3 phase motor supply to W1, U1 and V1. If the motor rotates in the wrong direction, swap two of the phases of the motor supply.

To reconnect the motor windings in delta, join W1 to U2, U1 to V2 and V1 to W2 and then connect the 3 phase motor supply one to each of the joined ends. If the motor rotates in the wrong direction, swap two phases of the motor supply.
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