11

ElectricityIntroduction

2

Electricity Current

Four (4) requirements for an electrical current.1 An abundance of electrons (-) 2 A scarcity of electrons (+) 3 A conducting material4 The conducting material connecting the area of abundance and the area of

scarcity.

3

Electrical Current--cont.

Four common methods of developing a surplus of electrons:

1. Electromechanical

2. Electrochemical

3. Thermoelectrical

4. Photoelectrical

4

1. Electromechanical

• Generators and alternators are electromechanical devices.

• An electromechanical device produces electricity when it rotates.

• Generators/alternators produce electricity through electromagnetic induction.

What are the four (4) common sources of power to rotate generators and alternators?

How efficient is a generator in converting mechanical power to electricity?

5

2. Electrochemical

Electrochemical reactions can either produce electricity,

Chemical reaction produces a voltage

A voltage causes a chemical reaction

or use electricity.

6

3. ThermoelectricalThermoelectrical devices can either uses electricity to produce heat,

A thermocouple uses a heat to produce electricity.

An electric heater produces heat using electricity.

or use heat to produce electricity.

How efficient is an electric heater in converting electricity to heat?

7

4. Photoelectrical

Photoelectricity is the emission of electrons from materials upon absorption of electromagnetic radiation.

Photovoltaic Cell (PV Cell)How efficient is a good quality PV cell?

8

Electrical current—cont.

There are three (3) components of electrical/mechanical systems currents, magnetic fields and motion. Different combinations have different outcomes.

€

Magnetic field+ Motion=Current

€

Current + Magnetic field=Motion

Electric generator

Electric motor

9

Electrical Theory - Summary• Electricity is a form of energy that can produce light, heat,

magnetism, chemical changes and motion.

– Light occurs when electricity passes through a filament.

– Heat is produced when electricity flows through a resistance.

– A magnet field forms around any conductor carrying electricity.

– Electricity passing through water causes the hydrogen and oxygen to split.

– Like poles repel each other (motor)

10

Principles of Electricity

11

Introduction

• Electricity is the primary source of power for stationary equipment.

• A basic understanding of the principles of electricity is a requirement for using electrical powered equipment efficiently and safely.

12

Electrical TermsTo understanding electricity you must know and be able to explain the following sixteen (16) electrical terms:

1 Resistance

2 Amperes

3 Volts

4 Ohms law

5 Conductor

6 Insulator

7 Electrical circuit

8 Series circuit

9 Parallel circuit

10 AC current

11 DC current

12 Electrical power

13 Electrical energy

14 Resistance loads

15 Reactant loads

16 Power Factor

13

1. Resistance

• Resistance: a measure of the difficulty encountered by the electrons as they flow through a conductor.– Resistance is a characteristic of all materials.

– Electricity passing through a resistance causes heat.

– Resistance is measured in units of Ohms ()

An Ohm is defined as the resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces a current of 1 ampere.

Why do the connections on a extension cord get hot?

14

2. Amperes

Amperes: the measure of the rate of current flow.

What does the rate of flow mean?

1 amp = 6.24 × 1018 electrons per second

A current (amperage) occurs whenever there is a source of electricity, conductors and a complete circuit.

Standard domestic circuits are fused at 15 or 20 amps.

What does this mean?

15

3. Volts

Voltage (E or V): the electromotive force (potential)

available to cause electrons to flow.

Voltage is always measured by comparing the difference (potential) between two points.

What does the term potential mean?

What is the unit of measure for voltage?

Standard domestic current is 120V.

Are all U.S. electrical circuits 120V?

16

4. Ohm’s Law

Ohm’s law explains the relationship between voltage, amperage and resistance.

Ohm’s law states that the flow of electricity through a conductor is directly proportional to the electromotive force that produces it.

Expressed as an equation:

€

E = IR

E = ( )electromotive force volts

I= ( )electrical intensity amps

R = ( ) resistance Ohms

17

Ohm’s Law Example

What is the voltage in a circuit with current of 6 amps and a resistance of 12 ?

€

E = IR

= 6 amp x 12 Ohm = 72 V

18

Ohm’s Law Example

What is the current flow in a circuit with a voltage of 120 volts and a resistance of 0.23 ?

€

E = IR

I =ER

=120 V0.23 Ω

= 521.7 A

Ohms law can also be used to teach electrical safety.

How does this teach electrical safety?

19

5. Conductor

Conductor: any material that has a low resistance to the flow of electricity.

Material Ohms/cmil-ftSilver 9.8

Copper 10.37

Gold 17.7

Aluminum 17.02

Steel 95.8

What type material makes a good conductor? Why?

Is the resistance the same for all metals?

Is the resistance of a conductor constant?

20

6. InsulatorAn insulator is any material that provides a high resistance to the flow of electricity.

What types of materials make good electrical insulators?

Is the resistivity of an electrical insulator constant?

How are the insulating qualities of a material rated?

21

7. Electrical Circuit

An electrical circuit is a network of conductors and electrical components that form a complete path for electricity.

Electricity that leaves the source can pass through the switch, the light and return to the source.

Is the illustration a circuit?

Will the bulb be lit?

22

8. Series CircuitIn a series circuit the the electricity has no alternative paths from the source to the loads and back.

An Amp meter must be in series with the load to measure current (amps).

This is a series circuit because an electron leaving the source must travel through the switch and both lights before it can return to the source.

Can you give an example of this type of circuit?

23

9. Parallel circuitIn parallel circuit the electricity has alternative paths.

A volt meter is attached parallel to the load to measure voltage.

This is a parallel circuit because the electricity has alternative paths.Some will go through the blue light and some will go through the white light.

Can you give an example of this type of circuit?

24

10. Alternating Current

• The amperage and voltage varies over time and periodically reverses direction (cycles).

• U.S. standard domestic electrical service is 60 cycle.

Does current flow all the time?

25

11. Direct Current-cont.• Direct current

– The electrons move in one direction only.

– Amperage is constant.– Voltage is constant

• The type of current used in batteries.

Why isn’t AC current used in batteries?

26

12. Electrical Power

Electrical power is the rate at which electric energy is transferred in an electric circuit.

€

Watts= Amperes x Volts

€

Volts=Watts

Amperes

€

Amperes=Watts

Volts

The rate of energy transfer is measured in units of Watts.

Watts are determine by multiplying the Voltage X the amperage.

Which also means:

Is there a conversion from Watts to horsepower?

Horsepower is the measure of mechanical power.

27

12. Electrical Power-cont.

Electrical Power exampleDetermine the power consumed by a resistor in a 12 volt system when the current is 2.1 amps.

€

Load (amp) =Watts

Volts=

1500 W

120 V= 12.5 amp

Electrical Power exampleDetermine the amount of load a 1,500 W appliance will place on a circuit if it operates on 120 V..€

Power (W) = volts x amps = 2.1 amp x 12 V = 25.2 W

28

12. Electrical Power--Electrical wheel• The electrical wheel Illustrates Ohm’s

law and the electrical power equation.

• The value at the point of the 4 pie slices can be found using any one of the three equations on the rim of the pie slice.

• Example: E (Volts) can be determined by

€

P • R P

I

I • R

29

13. Electrical Energy

Electrical energy is energy provided by the flow of electrons through an circuit.

Electrical energy is measured in units of Watt-hours.

What do the letters kWh on the face of the meter mean?

What is the purpose of this type of meter?

30

13. Electrical Energy-cont.

Determine the amount of energy a 100 Watt light bulb will use when operated for 8 hours.

€

Energy (Wh) = Power x Time

= 100 Watts x 8 hour

= 800 Wh

What will it cost to operate the light bulb if the electrical energy costs 0.12 $/kWh?

€

$ = 0.12 $

kWh x 100 W x

1 kW

1,000 W x 8 h = 0.096 $

Online energy calculator http://www.csgnetwork.com/elecenergycalcs.html

31

13. Electrical Energy-Electricity costs

• Watt-hour (Whr) is the measure of energy used. • Used to determine energy cost.• Domestic users the monthly cost is a combination of:

• monthly service charge• kWh used x rate (kWh x $/kWh)• taxes• energy charge

32

13. Electrical Energy—Electrical use rates

• Not all of the kWh’s used cost the same.• Some utilities may contract for a base line use and charge more for

electricity used above a baseline.• Some large users may be able to negotiated a rate structure that reduces

the cost per kWh as the amount used increases.

33

13. Electrical Energy—Base line Structure

• Example of baseline structure.– The user contracts 120 kWh per month for a rate of $0.12 kWr and 120%

increase for any monthly use above 120 kWh. • What is the bill for a month when 134 kWh’s were used?

€

Baseline quanity 120 kWh x $0.12 = $ 14.40

120 % of baseline 34 kWh x $0.144 = 7.90

Monthly cost $ 19.30

Remember, monthly charges, energy costs, etc. will also be add to the monthly bill.

34

13. Electrical Energy—Tiered rates

• Example tiered electrical rates:– First 500 kwh @ $0.07/kWh– Next 1,000 kwh @ $0.065/kWh– Over 1500 kWh @ $0.057/kWh

€

500 kWh x $ 0.07

kWh= 35.00

1,000 kwh x 0.065 $

kWh= 65.00

1,000 kWh x 0.057 $

kWh= 56.00

$ 156.50

Determine the charge for 2500 kWh of electricity using the tiered rate structure.

35

13. Electrical Energy--Additional Factors

• Fuel charge• Demand charges• Off peak use• Volunteer load cycling

36

14. Resistance loads

Resistance loads convert electrical energy to heat.

What are some examples of resistance loads?

37

Examples of reactance loads are motors and fluorescent lights.

15. Reactance loads

Reactance is the opposition of a circuit element to a change in the electrical current or voltage.

38

16. Power Factor

Power factor in a electrical system is the ratio of the real power flowing to the load compared to the apparent power in the circuit.

In some circuits the apparent load is the Watts (volts x amps), but due to energy stored in the load or non linear loads the real power will be less than apparent power.

Power factor occurs in circuits with reactance loads.

39

Power Factor—cont.

In AC resistive circuits all of the power is consumed so none is stored in the load and no distortion occurs.

Notice: the power, voltage and current curves are in phase--the peaks and lows are aligned vertically.In this situation the power factor is 1.0.

40

Power Factor - Reactive Loads

When the load is reactive the current lags the voltage.This causes a phase shift--the peaks and lows are not aligned vertically.Notice: during the time the instantaneous power curve is below zero, the current is negative.

Negative current means that for this portion of the cycle, power is flowing back to the source.

During this part of the cycle, the actual power used is less than the indicated power use.The power factor is less than one (1).

41

Questions