Guided by -

Prof. Raj Patel

Prepared by -14024010950 7: Anish Singh

14024010950 8: Manish Singh150243109011 : Krunal Panchal150243109501: Shubham Champaneri

Introduction of Choke

A coil of copper wire wound on laminated iron core has negligible resistance is known as choke coil.

When an ac voltage is applied to the purely inductive coil, an emf known as self-induced emf is induced in the coil due to self-inductance of the coil which opposes the applied voltage.

In the case of tube light, the sudden stop of current through the choke produces voltage of several hundreds volts (approx. 900 to 1000V) across it, because of self inductance of coil.

The high voltage starts flow of electrons from one filament to the other through the gas filled inside the tube.

Design Procedure of choke(No air- gap)

The Design Procedure of choke coil is similar to the single phase small transformer design.

Similar terms are use in this case also. The only different is that , it has only one winding support on the iron

core. Therefore, the Turns per volt is found on the basis of ½ output VA this

means if voltage V is applied across choke and I current through the choke, then is taken to find Te from the reference table.

2

VI

Steps in designing the choke

= = ,find Te for this value from the table.

EMF equation E = 4.44Φmf N Bm is given. If not take Bm= 1Wb/m2

.

Stacking factor Ks=0.9 is assumed

Gross area Ai /0.9

2

VI

2

VA

2

Q

m

miB

Aφ=

Square section is used. Width of central limb A = For winding, Turns T=V x Te

Area of the conductor wire =I/δ δ is given = 2.5A/mm2 From this area (a) = π/4 d2

From above equation find d. Refer standard conductor size table and find the matching size d of conductor and

with insertion diameter d1

Space in window for winding = and

Increase the space area by 20% to accommodate former insulation, packing etc. The total area required = 1.2

gA

fS

aT × 2

18.0

=d

dSf

fS

aT ×

2

Design of variable air-gap single phase and 3 phase choke coil

In this section we have study design procedure of choke operating on (I) single phase (II)Three phase with adjustable air-gap between limbs of iron core.

Construction

Iron core of one part variable by rotating wheel and one part is fixed.

Copper coils with N/2 turns.

Rotating wheel to adjust air-gap.

Reluctance is the opposition to the magnetic flux (Φ). Reluctance of air gap is very high as compared with reluctance of iron

material. To produce the same flux more ampere turns (NI) i.e. m.m.f is required

in air compared with ampere turns for iron parts. Generally for the choke coil made copper material R<<L and R is

neglected.

In circuit R= Resistance of coil L= Inductance of coil N=Number of turns of coil V=voltage with frequency f

According to basic equation,dt

diLiRV +=

dt

dNL

φ=and

( )φNdtiRv +=

dt

dNiR

φ+=

Step in Designing a Variable choke

A. For Magnetic part

B. For Electric part

C. Mechanical dimension

D. To find R,L,Z of the coil

For Magnetic part

1. To find constant k

where µ0=Permeability

f= frequency

Vph=phase voltage in r.m.s

Iph=phase voltage current in r.m.s

g

phphig fL

IVABK πµ2. 0

==

2. Knowing the relation

2

2.

gi

ig

B

KA

KAB

=

=

gi

B

KA =

3. Assume staking factor Ks=0.9

9.0≅=gi

isA

AK

igii

s

igi AA

A

K

AA ≥== ;

9.0

4. AT is Amp.Turns (m.m.f) for the air gap lg.

(lg is total length of each air gap)

if lg’ is the length of each air gap

then lg= 2 lg’ for single phase choke

and lg= 1.5 lg’ for 3 phase values

AT required for iron part = AT i

ATi << ATg

ATi = 10 to 20 % of ATg

so that ATtotal = ATi + ATg

Attotal =1.1 to 1.2[Atg]

0

gl.

µg

gB

AT =

For Electric part

1. Number of Turn per coil

= AT/I where I= current There are 2 coil of N/2 turns for single phase variable choke There are 3 coil each of N turns for a 3-phase variable choke.

thus number of turns for the coil are decided.

2. Current density (δ)

Generally enameled copper conductors are used for the choke winding.

δ=2.3 to 2.5 Amp/mm2

for single phase choke current is I

for 3-phase choke current is taken i.e. Iph

3. To find diameter (d) of bare conductor

C.S. area of bare conductor

a =

Hence

2

4d

π

πa

d.4=

4. Use of standard size conductor tables

From these table exact or nearest size of conductor is selected.

(d and a )

d’ = diameter of insulated conductor

So, area of insulated conductor

a’ = mm21

4d

π 2

Mechanical dimension

1. Window size

average value of space factor sf=0.8

sf= active area/gross area

these is for single phase choke

Window area for single phase choke

Window area for 3-phase choke

gross area of window Aw=1.2 to 1.25 Aw’

2

1

d

d

'

'2

2

wA

aN ××

=

sf

aNAw

''

×=

sf

aNAw

'2'

××=

2. Depth df and height hf of coil to be accommodated in the window space.

hf =actual height of coil

hf’ =available height

df =actual depth of coil

df’ =depth of coil

Window area Aw=Hw . Ww

2

ww

AW =

2ww 2WA =

Some clearance on both side 10+10=20mm be kept for formar etc. as shown in the figure.

Available height for winding hf’=Hw-20mm

Height wise turns per larger Nh=

Depth wise turns per layer Nd=

Actual depth of coil, df=df’+5mm

Actual height of coil, hf = hf’+ (2×5)

1

'

d

hf

hN

N

3. To find and distance between the two coils in the window (dc) and overall dimension.

dc=Ww-2df

Distance (D) between of two lines.

D =

D = Ww + A

Total width = D+A

= Ww+2A

22

AAWw ++

To find R,L,Z of the coil

•

where = Resistivity of copper = 1.73 x 10-8

a=C.S area of conductor• Impedance of coil with maximum air-gap

• Reactance XL of coil = Ω

AND XL = 2πfL Ω

L= Henry

Ω=a

lR

ρ

Ω=ph

ph

I

VZ

22 RZ −

f

Xl

π2

ρ

Choke main dimensions

Single phase variable choke 3-phase variable choke

Thank You….