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Reg:Transformer Polarity

04/28/2015 2:16 AM

Based on the transformer winding wound direction, the direction of induced voltages are changed. Can anyone explain how?

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#1

Re: Reg:Transformer Polarity

04/28/2015 2:25 AM

Lefty loosey, righty tighty.

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#2
In reply to #1

Re: Reg:Transformer Polarity

04/28/2015 2:26 AM

Hoity-toity.

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#9
In reply to #1

Re: Reg:Transformer Polarity

04/28/2015 7:15 PM

Technically a correct on topic answer but you would have to know the basics on transformers to understand the reference in which case you would already know the answer and so wouldn't be asking the question in the first place. On topic, yes, helpful to the OP, ahh no.

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#11
In reply to #9

Re: Reg:Transformer Polarity

04/28/2015 7:39 PM

As far as I am aware, that phrase relates to the how a right hand screw thread works, and has nothing at all to do with transformer theory.

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#12
In reply to #11

Re: Reg:Transformer Polarity

04/28/2015 8:04 PM

It also works for the right-hand rules mentioned in Post #3.

Perhaps the implied example references to screw threads is an American thing only as we didn't have that down here when we learned about current flow and magnetic fields, although I vaguely remember seeing it in an American magnetics text book or paper on the subject (including big picture of a wood screw).

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#3

Re: Reg:Transformer Polarity

04/28/2015 2:48 AM

I studied in different languages and tried to translate some theoretical rules. Comes from Dutch Wikipedia:

The solenoid part might be the most inspiring.

Right-hand rule

Within physics there are several left and right rules. All these rules are intended direction (or sense ) of a variable (such as electric current , electromotive force , magnetic induction , Lorentz force and motion in a magnetic field ) to be determined by using the left or right hand. Most of these rules are applicable to electromagnetic phenomena, but the general right-hand rule applies to all cross products. The right hand rule is also known under the name of corkscrew rule, since instead of a right hand can also be used a corkscrew. In place of the right hand can also (in a slightly different manner), the left hand may be used. One therefore also speaks of the left line.

Various left and right rules are:

  • The right-hand rule, the left line and corkscrew rule for cross products .
  • The left hand rule to the direction of the Lorentz force for determining that a current-carrying conductor having under the influence of an external magnetic field. This is also known as the left hand rule of Fleming for electric motors.
  • The right-hand rule of Fleming for generators, in order to determine the direction of the current induced in a conductor as it moves through a magnetic field.
  • The right-hand rule to determine the direction of the induced electromotive force on a conductor moving in a magnetic field.
  • The rule of the right hand handle, or the rule of Maxwell, in order to determine the direction of the magnetic field caused by a current carrying conductor.
  • The rule of the right handle for solenoids.
  • The rule of Ampere, which aims to determine the direction a compass needle to point in the influence of a current carrying conductor.

Content

rules for cross products

Graphic representation of the cross product of a and b. The vector n is perpendicular to a and b, and to designate the movement of a corkscrew which is rotated from a to b.

The corkscrew line, right-hand or left-hand rule, a rule is used to determine the direction of a cross product of vectors . Consider the following cross product:

Either is the cross product of with . The direction of is then determined by vector to vector to rotate as if a corkscrew uses, in which the direction of rotation of the direction of the corkscrew determines.

Instead of making use of a corkscrew, may also make use of the left hand. Place this left along the flat , With the fingers in the direction vector and to point in such a way that in the palm of the hand is picked up. The sprawling thumb indicates the direction of to.

However, the right hand can also be used. Then it must be the thumb, the index finger and the middle finger of the right hand extend in such a way that all three of them with each other at an angle of 90 degrees with each other (like a pistol). Then assigns one thumb in the direction of and the index finger in the direction of than the middle finger indicates the direction of to.

Determining the direction of the Lorentz force

Left Hand Rule

The above rule of cross-products may, within the electromagnetics are used to control the direction of the Lorentz force to an electrical current-carrying conductor in a magnetic field to be determined.

The direction of the Lorentz force is described mathematically by the formula:

either, the Lorentz force is the cross product of the length with the magnetic field multiplied by the current of the conductor. The direction of the cross product can be determined by to to rotate as if one uses a corkscrew, wherein the direction of rotation of the corkscrew determines the direction of the cross product.

However, one can also use the left hand. Do this, place the flat left-hand side along the wire, with the fingers in the direction (sense) of the current and such that the field lines in the palm of the hand are collected. The expansive than thumb indicates the direction of the Lorentz force to which is exerted on the wire. The force on the magnetic pole is in the opposite direction.

Left Hand Rule Fleming

Another way to use the left hand is through the left hand rule of Fleming for electric motors, also known as the line of the three fingers of the left hand. This is especially common in English-speaking countries. You do so constitutes a pistol to stabbing with your left hand through the forefinger straight ahead and leave form a perpendicular angle with your thumb. Your thumb sticking up than proud. Next, create the middle a perpendicular angle with the index finger. This then points to the right and indicates the direction of the current intensity to. (Se c ond finger = C urrent) Your index finger indicates the direction of the magnetic field lines to (F irst finger = F ield), and your thumb indicates the direction of the Lorentz force on. (Th = Th umb rest).

This mnemonic or mnemonic was invented by John Ambrose Fleming . An alternative mnemonic for this is the so-called FBI rule. The F stands for the strength, B for the magnetic field and the I to the flow direction. The order of the letters will be matched to the order of the fingers. So the F for the thumb, forefinger and B to the I to the middle finger.

Applying the right hand, as described in the previous section for random vectors, leads (of course) also the correct result, but should not be confused with the right hand rule Fleming for generators.

Fleming's right hand rule for generators

Right Hand Rule Fleming

The right-hand rule of Fleming for generators being used for the determination of the direction of the current induced in a conductor as it moves through a magnetic field. The line should not be confused with the left hand rule discussed above Fleming for electric motors. Now serves namely the right to use and allows the thumb to the direction of movement (thumb = motion), the index for the field (first finger = field) and the middle of the current (second finger = current). Both lines of Fleming can be kept apart by remembering that Flemings ri g ht hand rule applies g eneratoren.

Another mnemonic for the right-hand rule of Fleming's MFC-line, where MFC abbreviation of Manchester Football Club. The M stands for motion (movement), the F field (field) and C for current (current). The order of the letters corresponds to the order of the fingers. The M for the thumb, forefinger and F for the C for the middle finger.

Determining the direction of the induced electromotive force

The right-hand rule can be used to determine the direction of the induced electromotive force (emf) in a conductor moving in a magnetic field.

Insert one's right hand so that the field lines along the palm that the onset and stretched thumb indicates the direction of the movement of the wire, then designate the fingertips in the direction of the induced electromotive force.

The rule of the right handle

Direction of the magnetic field, given that the electric current flows in the direction of the thumb.

An electric current through a wire generates a magnetic field . To determine the direction of this field, you point your thumb of the right hand in the direction of flow (Ie, from plus to minus, against the direction of the electrons in). By curving the fingers, which indicate the direction of . That is to say, in circles around the wire, against the hands of the clock. This rule is known as the rule of the right handle, or sometimes as the screwdriver line or right-hand rule.

Another approach to this rule is the corkscrew rule or rule of Maxwell, named after James Maxwell . By turning an imaginary corkscrew in the direction of the electric current in the power cord, the required direction of rotation of the handle indicates how the lines of force run from the electromagnetic field.

In this figure, the direction of a positive angle (counter-clockwise, so by convention positively vectors) indicated. The corkscrew that makes the rotation, is from bottom to top. This movement is consistent with the direction of the indicated vector.

rule of the right handle for solenoids

Magnetic field created by a solenoid

The rule of the right hand grip may be used for determining by a solenoid generated magnetic field. One seizes the solenoid with the right hand, such that the index fingers on the coil windings are in accordance with the conventional current direction, then the stretched thumb pointing in the direction of the magnetic field inside the coil.

The rule of Ampere

The rule of Ampere coined by André-Marie Ampère , French mathematician and physicist after whom the SI -basiseenheid amps and Ampere's law have been mentioned. Self Ampere named the swimmers rule: [1]

"Do you, that you can swim in the direction of the electric current, so that the positive flow to the feet in and exits at the head, and you look at the magnetic needle, then moves to the North Pole in the direction of the outstretched left arm. "

These prepared by Ampere rule indicates the relationship between the deflection direction of a freely movable compass needle in the magnetic field of a straight conductor and the direction of the electric current in these conductor. In fact, this so down to the rule described above of the right hand, which, after all, the direction of the electric current induced by a magnetic field is determined. The deflection direction of the compass needle can therefore also with the right hand or with a corkscrew be determined:

  • Do you put your right hand in an electric current, such that the flow of the wrist to the fingers flows and palm of the hand to the magnetic needle is directed than differs Arctic needle off to the side of the stretched thumb. In other words, you bring the right hand above a conductor, the palm facing the conductor and the fingertips directed along the flow direction, of the magnetic needle, the Arctic will be placed under the guide, move to the side of the stretched thumb.
  • Due to an imaginary corkscrew in turning the direction of the electric current in the power cord, the required thread direction of the handle indicates how the lines of flux of the magnetic field run. A magnetic needle will orient themselves according to these field lines, such that the north pole in the direction of the field lines will point and the South Pole against it.

of the left and right lines

The left and right hand are rules (under different names) widely used in the electromagnetism for, inter alia, the determination of the flow direction, the direction of the magnetic field lines and the direction of the Lorentz force. Applications in other areas of physics are:


Also with electromagnetic waves of the corkscrew rule is used to determine the relationship between the direction of the magnetic field, the electric field and the direction of propagation of the wave. If a material corkscrew rule is not obeyed, it is called a metamaterial or left-handed material. In such materials is the refractive index negative.

Left- and right-handed

A helix / screw-thread is right-handed as a displacement along the helix in a clockwise direction is associated with a movement of the observer; a light-transmissive substance is dextrorotatory when the polarization direction of light passing through the fabric is turned on corresponding manner (see Optical isomerism ).

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#10
In reply to #3

Re: Reg:Transformer Polarity

04/28/2015 7:18 PM

Yea that's pretty clear and answers the question (perhaps in a little too much detail).

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#14
In reply to #3

Re: Reg:Transformer Polarity

04/30/2015 10:14 AM

Wow! All you wanted to know and didn't have to ask.

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#4

Re: Reg:Transformer Polarity

04/28/2015 4:19 AM

Same way as when you drive your car...

Turn the steering wheel one way you turn right...

Turn it the other way...

You go LEFT ...

Del

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#5

Re: Reg:Transformer Polarity

04/28/2015 5:32 AM

Right and left hand rules show the direction but don't explain the reason.

Perhaps the easiest explanation that I can provide is for you to first read and understand Lenz's Law.

The law basically states that the polarity of an induced EMF in a coil will be such that it opposes the force producing it.

A rising current flowing in a coil (ie. +ve at left hand end) will produce a rising magnetic field (coming out of the coil) which will cut across those same coils and induce an EMF in them (self induction) which is in the opposite direction to the current producing it (ie. +ve at right hand end). When the current is falling, the magnetic field will collapse (going into the coil) and, because it is now intersecting the coil in the opposite direction, will induce an EMF in the coil which again opposes the force producing it by attempting to maintain the current flow, and so is in the same direction as the original current (ie. +ve at left hand end).

If you now introduce another coil which is wound in the same direction into close proximity with the first, then it can be seen that the rising magnetic field of the first coil will cut across the wire turns of the second coil, and induce an EMF in them (mutual induction).

The original rising magnetic field was coming out of the wire, and the falling magnetic field was going into the wire, so you can see that the rising field coming out of the first coil is going into the second coil, and so the polarity of that coil is going to be the same as the first coil (ie.+ve at the left hand end).

The magnetic force lines cutting across each turn of coil wire will induce a voltage in that wire in accordance with Lenz's law - you can use Fleming's left and right hand rules to easily determine the actual direction. This will cause one end of the coil to be +ve and the other -ve. If you now wind that coil in the opposite direction, the magnetic field still produces the exact same effect but the coil polarity will be reversed.

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#8
In reply to #5

Re: Reg:Transformer Polarity

04/28/2015 12:50 PM

So, nothing to do with the Lyn One Finger Rule, then?

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#6

Re: Reg:Transformer Polarity

04/28/2015 9:29 AM

I suggest you read Lenz Law and it's application.

Also; There are several online videos that illustrate the reaction in real time.

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#7

Re: Reg:Transformer Polarity

04/28/2015 12:48 PM

It's just a fact of life, Mildred. Some are wound one way, and some the other.Try swapping the wires at one of the pairs of terminals if it offends.

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#13

Re: Reg:Transformer Polarity

04/29/2015 3:09 AM

You post as though you are surprised that the relationship of the direction of the winding one of the coils to the other makes a difference.

Why are you surprised that such a change makes a 180° change in phasing?

If you have done a reasonable study of the facts (and had a reasonable education on the subject), you should not be surprised enough to post here. You would have understood why....

Furthermore, if this is a problem (the phasing is wrong for example) then you only need to swap the connections to one side only of the transformer to change it by 180°......change both sides together and you are back where you started again!!!

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