ECM216 BUILDING SERVICES Bab 1.3 Generator and Alternator

7/29/2019 ECM216 BUILDING SERVICES Bab 1.3 Generator and Alternator

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EDITED BY

AZUAN AHMAD FAUZI 2011803188

UITM PULAU PINANG MAC 2013

GENERATOR & ALTERNATER

2 type of generator :1. DC generator2. AC alternator

Both generator work on same scientific principle where electric current produced byelectromagnet induction . Only differ in the way they are built and used.

BASIC PRINCIPLE ON HOW SIMPLE GENERATOR / ALTERNATOR WORK Generator / alternator changes M.E E.E A turbine, diesel engine or some other machine that produce M.E must drive every

generator.

Generator/ alternator produce electricity by a principal loop/coil near a magnet or bymoving a magnet near the coil.

If a coil of wire is rotated between the poles of magnet the two sides of the coil cut thelines of force and this generators electricity in the coil.

Connection between loop coil and external circuit;o if uses slip ring produce A.Co if uses commutator produce D.C

This process is called electromagnetic induction. Electricity produce is called an inducedvoltage or induce electromotive force (EMF).

Voltage that generator / alternator produces can be increased by,1. Strength of magnetic field.2. Speed at which the loop rotate.3. Number of loops of wires that cut the magnetic field.

GENERATION OF DIRECT CURRENT (DC)

DC flows in one direction . It can be generated from various source such as :1. Dry & wet cell batteries2. Photo voltaic cells3. DDC dynamos (small DC generator)4. DC generators (large DC dynamos)

DC can also be produced from AC by usage of rectifier / converter. D.C generators to change from simple generator must :

o The current must be conducted from the rotating loop of wire.o The current must be made to more in only one direction

Device : Commutator How DC work?

o Commutator rotate with loop of wire . Each half commutator called segment &insulated from the other half. Each end of rotating loop wire connect to

commutator segment. 2 carbon brushes connected to the outside circuit.

A simplified basic dc generator

Advantages of DC : Disadvantages of DC : Power generation can be from large to

the portable generator depending uponusage.

Power generation from small tominiature batteries for small electric

gadgets (e.g : watches , calculators etc.) Can utilizes fossil fuel efficiently. Reliable quick power back-up during

emergency ( e.g : blackout )

Unable to change to different rangeof voltage

Very dangerous for public utilizationif high voltage


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GENERATION OF AC

AC flow in alternative direction (both) . Can be generated by alternator at power station. Advantage of AC :

o Voltage can be raise / lowered economically by transformer high voltage forgeneration & transmission.

o AC motor less complex than DC motor can be built without brushes & commutator less maintenance

AC is electric current that flows for an interval of time in one direction and then inopposite direction, current flow in alternately reversed directions thought or around acircuit.

To change simple DC generator into AC generator :o Current must be conducted from rotating loop of wire.o Current must be made to more in both direction.

Device : Slip rings Done by help of collector rings/slip rings and carbon brushes. Each end of loop of wire

connected to a ring. The ring rotate with the loop of wire. Brushes rest against each ringand connected to a wire. Current produce in the loop of wire flow in and out of generatorthru the rings and brushes.

The movement of alternating current

Graph of AC from a power supply

This shape is called a sine wave


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Advantages of alternating current Disadvantages of alternating current

o An AC voltage can be easilytransformed to a higher or lowervoltage, with very little loss of power,by passing it through a device known astransformer.

o Alternating current can be convertedinto direct current very easily so that

direct current can be made availableto any equipment which needs it.

o It is much easier and cheaper toconvert AC to DC than to convert DC

to AC.

o AC is the greater amount of insulationrequired for wires carrying AC current.

o This is because AC voltage is muchgreater, it is more dangerous than DC.

Electromagnetic force (voltage) can be increase by

1. Strength of magnetic field2. The speed of coil/loops/armature rotates3. No. of windings


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SINGLE PHASE & THREE , STAR DELTA CONNECTION

1. THREE PHASE In mostly countries , power is generated as a three phase 60 hertz voltage. The term three phase means that there are three separate voltage waveforms

produced by the alternator (generator that produced AC voltage) For the alternator to produce the three phase , the internal winding of the

alternator called the stator are wound 120 apart , the three voltages are

120out of phase with each other. The winding of the stator are connected to form one of the two basic three

phase connections. These connections are the delta and wye (star)

2. WYE (STAR) CONNECTION Made by joining one end of each of the windings together. One end of each of the windings is joined at the centre point. The wye connection can be used to provide an increase in the output or line

voltage. The phase voltage produced across one of the windings. The line voltage voltage produced across the output points of points of the

connection. In wye connection , phase current and line current are equal. But the voltages are different. The line voltage is 1.732 or 3 t imes greater

than the phase voltage.

3. DELTA CONNECTION The value of phase voltage and line voltage are equal for the delta connection. But the current is different. The line current is 1.732 times greater than the

phase current. This reason make the delta connection is so popular in industry.

4. SINGLE PHASE SERVICES A single phase 240/120 volt system can be obtained by connecting a single

transformer to two lines of a three phase system. Single phase services produce voltages that are 180 out of phase with each

other. Single phase services generally provide a 120/240 volt connection by grounding

the center tap of a transformer secondary and using it as neutral conductor.

REAL REACTIVE AND APPARENT POWER

1. AC power Power is defined as the rate of flow of energy past a given point. Alternating current (AC) circuits contain 3 basic types of loads:

resistive inductive capacitive

In AC circuits, energy storage element such as inductance & capacitance mayresult in periodic reversals of the direction of energy flow.

2. Real Power In a direct current (DC) circuits, the true/ real power (watt) is always equal to the

voltage multiplied by the current. This is because the current and voltage are never out of phase with each

other. This is also true for an AC circuit that contains only pure resistance since the

voltage and current are in phase. The portion of power flow that, averaged over a complete cycle of the AC

wave form, result in net transfer of energy in one direction is known as real

power.

3. Reactive Power In a circuit that contains pure inductance, there is no true power or watts. The

portion of power flow due the stored energy, which returns to the source in each

cycle, is known as reactive power. In this type of circuit, the voltage multiplied by the current equals a value known as

VARS ( volt- amps reactive) & often referred to as watt less power

4. Apparent Power the apparent power or volt-amps of an AC circuit is the applied voltage multiplied

by the current flow in the circuit.

The amount of apparent power as compare to the true power or VARS isdetermined by the element of the circuit itself.

The apparent power is found by adding the watts & VARS together in the samemanner that the resistance & inductive reactance were added to find the totalvalue of impedance


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POWER FACTOR

The power factor of an alternating current (AC) circuit is a ratio of the true / realpower to the apparent power

Power Factor , PF = W ( true power )VA ( apparent power)

Ex : PF = 400 watts500 volt- amps

=80%

In the circuit, the power factor is 80%. this means that 80% of the load is resistiveand 20% is reactive.

If the load is pure resistive, the power factor would be 100% or unity. If the applied voltage is 120 volt, 4.16 amps of current must supply to operate the

load(500 volt-amps) However the actual amount current being used to operate the load is 3.33 amps. Low PF means less true/real power is transmitted. High PF means more true/real power is transmitted For circuit with more resistance (R) + capacitive reactance

o Capacitor in a circuit will increase PF For circuit with more resistance (R) + inductive reactance

o Adding inductor in a circuit will decrease PF Lower PF will be charged more because less usage of real power.

TRANSFORMERS

Transformers is a electrical device consisting of one or more coil of wire placed in closeproximity to one or more other coil, used to couple two or more AC circuit together byemploying the induction between the coil

The coil connected to power source is primary and other is secondaryThe connection can be in delta-delta or delta-star depend on how many wire usage is needed

ECM216 BUILDING SERVICES Bab 1.3 Generator and Alternator

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