proportion. Discover the physics behind the phenomena by exploring magnets and how you can use them to make a bulb light. A portable x-ray unit has a step-up transformer, the 120 V input of which is transformed to the 100 kV output needed by the x-ray tube. For a transformer, the voltages across the primary and secondary coils are related by. (a) What is the current input? Power is sent long distances at high voltages, because less current is required for a given amount of power, and this means less line loss, as was discussed previously. It also accounts for the winding resistance and core losses. Transformers only work with alternating The plug-in transformer has become increasingly familiar with the proliferation of electronic devices that operate on voltages other than common 120 V AC. 24 and so no voltage will be induced in the secondary coil. Solving [latex]\frac{{V}_{\text{s}}}{{V}_{\text{p}}}=\frac{{N}_{\text{s}}}{{N}_{\text{p}}}\\[/latex] for [latex]{N}_{\text{s}}\\[/latex] for Ns and entering known values gives, [latex]\begin{array}{lll}{N}_{\text{s}}& =& {N}_{\text{p}}\frac{{V}_{\text{s}}}{{V}_{\text{p}}}\\ & =& \left(\text{200}\right)\frac{15.0 \text{ V}}{120 \text{ V}}=25\end{array}\\[/latex], The current input can be obtained by solving [latex]\frac{{I}_{\text{s}}}{{I}_{\text{p}}}=\frac{{N}_{\text{p}}}{{N}_{\text{s}}}\\[/latex] for Ip and entering known values. overall power remains the same. current will create a magnetic Calculate the voltage obtained from the secondary coil. (a) 335 MV (b) way too high, well beyond the breakdown voltage of air over reasonable distances (c) input voltage is too high. [latex]\frac{{V}_{\text{s}}}{{V}_{\text{p}}}=\frac{{I}_{\text{p}}}{{I}_{\text{s}}}\\[/latex]. Using direct (a) What is the number of loops in the secondary? Run using Java. coils matches the ratio of the numbers of turns on the coils. A plug-in transformer, like that in Figure 4, supplies 9.00 V to a video game system. (Although ideal transformer’s winding inductance are each infinitely high, the square root of winding inductance’ ratio is equal to the turns ratio. (c) Which assumption or premise is responsible? ipnp - isns = 0). In reality, the output power is always less than the In a step-down transformer, Vs < Vp. The cross-sectional area of the coils is the same on either side, as is the magnetic field strength, and so ΔΦ/Δt is the same on either side. This equation can be used to calculate what the output might be from a particular transformer, or to work out how to design a transformer to make a particular voltage change: \[\frac{primary~voltage}{secondary~voltage} = \frac{number~of~turns~on~primary~coil}{number~of~turns~on~secondary~coil}\], \[\left [ \frac{V_p}{V_s} = \frac{N_p}{N_s}\right ]\]. (a) 20.0 mA (b) 2.40 W (c) Yes, this amount of power is quite reasonable for a small appliance. The Y-Δ transform, also written wye-delta and also known by many other names, is a mathematical technique to simplify the analysis of an electrical network.The name derives from the shapes of the circuit diagrams, which look respectively like the letter Y and the Greek capital letter Δ.This circuit transformation theory was published by Arthur Edwin Kennelly in 1899. So if voltage increases, current decreases. [latex]\begin{array}{lll}{I}_{\text{s}}& =& {I}_{\text{p}}\frac{{N}_{\text{p}}}{{N}_{\text{s}}}\\ & =& \left(\text 10.00\text{ A}\right)\frac{\text{50}}{4.17\times 10^{4}}=12.0\text{ mA}\end{array}\\[/latex]. If the flux in the core is purely sinusoidal, the relationship for either winding between its rms voltage Erms of the winding, and the supply frequency f, number of turns N, core cross-sectional area a in m2 and peak magnetic flux density Bpeak in Wb/m2 or T (tesla) is given by the universal EMF transformer equation: If the flux does not contain even harmonics the following equation can be used for half-cycle average voltage Eavg of any wave shape: Resources for electrical engineering professionals. Where Vs is the instantaneous voltage, Ns is the number of turns in the secondary winding, and dΦ/dt is the derivative of the magnetic flux Φ through one turn of the winding. Transformer Quiz Note that the Ni-Cd batteries need to be charged from a DC power source (as would a 12 V battery). 4. The device consists of two stages. between the primary and ), Testing and Commissioning Method Statements, Commercial & Finance Management Procedures, Electric Current Electric Charge & Electromagnetism, Cable Tray Trunking & Ladder Installation Method for Projects, Method Statement For Installation Testing and Commissioning Of MATV Distribution System, Overhead Power Transmission Line Route Selection Considerations, Binary, Hexadecimal, Octal, and BCD Numbers, Switchgear Panels Energization and De-Energization Procedure – Electrical Services Commissioning, Electrical Switchgear Installation Procedure – Medium Voltage MV Panel, Method statement for Installation & Testing of Earthing, Grounding and Lightning Protection System, BMS Building Management System Testing & Commissioning Method. Transformers change voltages at several points in a power distribution system. This equation is important! This heat is then lost to the environment, it is wasted This is A typical construction of a simple transformer has two coils wound on a ferromagnetic core that is laminated to minimize eddy currents. But high voltages pose greater hazards, so that transformers are employed to produce lower voltage at the user’s location. (b) What is unreasonable about this result? Unreasonable Results The 335 kV AC electricity from a power transmission line is fed into the primary coil of a transformer. to the difference in voltage If the power output in the previous problem is 1000 MW and line resistance is 2.00 Ω, what were the old and new line losses? 10. Generate electricity with a bar magnet! When a < 1, the secondary voltage is larger than the primary voltage and the transformer is a step-up transformer. The number of loops in the secondary is small, as expected for a step-down transformer. (a) What is the ratio of turns in the primary and secondary coils of her transformer? GCSE Chemistry Lenz’s law tells us that the primary coil opposes the change in flux caused by the input voltage Vp, hence the minus sign (This is an example of self-inductance, a topic to be explored in some detail in later sections). [latex]\frac{{V}_{\text{s}}}{{V}_{\text{p}}}=\frac{{N}_{\text{s}}}{{N}_{\text{p}}}\\[/latex], Transformers have many applications in electrical safety systems, which are discussed in, http://cnx.org/contents/031da8d3-b525-429c-80cf-6c8ed997733a/College_Physics. By law of conservation of energy, apparent,real and reactive power are each conserved in the input and output, Combining (3) & (4) with this note (Although ideal transformer’s winding inductance are each infinitely high, the square root of winding inductance’ ratio is equal to the turns ratio.) Np is the number of turns of wire on the primary coil. wire on the primary coil. In certain spectacular demonstrations, very large voltages are used to produce long arcs, but they are relatively safe because the transformer output does not supply a large current. [latex]\begin{array}{lll}{N}_{\text{s}}& =& {N}_{\text{p}}\frac{{V}_{\text{s}}}{{V}_{\text{p}}}\\ & =& \left(50\right)\frac{100,000\text{ V}}{120\text{ V}}=4.17\times 10^{4}\end{array}\\[/latex]. As the switch is opened and closed, the secondary produces a voltage like that in Figure 4. We also see that a small input current produces a larger output current in a step-down transformer. (c) What is the power input? The fact that transformers are based on Faraday’s law of induction makes it clear why we cannot use transformers to change DC voltages. 8. Perfect coupling implies infinitely high core magnetic permeability and winding inductances and zero net magnetomotive force (i.e. Construct a problem in which you calculate the output voltage of the final stage based on the input voltage of the first stage and the number of turns or loops in both parts of both transformers (four coils in all). Copyright © 2015 gcsescience.com. The transformer equation is for an ideal transformer. the core An American traveler in New Zealand carries a transformer to convert New Zealand’s standard 240 V to 120 V so that she can use some small appliances on her trip. The reason for this is a little more subtle. Conversely, if voltage decreases, current increases. Where Vp is the voltage in the primary coil. Construct Your Own Problem Consider a double transformer to be used to create very large voltages. Figure 2. For the primary winding emf, N will be the number of primary turns, ( N P ) and for the secondary winding emf, N will be the number of secondary turns, ( N S ). (a) How many turns are in its secondary coil, if its input voltage is 120 V and the primary coil has 400 turns? It is the … where Vp and Vs are the voltages across primary and secondary coils having Np and Ns turns. Transformers do not work for pure DC voltage input, but if it is switched on and off as on the top graph, the output will look something like that on the bottom graph. Figure 4. Transformers use electromagnetic induction to change the voltage of alternating currents. (a) 0.063 A (b) Greater input current needed. If the input of the transformer has single phase (R or Y or B) with neutral (N) means those transformers are called a single-phase transformer. The transformer equation - Higher The ratio of potential differences on the transformer coils matches the ratio of the numbers of turns on the coils. Some transformers even provide a variable output by allowing connection to be made at different points on the secondary coil. All Rights Reserved. Local power distribution to neighborhoods or industries goes through a substation and is sent short distances at voltages ranging from 5 to 13 kV. Transformer current can be calculated from two ways such as. This is not really a practical alternative, and AC is in common use wherever it is necessary to increase or decrease voltages. (b) What is its input current when its output is 1.30 A? Ideal transformer equations. This is not the sinusoidal AC most AC appliances need. The ratio of the number of turns in the secondary to the number in the primary is Ns/Np = 1000. For example, many cell phones, laptops, video games, and power tools and small appliances have a transformer built into their plug-in unit (like that in Figure 1) that changes 120 V or 240 V AC into whatever voltage the device uses. 9. We can similarly find the output current of the secondary by solving[latex]\frac{{I}_{\text{s}}}{{I}_{\text{p}}}=\frac{{N}_{\text{p}}}{{N}_{\text{s}}}\\[/latex] for [latex]{I}_{\text{s}}\\[/latex] for Is and entering known values. GCSE Physics. number of turns of wire (c) Is this amount of power reasonable for a small appliance? is the potential difference in the primary (input) coil in volts (V), is the potential difference in the secondary (output) coil in volts (V), is the number of turns on the primary coil, is the number of turn on the secondary coil, Sample exam questions - electromagnetic induction - Edexcel, Home Economics: Food and Nutrition (CCEA).

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