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. OldWorldBlues

    Easy way to calculate losses for re-purposing a transformer?

    Hi everyone! This is my first thread :) I've been working a bit with AC and radio, and would like to make a simple(-ish) circuit in which a 1-volt peak audio signal is stepped up to around 5 volts with a transformer, and is fed into a crystal oscillator to make a crude-but-effective AM...
  2. carllacan

    Transformer under an external magnetic field.

    What happens to the current through a transformer windings if the whole system is under a uniform magnetic field in the direction of the coils and with frequency equal to that of the AC in current? I think the current induced in the primary solenoid should generate a field that would make up...
  3. K

    Help understanding auto transformer shorting

    Will someone please help me understand the significance of shorting an auto transformer? This feeds a motor. At reduced voltage, the motor starts at 65% of line voltage, a run contactor pulls in bypassing the transformer and the shorting contactor pulls into take the transformer out of the...
  4. S

    I Phase differences in Transformers

    How is the phase difference between the current in the primary coil and induced e.m.f. in the secondary coil be 90*??
  5. billyray

    Transformer equations in the Hughes book

    <<Moderator's note. This question go no answers in the homework forum. I hope it might do better here>> 1. Homework Statement A 415V to 11 kV transformer has a rating of 200 kVA. The winding resistance and leakage reactance when referred to the primary are 0.014 Ω and 0.057 Ω respectively...
  6. billyray

    Transformer Regulation Homework: Hughes Electrical Book

    Homework Statement [/B]Homework Equations I have used the Hughes electrical book for the equations to solve the above. I have very little notes from college to help. I have found these equations fit and am confident on it but not 100% can anyone who knows transformers please advise if they...
  7. marmstrong941

    Find Iron Core Plates for Transformer Prototypes - Top Sources Listed Here!

    Hi I am looking for places I can get iron core plates to make transformers. These are needed for prototypes I want to make. I have looked at microwave power supply’s. They would work but I would need to find a few with the same ones in them. I need just the cores and I will wire the copper up...
  8. Cardinalmont

    I Short Circuiting the Secondary of a Transformer/Self Impedence

    Thank you for reading my post. I was watching the video this video on transformers and saw an amazing demo: From 4:00-5:20 the guy does an experiment where he has a simple transformer circuit set up: On the primary side of the transformer he has an AC power supply, and a lightbulb. On the...
  9. P

    Is it possible to eliminate back EMF in a transformer and achieve free energy?

    I have been reading about mag-amps which gave me an idea for a more efficient transformer. So the core is in the shape of a square or rectangle with a center piece dividing it into two. The construction of the outer core is larger (less reluctance) than the middle leg (greater reluctance). The...
  10. L

    Understand AC Transformer Polarity for Three-Phase Connections

    my transformer book does not cover an area i am interested in and was wondering if someone would direct me to literature that would help me understand something and if you wouldn't mind trying to explain it to me yourself that would also be appreciated. you have three single phase transformers...
  11. MalachiK

    B Phase difference in a transformer

    Today I took two coils and connected one of them (coil A) to an AC power supply. I held the second coil (coil B) close to the first one and then connected them both to a dual trace CRO. As expected, an emf was induced in coil B and the traces on the scope were 90 degrees out of phase. As I...
  12. Mzzed

    Switch mode DC transformer equations?

    I would like to know if there are any general equations (such as the AC transformer equations) that describe a switch mode DC transformer. By this i mean a constant frequency DC signal (50% duty cycle) that ranges from 0V to some max voltage on the primary coil and outputs some higher voltage on...
  13. J

    Sequence Diagram For a Transformer

    Homework Statement I think two diagrams are wrong here. I've marked in red.[/B] Homework Equations Do you also think the 2 diagrams are wrong? I think for 1st red circle, at delta-- the a1 switch should be open whereas for second red circle at star grounded-- the a1 switch should be closed...
  14. J

    Clock Notation of Star-Delta 3-phase transformer

    Homework Statement Homework Equations Dot is A2. A1-A2 of star is in phase with A1-A2 of delta The Attempt at a Solution I'm getting answer as Y-Delta - 1. Assuming Y is HV. How is C right answer?
  15. clembo

    Transformer exceeding its rated maximum temperature

    Homework Statement An oil-filled transformer has a c.m.r. of 500 kVA which allows it to run continuously in an ambient of 35°C with an oil temperature rise of 50°C. The transformer has a time constant of 1.5. hours and the ratio of copper losses to iron losses at c.m.r. is 1.5:1. After...
  16. J

    Condition for parallel AC Mains power transformer operation

    Homework Statement Homework Equations I think both A and C are right answers. The Attempt at a Solution 1 condition is pu Z(leakage) must be same on respective KVA rating for load sharing. Now: Zpu = Z(actual)/Z(base) ----equation 1 For Zpu of both transformers to be same, the right side...
  17. J

    Transformer Delta to single phase

    Homework Statement Homework Equations For Delta line current = 1.732 times phase current. Line voltage = phase voltage The Attempt at a Solution I don't know how to start this. This is original connection This is new one The voltage should be 3 times because of additive polarity. Not sure...
  18. D

    Two AC Sources with One Transformer

    I want to program a little power grid game and have the problem of connecting things via transformers. Imagine the following setup: You can see the AC voltage sources as generators (or together with the resistor as a "consumer", if the amplitude is 0). What I need to figure out are the...
  19. DrClaude

    Problem transformer and Christmas lights

    I have a very nice Christmas electric candlestick that is I can no longer get to work properly. Originally, it came with incandescent light bulbs running in 6 V DC. Some of the lights have burned out, so I looked for replacements and can now only find LED lights. The ones I got are labelled...
  20. J

    Transformer cooling for Hermetically-sealed units

    Hello, I have question about transformer. How is Hermetically-sealed transformer cooled? I know that in air-breathing type we have conservator, breather, etc…for cooling. But, where the expansion oil goes in hermetically sealed? How it works?
  21. Manoj Sahu

    Secure Your Transformer Chamber with Automated Actions

    I have a transformer chamber with 2 doors. What I have to do- If any of the door is opened, this should happen- 1. 2 CFL inside transformer chamber should start 2. Simultaneously, a buzzer/hooter should be ON. 3. After opening the door, I should have option to reset the hooter. how do I do it?
  22. G

    Microwave oven transformer - safe use and setup questions

    Before we start, this transformer will be used in a closed shop, on a clear bench and via a remote switch. I will be in full view of the setup. I hope to try some Lichtenberg patterns. I see that the secondary, c. 2000V winding is referenced to the transformer core. What is the purpose of...
  23. J

    How does transformer taps work?

    In the question below i know 200/480 V is rated voltage at primary and secondary side of a transformer, but '13' is what i do not know. Also how does the solution work out? i have tried every possible thing. Thanks(Sorry if i could not phrase my question in accordance to the pattern)
  24. PJP

    Which fuse should i use for a step down transformer

    hello every one! I'm working on a project to vibrate an iron string with an electromagnet. I've a 230 v step down transformer with "12-0-12 1 amp" output and a 230 v "12-0-12 5 amp" output. I'm confused with which FUSE should i go with. i have a 3 amp and a 5 amp fuse. also I'm planning to use...
  25. lekh2003

    Graphs of Current through a Transformer

    I have created a make-shift transformer using a circular core and some wire: It is quite basic, but I have some questions about the currents induced when one side of this transformer has a 220 V AC current passed through it. I have an oscilloscope from which I have the graph: The perfect...
  26. S

    I Transformer Output in Non-inertial Frame: Frequency Change?

    In this example I'd like to know about the output of the transformer. What happens if an electromagnetic transformer is powered by a sine-wave and simultaneously accelerating at non-relativistic speeds? I assume the output will still be a sine-wave but the frequency will change. Is this correct?
  27. Cocoleia

    Current and power with transformers

    Homework Statement I am working on the following problem: And ideal single phase transformer 240V/2880V is supplied with a 240V source via a resistance cable of 3ohm. If we connect a R=720ohm resistance to this, determine the primary current and the dissipated power in R. (I'm sorry if some...
  28. teroenza

    Unclear Transformer Specifications

    Can someone help me better understand the specs for this old transformer I found? I'm confused why the input and output power see to differ greatly (115V*1.2A ~140W while 40,000V*2mA~ 80W). Also, the fuse rating is unclear to me. Does that mean 1 and 2/10 amp?
  29. J

    Mean Magnetic Path Length of the Magnetic core of a transformer

    For the Image given, i have to calculate reluctances of air gap and core which depends on respective mean path lengths. For the left hand core, the mean path length calculated in the solution manual is 1.11 meter . However what I don't understand is that why is the length of the air gap included...
  30. J

    Engineering Transformer -- find equivalent circuit from efficiency and V.R

    Homework Statement For 200 KVA, 4000/1000 V transformer. 1 phase. Efficiency is 0.97 at full load and 60% load at unity power factor. No load pf = 0.25 Full load Voltage regulation at 0.8 pf lag is 5% Find transformer ckt parameters for referred to lv side Homework Equations efficiency is...
  31. M

    Replacing Audio Transformers in Radio Receivers

    hello can somebody help me, what can i use in place of audio transformer because i was in electronics shop the man he told they don't use anymore audio transformer in radio receiver what to use in place of audio transformer?thnx
  32. J

    Step-Up Current Via Transformer

    I'm a mechanical engineer by trade, but I am working on developing a testing apparatus that oscillates a neodymium magnet between two solenoids offset by by a 180 degree phase shift. Basically, one solenoid pushes, the other pulls. To get this, current is essential. I need each solenoid to get a...
  33. B

    Optimizing Transformer Capacity for Increased Loads

    Hello, I have a 1000 kva 13.8/400v transformer. I want to add additional loads to its 60% present load. The nameplate says max. ambient temp. is 55 deg. Cel. and max temp. rise is 50 deg. Cel. Can I load it to 90% continuous load after the additional capacities, and, is temp. rise equivalent to...
  34. F

    Resistor instead of a step-down transformer

    As a quick and dirty/cheap solution, can a resistor be used instead of a step-down transformer ( stepping down from 230V AC mains to 3 V AC) to drive some simple electronic circuit such as a few LEDs or transistor radio etc ?
  35. Plat

    High-frequency transformers - how are they different?

    I apologize for being somewhat scatter-brained here, I just have too many questions on this topic. I know high-frequency transformers use ferrite cores instead of laminated silicon-steel, but what other differences are there? Does their reactance still follow the standard formula: 2*Pi*F*L ...
  36. K

    Exploring Transformer Connections for Step Up/Down Transformers

    Hi Take a look at the picture below, I am curious of what transformer connections are used at each step up/step down transformer. I am sure that there are several way of connecting them and each have their pros and cons, but what are the most usual connections? Lets start at the consumer and...
  37. J

    Understanding the Grounding of Transformers in Marine Electrical Systems

    Hi, can somebody help me please. I have situation like on picture in link. So, marine electrical system 440V, transformed to 230V for heater. But, my question is, why transformer is grounded on such way. I don't understand this grounding. thank you.
  38. Plat

    Mains transformer with 1.4 ohm primary winding?

    I don't understand how this is possible. This is a rather large transformer in a stereo system amplifier. The transformer is a simple step-down with 120V mains primary to a center-tapped secondary providing both 38V and 76V. According to ohm's law, at 120V this thing should draw about 85 amps...
  39. E

    Effect of saturation on transformer inductance

    Hi all How is the inductance affected when the transformer core has reached saturation? I can not seem to get my head around it, and I hope someone can help me understand it, thanks. Kind wishes
  40. Abdul Wali

    Understanding Key Parameters in Transformer Oil Testing

    Hi, when it comes to Transformer Oil testing, there are some parameters that we need to consider but i don't understand their definitions and i can't find their explanations online, so may someone please define these terms for me that what these terms actually mean? the terms are as follows...
  41. JaredJames

    Smoothing DC Output from Transformer

    I have a power supply which takes 230 VAC input and gives 24 VDC output. I use it to drive some differential pressure sensors (24 VDC supply and 0-10 VDC signal output). It is stated to have a noise of 80 mV peak to peak. This can equate to a 25 Pa variation in readings I'm finding with...
  42. N

    Transformer voltage regulation and calculations

    This particular question is for an assignment. However, I believe that I have the final (correct) answer, but want to check the understanding. I am required to calculate the resistance of the secondary winding of a transformer. The transformer is a 415:11000 V step-up, rated at 200kVA but with...
  43. anorlunda

    How can DC-to-DC power transformers improve efficiency in power electronics?

    I am sharing this to brag about my former boss and mentor Lionel Barthold. He is well into his 90s, but his mind is so sharp that he continues with brilliant inventions. I'm very proud of him. What would power level DC-DC transformers be good for? Connecting different voltage level HVDC lines...
  44. T

    Booster transformer topology for transmission application

    Hi, Regarding transmission line booster transformer topologies I'm curious as to what would happen over all the possible permutations. I refer you to the following: http://top10electrical.blogspot.com.au/2015/03/booster-transformer.html I presume that in real life the booster transformers...
  45. R

    Question about the power rating of a transformer

    In some aerospace applications you need high voltages in the range of kilovolts. This is commonly supplied by transformers. However, transformers because of their iron cores are heavy. But in aerospace being lightweight is a key requirement. In the thread "Question about power capacity of...
  46. marcophys

    DC12V 12A car window motor - what spec for a 220V PSU?

    I have a combined motor and screw drive (to 90 deg). It's original purpose was to convert car windows to electric drive... my guess is that it is at least 25 years old, and made in Japan. For scale... the width of the motor casing is 50mm (as you look at it) I'm making a motorised turntable...
  47. P

    Basics of a Resolver transformer....

    Can somebody please explain me the basics of resolver. How it works? How it calculates angle and velocity? Atleast any proper links. Please help.
  48. EddieP

    B Transformer core saturation- is this core saturating?

    Please excuse me if this is a very basic question, but I am just hoping someone can enlighten me on something. I am using the program FEMM to simulate a transformer. Unfortunately, I am unable to find data on the BH Curve of the material I’m using for the core, and I am worried that my...
  49. C

    Electrical Efficiency of Ionized Air?

    Alright It's been over a year since I've posted and received amazing help the last time I did. Now I've a question I cannot seem to find an answer to. Say you have an electrical charge and use a transformer to step up the voltage high enough to where it arcs in air. Then you have a conductive...
  50. Asmaa Mohammad

    The efficiency of a transformer

    Homework Statement A step-down transformer has an efficiency of 90%, the voltage of it primary coil is 200V and its current is 0.5A, and its secondary coil has a voltage of 9V and a current of 10A and its number of turns is 90 turns. Calculate the number of turns of the primary coil. Homework...
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