Transformer Definition and 809 Threads

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. B

    Calculating magnetomotive force in a transformer

    If I have a transformer with a known primary inductance and number of turns, and the output is open circuited, how would I go about calculating the magnetomotive force created by the magnetizing current?
  2. A

    Can a Variac handle the current output of a 2300V microwave oven transformer?

    If one had a microwave oven transformer (MOT) from a microwave that was said to be 1200W, and the transformer itself had an output of 2300V, would that mean that the current would be: Power = Current * Voltage 1200W = Current * 2300V Current = 0.52A The reason I ask is because: I'm...
  3. B

    What size inductance for a flyback transformer?

    I'm looking over some equations for the output of a flyback transformer (essentially the same as for a buck-boost converter) and I notice that as long as the flyback operates in the continuous mode, the inductance doesn't enter into the equation. Of course since no inductor is ideal, there must...
  4. P

    Primary Voltage for 10T/500T Transformer

    What should be the maximum and minimum primary voltage of output transformer with 10 turns of 22 SWG primary winding and 500 turns of 34 SWG Secondary winding?
  5. P

    Transformer Impedance and Ratio Calculations

    Homework Statement See attached for a view of the problem Variables a=transformation ratio= 1/5 Ip=2Amps ZL=2 ohm resistor Homework Equations Q1 : Find the current magnitude of the current IL and the Voltage VL Q2 : Find the input impedence. The Attempt at a Solution OK, my...
  6. J

    Transformers: Solving for i_1 and i_2 with Primary and Secondary Coils

    Homework Statement Primary coil of a transformer with an emf E(t),resistance R_1 and inductance L_1.Secondary coil resistance R_2 and inductance L_2. Let i_1 and i_2 be the respective currents in each coil. Homework Equations L_1\frac{di_1}{dt}+R_1i_1+M\frac{di_2}{dt}=E(t) and...
  7. M

    Transformer: Excitation Frequency and Turns Ratio

    Another transformer question: if I have an oil-filled transformer coil and I calculate the turns ratio with voltage in / voltage out at 60 Hz, why, when I increase the frequency to 23 kHz would the turns ratio appear to change? Is it because of the inductance of the primary coil? My boss'...
  8. N

    How Do You Calculate Transformer Efficiency with Given Power and Voltage?

    Homework Statement What is the the efficiency of a transformer with 13w of primary power. 120Vp, Np unknow 12Vs, 90Np Homework Equations The Attempt at a Solution eff= Psec/ Pri * 100
  9. S

    Transformer with wire running through as secondary

    I want to confirm that I'm thinking about this in the right way... Imagine a transformer. The primary has an integer number of turns. Now imagine the secondary has less than 1 turn, i.e., just a piece of wire passing through, forming essentially half a turn. I know voltage is induced in...
  10. A

    Rectified AC through an AC transformer

    Like the title says, I am wondering if it is possible to rectify an AC signal and run it through an AC transformer. The rise and fall in voltage still exists so it should work, or are AC transformers made specifically for an AC signal and other information needs to be taken into account?
  11. B

    A weird thing happened when our transformer blew up

    A few nights ago, the pole on the side of the road that holds our transformer snapped, the transformer exploded and set the pole on fire. In my plant we were running on 2 out of 3 phases for a while until we completely lost power. Now here's the "weird" thing... Just about every motor...
  12. C

    Replacing an Audio Transformer: EI-19 Output Specs and Replacement Guide

    I need to replace an Audio transformer, EI-19 Output Transformer. What should I replace it with? I can't find the primary to secondary ratio, or the voltage ratings. Is there something special about audio transformers compared to step up/down transformers used in AC to DC converters? If so, what...
  13. K

    Problems with Inverter and transformer

    Hi, i am building an inverter 12VDC- 120VAC, 50 Hz with square wave as gate signal for MOSFET. Looks like my circuit works fine because i am getting square out -12 to 12 AC. Now i am using transformer to step up 12 VAC to 120 VAC. But i am experiencing some problems. But i am supplying...
  14. B

    Can a Transformer Rated at 225 VA Only Supply 25 mA on the Secondary Side?

    When a transformer is rated 225 VA, Vprimary=120 V and Vsecondary=9KV, Isecondary=25 mA, does this mean that on the secondary side the transformer can only supply 25 mA, no more, no less than rated current. Thanks
  15. A

    Magnetic circuits and transformer

    I am a UG electrical engineering student. I studied about magnetic circuits and transformers recently in one of my departmental courses. I want to find out if I can implement this knowledge practically. So can anybody suggest some interesting projects on magnetic circuits or transformers...
  16. Phrak

    Inductor and Transformer Design Equations

    I thought it would be a good idea to write this down, all in one place, finally. Any errors, or impovements needed? Should it be in gaussian units?
  17. B

    Why does the magnetic flux in a CT core decrease with connected load?

    Hi Guys, :smile: I am grappling with a peculier (but somewhat common) problem with Current Transformer (CT) magnetic circuit. I will be very grateful if someone could help me out with my problem. 1)In an ideal Voltage Transformer (VT), the magnetic flux developed in the core remains...
  18. W

    Output of a transformer plugged into a DC voltage source by mistake?

    Homework Statement What would be the output of a transformer plugged into a DC voltage source by mistake? Homework Equations N/A The Attempt at a Solution Judging from the phrasing of the question, I am assuming that a transformer should not be plugged into a DC voltage source...
  19. X

    Step Up Transformer: Exploring Conservation of Energy

    It is understood that you cannot have something from nothing, but how is this the case with a step up transformer? It seems that stepping up the voltage is stepping up the potential energy and since more windings actually increase the resistance there will be lower current which is how most...
  20. S

    Electrical Engineering: Transformer Question for Power Shower

    Hi, I'm an apprentice multiskilled engineer, thought I prefer electrical engineering anywho, my power shower at home stopped working and upon testing there was no ouput from the transformer, 230v/24v DC and it got me thinking, I'm aware of the step up/down voltage theory etc and the windings...
  21. W

    Transformer efficiency/primary current (help )

    Transformer efficiency/primary current (help!) Real transformers are not 100% efficient. That is, the efficiency, in percent, is represented by e = (100%) Ps/Pp. A step-down transformer has an efficiency of 92.5% is used to obtain 23.0 V from the 125 V household voltage. The current in the...
  22. C

    Impedance matching transformer question

    1. It is required to pass a current of between 6.0A and 6.5A through an impedance of (1.6 + 1.2i) ohms. With only a 230V supply available, it is proposed to use a transformer for impedance matching. A transformer is available with a turns ratio of 16:1. A laboratory test showed that with the...
  23. K

    I am trying to work out the BW of my transformer

    I am trying to work out the BW of my transformer. My source resistance, Rs, is 50R. My load resistance, RL=50R. The windings ratio ,N, is 1:1. The magnetising current, Lmag=7.96uH. The data i have suggests that to find the lower -3dB point, you refer the secondary load to the primary. This...
  24. S

    P.d. increases in a step up transformer

    just tell me how the p.d. increases in a step up transformer. (Please don't use formulas for this.) if we take a conductor of same length and thickness as the 1st one for the secondary coil, the voltage doesn't increase. but why does it,if we increase the length. I mean,how can that affect...
  25. H

    Guys, I have a question regarding a mathematical equation of a transformer

    I have been trying to figure it out, but nothing seems to help. my question is simple, how are we able to derive a mathematical equation of a transformer for convesion of Delta connection to star or star to delta ?
  26. B

    Engineering Why Conduct Open-Circuit and Short-Circuit Tests on a Transformer?

    Homework Statement Hi. Why does one conduct an open-circuit and a short-circuit test on a transformer to determine its equivalent circuit parameters? I've read that a) the open-circuit test determines the parallel parameters - the R and X equating to the core loss, and b) the short-circuit...
  27. B

    Engineering Transformer Equivalent Circuit Questions

    Hi. Why does one conduct an open-circuit and a short-circuit test on a transformer to determine its equivalent circuit parameters? I've read that a) the open-circuit test determines the parallel parameters - the R and X equating to the core loss, and b) the short-circuit test determines the...
  28. B

    What Is an Impedance Matching Transformer?

    Hi All, I am building a circuit that i need to get a better understanding of before jumping in head first, it says it requires an Impedance Matching Transformer. I don't get this with the Attached Circuit, is it the whole Primary circuit has to match the whole Secondry Circuit Impedance...
  29. L

    Transformer short circuit fault calculation clarification

    Hi, I'm trying to perform a short circuit fault calculation on this transformer and load I have when a 3 phase bolted short (worse case) occurs. The transformer specs are below: Z(transformer)=5%, Z(cable)= .00306 + j.0027, Delta/Star 6.6kV/400V I can understand calculating the short circuit...
  30. E

    Where can I find a 100V DC power supply with 15A output?

    Hi all, I am looking for a transformer to convert the 115VAC from the wall to ~100VAC, 10-15A, and 1-1.5kW. Is something like this commercially available? Otherwise how difficult would it be to make? Thanks a lot.
  31. I

    Transformer Grounding: Advantages & Disadvantages for System Protection

    what are the advantages and disadvantages of different types of transformer grounding -with regard to system protection and fault current reduction? we have the following grounding types YN - YN YN - Delta Delta - YN Delta - Delta where can i find a good resource that explains this?
  32. B

    Step down Transformer 240v AC to 12v 100amp

    Hi All, I have a step down Transformer 240v AC to 12v 100amp output. My question is, can i use this as a step up transformer as well by connecting to the other side of it? My supply voltage is of course 240v AC, this can be controlled with a 240v 10amp Variac to take it easy on things...
  33. C

    Calculating "theta" Using Step Up Transformer

    Hi, so I know that VI = P cos (theta), but during an experiment using a step up transformer, I got the primary voltage 7.42V, primary current 0.41A, and primary power 3.2W. How then should I calculate the angle theta. I can't use arcosine, 'cause that will give me undefined. Thanks a lot.
  34. A

    Can we use step up transformer as step down

    can we use step up transformer as step down without any change?
  35. E

    Transformer designing software

    Hi Any body who can send me the link to a free low power sinewave transformer designing software and also of some free ebook on this subject.
  36. R

    Difference between direct coupled and transformer coupled?

    what is the difference between direct coupled and transformer coupled?(mechanical configurations with the required turns ratios of 1:25 direct coupled and 1:1.79 transformer coupled)
  37. S

    Finding a Transformer for my application.

    I am electro-statically trapping particles for chemical and physical studies. I do not want to discuss the details of my research. AC Calibrators are very expensive and I don't need the precision. I did find a power amplifier that could step up my sine wave generator to the values I want...
  38. M

    Basics of using the isolating transformer

    Hello, I have a differential signal going into an instrumentation amplifier (AD620). I would like to employ galvanic isolation on the inputs of AD620. Would anyone be so kind and tell me how it shall be wired? I don't know much about signal isolation. Shall 1:1 or 1:1:1 transformer be used...
  39. D

    Transformer Magnetizing Reactance

    In the case of an open-circuit test of transformer, when I increase the supply voltage, i realize the magnetising reactance (Xm) decreases, why does this happen?
  40. L

    Where Does Extra Voltage in a Step-Up Transformer Come From?

    In a step-up transformer, since you can increase the voltage by increasing the number of turns on the second circut, where does this extra voltage come from? why does this not violate conservation of energy?
  41. A

    Transformer when output circuit is open

    can u explain what hapens output circuit is open and no current is flowing through output coil? isn't it that a large current flows through the input?and the wire burns...i know it doesn't hapen...but why?when there is no back emf in primary?
  42. J

    Why Are Transformer Inductance and Capacitance Modeled in Parallel?

    Here is my question. It is rather simple quetion. But I am a beginer in this field so please help me. In the case of equivalent ciruit of the tranformer it is taken that the inductance and the capacitance in the primary coil of the transformer is taken parrallel and the inductance and...
  43. W

    Electromagnetic induction in transformer

    Hello!I would like to ask about Electromagnetic induction in transformer.As we learn that an alternating voltage is connected to the primary coil,the alternating current in the primary coil produces a magnetic flux linkage with the secondary coil which constantly changes.\phi=magnetic flux...
  44. S

    How to work out the turn ratio on a transformer

    I would like to know how to work out the turn ratio on a transformer from having just the input and output voltages.
  45. G

    Transformer resistance question

    Does the resistance in the secondary circuit connected to a transformer provide for a certain resistance in the primary circuit?
  46. M

    Electric power transformer problem

    An average of 120 kW of electric power is sent to a small town from a power plant 10 km away. The transmission lines have a total resistance of 0.40 ohms. Calculate the power loss if the power is transmitted at 240 V. The solution is I=P/V=500 A, then the power loss in the lines...
  47. M

    Determine Transformer KVA output and Power Factor

    1. Two transformers T1 and T2 in parallel supply a common load at a lagging pf of 0.8, their per unit impedance are 0.04+j0.09 and 0.01+j0.07 at the same kva ratings of 3000KVA each and load power = 5500KVA Determine the kva output of each transfromer and power factor This is how i worked...
  48. R

    Linear system and potential transformer

    Hi, Does anyone knows how to prove that a potential transformer is a linear system or not? Can I use principle of superposition with time-domain impulse to prove it? Is there other ways other than the principle of superposition to prove linearity of a potential transformer? Is there a way to...
  49. C

    Is 12v DC from a battery same as 12v DC from a transformer?

    can anyone please help me, i want to know that whether 12v DC from a battery is same as 12v DC from a transformer ( after a 4 diode bridge has been fixed to it )... please help, because i want to expeiment something, i removed the 12v battery of my UPS and put in its place a 12v transformer, but...
  50. f95toli

    Isolating transformer in the UK

    For a while now I have been having some problems with ground loops that are due to the diagnostics (in this case thermometry) in the my measurement setup. Unfortunately there is no "easy" way to solve this problem without breaking the connection to Earth (=safety ground) and let some of the...
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