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45-462: Cars are arranged as married pairs , where each car contains a complete set of controls for an engineer , conductor , or brakeman . However, the 'B' Cars (denoted by odd-numbered car designations) contain a handicapped accessible restroom , which is larger than the restroom provided on the M1 and M3 railcars and designed to accommodate a wheelchair, as well as an attendant and/or service animal (such as

90-409: 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 the ideal transformer identity : where L {\displaystyle L}

135-507: A guide dog , hearing dog or service dog ) accompanying the passenger. The enlarged bathroom reduces the number of seats in the car. The M7 was built as two separate but similar models due to the different electrical and signaling systems on the LIRR and Metro-North. These two models, the M7 and M7A, share most of their attributes, but have a few notable differences. Most prominently, the styling of

180-584: A twin car . In US passenger railroad parlance, twin units are also known as married pairs . On passenger railroads, light rail , and monorail services, married pairs may have machinery necessary for full operation of the cars split between them. Items that are typically shared include transformers , motor controllers , dynamic braking grids, cabs, current collectors , batteries, and air compressors . This provides significant savings in both cost of equipment and weight, which increases performance and decreases energy consumption. The cost of operating such

225-403: 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

270-464: 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 the invention of the first constant-potential transformer in 1885, transformers have become essential for

315-670: 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

360-493: 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

405-432: 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

450-464: A pair may be slightly higher when the extra car in such a pair is not needed to meet level-of-service demands at a particular time. This rail-transport related article is a stub . You can help Misplaced Pages by expanding it . Transformer In electrical engineering , 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

495-433: 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

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540-468: 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

585-422: 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 a flux equal and opposite to that produced by

630-519: 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

675-402: 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

720-425: 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

765-421: 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

810-405: 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 the ratio of eq. 1 & eq. 2: where for a step-up transformer a < 1 and for a step-down transformer

855-419: 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 the transformer's primary winding creates

900-468: 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

945-464: 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 . Ideal transformer equations By Faraday's law of induction: where V {\displaystyle V}

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990-482: The 2016 film The Girl on the Train . On April 19, 2021, the LIRR proposed equipping two pairs of M7 railcars with batteries for travel in diesel territory, pending feasibility studies. Married pair A twin unit , twinset , or double unit is a set of two railroad cars or locomotives which are permanently coupled and treated as if they were a single unit. A twinset of cars or coaches can also be called

1035-647: The LIRR M7 began on the Ronkonkoma Branch. After several successful tests, LIRR M7 revenue service began on the Long Beach Branch on October 30, 2002, and Metro-North's first M7A started scheduled service in April 2004. All M7s were delivered by early 2007. The M7 cars swayed from side to side more than intended when introduced to service, and required modifications to reduce the sway. In late 2006

1080-439: The LIRR fleet performed significantly better, stripped M1s from both railroads were reactivated, and diminished schedules were instituted until the M7 fleet was able to resume full operation. As of 2007, the fleet has the highest mean distance between failures out of the entire LIRR fleet. This partly had to do with the fleet's newness, and so the fleet often needed to be tested for reliability. The Metro-North M7As were used in

1125-492: The MTA began a replacement of all M7 armrests after paying out over $ 100,000 to customers who filed complaints. The factory-installed armrests were notorious for slipping into trouser pockets and then tearing them when sitting. The new design is of a different profile and is coated in a more fabric-friendly rubber. Some passengers complained about having fewer seats per B car, a consequence of the larger ADA-compliant restrooms, and about

1170-465: The cars are built for the different types of third rail used by the two railroads: the M7 is equipped for the LIRR's over-running third rail, while the M7A is equipped for Metro-North's under-running third rail. For this reason, the two cars are not interchangeable between the two railroads. In late 1999, a contract was awarded to Bombardier for 836 LIRR M7s. Delivery began in early 2002, and test trains for

1215-456: 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

1260-400: 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

1305-440: 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

1350-407: The end of the car is different; on the M7, it is mostly black with a single horizontal yellow stripe, while on the M7A it is mostly blue with several white stripes. This is the primary cosmetic difference, and the cars otherwise look nearly identical. Other, more minor, aesthetic differences include illuminated number boards, present on the M7 but absent on the M7A. Aside from differences in appearance,

1395-448: 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

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1440-424: 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

1485-461: 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)

1530-412: 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

1575-445: 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

1620-455: 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

1665-662: 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

1710-444: 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

1755-401: 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

1800-439: 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 the core magnetomotive force cancels to zero. According to Faraday's law , since

1845-436: 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

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1890-423: 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

1935-637: 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

1980-415: 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 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

2025-644: The width of the seats. Metro-North's management received feedback about the M7, which influenced the development of the M8 railcars for the New Haven Line . In the fall of 2006, the M7As started to experience serious braking problems due to foliage on the right-of-way, a condition known as " Slip-Slide ." This caused nearly 2/3 of the Metro-North fleet to be taken out of service, due to flat spots on wheels. While

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