What is the Energy but for Real

8/17/2019 What is the Energy but for Real

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What Is The Energy, But For Real?

What is the energy, but for real? (photo credit: borongaja.com)

The basics of energy

Energy is best defined as “the capacity for doing work” . Electricity is but one of many forms of energy. Other

familiar forms of or descriptions of energy are thermal or heat, light, mechanical, and so on. Energy is also described

as kinetic, that energy associated with a moving body, and potential energy, that energy associated with an object’s

position.

For centuries mankind has used energy in its various forms to enhance its standard of living. In many cases, ways

have been devised to change energy from one form to another to increase its usefulness. An example as old as

mankind is the burning of a fuel to produce heat and light.

Electric power systems thus provide a service, energy in a usable form, not a product, to consumers.

Electrical energy possesses unique characteristics that made it an extremely valuable form of energy. It has

four unique properties //

It can be produced at one location and transmitted to another instantaneously;

It can be transformed to other energy forms and thereby used in a variety of ways;

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It can be delivered by a system of wires, and control;

It cannot be stored.

Consistent terminology has always been an issue when discussing electricity and electric power. Convention is to use

a system of measurement based on the MKS (meter, kilogram, second) system. Table below summarizes the terms

used to describe various aspects of electricity and shows some of the interrelationships between them.

There is an electric charge associated with electrons. This charge is described by a quantity called acoulomb.

The rate of flow of these charges is called the electric current and is described by a quantity called an ampere. One

ampere is equal to the flow of one coulomb of charge during one second across a reference point.

The capital letter I , is used to indicate current and the quantity is sometimes referred to as amps. In

many texts, electric current is described as a physical flow of electrons. It is not. The electrons do not

flow.

Rather electricity is a flow of energy as a result of electron vibrations. The mechanism is the transfer of energy from

one electron to another as they collide, one with another.

Electromagnetic force (EMF), voltage, and difference in potential are different descriptions of the notion of what

causes these charges to flow. A physics text would define voltage as the energy per a unit of charge where energy is

measured by a quantity called a watt-second.

Quantity Name or Unit Symbol Relationships

Electric charge Coulomb q

Time Seconds, Hours t

Current Amperes I I = q / t = V / R

Resistance Ohms R R = V / I

Inductive Reactance Ohms XL XL = 2·π·f·L

Capacitive Reactance Ohms XC XC = 1 / (2·π·f ·C)

Impedance Ohms Z Z = R + j(XL+ XC)

Voltage Electromagnetic force(EMF), Volts, kilovolts

E, V, kV V = I · RV = J / Q

Power or Real Power Watts, kiloWatts,megaWatts

P P = V · I

P = I2 · R

P = V2 / R

Reactive Power VArs, kiloVArs,megaVArs

Q Q = I2 · XL

Q = I2 · XC

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Apparent Power kiloVolt amperes S S = P + jQ

Energy kiloWatthours,megaWatthours, Joules

J J = V · I · t

J = I2 · R · t

Frequency Hertz, cycles per second f

An engineering text would say that a difference in potential (or of voltage) of one volt causes a current of one ampere

to flow through a circuit that has a resistance of one ohm.

The letter E is used when referring to a voltage source such as a generator or a battery and is often called an

electromagnetic force. The letter V is used in all other instances. In both cases the quantity is measured by a quantit

called a volt.

One volt is equal to one watt-second of energy per one coulomb of charge.

Voltage can be thought of as electric potential to deliver energy. Differences in voltage measure the work that would

have to be done to move a unit charge from a point of one voltage to that of another voltage. When a source of

voltage is applied to a wire, a current will flow. The material in the wire offers some resistance to the flow of current.

This resistance is described by a quantity called an ohm .

One ohm is defined as the resistance of a circuit element when an applied voltage of one volt results in a current of

one ampere. The resistance of wire depends on the material it is made of, the cross-sectional area of the wire and its

length. For a given material, the larger the cross-sectional area the lower the resistance .

The letter R is used to represent resistance in ohms. The relationship between voltage, current and resistance is

known as Ohm’s Law. That is, voltage =current x resistance. This relationship is applicable for direct current

conditions.

Electricity is a form of energy which is measured by a quantity called a watt-second . Electric

customers usually see their bills keyed to their watt-hour usage.A related but different quantity is

electric power. The unit of power is the Watt.

In an electric power system the magnitudes of many quantities are such that larger units are needed to describe them

The larger increments usually encountered are described by the addition of the term kilo or the term mega to the bas

unit.

For example, a kiloVolt is 1,000 Volts; a kiloWatt is 1,000 Watts, a megaWatt is 1,000,000 Watts or 1,000 kiloWatts, akiloWatthour is 1,000 Watthours.

Reference // Understanding electric power systems by Jack Casazza/Frank Delea

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What is the Energy but for Real