# What is Transformer: Definition and 807 Discussions

A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any one coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force across any other coils wound around the same core. Electrical energy can be transferred between separate coils without a metallic (conductive) connection between the two circuits. Faraday's law of induction, discovered in 1831, describes the induced voltage effect in any coil due to a changing magnetic flux encircled by the coil.
Transformers are most commonly used for increasing low AC voltages at high current (a step-up transformer) or decreasing high AC voltages at low current (a step-down transformer) in electric power applications, and for coupling the stages of signal-processing circuits. Transformers can also be used for isolation, where the voltage in equals the voltage out, with separate coils not electrically bonded to one another.
Since the invention of the first constant-potential transformer in 1885, transformers have become essential for the transmission, distribution, and utilization of alternating current electric power. A wide range of transformer designs is encountered in electronic and electric power applications. Transformers range in size from RF transformers less than a cubic centimeter in volume, to units weighing hundreds of tons used to interconnect the power grid.

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1. ### Why is impedance given as a simple Ohms unit when it's frequency dependent?

I've been trying to learn Impedance for over a year and this one thing is screwing me up. When they(any source) give an output or input Impedance it's always given in ohms. I went into learning about angular velocity, imaginary numbers, complex numbers- I haven't completed it but I feel I have...
2. ### Inrush current in a transformer chain

This is the proposal, except the two middle voltages are 110V, not 12V. Say the max switch-on inrush current of XFMR1 is xA with the secondary open, would the value change significantly in the above arrangement, with the secondary of XFMR2 open?
3. ### I Mutual inductance in a transformer

Hello! I have a question regarding the mutual inductance of two coils in a transformer. In the formulas for linked coils ##M=k*\sqrt{(L_1*L_2)}## where ##k=1## for a perfect coupling. I wanted to check my understanding about mutual inductance and see how it can be determined. When I vary the...
4. ### Question about generating split phase power

in a split phase transformer, how is the neutral wire shared. since the split phases of the hot wired are 180 apart, what happens in the neutral wire. my question stems from having two single phase inverters and wanting to hook them up to a home panel board with a common neutral the two...
5. ### Finding transformer's wire wrapping direction without taking it apart.

So I have the following transformer Is their a particular name for the kind of transformer I have above? I've learned the right side middle is called a center tap, and is used for some weird signallying things in engineering and I don't plan to use it. It's the left part that concerns me...
6. ### Maximum power from a transformer

Hi, I was having a discussion with a colleague today now I'm second guessing myself. My understanding of nameplate kVA is that it is based on 'ambient temperature, temperature rise, heat transfer, thermal mass, thermal time constant, materials used, and expected transformer life'. However...
7. ### B Melting a nail with high currents

Hi. I melted a nail using a transformer with 500 windings on the primary and 5 on the secondary and 220 V input voltage, but I can't make the numbers work out. I measured the output voltage to be around 2 V, which makes sense. Trying to measure the resistance of the nail directly with a...
8. ### I Magnetic Field Intensity At the Inductor's Air Gap (+Fringing Flux)

Hi there! Sorry for the unclear images in the previous post. This time I upload pdf files for my derivation and the reference paper. So, when I design a switching power supply, usually I make an air gap at the transformer's core. This will alter the BH curve, preventing the core saturation...
9. ### Sizing an Isolation Transformer for a DC Power Supply

Good afternoon, How should an upstream isolation transformer be sized for a dc power supply? For example, if we have a power supply with the following specs: Input Voltage: 120 VAC Input Current: 2 Amps Inrush Current: 22 Amps Efficiency: 90% Power Factor: 0.55 Output Voltage: 24 VDC Output...
10. ### Inducing Voltage in a Transformer: How Does It Work?

A changing current in a transformer primary produces a changing magnetic field, which induces a voltage in the secondary (correct?), but if no circuits are closed on the secondary, there's no current in the secondary (and therefore primary as well). So how is this voltage induced?
11. ### How to wind a 5K audio tube amplifier transformer?

60 watt tube amp needs a 5k primary and 8 ohm secondary transformer. I have wound voltage transformers on my lathe many times. Audio transformer is no different. Online impedance transformer calculator says, 5k to 8 ohms in 25:1 ratio. Online info says, audio transformer should be 60w x 5 =...
12. ### Transformer frequency contradiction on induction heating

As a transformer freq bet higher, inside induction get more efficient i.e. less loss: 1. Hysteresis loss = η * Bmax^n * f * V. 2. Eddy current loss( proportional to B2mf2Bm2f2 )Now it seems that losses increases with increase in efficiency... But the above equations are valid when max flux...

14. ### High voltage transformer windings position

Good morning all! I have a quick question regarding high voltage transformers, can someone explain why we need to put the low voltage winding the closest to the core and the high voltage winding on the "outside"? Have a nice day!
15. ### "Ground" and "Center Tapped" Power Transformer Secondary in guitar amp

Hello - thank you for reading this, and thank you in advance to anyone who replies and clarifies the mystery of "ground." I have finally gained a full understanding of how a full-wave rectifier, two-power tube electric guitar amplifier works in a push-pull manner, but one thing remains after I...
16. ### Grounding of secondary side transformer

Hello, I am a mech engineer teaching myself electrical engineering so please forgive my ignorance. Could someone explain to me how the coil stays open when grounded in the figure 2-12b. With my limited understanding I can see that in 2-13a the if the side of the circuit on the left of the coil...
17. ### How to Make a 24V Transformer Output 24V?

My friend bought a condo last winter and now in cooling season her AC unit (water source heat pump) is faulting-off sporadically. I've done some basic troubleshooting, and the unit is showing a over/under voltage fault on its LED. It's a 208V/1ph unit. According to the manual, the controller...
18. ### Transformer modelling for harmonic studies

Why transformer core is modeled as resistance even though it is frequency dependent.With increasing frequency current rises. Doesn't it seem capacitive reactance behaviour? Which decrease with increasing omega?
19. ### What is the Power Loss in a Transformer?

##\frac{N_S}{N_P} = \frac{240}{12\times 10^3} = \frac{1}{50}## ##I_S = \frac{N_P}{N_S}I_P = \frac{N_P}{N_S}I_P = 50\times 2 = 100## Amps ##P_{loss} = I_S^2R##, but I don't know how to find R
20. ### Engineering Which side of a transformer secondary to be ground referenced?

The video is located here. My question, if the secondary side is isolated and the control circuit has no connection to the primary side, why do I have to ground X2 only? This a floating AC system, so why does it matter which side is used as the reference? What will happen if I grounded the X1...
21. ### Is transformer always 'source' to which current returns?

I am not sure if I should use the word 'current' or 'charge' but my question is whether, in a typical U.S. residential 120/240 split phase system, is the local transformer always the source to which current (charge?) must return? Or can it bypass and go direct to other PoCo elements/generators...
22. ### Understanding a Single Transistor Flyback Transformer Driver?

I've been watching a few analyses of CRT flyback transformer drivers and can't understand why the transistor would shut off. To my naive perspective, it appears that the transistor should never shut off due to the positive DC voltage applied constantly to the base. I'm aware that this isn't the...
23. ### I Can a One Direction Transformer Prevent Reverse Induction in Primary Coil?

Hi, Is it possible to have a transformer/coupled inductors whereby current changes in once coil cause current changes (induction) in another coil but not vice versa? To put it in other words, is it possible to have such a design of a transformer where for example changes in current in primary...

25. ### Why a transformer cannot use DC (Ampere's law)?

A direct current in the primary winding results in a constant magnetic field going through the center of the coil. If we have a magnetic core and a second winding, why doesn't the magnetic flux going through the core result in a current in the secondary coil, as well, according to Ampere's law?
26. ### Engineering Alternating current circuit with transformer

Hi, I don't understand how to solve the problem below for (a). First I transform the cirucuit to direct current problem using jw method. Now i see that U=-I2Z. Z=R2+Zc3=R2+1/jwC3=4,5+1/[j(1000)(10^-3*0,25)]. Then I use impedance transformation to get rid of the transformator(using Z0), but then...
27. ### Current and resistance in the power loss of a transformer

a) Output voltage = 2 x 6 = 12 V Current in R = 12 V / 13.5 kΩ = 8.9 x 10-4 A That is the correct answer based on the solution but I don't understand why when calculating the current in R, the resistance of secondary coil is not considered. I thought it should be like this: Current in R = 12...
28. ### Are there 2 correct answers to this transformer homework problem?

Answer B would increase the n1/n2 ratio and increase the deflection. Making it correct. But also, Answer A would increase the current through the primary coil, and hence the power. This would increase the power in the secondary coil hence I2, leading to lower voltage V2. Making it also correct...
29. ### B Are silicon iron sheets really necessary for a commercial transformer?

Hi, everyone. I just finished studying the principle on which a transformer works. It relies on Faraday's law of induction. And my high school physics book uses the following picture for illustration: Roughly speaking, the...
30. ### Engineering Cadence Transformer dot convention and polarity (xfmr)

Here is the circuit... Here is my work so far in cadence (I haven't put in values for other components in because the moment I saw the dot convention I started trying to figure that out). Where I'm at -There apparently isn't a way in Cadence Virtuoso (the program my class uses) to change the...
31. ### Transformer; make primary voltage x10 of the secondary voltage

I understand that transformers function using electromagnetic induction and Faraday's Law. This implies; Vs=-Ns (dΦ)/(dt) Meaning the secondary voltage is proportional to the number of turns on the secondary coil. Vs∝Ns Using the relationship; Vp/Vs=Np/Ns If we want Vs=10Vp that would imply...
32. ### Engineering Transfer function of AC Transformer

I'm solving this exercise, first I did a force diagram for the transformer nucleus and I got this: ∑Fx = ma P(t) - Fk - Fb = ma P(t) = mx''+ bx' + kx So I got that dynamic equation, my question is, after transform that dynamic equation to Laplace Domain how can I relate it with the Output...
33. ### What's different in a transformer core when coupling high & low power?

This is one of those 'oh, I am not sure I know the answer' kind of thoughts. The strength of magnetic flux in a transformer core is a function of volts per turn, Faraday figured that one out. So, if I have a light load on a secondary (let's say it is pure ohmic for now, let's not confuse it)...
34. ### Designing a Power Transformer: Tips and Techniques

We need all the project including all details with schema, If you are talented for drawing the project, please contact me. 50/62,5 MVA, 154/33 kVA
35. ### Solving the operating point of a transformer with a nonlinear B-H curve

What are the possible ways of solving the operating point of air gapped transformer with nonlinear B-H curve? For example let's consider 3C90 E34 sized core with 0.5 mm airgap. I know that the magnetomotive force over the ferrite part can be formulated as function of the reluctances...

I need help to get the percentage current loading on this transformer with the following parameters transformer size is 500KVA Primary voltage is 11KV Secondary voltage is 415v power factor is 0.8 current in Red phase is 315A Current in yellow phase is 302A Current in blue phase is 317A Neutral...
37. ### Changing galvanometer reading in the secondary coil of a transformer?

The present setup is a step-down transformer. Im thinking if n1 is decreased to match or be less than n2, then it will be a step up transformer. so A. (but answers say B)?
38. ### Looking for advice on a buck boost transformer....

I have a 45kva GE transformer in the pics and here. Its set up for 480 to 208, i need to wire it for 250v to 208v. Could someone please point me to the correct diagrams for this general type of transformer? Thank you
39. ### 33KV potential transformer design

I am in a team of designing a 33KV potential transformer. We done secondary turn as 75 and primary turns as 15000 with core cross sectional area of 5000 sq.mm. As per IS standard we need to maintain a accuracy class of 0.2 at 50VA burden but we can't able to achieve it. Someone please help us to...
40. ### Connecting a step-up transformer backward

I deduced that this is a step-up transformer wired backward because of the number of turns in each coil. The inner coil has a less number of terms and by the problem's wording, the inner coil is the primary coil. I'm not sure what would actually happen, a hypothesis (that I am not confident on)...
41. ### Engineering Calculating Power Lost in a Resistor (within Transformer Circuit)

Hi, I have a simple question that I don't have a fundamental understanding of: do resistors dissipate reactive power (in addition to active power)? For context, when we are looking at a transformer (single phase) equivalent circuit (similar to the one in the image attached), we are asked to...
42. ### Calculate Ip: 9V, 120V Transformer Equation

Okay, so according to the transformer equation, VpIp = VsIs In this question, I know I have to calculate Ip. I think given, Vp = 9V, Vs = 120 V Now I don't know what to use in the value of Is. Please help! The answer is 2.32 A.
43. ### Engineering How does this Bipolar RF Amplifier + Output Transformer circuit work?

I am trying to create a receiver for a personal project I am working on. This is the RF amplifier that I was given by a book I am following. How does this circuit work? Usually for a BJT amplifier I find the DC bias point and then use the small signal model after I bias the circuit? I understand...
44. ### Transformer Coupled Class A amplifier Single supply

How can Vce vary from 0 to 2Vcc? In class, I learned that it was due to Lenz Law working in the transformer and a voltage of Vcc being induced to reverse the change in Ic. However, I cannot picture this. Can someone please explain with a diagram of how this comes about in the transformer windings.
45. ### Linear transformer driver explanation

Ok, so to be honest I am not really sure to which subcategory this belongs, but I think it is high energy physics. So my question will be rather brief and vague , can you explain me the working principle of a linear transformer driver? Google wasn't of that much help with this one as it seems...
46. ### DIY Electromagnetic Induction Experiment

So I was watching this video containing DIY experiments on electromagnetic induction . At minute 4:45, the dude pretty much creates a transformer without using an iron core. He runs 30-50 kHz AC in a coil (forming the primary circuit) and then brings another coil with its ends attached to a...
47. ### Transformer without separate primary and secondary windings....

I have always longed to make a system where I can get AC over a wide range of voltages. This system would help me test how my other experiments behave when they are powered from the mains. In order to get different voltages, I need to design my own transformer where the secondary has been tapped...
48. ### Engineering Therefore, R's=0.057/26.5^2=0.000078 Ω2% of 415 V is 8.3 V

Primary winding voltage v1 = 415V Secondary winding voltage v2 = 11kv Rating of transformer is 200KVA winding resistance Rieq = 0.14 Ω winding leaking reactance Xieq = 0.057 Ω A) % regulation at 0.8 power factor lagging Primary winding current I1 = 200/415 = 482a Power factor CosΦ =...
49. ### Power absorbed and B vs H plot for microwave oven transformer

A DI-149 data acquisition module was used to record a microwave oven transformer (MOT) primary voltage and current time histories. The secondary of the MOT was open. The DI-149 analog input specs are: +- 10 volts full scale, 5000 samples per second for each channel (assuming two channels being...
50. ### Need help with a parallel inductance calculation for this transformer

I have a transformer with the primary winding connected to a 115 volts 60Hz supply, the current is 0.230 amps AC, with a resistance of 25.3 ohms. The secondary winding is connected to an inductive load. The voltage across the secondary winding when the load is connected is 13.14 voltage AC with...