Design and Construction of Constant Voltage Transformer

Abstract

This paper presents the design and construction of constant voltage transformer by means of conventional power transformer core structures. The constant voltage transformer is suitable for use to mitigate the power quality problems associated with the Sri Lankan industrial sector. However, even in today's age of information, many Sri Lankan industrial facilities are not aware of one attractive constant voltage transformer feature-"the ability to mitigate the effects of voltage sags". This method of maintaining the power quality has proven more effective and reliable in international arena

Full text

First
International
Conference
on
Industrial
and
Information
Systems,
ICIIS
2006,
8
-
11
August
2006,
Sri
Lanka
Design
and
Construction
of
Constant
Voltage
Trans
former
Mendis
N.N.R,
Yatiyana
E.M.M.B,
Wijesinghe
K.C,
Lucas
J.R
and
Perera
R.
Department
of
Electrical
Engineering,
Faculty
of
Engineering,
University
of
Moratuwa
Sri
Lanka
,ha
roidik.com,
yatiyana
c
AK,
Kasun
ya
oo.co,
lVucas
e
ect.mrt"ac.k,
*hyrp
gelect.mrt.ac.lk
Abstract
-
This
paper
presents
the
design
and
construction of
Constant
Voltage
Transformer
by
means
of
conventional
power
transformer
core
structures.
The
Constant
Voltage
Transformer
is
suitable
for
use
to
mitigate
the
power
quality
problems
associated
with
the
Sri
Lankan
industrial
sector.
However,
even
in
today's
age
of
information,
many
Sri
Lankan
industrial
facilities
are
not
aware
of
one
attractive
Constant
Voltage
Transformer
feature
-
"the
ability
to
mitigate
the
effects
of
voltage
sags".
This
method
of
maintaining
the
power
quality
has
proven
more
effective
and
reliable
in
international
arena
1.
INRODUCTION
Sri
Lanka
is
a
country
where
variation
in
quality
of
power
supply
is
too
irregular.
"Poor
Power
Quality"
affects
adversely
to
all
over
the
sectors
of
the
economy,
resulting
a
huge
loss
of
revenue
to
the
county
annually
in
tangible
and
intangible
forms.
Although
the
most
electrical
equipments
can
operate
without
problems
even
if
voltage
varies
by
up
to
6%,
may
out
of
tolerance
voltages
still
occur
the
generally
classified
as
sags,
surges
and
brownouts.
These
problems
disrupt
the
smooth
functionality
of
the
industrial
processes.
Ferroresonant
Voltage
Transforner
is
popularly
known,
as
CVT
are
robust
and
simple.
It
provides
an
A.C
output
voltage
of
nearly
constant
magnitude
even
when
the
input
voltage
changes
over
a
specified
range.
It
is
also
completely
and
continuously
short
circuited
in
use,
without
any
adverse
reaction.
Ferro
resonance
regulators
are
the
best
and
most
reliable
power
conditioners
for
applications
ranging
from
process
control
and
automation
to
remote
sites
and
third
world
applications.
And
many
more
other
power
quality
features
ensure
the
use
of
it
as
an
excellent
choice
for
mitigating
power
quality
problems
in
Sri
Lanka,
where
variations
in
the
quality
of
the
power
supply
are
all
too
irregular,
but
where
maintenance
facilities
are
at
a
premium.
In
this
paper,
a
method
of
design
involving
the
conventional
power
transforner
cores
is
presented.
Based
on
the
analysis,
step
-
by
-
step
procedure
is
evolved
for
optimizing
the
design
[
1
]
of
the
constant
voltage
transforner.
Based
on
this
procedure,
a
proto
type
was
built
and
tested
.The
test
results
indicated
good
argument
between
the
predicted
results
through
analysis
and
experimental
measurements,
thus
validating
the
design
procedure.
2.
THEORY
OF
OPERATION
The
operational
theory
of
a
constant
voltage
transforner
is
based
on
a
well-known
phenomenon
known
as
"Ferroresonance"
or
Non-Linear
Resonance.
Some
literature
compares
the
circuit
it
to
that
of
a
Zener
diode.
Ferroresonance
is
the
property
of
a
transformer
design
in
which
the
transforner
consists
with
two
separate
magnetic
paths
with
limited
coupling
between
them.
The
output
contains
a
resonant
circuit
and
it
draws
power
from
the
primary
to
replace
the
power
deliver
to
the
load.
The
B-H
characteristic
of
the
transforner
is
given
in
(Fig-
1).
It
operates
in
the
region
where
denoted
as
"saturated
region".
The
following
illustrate
the
way
of
achieving
the
constant
voltage
at
a
load
end.
Transforner
output
voltage
equation.
is
given
by
following
E(av)output
=4.44BNAJ
Where
B
=
saturated
flux
density
(T)
N
=
no
of
turns
at
out
put
f
=
operating
frequency
(Hz)
A
=
cross
section
area
(m2)
Let
consider
the
working
flux
range
(X-Y)
of
the
transforner
shown
in
(Fig
-1).
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First
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ICIIS
2006,
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August
2006,
Sri
Lanka
AB=
Bx
By
But
AB
O
yin
Therfore
Bx
By
(N,
A
and
f
are
cons
tan
t
for
a
given
transformer)
Fig
2
-
Equivalent
circuit
of
a
ferro
resonance
regulator
A
constant
voltage
is
achieved
during
its
operation.
Where
L-linear
inductor
C-linear
capacitor
R-Load
resistor
The
known
parameters
are
Vl-
Input
voltage
(Voltage
regulation)
that
take
just
before
the
f
-
Source
frequency
Magnetizing
force
(H)
W
Output
watts
(VO2
/R)
Parameters
to
be
calculated
Fig
I
-
B-H
curve
Characteristic
3.
DESIGNING
THE
PARAMETERS
The
design
of
constant
voltage
transformer
is
basically
based
on
designing
of
its
electrical
parameters
and
mechanical
parameters.
The
electrical
parameters
are
associated
with
capacitance,
inductance
estimation,
regulated
voltage
input
range
and
short
circuit
current.
etc.
The
mechanical
parameters
are
dealt
with
calculation
of
core
dimensions.
3.1
ELECTRICAL
PARAMETER
CALCULATION
The
equivalent
circuit
of
a
ferroresonance
regulator
is
shown
in
(Fig
-2).
During
the
design
process
the
values
for
linear
inductor
(L),
Linear
capacitor
(C)
and
Short
circuit
current
(Is)
should
be
derived.
During
the
above
parameter
estimation
the
saturating
reactor
(SR)
is
neglected
due
to
its
high
impedance
at
low
line
condition
compared
to
L,
C
and
R.
[1]
L
C
Cos
VO
VL
Is
Ii
-Inductor
value
-Capacitor
value
-Input
power
factor
-Voltage
where
SR
designed
to
saturate
-Voltage
across
the
inductor
-Short
circuit
current
(when
R=O)
-Input
Current
(Li2+Cv2)
-Determines
the
physical
size
of
L
and
C.
The
equivalent
circuit
(Fig
-2)
is
used
to
derive
the
expressions
for
electric
parameters.
By
applying
the
circuit
laws,
the
expressions
are
derived
to
evaluate
the
values
for
C,
L,
Cos
(I)
VO
and
Is.
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41
VL
L
*
.......................
....................................................
SR
e>
tvo
I
ioti
Flux
Density
(B)
x
y
B-H
LOOP
FOR
SR

First
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CVo2
+Li2=
_2
2
I1
-tan
(t]
w
L
Cos(t)
(1)
(2)
(3)
(4)
Fig
3
-
Power
factor
variation
Equation
(3)
gives
the
physical
size
of
equipment
and
equation
(4)
gives
the
short
circuit
current.
Both
equation
plots
against
k
value
for
different
input
power
factor
values.
According
to
the
graph
in
(Fig-3)
the
best
value
k
(
Vo/Vl)
is
1.6.
The
value
is
chosen
such
that
it
gives
a
small
short
circuit
current
and
smaller
size
at
higher
power
factor
of
0.97.
The
subsequent
expressions
for
the
equations
(1),
(2),
(3)
and
(4)
can
be
expressed
as
follows.
L
1.48V12/
(W*w)
C
W/
(1.95*Vl2w)
(
CV2o
+
Li2
)
2.84WIw
Considering
all
the
practical
issues
and
referring
the
phasor
diagrams
associate
with
the
equivalent
circuit
in
(Fig
-2).
The
basic
design
equations
can
be
summarised
as
in
below.
(1)
Cos
(I
0.97
(2)
i1
W/(0.97
*V1)
(3)
L
1.48
*V12/(W*w)
and
VL
=
1.53
V1
(4)
Design
saturating
reactor
to
saturate
at
1.6
VI
Due
the
non-linearity
of
the
saturating
inductor
(SR)
the
practical
value
of
the
capacitor
is
given
by
(4)
(5)
C
=W/(1.77*Vl*w),
io
i0
1.1
(6)
CV2o
=
1.445
W
/
w
(7)
0
1.1
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w
(k
i2
C
iW-
wVor
K
Cos/
Where
K=Vo/V1,w
=omega
kVl2
L=
Ww
[
Cos$VI
-C
2
Sin2$]
is
i
1
CosJ
I
QCOSj
Q
_Sin2(j

First
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4.2
MECHANICAL
PARAMETER
CALCULATION
The
core
is
three-limed
shell
with
a
magnetic
leakage
path
(Shunt),
dividing
the
winding
space.
The
secondary
limb
consists
of
two
windings
called
capacitive
winding
and
output
winding
(Secondary
winding).
Secondawy
winding
Priame
whnlng
Air
gap
Capaidtive
wMndirig
Fig.4
-Basic
core
structure
of
the
constant
voltage
transformer
The
mechanical
parameters
(Core
dimensions)
are
derived,
referring
the
conventional
power
transformer
core
equations.
Some
of
basic
equations
associate
with
core
parameters
estimation
can
be
stated
as
follows.
[5]
5.
DESIGN
OF
FILTER
CIRCUIT
The
saturation
of
the
core
leads
to
there
being
harmonic
fluxes
present.
These
cause
distortion
of
the
output
voltage
waveform.
Therefore
to
restore
the
quality
of
the
voltage
form
the
filter
circuit
is
incorporated.
Filtering
is
achieved
by.
And
also
a
"compensating
winding
"
can
be
introduced,
in
which
it
produces
a
small
voltage
that
is
used
to
buck
the
out
put
voltage.
ADD
COMPENSATING
WINDING
PRIMARY
ADD
A
CHOKE
230V
NEW
G
~~~~~~~~~~~~~~~~V0
INCREASE
TAPPING
POINT
------l,-
TO
OVERCOME
VOLTAGE
C
DROP
IN
COWP
ENSATING
WDG.
V0
Fig
5
-
Regulator
with
filter
circuit
(1)A=
1.5*kVA
calculation
17.26
*
S
*
P
(2)
W*a=
f*B
calculation
NT
108
-
Cross
section
area
The
value
for
choke
should
be
calculated
such
that,
L
total
=
Leakage
inductance
+
Choke
inductance
-
Window
size
5.
TEST
RESULTS
The
regulated
input
voltage
range
is
in
between
1
90V
to
250
V.
(3)
-=-
V
28.64*f*a*B
calculation
-
Per
turn
voltage
Output
vs
Input
ourye
for
25
(C
I
a
51F}
..250
Where
W
a
f
B
p
S
N
Window
area
in
square
inches
Cross
section
area
in
square
inches
Frequency
in
hertz
Flux
density
in
gauss
Power
in
watts
Current
density
(CMIA)
Number
of
turns
Voltage
in
volts
V
ic00
I,I
np.t
anoev
U
so
1
150
200
25
3U
\AIQm
Fig
6
-
V
out
vs.
V
in
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iso

First
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(Fig
-6)
shows,
output
voltage
is
nearly
constant
after
saturation.
The
saturation
voltage
is
230
V.
For
250
VA
loads
input
voltage
working
range
is
190-250V.
For
the
above
input
range
output
is
within
1%.
The
efficiency
is
in
between
75-80%.
According
to
the
graph
the
efficiency
of
the
regulator
is
almost
80%
at
the
full
load
conditions.
This
is
one
of
the
drawbacks
of
the
regulator.
And
also
the
transformer
is
less
efficient
at
light
load
conditions.
As
a
result,
there
is
a
fixed
amount
of
power
required
to
maintain
the
saturation.
Losses
are
introduced
due
to
the
saturation
of
the
core
and
the
considerable
current
circulating
in
the
secondary
winding.
1E0-
40
-
Q
I
0
40
so
120
160
200
240
Fig
7-
Efficiency
curve
for
25OwLoad
(13.5gf)
The
output
waveform
contains
odd
harmonics.
The
major
harmonics
are
3rd,
5th
and
7th.
Without
having
the
arrangement
as
in
Fig
(5)
the
THD
level
is
around
17%
at
230
V.
The
secondary
of
the
constant
voltage
transformer
is
driven
in
to
the
saturation
mode
of
operation;
hence
it
introduces
a
non-linear
magnetic
behaviour
at
the
output.
Therefore
it
contains
considerable
amount
of
harmonics.
According
the
waveform
observed
it
contains
3rd
harmonics,
5th
and
7th
harmonics
in
large
proportions.
But
it
was
reduced
by
10%,
introducing
a
filter
circuit
at
output
as
in
(Fig
-5).
6.
TECHNICAL
SPECIFICATIONS
OF
THE
TRASFORMER
Rated
Capacity
250
VA
Input
Voltage
Range
190
V
-
250
V
A.C,
1
CD
Frequency
50
+
2.5
Hz
Output
Voltage
230
V
A.C,
1
(D
Line
Regulation
1%
@
rated
load
Load
Regulation
2%0
THD
7°O
Efficiency
80%0
Capacitor
Range
12.5
iF
-14
iF
Short
Circuit
Current
1.6*
rated
current
Total
Harmonic
Distortion
(THD)
was
recorded
700
noh
e10
I
10III
60
40
20
0
l[I1U
2
|
14
15
2
1
1r
1
3
5
Harn1.
IU-
n
be
Fig
-8
Harmonics
at
output
without
filter
CONCLUSION
The
exhilarating
work
associated
with
construction
had
anticipated.
The
initial
studies
opened
up
Sri
Lanka
for
new
technology,
methodologies
and
research
avenues,
which
were
unheard,
therefore
unexplored
before.
The
main
objective
of
introducing
the
constant
voltage
transformer
technology
to
Sri
Lanka
was
achieved.
Analyzing
constant
voltage
transformer
technology,
implementation
of
core
by
scarce
resources
and
tuning
the
matching
capacitor
value
proved
to
be
difficult.
Actual
implementation
was
faced
by
many
challenges
such
as
lack
of
technological
knowledge,
machine
limitation,
and
labour
management.
Group
can
state
with
pride
that
most
of
the
issues
hindering
the
project
were
dealt
with
and
overcome
successfully.
The
achievement
is
expected
to
bring
more
attention
to
constant
voltage
transformer
concept,
where
it
should
undergo
research
to
develop
for
a
better
version.
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2006,
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ACKNOWLEDGMENT
The
Author
thanks
Mr.
Kosal
Gunawardne,
Lanka
Transformer
(Pvt)
Limited,
Sri
Lanka
for
the
help
rendered
during
the
implementation
of
the
project.
And
also
the
appreciation
goes
to
Professor
Rohan
Lucas
and
Professor
Ranith
Prera
for
their
great
advices
during
the
design
and
implementation
of
the
project
REFERENCES:
[1]
Harry
P.Hart
&
Robert
J.Kakalec,
"The
Derivation
and
Application
of
Design
Equation
for
Ferroresonant
Voltage
regulators
and
Regulated
Rectifiers"
[2]
B.Friedman,
"The
Analysis
and
Design
of
Constant
Voltage
Regulator",
IEEE
Trans.-
Components
parts,
Mar.
1956,
pp.
1
1-14
[3]
H.P.
Hart
and
R.J.
Kaklec,
"The
Derivation
and
Application
of
design
equations
for
Ferroresonant
Voltage
Regulators
and
Regulated
Rectifiers"
IEEE
Trans.
on
Mngn.,
Mar.
1971,
pp.
205-21
1.
[4]
IEEE
Standard
44911984
for
Ferroresonant
Voltage
Regulators
[5]
Eric
Lowdon,(1985)
Practical
Transformer
Design
Handbook,
First
Edition,51-82,BPB
Publication,
New
Delhi.
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