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83-503: The Indian locomotive class WCAM-1 was a class of dual-voltage (25 kV AC and 1.5 kV DC) electric locomotives that was developed in 1973 by Chittaranjan Locomotive Works for Indian Railways . The model name stands for broad gauge ( W ), DC Current ( C ), AC Current ( A ), Mixed traffic ( M ) locomotive, 1st generation ( 1 ). They entered service in March 1973. A total of 53 WCAM-1 were built at CLW between 1973 and 1979, which made them

166-427: A battery is determined by the chemistry of that cell (see Galvanic cell § Cell voltage ). Cells can be combined in series for multiples of that voltage, or additional circuitry added to adjust the voltage to a different level. Mechanical generators can usually be constructed to any voltage in a range of feasibility. Nominal voltages of familiar sources: In 1800, as the result of a professional disagreement over

249-495: A DC motor can be increased by field weakening. Reducing the field strength is done by inserting resistance in series with a shunt field, or inserting resistances around a series-connected field winding, to reduce current in the field winding. When the field is weakened, the back-emf reduces, so a larger current flows through the armature winding and this increases the speed. Field weakening is not used on its own but in combination with other methods, such as series–parallel control. In

332-400: A circuit known as a chopper , the average voltage applied to the motor is varied by switching the supply voltage very rapidly. As the on to off ratio is varied to alter the average applied voltage, the speed of the motor varies. The percentage on time multiplied by the supply voltage gives the average voltage applied to the motor. Therefore, with a 100 V supply and a 25% on time,

415-428: A constant direction, direct current commutators make the current reverse in direction every half a cycle (in a two-pole motor) thus causing the motor to continue to rotate in the same direction. A problem with the motor shown above is that when the plane of the coil is parallel to the magnetic field—i.e. when the rotor poles are 90 degrees from the stator poles—the torque is zero. In the pictures above, this occurs when

498-490: A few (Nos. 21805, 21807, 21812, 21828, 21838, 21844, 21845, and 21850) had both vacuum and air brakes. They lacked dynamic brakes. The WCAM-1 did not use a variable ratio auto-transformer in AC mode like the others; it used a fixed-ratio transformer and rectifier bank to convert the OHE supply to 1500 V DC. The design of the transformers and notches made this a hard machine to operate, with

581-429: A gear ratio of 16:61 under DC for BOX wagons (in tonnes):- Following is the capacity of WCAM-1 locomotive with gear ratio 16:61 under DC for ICF coaches (in tonnes):- Following is the capacity of WCAM-1 locomotive fitted with TAO659 with a gear ratio of 16:61 under DC for BOX wagons (in tonnes):- Following is the capacity of WCAM-1 locomotive with a gear ratio of 21:58 under AC for ICF coaches (in tonnes):- Following

664-412: A generator and produce an Electromotive force (EMF). During normal operation, the spinning of the motor produces a voltage, known as the counter-EMF (CEMF) or back EMF, because it opposes the applied voltage on the motor. The back EMF is the reason that the motor when free-running does not appear to have the same low electrical resistance as the wire contained in its winding. This is the same EMF that

747-629: A method of providing a speed-controlled motor from an AC supply, though it is not without its advantages in DC schemes. The AC supply is used to drive an AC motor, usually an induction motor that drives a DC generator or dynamo . The DC output from the armature is directly connected to the armature of the DC motor (sometimes but not always of identical construction). The shunt field windings of both DC machines are independently excited through variable resistors. Extremely good speed control from standstill to full speed, and consistent torque, can be obtained by varying

830-399: A motor is given by the following equation: The mechanical power produced by the motor is given by: As an unloaded DC motor spins, it generates a backwards-flowing electromotive force that resists the current being applied to the motor. The current through the motor drops as the rotational speed increases, and a free-spinning motor has very little current. It is only when a load is applied to

913-402: A motor, the armature does not rotate, the counter EMF is zero and the only factor limiting the armature current is the armature resistance. As the prospective current through the armature is very large, the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter EMF. As the motor rotation builds up, the resistance

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996-441: A ratio because the cgs unit of voltage is inconveniently small and one volt in this definition is approximately the emf of a Daniell cell , the standard source of voltage in the telegraph systems of the day. At that time, the volt was defined as the potential difference [i.e., what is nowadays called the "voltage (difference)"] across a conductor when a current of one ampere dissipates one watt of power. The "international volt"

1079-533: A series-connected array of several thousand or tens of thousands of junctions , excited by microwave signals between 10 and 80 GHz (depending on the array design). Empirically, several experiments have shown that the method is independent of device design, material, measurement setup, etc., and no correction terms are required in a practical implementation. In the water-flow analogy , sometimes used to explain electric circuits by comparing them with water-filled pipes, voltage (difference in electric potential)

1162-608: A set point, the relay will deenergize the motor's armature. A locked rotor condition prevents a motor from accelerating after its starting sequence has been initiated. Distance relays protect motors from locked-rotor faults. Undervoltage motor protection is typically incorporated into motor controllers or starters. In addition, motors can be protected from overvoltages or surges with isolation transformers , power conditioning equipment , MOVs , arresters and harmonic filters. Environmental conditions, such as dust, explosive vapors, water, and high ambient temperatures, can adversely affect

1245-400: A short circuit. The power leads are shorted together through the commutator plates, and the coil is also short-circuited through both brushes (the coil is shorted twice, once through each brush independently). Note that this problem is independent of the non-starting problem above; even if there were a high current in the coil at this position, there would still be zero torque. The problem here

1328-410: A simple, two-pole, brushed , DC motor. When a current passes through the coil wound around a soft iron core situated inside an external magnetic field, the side of the positive pole is acted upon by an upwards force, while the other side is acted upon by a downward force. According to Fleming's left hand rule , the forces cause a turning effect on the coil, making it rotate. To make the motor rotate in

1411-410: A wound field DC motor can be changed by reversing either the field or armature connections but not both. This is commonly done with a special set of contactors (direction contactors). The effective voltage can be varied by inserting a series resistor or by an electronically controlled switching device made of thyristors , transistors , or, formerly, mercury arc rectifiers . Series–parallel control

1494-414: Is also equivalent to electronvolts per elementary charge : The volt is named after Alessandro Volta . As with every SI unit named for a person, its symbol starts with an upper case letter (V), but when written in full, it follows the rules for capitalisation of a common noun ; i.e., volt becomes capitalised at the beginning of a sentence and in titles but is otherwise in lower case. Historically

1577-440: Is an internally commutated electric motor designed to be run from a direct current power source and utilizing an electric brush for contact . Brushed motors were the first commercially important application of electric power to driving mechanical energy, and DC distribution systems were used for more than 100 years to operate motors in commercial and industrial buildings. Brushed DC motors can be varied in speed by changing

1660-584: Is characterized by a linear relationship between stall torque when the torque is maximum with the shaft at standstill and no-load speed with no applied shaft torque and maximum output speed. There is a quadratic power relationship between these two speed-axis points. To extend a DC motor's service life, protective devices and motor controllers are used to protect it from mechanical damage, excessive moisture, high dielectric stress and high temperature or thermal overloading. These protective devices sense motor fault conditions and either activate an alarm to notify

1743-433: Is completely inadequate, such as driving the capstan of a tape transport, or any similar instance where to speed up and slow down often and quickly is a requirement. Another disadvantage is that, since the coils have a measure of self inductance , current flowing in them cannot suddenly stop. The current attempts to jump the opening gap between the commutator segment and the brush, causing arcing. Even for fans and flywheels,

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1826-438: Is gradually cut out. The series wound DC motor's most notable characteristic is that its speed is almost entirely dependent on the torque required to drive the load. This suits large inertial loads as motor accelerates from maximum torque, torque reducing gradually as speed increases. As the series motor's speed can be dangerously high, series motors are often geared or direct-connected to the load. A permanent magnet DC motor

1909-606: Is likened to difference in water pressure , while current is proportional to the amount of water flowing. A resistor would be a reduced diameter somewhere in the piping or something akin to a radiator offering resistance to flow. The relationship between voltage and current is defined (in ohmic devices like resistors ) by Ohm's law . Ohm's Law is analogous to the Hagen–Poiseuille equation , as both are linear models relating flux and potential in their respective systems. The voltage produced by each electrochemical cell in

1992-404: Is necessary to move the brushes to the opposite side of the normal neutral plane. The effect can be considered to be somewhat similar to timing advance in an internal combustion engine. Generally a dynamo that has been designed to run at a certain fixed speed will have its brushes permanently fixed to align the field for highest efficiency at that speed. DC machines with wound stators compensate

2075-405: Is often used in traction applications such as electric locomotives , and trams . Another application is starter motors for petrol and small diesel engines. Series motors must never be used in applications where the drive can fail (such as belt drives). As the motor accelerates, the armature (and hence field) current reduces. The reduction in field causes the motor to speed up, and in extreme cases

2158-460: Is produced when the motor is used as a generator (for example when an electrical load, such as a light bulb, is placed across the terminals of the motor and the motor shaft is driven with an external torque). Therefore, the total voltage drop across a motor consists of the CEMF voltage drop, and the parasitic voltage drop resulting from the internal resistance of the armature's windings. The current through

2241-456: Is sometimes seen in homebuilt hobby motors, e.g. for science fairs and such designs can be found in some published science project books. A clear downside of this simple solution is that the motor now coasts through a substantial arc of rotation twice per revolution and the torque is pulsed. This may work for electric fans or to keep a flywheel spinning but there are many applications, even where starting and stopping are not necessary, for which it

2324-412: Is that this short uselessly consumes power without producing any motion (nor even any coil current.) In a low-current battery-powered demonstration this short-circuiting is generally not considered harmful. However, if a two-pole motor were designed to do actual work with several hundred watts of power output, this shorting could result in severe commutator overheating, brush damage, and potential welding of

2407-566: Is the elementary charge and h is the Planck constant ), a "conventional" value K J-90 = 0.4835979 GHz/μV was used for the purpose of defining the volt. As a consequence of the 2019 revision of the SI , as of 2019 the Josephson constant has an exact value of K J = 483 597 .848 416 98 ... GHz/V , which replaced the conventional value K J-90 . This standard is typically realized using

2490-404: Is the capacity of WCAM-1 locomotive with gear ratio 16:61 under AC for ICF coaches (in tonnes):- Following is the capacity of WCAM-1 locomotive with a gear ratio of 16:61 under AC for BOXN wagons (in tonnes):- Following is the capacity of WCAM-1 locomotive with gear ratio 16:61 under DC for 4 wheeler wagons (in tonnes):- Following is the capacity of WCAM-1 locomotive fitted with TAO659A1 with

2573-400: Is the capacity of WCAM-1 locomotive with gear ratio 21:58 under DC for ICF coaches (in tonnes):- Volt One volt is defined as the electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. It can be expressed in terms of SI base units ( m , kg , s , and A ) as Equivalently, it is

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2656-402: Is wider than the ends of the brushes. This increases the zero-torque range of angular positions but eliminates the shorting problem; if the motor is started spinning by an outside force it will continue spinning. With this modification, it can also be effectively turned off simply by stalling (stopping) it in a position in the zero-torque (i.e. commutator non-contacting) angle range. This design

2739-400: The thermal efficiency of a motor. The counter-emf aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate. At that instant the counter-emf is zero and the only factor limiting the armature current is the armature resistance and inductance. Usually the armature resistance of a motor is less than 1 Ω; therefore

2822-491: The " conventional " volt, V 90 , defined in 1987 by the 18th General Conference on Weights and Measures and in use from 1990 to 2019, was implemented using the Josephson effect for exact frequency-to-voltage conversion, combined with the caesium frequency standard . Though the Josephson effect is still used to realize a volt, the constant used has changed slightly. For the Josephson constant , K J = 2 e / h (where e

2905-497: The 30 notches, 1-21 were DC notches allowing series operation of traction motors. Rest of the 8 notches allow series-parallel combination under DC. Under AC, the combinations were 3S-2P and 2S-3P. These locomotives could run in parallel combination but it was discouraged due to power problems under DC. Under AC, the locomotives were run under parallel notches nearly always. Although these engines were not rebuilt to use only parallel combination under AC. Field weakening of traction motors

2988-678: The British Association for the Advancement of Science had defined the volt, ohm, and farad. In 1881, the International Electrical Congress, now the International Electrotechnical Commission (IEC), approved the volt as the unit for electromotive force. They made the volt equal to 10 cgs units of voltage, the cgs system at the time being the customary system of units in science. They chose such

3071-523: The WCAM-1s were relegated to secondary passenger trains, including: These trains were being hauled by the WCAM-1 locomotives, before their final retirement in 2015. Source: Following is the capacity of WCAM-1 locomotive with gear ratio 16:61 under AC for 4 wheeler wagons (in tonnes) :- Following is the capacity of WCAM-1 locomotive with a gear ratio of 16:61 under AC for BOX wagons (in tonnes):- Following

3154-595: The armature currents, allowing a moderate sized thyristor unit to control a much larger motor than it could control directly. For example, in one installation, a 300 amp thyristor unit controls the field of the generator. The generator output current is in excess of 15,000 amperes, which would be prohibitively expensive (and inefficient) to control directly with thyristors. A DC motor 's speed and torque characteristics vary according to three different magnetization sources, separately excited field, self-excited field or permanent-field, which are used selectively to control

3237-408: The average voltage at the motor will be 25 V. During the off time, the armature's inductance causes the current to continue through a diode called a flyback diode , in parallel with the motor. At this point in the cycle, the supply current will be zero, and therefore the average motor current will always be higher than the supply current unless the percentage on time is 100%. At 100% on time,

3320-411: The brushes—if they were metallic—to the commutator. Carbon brushes, which are often used, would not weld. In any case, a short like this is very wasteful, drains batteries rapidly and, at a minimum, requires power supply components to be designed to much higher standards than would be needed just to run the motor without the shorting. One simple solution is to put a gap between the commutator plates which

3403-535: The clear weaknesses remaining in this design—especially that it is not self-starting from all positions—make it impractical for working use, especially considering the better alternatives that exist. Unlike the demonstration motor above, DC motors are commonly designed with more than two poles, are able to start from any position, and do not have any position where current can flow without producing electromotive power by passing through some coil. Many common small brushed DC motors used in toys and small consumer appliances,

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3486-401: The combined resistance across the brushes, armature winding and series field winding, if any: The DC motor's torque is proportional to the product of the armature current and the machine's total flux strength: where Since we have where With the shunt wound motor's high-resistance field winding connected in parallel with the armature, V m , R m and Ø are constant such that

3569-517: The control circuit and de-energize the motor. Heaters are external thermal overload protectors connected in series with the motor's windings and mounted in the motor contactor . Solder pot heaters melt in an overload condition, which cause the motor control circuit to de-energize the motor. Bimetallic heaters function the same way as embedded bimetallic protectors. Fuses and circuit breakers are overcurrent or short circuit protectors. Ground fault relays also provide overcurrent protection. They monitor

3652-437: The core of the coil is horizontal—the position it is just about to reach in the second-to-last picture on the right. The motor would not be able to start in this position. However, once it was started, it would continue to rotate through this position by momentum. There is a second problem with this simple pole design. At the zero-torque position, both commutator brushes are touching (bridging) both commutator plates, resulting in

3735-406: The current through the armature would be very large when the power is applied. This current can make an excessive voltage drop affecting other equipment in the circuit and even trip overload protective devices. Therefore, the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-emf. As the motor rotation builds up,

3818-426: The differential speed between the rails and the wheels it can also cause serious damage to the rails and wheel treads as they heat and cool rapidly. Field weakening is used in some electronic controls to increase the top speed of an electric vehicle. The simplest form uses a contactor and field-weakening resistor; the electronic control monitors the motor current and switches the field weakening resistor into circuit when

3901-399: The distortion with commutating field windings and compensation windings . Brushed DC motors are constructed with wound rotors and either wound or permanent-magnet stators. The field coils have conventionally existed in four basic formats: separately excited ( sepex ), series -wound , shunt -wound , and a combination of the latter two, compound-wound . In a series-wound motor ,

3984-403: The electric current between the motor's windings and earth system ground . In motor-generators, reverse current relays prevent the battery from discharging and motorizing the generator. Since D.C. motor field loss can cause a hazardous runaway or overspeed condition, loss of field relays are connected in parallel with the motor's field to sense field current. When the field current decreases below

4067-412: The field coils are connected electrically in series with the armature coils (via the brushes). In a shunt-wound motor, the field coils are connected in parallel, or shunted to the armature coils. In a separately excited (sepex) motor, the field coils are supplied from an independent source, such as a motor–generator , and the field current is unaffected by changes in the armature current. The sepex system

4150-414: The field has been applied radially—in and away from the rotation axis of the motor. However some designs have the field flowing along the axis of the motor, with the rotor cutting the field lines as it rotates. This allows for much stronger magnetic fields, particularly if halbach arrays are employed. This, in turn, gives power to the motor at lower speeds. However, the focused flux density cannot rise about

4233-453: The first Bi-current charged locomotives in the country. Initially all were vacuum braked but were retrofitted with air brakes to make them dual braked . Some also had their vacuum brakes replaced with air brakes. Introduced in 1975. One of the single pantographs on the WCAM-1 is used in DC traction; the other one carries AC current. The two pantographs were not identical, though similar in design. Originally built with vacuum brakes only, although

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4316-462: The first electric locomotives to enter Western Railway's Mumbai division; prior to that steam and diesel locomotives used to haul trains in Western Railway's Mumbai division. These brought an end to the steam era in this division. They were also the first locomotives allotted to Valsad (BL) shed. Their top speed under DC was the lowest, as compared to other Bi-current charged locomotives. They were

4399-443: The fusible links tending to blow often. Of the 28 notches, notches 4, 14, 21, and 28 were used for continuous operation, although notch 4 was intended for low-speed shunting and was very ineffective. Notches 14, 21, and 28 were the terminal notches of the series, series-parallel, and parallel circuit notch sequences. In DC mode, the WCAM-1 used resistor banks for speed control. However they were very robust machines and relatively easy in

4482-415: The galvanic response advocated by Luigi Galvani , Alessandro Volta developed the so-called voltaic pile , a forerunner of the battery , which produced a steady electric current . Volta had determined that the most effective pair of dissimilar metals to produce electricity was zinc and silver . In 1861, Latimer Clark and Sir Charles Bright coined the name "volt" for the unit of resistance. By 1873,

4565-407: The generator and/or motor field current. This method of control was the de facto method from its development until it was superseded by solid state thyristor systems. It found service in almost any environment where good speed control was required, from passenger lifts through to large mine pit head winding gear and even industrial process machinery and electric cranes. Its principal disadvantage

4648-525: The handling characteristics. WCAM-1's had three traction modes (series, series-parallel, parallel) in both DC and AC mode, but using the parallel mode in DC was discouraged because of power problems. In practice this was not restrictive since series-parallel notches allowed reaching 75 km/h or so. In AC mode, the locos were almost always used with the motors in all-parallel mode. Unlike the WCAM-2 and WCAM-3 locos, no reconfiguration has been carried out to force

4731-617: The limited residual flux density of the permanent magnet despite high coercivity and like all electric machines, the flux density of magnetic core saturation is the design constraint. Generally, the rotational speed of a DC motor is proportional to the EMF in its coil (= the voltage applied to it minus voltage lost on its resistance), and the torque is proportional to the current. Speed control can be achieved by variable battery tappings, variable supply voltage, resistors or electronic controls. A simulation example can be found here and. The direction of

4814-636: The most numerous class of mainline dual-power AC-DC electric locomotive. The WCAM-1 was one of the most successful locomotives of Indian Railways, having served both passenger and freight trains for over 40 years between 1973 and 2015. This class was a bi-current version of the WAM-4 class. However, with the advent of new 3-phase locomotives like WAP-5 and WAP-7 , the aging fleet of WCAM-1 locomotives were relegated to hauling smaller passenger trains and have been fully withdrawn from mainline duties. All units have been scrapped with no locomotives preserved. The WCAM-1

4897-413: The motor can even destroy itself, although this is much less of a problem in fan-cooled motors (with self-driven fans). This can be a problem with railway motors in the event of a loss of adhesion since, unless quickly brought under control, the motors can reach speeds far higher than they would do under normal circumstances. This can not only cause problems for the motors themselves and the gears, but due to

4980-436: The motor current reduces below a preset value (this will be when the motor is at its full design speed). Once the resistor is in circuit, the motor will increase speed above its normal speed at its rated voltage. When motor current increases, the control will disconnect the resistor and low speed torque is made available. A Ward Leonard control is usually used for controlling a shunt or compound wound DC motor, and developed as

5063-423: The motor over the mechanical load's range. Self-excited field motors can be series, shunt, or a compound wound connected to the armature. Define The DC motor's counter emf is proportional to the product of the machine's total flux strength and armature speed: The DC motor's input voltage must overcome the counter emf as well as the voltage drop created by the armature current across the motor resistance, that is,

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5146-405: The motor that slows the rotor that the current draw through the motor increases. In a dynamo , a plane through the centers of the contact areas where a pair of brushes touch the commutator and parallel to the axis of rotation of the armature is referred to as the commutating plane . In this diagram the commutating plane is shown for just one of the brushes, assuming the other brush made contact on

5229-410: The no load to full load speed regulation is seldom more than 5%. Speed control is achieved three ways: The series motor responds to increased load by slowing down; the current increases and the torque rises in proportional to the square of the current since the same current flows in both the armature and the field windings. If the motor is stalled, the current is limited only by the total resistance of

5312-584: The operating voltage or the strength of the magnetic field. Depending on the connections of the field to the power supply, the speed and torque characteristics of a brushed motor can be altered to provide steady speed or speed inversely proportional to the mechanical load. Brushed motors continue to be used for electrical propulsion, cranes, paper machines and steel rolling mills. Since the brushes wear down and require replacement, brushless DC motors using power electronic devices have displaced brushed motors from many applications. The following graphics illustrate

5395-577: The operation of a DC motor. To protect a motor from these environmental conditions, the National Electrical Manufacturers Association (NEMA) and the International Electrotechnical Commission (IEC) have standardized motor enclosure designs based upon the environmental protection they provide from contaminants. Modern software can also be used in the design stage, such as Motor-CAD , to help increase

5478-440: The operator about ten seconds to slowly advance the rheostat across the contacts to gradually increase input power up to operating speed. There were two different classes of these rheostats, one used for starting only, and one for starting and speed regulation. The starting rheostat was less expensive, but had smaller resistance elements that would burn out if required to run a motor at a constant reduced speed. This starter includes

5561-407: The operator or automatically de-energize the motor when a faulty condition occurs. For overloaded conditions, motors are protected with thermal overload relays . Bi-metal thermal overload protectors are embedded in the motor's windings and made from two dissimilar metals. They are designed such that the bimetallic strips will bend in opposite directions when a temperature set point is reached to open

5644-399: The other side of the commutator with radial symmetry, 180 degrees from the brush shown. In a real dynamo, the field is never perfectly uniform. Instead, as the rotor spins it induces field effects which drag and distort the magnetic lines of the outer non-rotating stator. The faster the rotor spins, the further the degree of field distortion. Because the dynamo operates most efficiently with

5727-432: The potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it. It can be expressed in terms of SI base units ( m , kg , s , and A ) as It can also be expressed as amperes times ohms (current times resistance, Ohm's law ), webers per second (magnetic flux per time), watts per ampere (power per current), or joules per coulomb (energy per charge), which

5810-498: The resistance is gradually cut out. When electrical and DC motor technology was first developed, much of the equipment was constantly tended by an operator trained in the management of motor systems. The very first motor management systems were almost completely manual, with an attendant starting and stopping the motors, cleaning the equipment, repairing any mechanical failures, and so forth. The first DC motor-starters were also completely manual, as shown in this image. Normally it took

5893-419: The reverse direction. This results in a closer step-wise approximation to the ideal sinusoidal coil current, producing a more even torque than the two-pole motor where the current in each coil is closer to a square wave. Since current changes are half those of a comparable two-pole motor, arcing at the brushes is consequently less. If the shaft of a DC motor is turned by an external force, the motor will act like

5976-402: The rotor field at right angles to the stator field, it is necessary to either retard or advance the brush position to put the rotor's field into the correct position to be at a right angle to the distorted field. These field effects are reversed when the direction of spin is reversed. It is therefore difficult to build an efficient reversible commutated dynamo, since for highest field strength it

6059-554: The simplest mass-produced DC motors to be found, have three-pole armatures. The brushes can now bridge two adjacent commutator segments without causing a short circuit. These three-pole armatures also have the advantage that current from the brushes either flows through two coils in series or through just one coil. Starting with the current in an individual coil at half its nominal value (as a result of flowing through two coils in series), it rises to its nominal value and then falls to half this value. The sequence then continues with current in

6142-400: The supply and motor current are equal. The rapid switching wastes less energy than series resistors. This method is also called pulse-width modulation (PWM) and is often controlled by a microprocessor. An output filter is sometimes installed to smooth the average voltage applied to the motor and reduce motor noise. Since the series-wound DC motor develops its highest torque at low speed, it

6225-459: The use of all-parallel mode with AC. Weak field operation was available. They were briefly tried out for freight use by CR, but all finally ended up with WR. The top ones getting the WCAM-2P (see below). [5/02] However, CR's Indore-Pune weekly train had been hauled by a WR WCAM-1. Max. speed 100 km/h, 110 km/h after regearing. Traction motors were nose-suspended and axle-hung. Source: Of all

6308-400: The windings and the torque can be very high, but there is a danger of the windings becoming overheated. Series wound motors were widely used as traction motors in rail transport of every kind, but are being phased out in favour of power inverter -fed AC induction motors . The counter EMF aids the armature resistance to limit the current through the armature. When power is first applied to

6391-834: Was a class of locomotive used in the Indian Railways system. They were the first locomotives from the WCAM class. These locos were operational in routes around Mumbai. These locomotives worked on both AC as well as DC as their classification suggested. They hauled trains from DC section of suburban railway to AC section and thus performed a very critical task as they could easily operate on both AC and DC. However they performed poorly in DC mode compared to AC mode but they were very robust and had easy operating and handling characteristics. These were 1st class of Wide Gauge's (W) Bi-current charged (CA - runs both under AC and DC) and Mixed load series (M - hauls both passenger and freight trains). These were

6474-437: Was defined in 1893 as 1 ⁄ 1.434 of the emf of a Clark cell . This definition was abandoned in 1908 in favor of a definition based on the international ohm and international ampere until the entire set of "reproducible units" was abandoned in 1948. A 2019 revision of the SI , including defining the value of the elementary charge , took effect on 20 May 2019. Field weakening A brushed DC electric motor

6557-530: Was difficult to find a material capable of retaining a high-strength field. Only recently have advances in materials technology allowed the creation of high-intensity permanent magnets, such as neodymium magnets , allowing the development of compact, high-power motors without the extra volume of field coils and excitation means. But as these high-performance permanent magnets are applied more in electric motor and generator systems other problems are realized (see Permanent magnet synchronous generator ). Traditionally,

6640-728: Was possible at 21st and 30th notches. Voltage control was done by Tap changer operation under AC and Resistance notching under DC. Traction motors were charged by DC. Its prototypes were tested in the year 1971. All 53 WCAM-1s were based at Valsad Electric Loco Shed in Gujarat, and were withdrawn from service after the conversion of entire Mumbai region into AC traction. The WCAM-1 were employed on all express trains, including Shatabdi and Rajdhani Express (till Vadodara), until AC electrification of Mumbai area. The arrival of WCAM-2P engines did not reduce their work loads. Later on, with introduction of more modern AC locomotives and need for faster trains,

6723-521: Was sometimes used in DC traction motors to facilitate control of wheelslip . Permanent-magnet types have some performance advantages over direct-current, excited, synchronous types, and have become predominant in fractional horsepower applications. They are smaller, lighter, more efficient and more reliable than other singly-fed electric machines . Originally all large industrial DC motors used wound field or rotor magnets. Permanent magnets have conventionally only been useful in small motors because it

6806-555: Was that three machines were required to implement a scheme (five in very large installations, as the DC machines were often duplicated and controlled by a tandem variable resistor). In many applications, the motor-generator set was often left permanently running, to avoid the delays that would otherwise be caused by starting it up as required. Although electronic (thyristor) controllers have replaced most small to medium Ward-Leonard systems, some very large ones (thousands of horsepower) remain in service. The field currents are much lower than

6889-448: Was the standard method of controlling railway traction motors before the advent of power electronics . An electric locomotive or train would typically have four motors which could be grouped in three different ways: This provided three running speeds with minimal resistance losses. For starting and acceleration, additional control was provided by resistances. This system has been superseded by electronic control systems. The speed of

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