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51-420: A distributor consists of a rotating arm ('rotor') that is attached to the top of a rotating 'distributor shaft'. The rotor constantly receives high-voltage electricity from an ignition coil via brushes at the centre of the rotor. As the rotor spins, its tip passes close to (but does not touch) the output contacts for each cylinder . As the electrified tip passes each output contact, the high-voltage electricity

102-429: 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 coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force (EMF) across any other coils wound around the same core. Electrical energy can be transferred between separate coils without

153-512: A 'coil-on-plug' direct ignition system, whereby a small ignition coil is located directly above the spark plug for each cylinder. This design means that high-voltage electricity is only present in the small distance between each coil and the spark plug. See Saab Direct Ignition . The first mass-produced electric ignition was the Delco ignition system , which was introduced in the 1910 Cadillac Model 30 . In 1921, Arthur Atwater Kent Sr invented

204-403: A DC component flowing in the windings. A saturable reactor exploits saturation of the core to control alternating current. Knowledge of leakage inductance is also useful when transformers are operated in parallel. It can be shown that if the percent impedance and associated winding leakage reactance-to-resistance ( X / R ) ratio of two transformers were the same, the transformers would share

255-422: A camshaft. Older distributor designs used a cam on the distributor shaft that operates the contact breaker (also called points ). Opening the points causes a high induction voltage in the ignition coil. This design was superseded by an electronically controlled ignition coil with a sensor (usually Hall effect or optical) to control the timing of the ignition coil charging. In older distributors, adjusting

306-401: A flux equal and opposite to that produced by the primary winding. The windings are wound around a core of infinitely high magnetic permeability so that all of the magnetic flux passes through both the primary and secondary windings. With a voltage source connected to the primary winding and a load connected to the secondary winding, the transformer currents flow in the indicated directions and

357-517: A high-voltage spark at low engine speeds (RPM), making starting easier. Most older ignition coil systems used a single coil shared by all the spark plugs (via a distributor ). There were some exceptions, such as the Saab 92 and the Wartburg 353 using a separate coil for each cylinder and the 1948 Citroën 2CV using a wasted spark system with a double-ended ignition coil and no distributor. Since

408-670: A large transformer at other than its design frequency may require assessment of voltages, losses, and cooling to establish if safe operation is practical. Transformers may require protective relays to protect the transformer from overvoltage at higher than rated frequency. One example is in traction transformers used for electric multiple unit and high-speed train service operating across regions with different electrical standards. The converter equipment and traction transformers have to accommodate different input frequencies and voltage (ranging from as high as 50 Hz down to 16.7 Hz and rated up to 25 kV). At much higher frequencies

459-523: 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 used to change AC voltage levels, such transformers being termed step-up or step-down type to increase or decrease voltage level, respectively. Transformers can also be used to provide galvanic isolation between circuits as well as to couple stages of signal-processing circuits. Since

510-493: A nameplate that indicate the phase relationships between their terminals. This may be in the form of a phasor diagram, or using an alpha-numeric code to show the type of internal connection (wye or delta) for each winding. The EMF of a transformer at a given flux increases with frequency. By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve

561-432: A number of approximations. Analysis may be simplified by assuming that magnetizing branch impedance is relatively high and relocating the branch to the left of the primary impedances. This introduces error but allows combination of primary and referred secondary resistances and reactance by simple summation as two series impedances. Transformer equivalent circuit impedance and transformer ratio parameters can be derived from

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612-433: A permeability many times that of free space and the core thus serves to greatly reduce the magnetizing current and confine the flux to a path which closely couples the windings. Early transformer developers soon realized that cores constructed from solid iron resulted in prohibitive eddy current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires. Later designs constructed

663-468: A transformer design to limit the short-circuit current it will supply. Leaky transformers may be used to supply loads that exhibit negative resistance , such as electric arcs , mercury- and sodium- vapor lamps and neon signs or for safely handling loads that become periodically short-circuited such as electric arc welders . Air gaps are also used to keep a transformer from saturating, especially audio-frequency transformers in circuits that have

714-405: Is able to 'jump' across the small gap. This burst of electricity then travels to the spark plug (via high tension leads ), where it ignites the air-fuel mixture in the combustion chamber. On most overhead valve engines , the distributor shaft is driven by a gear on the camshaft , often shared with the oil pump ; on most overhead camshaft engines , the distributor shaft is attached directly to

765-519: Is at the expense of flux density at saturation. For instance, ferrite saturation occurs at a substantially lower flux density than laminated iron. Large power transformers are vulnerable to insulation failure due to transient voltages with high-frequency components, such as caused in switching or by lightning. Transformer energy losses are dominated by winding and core losses. Transformers' efficiency tends to improve with increasing transformer capacity. The efficiency of typical distribution transformers

816-402: Is between about 98 and 99 percent. As transformer losses vary with load, it is often useful to tabulate no-load loss , full-load loss, half-load loss, and so on. Hysteresis and eddy current losses are constant at all load levels and dominate at no load, while winding loss increases as load increases. The no-load loss can be significant, so that even an idle transformer constitutes a drain on

867-425: Is given by the universal EMF equation: A dot convention is often used in transformer circuit diagrams, nameplates or terminal markings to define the relative polarity of transformer windings. Positively increasing instantaneous current entering the primary winding's 'dot' end induces positive polarity voltage exiting the secondary winding's 'dot' end. Three-phase transformers used in electric power systems will have

918-421: Is rarely attempted; the 'real' transformer model's equivalent circuit shown below does not include parasitic capacitance. However, the capacitance effect can be measured by comparing open-circuit inductance, i.e. the inductance of a primary winding when the secondary circuit is open, to a short-circuit inductance when the secondary winding is shorted. The ideal transformer model assumes that all flux generated by

969-694: The air-fuel mixture . The ignition coil is constructed of two sets of coils wound around an iron core. Older engines often use a single ignition coil which has its output directed to each cylinder by a distributor , a design which is still used by various small engines (such as lawnmower engines). Modern car engines often use a distributor-less system (such as coil-on-plug ), whereby every cylinder has its own ignition coil. Diesel engines use compression ignition and therefore do not have ignition coils. An ignition coil consists of an iron core surrounded by two coils ( windings ) made from copper wire. The primary winding has relatively few turns of heavy wire, while

1020-408: The ignition timing is usually achieved through both mechanical advance and vacuum advance . Mechanical advance adjusts the timing based on the engine speed (rpm), using a set of hinged weights attached to the distributor shaft. These weights cause the breaker points mounting plate to slightly rotate, thereby advancing the ignition timing. Vacuum advance typically uses manifold vacuum to adjust

1071-468: The magnetizing branch of the model. Core losses are caused mostly by hysteresis and eddy current effects in the core and are proportional to the square of the core flux for operation at a given frequency. The finite permeability core requires a magnetizing current I M to maintain mutual flux in the core. Magnetizing current is in phase with the flux, the relationship between the two being non-linear due to saturation effects. However, all impedances of

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1122-433: The power grid . Ideal transformer equations By Faraday's law of induction: where V {\displaystyle V} is the instantaneous voltage , N {\displaystyle N} is the number of turns in a winding, dΦ/dt is the derivative of the magnetic flux Φ through one turn of the winding over time ( t ), and subscripts P and S denotes primary and secondary. Combining

1173-417: The secondary winding consists of thousands of turns of smaller wire and is insulated from the high voltage by enamel on the wires and layers of oiled paper insulation. When the electrical circuit connected from the power source (e.g. the car's battery) to the primary winding is closed (by a contact breaker or transistor ), current flows through the primary winding, which produces a magnetic field around

1224-446: The 1990s, ignition systems have mostly switched to a design where the distributor is omitted and ignition is instead electronically controlled. In these distributor-less systems, multiple smaller ignition coils are used, usually in the form of one coil for each cylinder or a wasted spark system with one coil for each pair of cylinders. The ignition coils for these can be combined into a single casing (a coil pack ) and located away from

1275-408: The air/fuel mixture. The timing of the circuit opening must be coordinated with the rotation of the engine, so that the burst of high-voltage electricity is produced at the optimal time to ignite the air/fuel mixture. Modern electronic ignition systems operate using the same principle of charging an electric circuit, however they use a capacitor charged to around 400 volts, rather than using

1326-427: The competing Unisparker ignition system. By the 1980s and 1990s, distributors had been largely replaced by electronic ignition systems. Ignition coil An ignition coil is used in the ignition system of a spark-ignition engine to transform the battery voltage to the much higher voltages required to operate the spark plug (s). The spark plugs then use this burst of high-voltage electricity to ignite

1377-507: The core magnetomotive force cancels to zero. According to Faraday's law , since the same magnetic flux passes through both the primary and secondary windings in an ideal transformer, a voltage is induced in each winding proportional to its number of turns. The transformer winding voltage ratio is equal to the winding turns ratio. An ideal transformer is a reasonable approximation for a typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to

1428-456: The core, the transformer is core form; when windings are surrounded by the core, the transformer is shell form. Shell form design may be more prevalent than core form design for distribution transformer applications due to the relative ease in stacking the core around winding coils. Core form design tends to, as a general rule, be more economical, and therefore more prevalent, than shell form design for high voltage power transformer applications at

1479-412: The core. This current flow lasts for a period of time to build up energy in the coil. Once the coil is charged, the circuit is opened, and the resulting oscillation in the magnetic field induces a high voltage in the secondary winding. This high-voltage electricity travels through several components (such as a distributor and spark plug wires ), before reaching the spark plug , where it is used to ignite

1530-400: The corresponding current ratio. The load impedance referred to the primary circuit is equal to the turns ratio squared times the secondary circuit load impedance. The ideal transformer model neglects many basic linear aspects of real transformers, including unavoidable losses and inefficiencies. (a) Core losses, collectively called magnetizing current losses, consisting of (b) Unlike

1581-440: The electrical supply. Designing energy efficient transformers for lower loss requires a larger core, good-quality silicon steel , or even amorphous steel for the core and thicker wire, increasing initial cost. The choice of construction represents a trade-off between initial cost and operating cost. Transformer losses arise from: Closed-core transformers are constructed in 'core form' or 'shell form'. When windings surround

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1632-448: The equivalent circuit shown are by definition linear and such non-linearity effects are not typically reflected in transformer equivalent circuits. With sinusoidal supply, core flux lags the induced EMF by 90°. With open-circuited secondary winding, magnetizing branch current I 0 equals transformer no-load current. The resulting model, though sometimes termed 'exact' equivalent circuit based on linearity assumptions, retains

1683-424: The following series loop impedances of the model: In normal course of circuit equivalence transformation, R S and X S are in practice usually referred to the primary side by multiplying these impedances by the turns ratio squared, ( N P / N S )  = a . Core loss and reactance is represented by the following shunt leg impedances of the model: R C and X M are collectively termed

1734-461: The following tests: open-circuit test , short-circuit test , winding resistance test, and transformer ratio test. If the flux in the core is purely sinusoidal , the relationship for either winding between its rms voltage E rms of the winding, and the supply frequency f , number of turns N , core cross-sectional area A in m and peak magnetic flux density B peak in Wb/m or T (tesla)

1785-412: The ideal model, the windings in a real transformer have non-zero resistances and inductances associated with: (c) similar to an inductor , parasitic capacitance and self-resonance phenomenon due to the electric field distribution. Three kinds of parasitic capacitance are usually considered and the closed-loop equations are provided Inclusion of capacitance into the transformer model is complicated, and

1836-465: The ideal transformer identity : where L {\displaystyle L} is winding self-inductance. By Ohm's law and ideal transformer identity: An ideal transformer is linear , lossless and perfectly coupled . Perfect coupling implies infinitely high core magnetic permeability and winding inductance and zero net magnetomotive force (i.e. i p n p  −  i s n s  = 0). A varying current in

1887-430: The ignition timing, for example to improve fuel economy and driveability when minimal power is required from the engine. Most distributors used on electronic fuel injection engines use electronics to adjust the ignition timing, instead of vacuum and centrifugal systems. This allows the ignition timing to be optimised based on factors other than engine speed and manifold vacuum. Since the early 2000s, many cars have used

1938-471: The induction charging of an ignition coil. Typical output voltages for modern ignition coils vary from 15 kV (for a lawnmower engine) to 40 kV (for a larger engine). A modern single-spark system has one coil per spark plug. To prevent premature sparking at the start of the primary pulse, a diode or secondary spark gap is installed in the coil to block the reverse pulse that would otherwise form. In older wasted spark systems for four-stroke engines,

1989-443: 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

2040-445: The limitations of early electric traction motors . Consequently, the transformers used to step-down the high overhead line voltages were much larger and heavier for the same power rating than those required for the higher frequencies. Operation of a transformer at its designed voltage but at a higher frequency than intended will lead to reduced magnetizing current. At a lower frequency, the magnetizing current will increase. Operation of

2091-455: The load power in proportion to their respective ratings. However, the impedance tolerances of commercial transformers are significant. Also, the impedance and X/R ratio of different capacity transformers tends to vary. Referring to the diagram, a practical transformer's physical behavior may be represented by an equivalent circuit model, which can incorporate an ideal transformer. Winding joule losses and leakage reactance are represented by

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2142-662: The lower end of their voltage and power rating ranges (less than or equal to, nominally, 230 kV or 75 MVA). At higher voltage and power ratings, shell form transformers tend to be more prevalent. Shell form design tends to be preferred for extra-high voltage and higher MVA applications because, though more labor-intensive to manufacture, shell form transformers are characterized as having inherently better kVA-to-weight ratio, better short-circuit strength characteristics and higher immunity to transit damage. Transformers for use at power or audio frequencies typically have cores made of high permeability silicon steel . The steel has

2193-444: The power supply. It is not directly a power loss, but results in inferior voltage regulation , causing the secondary voltage not to be directly proportional to the primary voltage, particularly under heavy load. Transformers are therefore normally designed to have very low leakage inductance. In some applications increased leakage is desired, and long magnetic paths, air gaps, or magnetic bypass shunts may deliberately be introduced in

2244-401: The primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths that take it outside the windings. Such flux is termed leakage flux , and results in leakage inductance in series with the mutually coupled transformer windings. Leakage flux results in energy being alternately stored in and discharged from the magnetic fields with each cycle of

2295-439: The ratio of eq. 1 & eq. 2: where for a step-up transformer a < 1 and for a step-down transformer a > 1. By the law of conservation of energy , apparent , real and reactive power are each conserved in the input and output: where S {\displaystyle S} is apparent power and I {\displaystyle I} is current . Combining Eq. 3 & Eq. 4 with this endnote gives

2346-436: The same impedance. However, properties such as core loss and conductor skin effect also increase with frequency. Aircraft and military equipment employ 400 Hz power supplies which reduce core and winding weight. Conversely, frequencies used for some railway electrification systems were much lower (e.g. 16.7 Hz and 25 Hz) than normal utility frequencies (50–60 Hz) for historical reasons concerned mainly with

2397-553: The secondary winding of the ignition coil has two output terminals, both of which connect to a spark plug. The reverse pulse triggers the spark plug in a cylinder contains no air/fuel mixture (since that cylinder is out of phase by 180 degrees). Formerly, ignition coils were made with varnish and paper insulated high-voltage windings, inserted into a drawn-steel can and filled with oil or asphalt for insulation and moisture protection. Later , ignition coils were instead cast in filled epoxy resins , which penetrate any voids forming within

2448-435: The spark plugs; however it is increasingly common for coil-on-plug systems to be used, whereby the individual ignition coils are small units attached directly to the top of each spark plug. An advantage of coil-on-plug systems is that in the event of a fault, a single ignition coil can be replaced rather than unnecessarily replacing the coils for all of the other cylinders. Primary winding In electrical engineering ,

2499-637: The transformer core size required drops dramatically: a physically small transformer can handle power levels that would require a massive iron core at mains frequency. The development of switching power semiconductor devices made switch-mode power supplies viable, to generate a high frequency, then change the voltage level with a small transformer. Transformers for higher frequency applications such as SMPS typically use core materials with much lower hysteresis and eddy-current losses than those for 50/60 Hz. Primary examples are iron-powder and ferrite cores. The lower frequency-dependant losses of these cores often

2550-418: The transformer's primary winding creates a varying magnetic flux in the transformer core, which is also encircled by the secondary winding. This varying flux at the secondary winding induces a varying electromotive force or voltage in the secondary winding. This electromagnetic induction phenomenon is the basis of transformer action and, in accordance with Lenz's law , the secondary current so produced creates

2601-476: The windings. The ignition coil is usually inserted into a metal can or plastic case with insulated terminals for the high voltage and low voltage connections. Early cars used a magneto ignition system, due to the lack of an electric power source (e.g. battery) in the car. Ignition coils replaced magneto ignition in new cars as batteries became a common inclusion in cars (for cranking and lighting). Compared with magneto ignition, an ignition coil system can provide

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