The document discusses automatic voltage regulation and V-curves. It defines voltage regulation as maintaining a constant desired voltage of an alternator. Voltage regulation is required to prevent damage to electrical components from voltages outside tolerance limits. There are different types of automatic voltage regulators that control excitation to maintain the output voltage, including manual, thyristor-type electronic regulators. The electronic regulators use components like voltage sensing, comparing, amplifying and correcting units. It also discusses the V-curve, which plots the variation of armature current with field current under different loading conditions like under, normal and over excitation.

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Automatic voltage
regulation & V-curves
M O H A M M A D S H O I A B B A B A R
E l e c t r i c a l E n g i n e e r i n g D e p a r t m e n t
U n i v e r s i t y o f G u j r a t

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Contents
we t r i e d t o c o v e r b r i e f l y a b o u t t h e
 v o l t a g e r e g u l a t i o n ,
 d i ff e r e n t t y p e s o f A u t o m a t i c Vo l t a g e R e g u l a t o r s
 t h e r e c o n s t r u c t i o n
 wo r k i n g p r i n c i p l e

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So let’s start with, What is
Voltage Regulation?
 I t i s a p r o c e s s c o n t r o l t o m a i n t a i n a c o n s t a n t
d e s i r e d v o l t a g e o f a n a l t e r n a t o r

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Definition
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• The voltage regulation of an alternator is defined as the change in terminal
voltage from no-load to full-load (the speed and field excitation being
constant) divided by full-load voltage.
Formula
 so if Vph = Rated terminal voltage
 Eph = No load induced emf
 % regulation = (Eph – Vph ) X 100/ Vph

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 E v e r y e l e c t r i c a l c o n s u m e r i s d e s i g n e d t o w o r k a t a
s p e c i f i e d v o l t a g e w i t h s o m e t o l e r a n c e .
 S o w h e n e v e r a v o l t a g e g o e s b e y o n d t h a t t o l e r a n c e
l i m i t , e l e c t r i c a l m a c h i n e r y g e t h i g h l y a f f e c t e d
 S p e c i f i c a l l y m o t o r s a s To r q u e ( τ ) ∝ V ²
 S o d u e t o a n i n a p p r o p r i a t e s u p p l y v o l t a g e , t h e
u l t i m a t e r e s u l t i s p r e m a t u r e f a i l u r e o f e l e c t r i c a l
c o m p o n e n t s
 To p r e v e n t t h i s w e u s e a v o l t a g e r e g u l a t o r
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Now let see, Why is voltage
regulation required?

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Now we have to understand
what is a voltage regulator?
 A voltage regulator is an electrical device that regulates
voltage to the desired level at all times.
 It utilizes electrical components or electro-mechanical
mechanism for maintaining a steady stream of voltage to the
machinery
 Which may be disrupted during power surges such as
starting of the highly rated motor, for example, starting of
FD fan.

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TYPES OF VOLTAGE REGULATIONS

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A) Manual Voltage Regulator
 If the rheostat is set to increase the resistance in the field circuit.
 less current flows through the field winding.
 the strength of the magnetic field in which the armature rotates
decreases.
 Consequently, the voltage output of the generator decreases
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B) Automatic Voltage Regulators(GENERAL TYPE)
wh i c h m a i n t a i n t h e o u t p u t v o l t a g e b y c o n t r o l l i n g
t h e e x c i t a t i o n o f t h e a l t e r n a t o r.

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1 . C o n t r o l s t h e v o l t a g e o f t h e s y s t e m a n d o p e r a t i o n o f t h e
m a c h i n e n e a r e r t o t h e s t e a d y s t a t e s t a b i l i t y.
2 . I t d i v i d e s t h e r e a c t i v e l o a d b e t w e e n t h e a l t e r n a t o r s
o p e r a t i n g i n p a r a l l e l .
3 . T h e a u t o m a t i c v o l t a g e r e g u l a t o r s r e d u c e t h e
o v e r v o l t a g e s w h i c h o c c u r b e c a u s e o f t h e s u d d e n l o s s o f
l o a d o n t h e s y s t e m .
4 . I t i n c r e a s e s t h e e x c i t a t i o n o f t h e s y s t e m u n d e r f a u l t
c o n d i t i o n s s o t h a t t h e m a x i m u m s y n c h r o n i z i n g p o w e r
e x i s t s a t t h e t i m e o f c l e a r a n c e o f t h e f a u l t .
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There are following main
functions of an AVR

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T h y r i s t o r - t y p e
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Electronic voltage
regulator
In a process control of voltage regulation by
electronic AVR involves the following components
1. voltage sensing unit – to check the present value of the
voltage
2. voltage comparing unit – to check error .i.e. difference in
voltage
3. amplifying unit – to amplify the error signal
4. correcting unit – to apply actions to process control as per
error to get desired output voltage

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 T h e v o l t a g e s e n s i n g u n i t t r a n s f o r m
d o w n , r e c t i f i e s a n d s m o o t h t h e
g e n e r a t o r o u t p u t v o l t a g e . T h i s
p r o d u c e s a l o w v o l t a g e D C s i g n a l
p r o p o r t i o n a t e t o A C g e n e r a t o r v o l t a g e .
 I n c o m p a r a t o r u n i t , i t i s c o m p a r e d t o
t h e s e t v a l u e ( D C v a l u e p r o d u c e d b y
r e f e r e n c e u n i t o f t h e Z e n e r d i o d e s a n d
r e s i s t a n c e ) .
 T h e c o r r e c t i o n i s t h e n a m p l i f i e d a n d
t h r o u g h t h y r i s t o r c o n t r o l i s u s e d t o
a l t e r t h e a l t e r n a t o r f i e l d c u r r e n t i n
o r d e r t o r e a c h t h e s e t v o l t a g e v a l u e .
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CIRCUIT CONCEPT

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AT HIGH LEVEL
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V CURVE OF ALTERNATOR

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V CURVE​ :
V-curve and power factor control of generator are closely
related to each other. V-curve of Generator is basically a
plot of variation of armature current with the change in
field current. For a constant power, V-curve can only be
obtained for generator connected to infinite bus / grid.
There does not exists any such curve for an isolated
generator.​

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V curve tells us about….
Relation between (Armature Current) and Field
Current at different loads .​
Field Current is used to fill the gap with magnetic
flux. Which depends upon the applied dc voltage to
the field winding.

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After having the concept behind the three cases discussed, it is
better to plot a curve between field current and armature
current. This curve is popularly known as V-curve of Generator
connected to infinite bus.
“V-curve of Generator is a plot of variation of armature current with
the change in field current. “ This curve for generator connected to
infinite bus is show below.

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Stages of Curve:
There are 3 stages of curves depending upon field current.

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Under excitation:
When the field current is sufficient to produce magnetic flux but no enough
to fill the air gap in alternator then this condition is called under excitation.
In this condition motor draws magnetizing current from armature winding
and alternator goes to leading power factor.

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Phasor Diagram of a loaded Alternator
Leading PF Load
Ia
IaRa
IaXsEph
Ia
IaZS
O A B
C
Φ
Eph = √ (Vph Cos Φ + Ia Ra)2 + (Vph Sin Φ - Ia Xs)2

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Normal Excitation:
If field current is increased and is sufficient to produce and fill the air gap
then no magnetizing current is required. This stage is called normal
excitation. At this stage power factor is unity.

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Phasor Diagram of a loaded Alternator
Unity PF Load
Ia IaRa
IaXs
Eph
Vph
IaZS
O A B
C
Reference as Voltage (V)
OA – Vph
AB – IaRa
BC – IaXs
AC – IaZs
OC – Eph
Consider Δ OBC
(OC)2 = (OB)2 + (BC)2
(Eph)2 = (OA+ AB)2 + (BC) 2
(Eph)2 = (Vph + IaRa)2 + (IaXs) 2
Eph = √ (Vph + IaRa)2 + (IaXs) 2

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Over excitation:
• If field current is further increased then flux passes through armature
winding and armature draws a demagnetizing current. This stage is called
over excitation and power factor is lagging in this stage.

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Phasor Diagram of a loaded Alternator
Lagging PF Load
Ia
IaRa
IaXs
Eph
Vph
IaZS
O A
B
C
Consider Δ OBC
(OC)2 = (OA)2 + (BC)2
(Eph)2 = (OA+ AB)2 + (BC) 2
(Eph)2 = (Vph + IaRa)2 + (IaXs) 2
Φ
Eph = √ (Vph Cos Φ + Ia Ra)2 + (Vph Sin Φ ± Ia Xs)2

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Figure shows the v curve of the alternator
Where A,B,C are full load, half load,and at no load respectively. And --
--shows unity power factor.

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Thank You@uog.edu.pk