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7/28/2019 Apuntes Sobre Maquinas de Soldar
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1.42 WELDING TRANSFORMERS
Figure 1.59shows a schematic diagram of a welding transformer having thin primary windings with a large number of turns.On the other hand, the secondary has more area of cross-section and less number of turns ensuring less voltage and very
high current in the secondary. One end of the secondary is connected to the welding electrode, whereas the other end is
connected to the pieces to be welded. If any high current flows, heat is produced due to the contact resistance between the
electrode and the pieces to be welded. The generated heat melts a tip of the electrode and the gap between the two pieces
is filled.
Figure 1.59 Welding Transformer
Figure 1.60 Volt-ampere Characteristic of a Welding Transformer
The winding used for the welding transformer is highly reactive. Otherwise, a separate reactor may be added in series with
the secondary winding.Figure 1.60shows the volt-ampere characteristic of a welding transformer.
1.42.1 Reactors Used with Welding Transformers
To control the arc, various reactors are used with welding transformers. Some methods to control the arc are given below:
i. Tapped reactor: With the help of taps on the reactor, the output current is regulated. This has limite number ofcurrent settings shown inFigure 1.61.
ii. Moving coil reactor:Figure 1.62shows a moving coil reactor in which the reactive distance between primary andsecondary is adjusted. The current becomes less if the distance between the coils is large.
Figure 1.61 Tapped Reactor
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Figure 1.62 Moving Coil Reactor
iii. Moving shunt reactor: Figure 1.63 shows a moving shunt reactor in which the position of the central magneticshunt can be adjusted. Change of the output current is obtained due to the adjustment of the shunted flux.
iv. Continuously variable reactor:Figure 1.64shows a continuously variable reactor in which the height of the reactoris continuously varied. Greater reactance is obtained due to greater core insertion and hence the output current
is less.
v. Saturable reactor:Figure 1.65shows a saturable reactor. To adjust the reactance of the reactor, the required DCexcitation is obtained from a DC controlled transducer. Reactor approaches saturation if the DC excitationcurrent is more. Therefore, changes of current are obtained due to the change of reactance.
Figure 1.63 Moving Shunt Reactor
Figure 1.64 Continuously Variable Reactor
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Figure 1.65 Saturable Reactor
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Designing Your Own Transformer
written by: Swagatam edited by: Lamar Stonecypher updated: 11/1/2011
Designing a transformer is not easy simply because the criteria involved with these
devices are critical and elaborate. However some meticulously arranged data regarding
the various calculations can make the procedure easier. Learn how to make a transformer
through using simple formulas.
Introduction
We have already studied a lot about transformers in Bright Hub and we know that its
simply a device used for either stepping-up or stepping down an applied input AC throughmagnetic induction in between its two windings.
Basically a transformer will have the following main components:
Iron core stampings (configured either as U/T or E/I, generally the later is used more
extensively)
Central plastic or ceramic bobbin surrounded by the above iron core stampings
Two windings (electrically isolated and magnetically coupled) using super enameled
copper wire made over the bobbin
Normally the winding which is designated to receive the input supply is termed as thePrimary and the winding which in response to this input produces the required induced
voltage as the output is termed as the secondary winding.
Designing your own transformer as per a specific application can be interesting, but not
feasible without calculating the various parameters typically involved with them. The
following discussion will take you through a few important steps and formulas and explain
how to make a transformer.
amorphous c core
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Calculating the Core Area (CA) of the Transformer
The Core Area is calculated through the formula given below:
CA = 1.152 (Output Voltage Output Current)
Calculating Turns per Volt (TPV)
It is done with the following formula:
TPV = 1 / (4.44 10-4 CA Flux Density AC frequency)
where the frequency will depend on the particular countrys specifications (either 60 or 50Hz), the standard value for the flux density of normal steel stampings may be taken as 1
Weber/sq.m, for ordinary steel material the value is 1.3 Weber/sq.m
Primary Winding Calculations
Basically three important parameters needs to be figured out while calculating the primary
winding of a transformer, they are as follows:
Current through the primary winding
Number of turns of the primary winding
Area of the primary winding
Lets trace out each of the above expressions:
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Primary Winding Current = (Secondary Volts Secondary Current) (Primary Volts
Efficiency), the average value for the efficiency of any transformer nay be presumed to be
0.9 as a standard figure.
Number of Turns = TPV Primary Volts
Primary Winding Area = Number of Turns / Turns per Sq. cm (from the table A)
Reading Table A is easy just find out the relevant figures (wire SWG and Turns per
sq.cm.) by tallying them with the closest matching value of your selected primary current.
Secondary Winding Calculations
As explained above, with the help ofTable A you should be able to find the SWG of the
wire to be used for the secondary winding and the TPV simply by matching them with the
selected secondary current.
The Number of turns for the secondary winding is also calculated as explained for the
primary winding, however considering high loading conditions of this winding, 4 % extra
turns is preferably added to the over all number of turns. Therefore the formula becomes:
Secondary Number of Turns = 1.04 (TPV secondary voltage),
Also secondary winding area = Secondary Turns / Turns per sq. cm. (from table A).
Calculating the Core Size of the Steel Laminations or the Stampings
The core size of the steel stampings to be used may be easily found from Table B by
suitably matching the relevant information with Total Winding Area of the transformer. The
Total Winding Area thus needs to be calculated first, its as follows:
Total Winding Area = (Primary Winding Area + Total Secondary Winding Area) Space for
External Insulation.
The third parameter i.e. the space for the insulation/former etc. may be taken
approximately 25 to 35 % of the sum of the first two parameters.
Therefore, the above formula becomes:
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Total Winding Area = (Primary Winding Area + Total Secondary Winding Area) 1.3
Normally, a core having a square central pillar is preferred and
used - other factors involved are also appropriately illustrated in the adjoining figure and
calculated as follows:
Gross Core Area = Core Area from Table B / 0.9 (sq.cm.)
Tongue Width = Gross Core Area (cm)
After calculating the Tongue Width, it may be used as a reference value and matched
appropriately in Table B to acquire the actual CORE TYPE.
Your quest regarding how to make a transformer gets over when you finally finish
calculating the stack height, using the formula:
Stack Height = Gross Core Area / Tongue Width.
Table A
The table below helps you to select the gauge and turns per sq. cm of copper wire by
matching them with the selected current rating of the winding appropriately.
SWG------- (AMP)------- Turns per Sq.cm.
10----------- 16.6---------- 8.7
11----------- 13.638------- 10.4
12----------- 10.961------- 12.8
13----------- 8.579--------- 16.1
14----------- 6.487--------- 21.5
http://img.bhs4.com/94/4/944284d6d3c6953e60bbde40d12fe9b0f7d88589_large.jpg7/28/2019 Apuntes Sobre Maquinas de Soldar
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15----------- 5.254--------- 26.8
16----------- 4.151--------- 35.2
17----------- 3.178--------- 45.4
18----------- 2.335--------- 60.8
19----------- 1.622--------- 87.4
20----------- 1.313--------- 106
21----------- 1.0377-------- 137
22----------- 0.7945-------- 176
23----------- 0.5838--------- 42
24----------- 0.4906--------- 286
25----------- 0.4054--------- 341
26----------- 0.3284--------- 415
27----------- 0.2726--------- 504
28----------- 0.2219--------- 609
29----------- 0.1874--------- 711
30----------- 0.1558--------- 881
31----------- 0.1364--------- 997
32----------- 0.1182--------- 1137
33----------- 0.1013--------- 1308
34----------- 0.0858--------- 1608
35----------- 0.0715--------- 1902
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36----------- 0.0586---------- 2286
37----------- 0.0469---------- 2800
38----------- 0.0365---------- 3507
39----------- 0.0274---------- 4838
40----------- 0.0233---------- 5595
41----------- 0.0197---------- 6543
42----------- 0.0162---------- 7755
43----------- 0.0131---------- 9337
44----------- 0.0104--------- 11457
45----------- 0.0079--------- 14392
46----------- 0.0059--------- 20223
47----------- 0.0041--------- 27546
48----------- 0.0026--------- 39706
49----------- 0.0015--------- 62134
50----------- 0.0010--------- 81242
Table B
This Table B enables you to make your own transformer design by comparing the
calculated Winding Area with the relevant required Tongue Width and Lamination Type
number.
Type-------------------Tongue----------Winding
No.---------------------Width-------------Area
17(E/I)--------------------1.270------------1.213
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12A(E/12I)---------------1.588-----------1.897
74(E/I)--------------------1.748-----------2.284
23(E/I)--------------------1.905-----------2.723
30(E/I)--------------------2.000-----------3.000
21(E/I)--------------------1.588-----------3.329
31(E/I)--------------------2.223-----------3.703
10(E/I)--------------------1.588-----------4.439
15(E/I)-------------------2.540-----------4.839
33(E/I)--------------------2.800----------5.880
1(E/I)----------------------2.461----------6.555
14(E/I)--------------------2.540----------6.555
11(E/I)---------------------1.905---------7.259
34(U/T)--------------------1/588---------7.259
3(E/I)-----------------------3.175---------7.562
9(U/T)----------------------2.223----------7.865
9A(U/T)----------------------2.223----------7.865
11A(E/I)-----------------------1.905-----------9.072
4A(E/I)-----------------------3.335-----------10.284
2(E/I)-----------------------1.905-----------10.891
16(E/I)---------------------3.810-----------10.891
5(E/I)----------------------3.810-----------12.704
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4AX(U/T) ----------------2.383-----------13.039
13(E/I)--------------------3.175-----------14.117
75(U/T)-------------------2.540-----------15.324
4(E/I)----------------------2.540----------15.865
7(E/I)----------------------5.080-----------18.969
6(E/I)----------------------3.810----------19.356
35A(U/T)-----------------3.810----------39.316
8(E/I)---------------------5.080----------49.803
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Kapp regulation diagram
From Encyclopedia Magnetica
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S. Zurek,Kapp regulation diagram,Encyclopedia Magnetica, {accessed 6 Apr 2013}
edited 1 Jan 2012 1 Feb 2013 reviewedbyJ. Leichton 1 Feb 2013
Kapp regulation diagram[1]
fot. S. Zurek, Encyclopedia Magnetica, license: CC-BY-3.0
Kapp regulation diagram - a graphical method of determining thevoltage regulationin a
transformercaused by changes inloadandpower factor.[1]
The output voltage of a mainspower transformerwhen loaded reduces for inductive load (power
factor lagging) and increases for capacitive load (power factor is leading).
The Kapp diagram is helpful in finding the voltage drop or increase (voltage regulation). The main
disadvantage is that the voltage regulationphasorsare much smaller than the radii of the main
circles, so the diagram has to be drawn on a very large scale to get sufficiently accurate results.[1]
http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#mw-headhttp://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#mw-headhttp://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#mw-headhttp://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#p-searchhttp://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#p-searchhttp://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#p-searchhttp://magnetica.shoutwiki.com/wiki/User:Stan_Zurekhttp://magnetica.shoutwiki.com/wiki/User:Stan_Zurekhttp://magnetica.shoutwiki.com/http://magnetica.shoutwiki.com/http://magnetica.shoutwiki.com/http://magnetica.shoutwiki.com/wiki/Help:Articles_with_reviewhttp://magnetica.shoutwiki.com/wiki/Help:Articles_with_reviewhttp://magnetica.shoutwiki.com/wiki/User:Jeanete_Leichthttp://magnetica.shoutwiki.com/wiki/User:Jeanete_Leichthttp://magnetica.shoutwiki.com/wiki/User:Jeanete_Leichthttp://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/w/index.php?title=Voltage_regulation&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Voltage_regulation&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Voltage_regulation&action=edit&redlink=1http://magnetica.shoutwiki.com/wiki/Transformerhttp://magnetica.shoutwiki.com/wiki/Transformerhttp://magnetica.shoutwiki.com/w/index.php?title=Load&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Load&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Load&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Power_factor&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Power_factor&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Power_factor&action=edit&redlink=1http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/w/index.php?title=Power_transformer&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Power_transformer&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Power_transformer&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Phasor&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Phasor&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Phasor&action=edit&redlink=1http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/wiki/File:Kapp_regulation_diagram_Magnetica.svghttp://magnetica.shoutwiki.com/w/index.php?title=File:Kapp_regulation_diagram_Magnetica.svg&page=1http://magnetica.shoutwiki.com/wiki/File:Kapp_regulation_diagram_Magnetica.svghttp://magnetica.shoutwiki.com/w/index.php?title=File:Kapp_regulation_diagram_Magnetica.svg&page=1http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/w/index.php?title=Phasor&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Power_transformer&action=edit&redlink=1http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/w/index.php?title=Power_factor&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Load&action=edit&redlink=1http://magnetica.shoutwiki.com/wiki/Transformerhttp://magnetica.shoutwiki.com/w/index.php?title=Voltage_regulation&action=edit&redlink=1http://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#cite_note-Rajput-0http://magnetica.shoutwiki.com/wiki/User:Jeanete_Leichthttp://magnetica.shoutwiki.com/wiki/Help:Articles_with_reviewhttp://magnetica.shoutwiki.com/http://magnetica.shoutwiki.com/wiki/User:Stan_Zurekhttp://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#p-searchhttp://magnetica.shoutwiki.com/wiki/Kapp_regulation_diagram#mw-head7/28/2019 Apuntes Sobre Maquinas de Soldar
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Drawing algorithm
In order to create the diagram it is necessary to know the equivalentreactanceX02 andresistanceR02
of the transformer asreferredto thesecondary side. The following algorithm should be used:
1. DrawphasorOL representing secondary terminal voltage V2 on load2. Draw OXrepresenting the phase of the secondary current at an angle2 to OL such that
cos2 is the power factor of the load
3. Draw phasor LM (I2 R02 - voltage drop on resistance referred to the secondary side) parallelto OX, and then MN(I2 X02 - voltage drop on reactance referred to the secondary side).
The resulting NL is the total voltage drop.
4. Transfer the impedance triangle NLM to OO'Pwhich gives O'L = ON= 0V2. Therefore, forgiven secondary current thelocusofNis a circle with centre O and radius 0V2, while the
locus ofL has the same radius but with the centreO'
5. To find the voltage drop on full load at any power factor the radius OQS should be drawn
at at angle to OX. If the impedance triangle is drawn in position UQTthen OU= OS. Thelength ofQS represents the voltage drop.
References
http://magnetica.shoutwiki.com/w/index.php?title=Reactance&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Reactance&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Reactance&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Resistance&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Resistance&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Resistance&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Referring&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Referring&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Referring&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Secondary_side&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Secondary_side&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Secondary_side&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Phasor&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Phasor&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Phasor&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Locus&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Locus&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Locus&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Locus&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Phasor&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Secondary_side&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Referring&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Resistance&action=edit&redlink=1http://magnetica.shoutwiki.com/w/index.php?title=Reactance&action=edit&redlink=17/28/2019 Apuntes Sobre Maquinas de Soldar
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Making a welder out of an old transformer.
Seeing the post a while back about the burnt out 3 phase
transformer has got
me thinking again.
After getting my old Forney welder, I have been playing around
with seeing
how hard it really is to design your own welder to operate the
way you want
it too. That has led me to experiments with a couple old 480V
to 120/240
volt transformers I have.
I have decided to post a little article on possible methods to
convert anold transformer into a welder. Opinions on my ideas is welcome.
This post will be very long.
The type of transformer you are looking for is one with a large
open core. A
single phase with two coils on a single donut core (two leg). Or
a three
phase one with three windings and three legs that are bridged at
the top and
bottom (three leg).
Those types have a large core that will have a lot of flux
leakage when
driven by only one leg.
Transformers that have the E-I core with the return path going
around both
sides of a single winding have very little flux leakage and you
will have a
problem designing a reasonable current limited transformer out
of it.
You get the current limiting action by arranging the windings on
the core so
that there is a large leakage path between them. The farther
apart you have
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the primary and secondary, the more flux leakage. The closer you
have them
located, the leakage and you will get less of a current limiting
action.
The primary produces flux when it energized. That flux tries totake the
easiest path to form a loop. Be it steel, air, or water. The
easiest path
for it to take is steel, when the coil is wound around a steel
donut, then
the magnetic flux generally prefers to go through that steel
donut to form a
loop. Path of least resistance. But if you put a shorted coil on
the other
side of the loop, then it stops the flux from passing throughthe complete
donut. The flux will jump across the middle of the donut between
the primary
and secondary to complete the flux loop. Longer, and narrower
the gap that
the flux has to jump across, the more counter EMF the secondary
has to
generate to force the primary EMF to jump that gap.
A tall but narrow donut with the primary on the right and
secondary on the
left leg. With the primary and secondary side by side. It will
take more amp
turns in the secondary to get the primary flux to bypass the
secondary.
If you have a wide but short donut with the primary and
secondary on the
right and left leg, the gap between the primary and secondary is
large. Then
the gap between the top and bottom part of the donut where the
flux has to
jump is short and wide. It takes a lot less current in the
secondary to
force the primary flux to jump the gap between the primary and
secondary.
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And example of a simple transformer for making a welder.
A 240/480 to 120/240 single or three phase transformer.
Single phase has....
One 240V primary and a 120V secondary on each leg. The primaries
are stungin series for 480V or in parallel for 240V. The secondary
windings are in
series for 120/240 center tapped. Or can be put in parallel for
120V. Often
the secondary windings are split between the legs to even out
loading, and
reduce leakage. That means that there is two 60V secondary
windings on each
side that is in series with the opposed one on the other side.
Three phase with three legs that are bridged at the top and
bottom. Each leg
has one primary and one secondary. wye or delta on primary and
secondary
If you are lucky, there is enough room between the existing
coils to wind
your custom windings.
If it is tightly packed, then you may have to remove all, or
part of, the
windings on one side to make room for your custom windings..
Pick a coil/side/leg for your primary. If you have a transformer
that has a
mixture of damaged windings and good ones, then pick a good one.
It should
have a 208,240 277, or 480V primary and one or more secondary
windings on
that leg of the transformer.
Remove the damaged windings. Then start experimenting.
Example. (from the experiments I did with one of my
transformers. 15KVA
240/480 to 120/240 single phase) Your transformer has a 240V
primary on each
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leg. Hook 120V to one primary. Run a single turn or a couple
turns around
the core and measure the voltage across it. If you have three
turns and you
get 3.6V AC then your transformer is running at 1.2V per turn.
Sincedesigned operating voltage for the transformer is twice what you
have the
primary hooked too, then designed operating level will be 2.4V
per turn.
When testing, you want to leave the transformer hooked to the
lowest
exciting voltage you have, that will make the testing safer, and
the
currents developed for that core the lowest possible.
Lets say that you have the above stated situation. 120V hooked
to a 240V
winding which yields you a 1.2V per turn. On a single phase
transformer.
That tells you that the primary on each leg has 100 turns.
Some will have a secondary by it's self on each leg that has 50
turns.
Some single phase transformers will have each secondary split
between both
legs, so you have two 25 turn secondary windings on each leg.
When you have the one primary excited with 120V you will have
120V on the
other primary and 60V or two 30V on the secondary windings on
each leg.
Now to find out the current characteristics of your transformer.
There is two factors that limit current in the setup. The
conductor
resistance. And the flux leakage. Conductor resistance makes the
windings
hot, so we want the windings big enough that that isn't a
factor.
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Lets say that your transformer has an available current of
2040Amp turns
into a shorted leg when the other leg is excited by 120V.
If you had a single turn large enough to handle that current on
that legthen you would have close to 2040A on that turn when it's
shorted, or 1.2V
when it's open.
(If you made that single turn with a 4 foot piece of 10g wire,
the current
would be limited by the wires resistance. 1.2V across 4 feet of
wire is
close to 300 amps. The wire will get hot very quickly. The wire
will begiving in, not the flux in the transformer. The voltage across
the leg doesn't
drop, the wire is just forced to drop the voltage across it's
length.)
Lets continue with that train of though.
If you had two turns of wire adequate for the current, you would
get 2.4V
when open, and 1020A when closed. That would be in about the
right range for
spot welding, but not for arc welding. So lets continue on.
10 turns would yield 12V at 204A
20 turns would yield 24V at 102A close but not quite.
30 turns would yield 36V at 68A getting real close to the right
voltage.
40 turns yield 48V which does quite well at 51A with the 1/16
6013 rod.
50 turns yields 60V that also does quite well at around 41A
Considering that the two low voltage windings I have are 25
turns each. I
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can have one winding plus 15 more turns of wire with it to get
40 turns, or
use both in series to get 50 turns.
So, my transformer without major modification can serve as a 40
or 50awelder with the addition one 15 turns of wire on one side. You
could use the
other unused 100 turn primary on that side for a 120V OC 20A
welder. Now if
I could only find 1/32 welding rod! :-)
For the secondary windings left over on the side that you are
driving as the
primary. since they are in the same coil as the driven primary,
there willbe no real current limiting. So you could use them as a CV
output to drive a
mig gun, If you hook them in parallel for 30V. Considering that
my
transformer is rated at 15KW you should have 120A continuous
duty on hand to
drive that mig gun.
That is what you could do with a very simple winding
arrangement.
Now, lets get to the complex winding arrangements for an arc
welder.
Lets go for a base 50V OC on all outputs.
Lets hook up the two secondary windings on the output (current
limited) side
in parallel so that we have 30V OC with a short circuit output
of 81A that
will allow us to make use of what is already there.
Take that as are base winding. The winding can handle up to 120A
continuously (two 60A windings in parallel)
For are 50A tap, run are base winding in series with 16
additional turn new
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winding. That yields 49V at close to 50A
For the 40A tap, we can't just use a 25 turn tap in series with
the base
winding because that will yield 60V OC. Remember we want a
nominal 50V OC.Here is where we get into the complex windings.
To do that, we have to have the additional 25 turn winding in
series with a
buck winding on the primary driven side. A buck winding on the
primary side
is close coupled with the driven winding so it will reduce the
output
voltage but it won't reduce the current available at the output
since therewon't be any current limiting action.
So, you will have a winding with 25 turns on the current limited
side plus 8
reverse turns on the driven side. That will yield you 40A at 50V
OC. (you
get the output current from 50 turns on the current limited
side, and you
use 8 buck turns to get the voltage down to spec) Now, it won't
be exactly
that because with the buck winding, you are not directly
shorting the
current limited side. So you may have to take a winding may have
to take a
turn off of each side until current comes up to spec for that
tap.
Now lets go for the 60A tap.
Lets take the base winding and add a 9 turn new winding to the
current
limited side.(9 turns of the new 15 turn winding for the 50A
tap) And run
that to a 7 turn boost winding on the primary driven side. That
will get you
60A at 50V. (34 turns on the current limited side plus 7 boost
turns)
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The highest we could wind this transformer for is 70A and still
maintain
100% duty cycle, which would be 29 current limited turns plus 12
boost
turns. (base winding plus 4 with 12 boost turns)
Now if we went with interment ant duty we could easily go 80A
which is the
base winding plus 12 boost windings. In actuality, that setup
would be
closer to 100A or higher because the current limited winding
will be driven
beyond shorted. It will actually be driven reverse polarity. (0V
- boost
voltage)
So, just experiment and move the winding around till you find
the current
you want.
You can tailor it to get about any OCV you want. If you want a
digging arc
or a rubbery arc, you can tailor it to fit your desires.
To get 100A out, at 50 OCV you will want to run it on a 50A 120V
breaker.
If you drive the primary at full rated 240V you will have to
arrange the
secondary and buck boost windings to compensate for a higher
amp turns that
is available on the current limited side, plus the additional
volt turns.
"Now wait a second" you say "how does all that help me find out
how much
current my transformer will put out?????????"
Well. Put some test windings on your transformer and Either run
you selected
transformer primary off of 120V or even 60Vor 30V from another
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transformer.
Have a current meter on the test windings and short them out for
a second to
see what you get. Rearrange the test windings and try again.
When you get the current down to a relatively low level at 30 or60 V then
you can step up to the next drive voltage level and check what
affect that
has. Rearrange the windings, and step up another voltage level.
I would not suggest that you power the selected primary to full
rated
voltage and then short a test winding on it with no prior
knowledge of the
transformer in question. You may be in for a little bit morecurrent than
you bargained on. Plus a lot of melted wires to boot.
One way of bringing up the power level more gradually is use a
large variac
to slowly bring up the voltage level on a shorted test winding
and see where
the current levels off. You will be able to see if the current
is climbing
way faster than you anticipated with the voltage, and if you
will need to
change your winding layout before bringing it to full voltage.
If you have a transformer that you have taken one of the coils
off one of
the legs, then you will have a lot more freedom to arrange the
windings.
If you have a three phase transformer with two bare legs then
that opens up
a world of possibilities. When you short a winding out on one
leg, then the
flux will shift to the other leg. You could use one winding on
one leg as an
output winding and have a winding on the other that is connected
to SCR's to
vary the current. When the SCR's are full on, then it forces all
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the current
to the output winding, and when they are full off, then none of
the current
is forced to the output. (it bypasses the output winding through
the open
SCR winding)Don't forget the secondary windings on the drive leg. They can
be run in
series with the primary to reduce the volts turn drive level at
a specified
supply voltage!!!
Now it is getting late, and I am getting tired, so I am going to
wrap this
up and post it to see what you people think.
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CURSO DE SOLDADURA SMAW (11)
20:15 No comments
Capitulo 11: MAQUINAS DE SOLDAR (transformador).
Aparato elctrico que transforma la corriente elctricabajando la tensin de la red de alimentacin a unatensin e intensidad adecuada para soldar. Dicha CAde baja tensin (65 a 75 voltios en vaco) y deintensidad regular. Permite obtener la fuente de calornecesaria para la soldadura.
El transformador consta de un ncleo que estcompuesto por lminas de acero al silicio y de dosbobinas de alambre; el de alta tensin, llamadoPRIMARIO y el de baja tensin llamadoSECUNDARIO.
La corriente que proviene de la lnea circula por
el primario.
Los transformadores se construyen paradiferentes tensiones, a fin de facilitar su conexin, entodas las redes de alimentacin.
La transformacin elctrica se explica de la formasiguiente: "La corriente elctrica que circula por el
primario genera un campo de lineas de fuerzamagntica en el ncleo, dicho campo actuando sobrela bobina secundaria, produce en este, una corrientede baja tensin y alta intensidad, la cul se aprovechapara soldar.
http://weldermex.blogspot.mx/2012/08/curso-de-soldadura-smaw-11.htmlhttp://weldermex.blogspot.mx/2012/08/curso-de-soldadura-smaw-11.htmlhttp://weldermex.blogspot.mx/2012/08/curso-de-soldadura-smaw-11.html#comment-formhttp://weldermex.blogspot.mx/2012/08/curso-de-soldadura-smaw-11.html#comment-formhttp://weldermex.blogspot.mx/2012/08/curso-de-soldadura-smaw-11.html#comment-formhttp://weldermex.blogspot.mx/2012/08/curso-de-soldadura-smaw-11.html7/28/2019 Apuntes Sobre Maquinas de Soldar
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CARACTERSTICAS
La regulacin de la intensidad se hacecomnmente por dos sistemas:
1- Regulacin por bobina desplazante: Consisteen alejar el primario y el secundario
entre s.
Observacin: Esta sistema es recomendable por
su regulacin gradual.
2- Regulacin por clavija: Funciona aumentandoo disminuyendo el nmero de espiras.
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Los transformadores se conocen tambin comoMAQUINAS ESTATICAS por no tener piezas mviles.
VENTAJAS
El uso del transformador se ha generalizado por:
-4- Bajo costo de adquisicin
-5- Mayor duracin y menor gasto demantenimiento
-6- Mayor rendimiento y menor consumo envaco
-7- Menor influencia del soplo magntico
DESVENTAJAS
Entre sus desventajas se pueden mencionar:
-8- Limitacin en el uso de algunos tipos deelectrodos
-9- Dificultad para establecer y mantener elarco
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MANTENIMIENTO
Debe mantenerse el equipo libre de polvo yhumedad
PRECAUCIN
Toda accin de limpieza debe efectuarse con lamquina desconectada
Al instalarla debe elegirse un lugar seco fijandoen la mquina, una conexin a tierra.
ACTIVIDAD
27- Nombre las dos formas para regular elamperaje en las mquinas estticas
28- Cules son los principales componentes deuna mquina esttica y a que se debe su nombre.
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TRANSFORMER DESIGN, CONSTRUCTION & THEORY
Presented here is an overview of transformers for hobbyists that want to expandtheir knowledge of this essential electrical component.
Of the 3 basic passive electrical components, R, L, C, the transformer is simply aspecial case of the inductor with either taps or multiple windings that are coupled.
It will operate over the full range of frequencies and may be either iron or aircored; most of the following discussions will concentrate on low frequency, iron
cored transformers.
The basic transformer to be discussed is the voltage (or power transformer), whichoperates at mains frequency and is step up or down. There are also special cases,
such as current transformers, pulse transformers and audio (output and driver)types that cater for a wider band of frequency.
3 phase transformers are simply a special case of the single-phase transformer
with the core arranged to give a balanced magnetic circuit.
Transformers consist of a core and windings; the core is usually an iron alloy tosuit the application and the windings consist of coils of insulated copper or
aluminium wire.
There is no absolutely correct design for any given transformer; as in all matters ofgood engineering there are many design and cost compromises to be made.
Having selected a core and decided on a flux density, the T/V figure is calculatedand then it is a matter of seeing if the turns will fit on the bobbin available for the
selected core.
THE CORE
All transformers follow the basic transformer equation and work by reason of thefact that the magnetic flux, produced by the primary applied voltage is constantly
changing. This is basic magnetic theory. It appears confusing as it is taught inmany systems of units. I will concentrate on the MKS system where the units are
Metres. DO NOT USE mm!!!This is a practical system where the unit of flux density is the TESLA. Normaltransformers operate at levels around 1T depending on the materials used.
Transformer equation:
N = E / 4.44 B F Ae Where:
N = turns
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E = applied voltage in volts4.44 is a constant for sine wavesB = desired flux density in Tesla
F = frequency in HzAe = transformer centre limb area in M
Stalloy or silicon iron, which is widely used as a core material is normally operatedat a flux density of 1T. Unisil, a grain orientated material, which is a little more
expensive can be run at 1.5 T. Special alloys for Mil and aerospace applications canbe run up to 2T where a compact design is a requirement.
Running at a higher flux density allows the turns/ volt to be reduced and the costof copper and copper losses; however this increases the losses in the iron andincreases the magnetising (idling) current. Design curves are available showing
watts loss per Kg at various flux densities.Traditional design theory would make copper and iron losses equal at normal load
levels (say 80% of full load)
An important fact of life with iron cores is Saturation. When we increase thevoltage across an iron cored coil the current will initially increase in a linear
manner. When we reach a certain level the current will start to increase muchmore rapidly than the voltage. This is the Knee point where a lot of transformers
are designed to operate.Note that Stalloy has a fairly rapid turn into saturation, Unisil much less so. Hence
lower distortion when used in the output transformer of a Hi-Fi amplifier.
To determine the operating level of an unknown core it is simply a matter ifwinding a know number of turns onto the core, and then plotting a V/A curve. At
the point at where it starts to turn into saturation will be the operating level, and itis then easy to read off the Turns/Volt from the plot.
Other core losses are determined by the circulation of eddy currents in thelaminations. Thinner lams and lower frequencies give lower losses, but increase
the cost of the lams. A solid core would have very high losses, hence the lams arelightly oxidised to give insulation between them. These losses are frequency
dependant.Most laminations available these days are lossless types.
This means that they are E & I shapes stamped out of sheet so as to leave nowaste. Many other forms will be encountered in vintage equipment.
Transformers should normally be laminated to leave as small a gap between lamsas possible, interleaving and tapping them together during assembly. The
exception to this is transformers carrying DC, as in Class A valve output stages,where the standing DC current could cause saturation and a small air gap, usually
made from thin paper is inserted between the E & I lams that are not nowinterleaved.
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Clamping bolts, when inserted through the lams should have an insulation washerbetween the lam face and the nuts. If this is not done there can be high currents
circulating through the bolt.
Toroidal transformer cores can be run at higher flux densities and have the
advantage of a much lower stray field, useful in audio applications
THE WINDINGS
These are usually of enamelled copper wire but various other insulations areavailable. The insulation should be as thin as possible consistent with a suitable
electrical withstand level. Windings often had a thin layer of paper between layersof winding. With present wire insulation this is not necessary every layer, and is
often replaced with Type 56 Polyester tape every few layers, again depending onapplication.
The normal wire current density is typically 3A per mm and this figure is oftenshown in wire tables.
Note that wire sizes, in SWG, AWG or mm are based on bare wire, not coateddiameter.
The current density figure is based on a max internal temperature for thetransformer of 120C; the limit for normal materials, other design factors may
dictate different values.Wire tables will also give the resistance/ Mtr of wire. This is used to calculate the
winding resistance from the mean length of turn. Note that copper resistivityincreases by 0.3% per C rise.
The transformer equation gives the primary turns; secondaries can then becalculated by the turns ratio. If very exact ratios are required it may be necessary
to increase the primary turns so as to get an integral number of turns on thesecondary of importance.
If an exact voltage is required it is often necessary to add compensating turns to asecondary to allow for the volt drops (calculated from mean length of turn and
resistance per mtr) in both primary and secondary.It can also be necessary to allow for the increase of resistance due to temperature
rise as well.Further compensation is sometimes necessary to allow for the imperfect coupling
between primary and secondary which appears as a parasitic loss.
Primaries and secondaries are normally wound on top of each other for goodcoupling; where additional safety separation is required, they may be wound side
by side with a centre insulated barrier (some transformer kits with pre-wound
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primaries are like this).This gives inferior coupling and additional compensating turns will be needed to
compensate for this.For very close coupling the primary and secondary will be wound together with Bi-filar wire. Where insulation levels make this impossible, the primary and secondary
are wound in several sections, one on top of the other. For balance this wouldusually be one more primary section than secondary section.
Wire is commonly insulated with synthetic enamels in either 1 or 2 coats. Mostmodern enamels can be vaporised with solder and are known as solderable types.
Where high levels of insulation are required in a small space (such as a switchmode transformer), then triple insulated wire can be used. This is certified for
supply to low voltage windings without additional insulation.
An earthed copper screen is often placed between the primary and secondary; thisis for both safety and as an interference screen against noise impulses.
Windings are not normally carried to the outside of the bobbin on multi-layerwindings due to the danger of a turn slipping down the side of the bobbin and
seeing a higher voltage, possibly causing breakdown. Paper margin tapes, a fewmm wide are often used here.
With EHT transformers this margin is often tapered inwards (wider) as the outerlayers are added and the winding voltage to earth increases.
Copper is the important part of the winding so thin insulation is used, as there isonly a relatively low voltage between turns and layers. This is usually capable of
withstanding a minimum of 120C.
The windings are often vacuum impregnated to seal against moisture and preventchafing movement under operating or fault conditions. It is possible to sprayvarnish them while building, or they can be paraffin wax impregnated in a
container of molten wax.For voltages above 6KV it is usual to seal the transformer in a can of specially
refined mineral oil.
Tapping points on windings can be brought out of the body of the winding bylooping the wire out and back again. Lead-out wires are often soldered on to the
winding at an appropriate point. These must be well insulated.
The forgoing should allow a reasonably competent person to design and build theirown transformers when size and cost are not the driving factors as in commercialapplications. It should always be remembered that these devices are connected tothe mains and can easily kill or start serious fires; all possible safety precautions
should be taken when using them.
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Ed Dinning 2009