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Transformer Question No.34 - Designing of choke/reactor
How to design a choke/reactor for 3phase 18amps 1.1mh
how to calculate
1) core area
2) no of turns
Author : Sudharsan - From: India
Sat, December 5th, 2009 - 14:10
The design of a linear ac inductor depends upon five related factors:
1 . Desired inductance
2. Applied voltage, (across inductor)
3. Frequency
4. Operating Flux density
5. Temperature Rise

With these requirements established, the designer must determine the maximum values for, Bac, which will not produce magnetic saturation, and make trade-offs that will yield the highest inductance for a given volume. The core material selected determines the maximum flux density that can be tolerated for a given design.
The ac inductor,  must support the applied voltage, Vac. The number of turns is calculated from Faraday's Law, which states:

The inductance of an iron-core inductor, with an air gap, may be expressed as:

Inductance is seen to be inversely dependent on the effective Magnetic Path Length, MPL, which is the sum of the air gap length, lg, and the ratio of the Magnetic Path Length, MPL, to material permeability, um.
When the core air gap, lg, is larger compared to the ratio, MPL/iim, because of the high material permeability, um, variations in, |tim, do not substantially affect the total effective Magnetic Path Length, MPL, or the inductance, L. The inductance equation then reduces to:

AC Inductor Design Example

Step No. 1 Design a linear ac inductor with the following specifications.
1. Applied voltage, VL = 120 volts
2. Line current, IL = 1.0 amps
3. Line frequency = 60 hertz.
4. Current density, J = 300 amp/cm2
5. Efficiency goal, μ(100) = 90%
6. Magnetic material = Silicon
7. Magnetic material permeability, μm = 1500
8. Flux density, Bac = 1.4 tesla
9. Window utilization, Ku = 0.4
10. Waveform factor, Kf = 4.44
11. Temperature rise goal, Tr = 50°C

Step No. 2 Calculate the apparent power, Pt or VA of the inductor, L.

Step No. 3 Calculate the area product, Ap.

Step No. 4 Select an suitable core frame ( e.g. EI lamination). The closest lamination to the calculated area product, Ap, is the El-100 with following charcteristics.

1. Core Number = EI-100
2. Magnetic Path Length, MPL = 15.2 cm
3. Core Weight, Wtfe = 676 grams
4. Mean Length Turn, MLT = 14.8 cm
5. Iron Area, Ac = 6.13 cm2
6. Window Area, Wa = 4.84 cm2
7. Area Product, Ap = 29.7 cm4
8. Core Geometry, Kg = 4.93 cm5
9. Surface Area, A, = 213 cm2
10. Winding length, G = 3.81 cm
11. Lamination tongue, E = 2.54 cm

Step No. 5 Calculate the number of inductor turns, NL.

1. Ruben, L., and Stephens, D. Gap Loss in Current-Limiting Transformer. Electromechanical Design,
April 1973, pp. 24-126.
Author : Hamid - From: Iran
Mon, December 7th, 2009 - 19:52
     thanks for ur reply , i have some more doubts in that design

1)  how to calculate saturation level
2) till what order of harmonics will be controlled in the choke
3) how to calculate total harmonic destortion (THD)
4)  how to design  3 phase reactors
5) difference in designing input and output choke for variable frequency drives(drives)
6) can we have very small air gap in chokes

ive bought a choke  3 phase 415v 250A 0.028mh (for110kw vfd) it is giving heavy noise & heat , the choke has very small air gap(almost no gap, top core virtually sits on bottom core ) , mechanically every thing is right ,is that  because of the small air gap the choke is giving problems another choke of different manufacturer is working fine , or what may the problem in choke , please guide me. 
Author : Sudharsan - From: India
Tue, December 8th, 2009 - 16:06

Fringing flux can cause a multitude of problems. Fringing flux can reduce the overall efficiency of the converter, by generating eddy currents that cause localized heating in the windings and/or the brackets.
When designing inductors, fringing flux must to be taken into consideration. If the fringing flux is not handled correctly, there will be premature core saturation. More and more magnetic components are now designed to operate in the sub-megahertz region. High frequency has really brought out the fringing flux and its parasitic eddy currents. Operating at high frequency has made the engineer very much aware of what fringing flux can do to hamper a design. So you must check the rated frequency of your chock and existing harmonics of system in operation cases.
There are designs where it is important to place the gap in an area to minimize the noise that is caused by the fringing flux at the gap. The gap placement for different core configurations is shown in below Figure.
The standard gap placement is shown in Figure A, C, and D. The EE or EC cores shown in Figure B, are best-suited, when the gap has to be isolated within the magnetic assembly to minimize fringing flux noise. When the gap is used as shown in Figure A, C, and D, then, only half the thickness of the calculated gap dimension is used in each leg of the core.

Author : Hamid - From: Iran
Wed, December 9th, 2009 - 09:11
     can u tell me what is saturation level in choke how it should be calculated.
     please tell whether  ive had calculated correctly or not for the  specfication  given below.

    ive designed a output choke for 110kw variable frequency drive  3 phase 415v 200A 0.028mh
( saturation level taken as 300%),

1) no of turns 5
2) core area 50.8 mm X 95.25 mm
3) copper strip 10X3 - 2nos
                         5X2   - 1nos

Author : sudharsan - From: india
Wed, December 9th, 2009 - 11:18
To standardize the definition of saturation, several unique points on the B-H loop are defined, as shown in below Figure.

By definition, saturation occurs when the peak exciting current (B) is twice the average exciting current (A) as shown in Figure below. Analytically, this means that:

Thu, December 10th, 2009 - 15:59
     how to practically implement saturation level in choke

1)  By  increasing core area  

    example:  for 200% of saturation increase core area into 2 times
                     for 300% of saturation increase core area into 3 times

2)  By increasing the airgap or no of gaps

3) Or by some other methods

plz guide me its really confusing 
Author : sudharsan - From: india
Thu, December 10th, 2009 - 17:14
Please refer to final formula in last my post. you can reduce saturation probability in coils by decreasing of MPL, increasing of N, decreasing of Bs with increasing of core area and increasing of Bl with using of beter core material (with suitable μr). 
Author : Hamid - From: Iran
Fri, December 11th, 2009 - 13:32
sir ive still have some doubts,in your previous answer can we increase or decrease saturation by all those each methods . can u please tell me how to calculate
1) MPL
2) N
3) Bs
4) B1 
Author : sudharsan - From: india
Sun, December 13th, 2009 - 14:25
Please note to reply#5 and below figure.

1) MPL (average of magnetic flux length)
2) N (number of winding turns)
3) Bs ( refer to reply#5)
4) B1 ( refer to reply#5)

Author : Hamid - From: Iran
Thu, December 17th, 2009 - 09:41
     how to find B1 in reply 5 
Author : sudharsan - From: india
Thu, December 17th, 2009 - 11:31
Refer to B-H curve. 
Author : Hamid - From: Iran
Wed, December 30th, 2009 - 13:37
how to calculate total harmonic distortion (THD)  
Author : sudharsan - From: india
Sat, January 2nd, 2010 - 14:23
   the formula for designing AC & DC choke are same ? 
Author : sudharsan - From: india
Thu, June 4th, 2015 - 10:57
Dear Sir,

Can you please give a same example for 3 phase Current Limiting Reactor as u have given for single phase inductor in your reply#1. 
Author : asim jamil - From: Pakistan
Sat, October 22nd, 2016 - 08:25
Dear sir,

Need some more clarifications in three phase Chokes designs.

1.Area of product

2. Area of Cross Action

3.No of turns calculation

4.Air gap length

5.Input and output chokes design difference.
Author : Deepak - From: india
Thu, October 27th, 2016 - 12:54
You can refer to:

Third Edition, Revised and Expanded
Kg Magnetics, Inc.
Idyllwild, California, U.S.A.
Author : M.S. Jafarpour (Hamid) - From: Iran
Wed, January 25th, 2017 - 20:15
sir you have explaine in a required way 
Author : fred jacob mmary - From: tanzanian
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