Single phase ac systems and basic terminology

Question 1

what is waveform

Answer 1

A periodic waveform is one which repeats itself after
certain time interval.

Question 2

what is a phasor, and what trig identity be used

Answer 2

A Phasor is a rotating vector which effectively
represents a sinusoidal function.

the length of the phasor is its RMS value.

sin (cos to sin+90)

Question 2

when is the sinsodial wave postive and negative or leading or lagging

And how to draw phasor of leading and lagging

Answer 2

If φ is positive,(towards left) it leads the reference sine wave
and lags if φ is negative.(towards right)

Lead more anticlockwise from reference, and lag is more clockwise from refereance

Question 3

phase of an AC and phase angle formula and meaning

Answer 3

fraction of time period that elapsed from the last reference chosen

PHASE angle
it is the corresponding electrical angle which has elasped after the quantity has passed through the given/ chosen reference

theta = 2pif*t = wt

Question 4

rms value

Answer 4

equivalent to its DC value
defined on its heating effect

or AC current when it flows through the same resistor for the same period of time as that of steady current(DC) flowing thru same resistor for same period of time as a result same heat is produced known as RMS

Question 5

average current value

Answer 5

2Imax/pi

Question 6

`phasor relationship

Answer 6

magnitude and phase of the quantity

choose the reference

represent the phase relationship

Question 7

what is impedance(Z) basic formula
and phase difference of current and voltage

Polar and rec form

Answer 7

opposes only AC current
|Z|=|V|/|I|

Z=(R+JXl) - rec
Z<+thetha(phase angle) - polar

Question 8

induction formula

Capacitor series

Pure Resistive

Answer 8

induction formula
Xl= wL (ohms)
I lags V by 90
Z=V/I=wL

Capacitor series
Z=-jXc (ohm)
Xc=1/CW

I leads V by 90

pure resistive

Apparent power(S) = Active both (VI) power(P)
cosΦ =1
power factor=1
reactive power = 0
V and I are in phase

unity
since S = P for resistive circuits. thus 1
P=VI

Question 9

Active power Reactive, Apparent with unit ISA

Answer 9

the power consumed by the load in an AC circuit is called as active power in watts (W) =(Avg Power/true power)

AC power which is not consumed but circulates between the source and the element
represented by Q represented by Visin(theta)
Unit VAR

the total power exsisting in the AC circuit is called as apparent power represented by S = Vrms * I rms
Or I^2R unit VA
Sqrt(P^2+Q^2)=S

Question 10

RL
RC
R

Answer 10

Active power(P) =
I lags V
power factor is btw 0-1
VIcosΦ (active power) ‘
VIsinΦ(Reactive power) ‘+’
tan^-1(X/R)
Z=√R^2+XL^2
V=I*√R^2+XL^2
V=IZ

tan^-1(XL/R)
RL(I lags V by phi)

I leads V
power factor is btw 0-1
VIcosΦ (active power)
VIsinΦ(Reactive power) ‘-‘
Apparent power=VI
tan^-1(Xc/R)
I leads V by phi

Z=√R^2+Xc^2)
V=IZ

Z=R-jXc
Z<-theta

Question 11

RLC inductive
Vl>Vc

RLC capacitive
Vl<Vc

RLC series circuit
Vl=Vc

Answer 11

Z =
√ R^2+(Xl-Xc)^2
V=IZ
V= I*√R^2+(Xl-Xc)^2
Φ tan^-1((Xl-Xc/R))
V leads I by Φ

Z =
√R^2+(Xc-Xl)^2
V=IZ
V= I*√R^2+(Xc-Xl)^2
Φ=tan^-1((Xc-Xl/R))
V leads I by Φ

Vl=Vc
V and I are in phase

Question 12

power factor defintion and formula

power factor of pure resistor circuit, and pure inductor and pure capacitor

Answer 12

ratio of active power to apparent power cos Φ = P/S

power factor = Rt/|Zt|
total resistance and impedance of circuit

unity
since S = P for resistive circuits. thus 1

The power factor of a pure inductor is Zero Lag
since P = 0 for a pure inductor.

The power factor of a pure Capacitor is Zero Lead since P = 0 for a pure capacitor.

thus power factor of inductive circuits is between Zero
and One and Lagging type & for capacitive circuits it is leading type and between Zero and One

Question 13

admitance, conductance and
susceptance
units defintion and formula

Answer 13

Admittance is the reciprocal of impedance, Z and is given the
symbol Y.
Y=1/Z [S]

Conductance ( G ) : Conductance is the reciprocal of resistance, R and is given the
symbol G.

G=1/R [S]

Susceptance is the reciprocal of a pure reactance, X and is given
the symbol B.
-jBl =1/Xl [S]
JBc=1/-Xc [S]

G-jBl=Y<- θ
G+jBc=Y<- θ

Question 14

RL parallel circuits
RC parallel circuits

Answer 14

Y= √G^2+Bl^2
I=VY
Y= G-jBl
=Y< θ
Φ = tan^-1(BL/G)
power factor cos(Φ) = G/Y
pavg=VIcos(Φ)

I lags V by Φ

Y = √G^2+Bc^2
I=VY
Y=G+jBc
Y< θ

Φ=tan^-1(Bc/G)
power factor
cos(Φ) = G/Y

I leads V

Pavg=VIcos(Φ)

Question 15

RLC IL>IC (Bl>Bc)
RLC Ic>IL (Bc>BL)
RLC IL=IC Bl=Bc

Answer 15

Y=
√G^2+(Bl-Bc)^2

Φ= tan^-1
((Bl-Bc)/G)

pavg=VIcos(Φ)
cos(Φ)=G/Y

RLC Ic>IL (Bc>BL)

Y=
√G^2+(Bc-Bl)^2

Φ= tan^-1
((Bc-Bl)/G)

pavg=VIcos(Φ)
cos(Φ)=G/Y

RLC IL=IC Bl=Bc
pavg =VI
cos(Φ)=1

Question 16

voltage and current full formula in single phase systems

Answer 16

√Vr^2+VL^2+2VrVLcos(θ)
√Ir^2+IL^2+2IrILcos(θ)
V = vr+vcoil

Question 17

power formula for average(active), reactive, apparent in term so I and R and power triangle

What should u do when reference foe diagram such as v or I has a angle

Answer 17

p=I^2R, q=1^2(Xla+Xlb), s=1^2Z

P = sqrt(S^2+Q^2)

Ignore angle, take it as 0

Question 18

Power factor improvement

Answer 18

Reducing phase difference btw volatage and current

Inductive loads used need reactive power
Capacitor installed parallel to reacirve power
Capacitor power shouldnt be installed in series as impedance will increase

Advantage
I squared R is reduced
Reactive power will he reduuced
A hivher power factor will help in utilizing the load
Improves performance of motor