Wellcome to Wellcome to Our Presenntation Our Presenntation

On On Alternating CurrentsAlternating Currents

Group Members Group Members Saiful Islam ID:131-15-2516Saiful Islam ID:131-15-2516Md. Jahirul Shahed ID:131-15-2479Md. Jahirul Shahed ID:131-15-2479

Alternating CurrentsAlternating CurrentsAn An alternating currentalternating current such as that such as that produced by a generator has no produced by a generator has no direction in the sense that direct current direction in the sense that direct current has. The magnitudes vary has. The magnitudes vary sinusoidallysinusoidally with time as given by:with time as given by:

Emax

iimaxmax

time, t

E = Emax sin i = imax sin

AC-voltage and current

Alternating CurrentAlternating Current

Alternating current Alternating current flows first in one flows first in one direction and then in the other direction.direction and then in the other direction.

RMS VALUESRMS VALUES

ALTERNATING CURRENT 5

Since voltage and current are always changing we Since voltage and current are always changing we need some way of averaging out their effect.need some way of averaging out their effect.

We use r.m.s values (root-mean-square)We use r.m.s values (root-mean-square) The r.m.s values are the DC values which give the The r.m.s values are the DC values which give the

same average power outputsame average power output

RMS VALUESRMS VALUES EQUATION EQUATION

ALTERNATING CURRENT 6

Pure Resistance in AC Pure Resistance in AC CircuitsCircuits

A

a.c. Source

R

V

Voltage and current are in phase, and Voltage and current are in phase, and Ohm’s law applies for effective currents Ohm’s law applies for effective currents

and voltages.and voltages.I=Io.e^iwt

Vmax

iimaxmax

VoltageCurrent

A Pure Inductor in AC A Pure Inductor in AC CircuitCircuit

A

L

V

a.c.

Vmax

iimaxmax

VoltageCurrent

The voltage peaks 90The voltage peaks 900 0 before the current before the current peaks. One builds as the other falls and peaks. One builds as the other falls and

vice versa.vice versa.I=Io.e^i(wt-90)I=Io.e^i(wt-90)

Inductive RInductive Reactanceeactance

ALTERNATING CURRENT 9

It measures how well an inductor can limit It measures how well an inductor can limit alternating currentalternating current

It depends on the frequency of the ac supply.It depends on the frequency of the ac supply. It depends on the size of the inductorIt depends on the size of the inductor

A Pure Capacitor in AC A Pure Capacitor in AC CircuitCircuit

Vmax

iimaxmax

VoltageCurrentA V

a.c.

C

The voltage peaks 90The voltage peaks 900 0 after after the current the current peaks. One builds as the other falls and peaks. One builds as the other falls and

vice versa.vice versa.I=Io.e^i(wt+90).I=Io.e^i(wt+90).

Capacitive RCapacitive Reactanceeactance

ALTERNATING CURRENT 11

Reactance is a measure of how a capacitor can limit Reactance is a measure of how a capacitor can limit alternating currentalternating current..

It is It is similarsimilar to resistance but differs in that it is to resistance but differs in that it is dependent on the frequency of the ac supply.dependent on the frequency of the ac supply.

It also depends on the size of the capacitor.It also depends on the size of the capacitor.

Series LRC CircuitsSeries LRC Circuits

L

VR VC

CRa.c.

VL

VT

ASeries ac circuit

Consider an Consider an inductorinductor LL,, a a capacitorcapacitor CC,, and a and a resistorresistor RR all connected in all connected in seriesseries with with an ac sourcean ac source. . I=Io(e^i(wt-angle).I=Io(e^i(wt-angle).

Phase in a Series AC Phase in a Series AC CircuitCircuitThe voltage The voltage leadsleads current in an inductor current in an inductor

and and lagslags current in a capacitor. current in a capacitor. In phaseIn phase for for resistance resistance RR..

450 900 1350

1800 2700 3600

V V = Vmax sin

VRVC

VL

Rotating Rotating phasor diagramphasor diagram generates voltage generates voltage waves for each element waves for each element RR, , LL, and , and C C showing showing phase relations. Current phase relations. Current i i is always is always in in phasephase with with VVR.R.

AAdvantagesdvantages

ALTERNATING CURRENT 14

The single greatest advantage of alternating current The single greatest advantage of alternating current is that AC current can be transformed and DC is that AC current can be transformed and DC current cannot be transformed.current cannot be transformed.

It can be controlled by a wide range of componentsIt can be controlled by a wide range of components eg.eg.resistors,capacitors and inductors.resistors,capacitors and inductors.

This allows high-voltage electrical power to be This allows high-voltage electrical power to be distributed with smaller wires and lower amperage.distributed with smaller wires and lower amperage.

RReferenceseferences

ALTERNATING CURRENT 15

• http://www.teachersdomain.orghttp://www.teachersdomain.org• http://www.peetvs.co.zahttp://www.peetvs.co.za• http://http://www.sjsu.eduwww.sjsu.edu• http://www.youtube.comhttp://www.youtube.com• http://http://www.wikipedia.comwww.wikipedia.com• http://www.upscale.utoronto.cahttp://www.upscale.utoronto.ca• NCEA A.S 3.6 Text Chapters 18-19NCEA A.S 3.6 Text Chapters 18-19• Yrd. Doç. Dr. Levent Çetin/ alternatif akımYrd. Doç. Dr. Levent Çetin/ alternatif akım

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