Summer Training Report on Maintenance of the Electric Loco's

GALAXY GLOBAL GROUP OF
INSTITUTIONS, DINARPUR (AMBALA)
To wards partial fulfillment of the requirement of K.U.K. for bachelor of
technology in Mechanical Engineering

REPORT ON
SOLENOID ELECTRIC ENGINE

SUBMITTED TO
ER. DEEPAK GUPTA
(PROJECT INCHARGE)
MR. N. GUPTA
H.O.D. (MECH.-ENGG.)

PROJECT GUIDE
ER. KRISHAN KANT
ER. MOHIT ASHRI
(ASSISTANT PROFESOR IN MECH. ENGG.)

SUBMITTED BY
ROHIT KUMAR 7309461
GURMEET SINGH 7309455
GURMAIL SINGH 7309456
SANJEEV KUMAR 7309454
AMIT KUMAR 7309449

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CONSTRUCTION

Step-1

We are using ac solenoid coil in our project to give angular motion to our crank shaft.

Coil detail:

Brand: IDEAL -2.0kg/15mm rat,cont, a.c 220v

When we provide current to the coil it core.

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Step-2
We design special crank shaft according to the solenoid coil. We use three iron dicks and
pass iron rode from it as shown below diagram.

Use bearing (608) on both side of crank shaft for support it on base and we use chain and
sprocket for transmit power to gear box.

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Step-3
We attach solenoid coil with crank shaft as shown below.

4

Step-4
We purchased one gear box of 1:4 ratios and fix in between crank shaft and wheel shaft
for providing torque to wheel.

5

Step-5
We design our project as 4 stork solenoid engine. For distribution different four stork
power we using simple technique, we use metal sheet and cut it in circular form then we
divide that circle in to 4 different portions as shown below and paste on wooden circular
piece.

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Step-6
We make one hole in centre of that wooden piece and insert one dc gear motor in it. We
provide ac current to the motor shaft with help of insulator and attach one iron foil with
that shaft this foil is connected with on the other side as shown below diagram.

We are running dc motor with help of dc supply and dc motor shaft is controlling ac
current with help of insulator and transmit power supply to solenoid coil for crank shaft
movement.

Power supply of dc motor: we are using fan regulator for increase and decrease of
power supply which transmit to the 12v step down transformer. Now we receive 12 v ac
supply and we need 12dc supply so, we use bridge rectifier to convert ac to dc. As we
increase fan regulator speed our dc motor move fast, if we decrease its speed it move
slow. According to this our dick transmits power supply to solenoid coil and coil rotate to
crank shaft.

Step-6

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Final look of model

CONPONENT USED
1. 4- Solenoid coil (ac coil)
2. Dc motor

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3. Power transmitting dick
4. Bearing
5. Crank shaft (design)
6. Washer
7. Gearbox
8. Chain and sprocket
9. Wheel
10. Wheel shaft
11. Wire
12. Body frame
Many more as per requirement…….

CONPONENT DETAIL
Used DC solenoid coil

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Solenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid
refers to a long, thin loop of wire, often wrapped around a metallic core, which produces
a magnetic field when an electric current is passed through it. Solenoids are important
because they can create controlled magnetic fields and can be used as electromagnets.
The term solenoid refers specifically to a magnet designed to produce a uniform magnetic
field in a volume of space (where some experiment might be carried out).

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In engineering, the term solenoid may also refer to a variety of transducer devices that
convert energy into linear motion. The term is also often used to refer to a solenoid
valve, which is an integrated device containing an electromechanical solenoid which
actuates either a pneumatic or hydraulic valve, or a solenoid switch, which is a specific
type of relay that internally uses an electromechanical solenoid to operate an electrical
switch; for example, an automobile starter solenoid, or a linear solenoid, which is an
electromechanical solenoid.

Magnetic field of a solenoid
Inside

This is a derivation of the magnetic field around a solenoid that is long enough so that
fringe effects can be ignored. In the diagram to the right, we immediately know that the
field points in the positive z direction inside the solenoid, and in the negative z direction
outside the solenoid.

A solenoid with 3 Ampèrian loops

We see this by applying the right hand grip rule for the field around a wire. If we wrap
our right hand around a wire with the thumb pointing in the direction of the current, the
curl of the fingers shows how the field behaves. Since we are dealing with a long
solenoid, all of the components of the magnetic field not pointing upwards cancel out by
symmetry. Outside, a similar cancellation occurs, and the field is only pointing
downwards.

Now consider imaginary the loop c that is located inside the solenoid. By Ampère's law,
we know that the line integral of B (the magnetic field vector) around this loop is zero,
since it encloses no electrical currents (it can be also assumed that the circuital electric

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field passing through the loop is constant under such conditions: a constant or constantly
changing current through the solenoid). We have shown above that the field is pointing
upwards inside the solenoid, so the horizontal portions of loop c doesn't contribute
anything to the integral. Thus the integral of the up side 1 is equal to the integral of the
down side 2. Since we can arbitrarily change the dimensions of the loop and get the same
result, the only physical explanation is that the integrands are actually equal, that is, the
magnetic field inside the solenoid is radially uniform. Note, though, that nothing
prohibits it from varying longitudinally which in fact it does.

Applications
Electromechanical solenoids

A 1920 explanation of a commercial solenoid used as an electromechanical actuator

Electromechanical solenoids consist of an electromagnetically inductive coil, wound
around a movable steel or iron slug (termed the armature). The coil is shaped such that
the armature can be moved in and out of the center, altering the coil's inductance and
thereby becoming an electromagnet. The armature is used to provide a mechanical force
to some mechanism (such as controlling a pneumatic valve). Although typically weak
over anything but very short distances, solenoids may be controlled directly by a
controller circuit, and thus have very low reaction times.

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The force applied to the armature is proportional to the change in inductance of the coil
with respect to the change in position of the armature, and the current flowing through the
coil (see Faraday's law of induction). The force applied to the armature will always
move the armature in a direction that increases the coil's inductance.

Electromechanical solenoids are commonly seen in electronic paintball markers,
pinball machines, dot matrix printers and fuel injectors.

Rotary solenoid

The rotary solenoid is an electromechanical device used to rotate a ratcheting mechanism
when power is applied. These were used in the 1950s for rotary snap-switch automation
in electromechanical controls. Repeated actuation of the rotary solenoid advances the
snap-switch forward one position. Two rotary actuators on opposite ends of the rotary
snap-switch shaft, can advance or reverse the switch position.

The rotary solenoid has a similar appearance to a linear solenoid, except that the core is
mounted in the center of a large flat disk, with two or three inclined grooves cut into the
underside of the disk. These grooves align with slots on the solenoid body, with ball
bearings in the grooves.

When the solenoid is activated, the core is drawn into the coil, and the disk rotates on the
ball bearings in the grooves as it moves towards the coil body. When power is removed, a
spring on the disk rotates it back to its starting position, also pulling the core out of the
coil.

Rotary voice coil

This is a rotational version of a solenoid. Typically the fixed magnet is on the outside,
and the coil part moves in an arc controlled by the current flow through the coils. Rotary
voice coils are widely employed in devices such as disk drives.

Pneumatic solenoid valves

A pneumatic solenoid valve is a switch for routing air to any pneumatic device, usually
an actuator, allowing a relatively small signal to control a large device. It is also the
interface between electronic controllers and pneumatic systems.

Hydraulic solenoid valves

Hydraulic solenoid valves are in general similar to pneumatic solenoid valves except
that they control the flow of hydraulic fluid (oil), often at around 3000 psi (210 bar, 21
MPa, 21 MN/m²). Hydraulic machinery uses solenoids to control the flow of oil to rams
or actuators to (for instance) bend sheets of titanium in aerospace manufacturing.
Solenoid-controlled valves are often used in irrigation systems, where a relatively weak
solenoid opens and closes a small pilot valve, which in turn activates the main valve by

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applying fluid pressure to a piston or diaphragm that is mechanically coupled to the main
valve. Solenoids are also in everyday household items such as washing machines to
control the flow and amount of water into the drum.

Transmission solenoids control fluid flow through an automatic transmission and are
typically installed in the transmission valve body.

Automobile starter solenoid

In a car or truck, the starter solenoid is part of an automobile starting system. The starter
solenoid receives a large electric current from the car battery and a small electric
current from the ignition switch. When the ignition switch is turned on (i.e. when the key
is turned to start the car), the small electric current forces the starter solenoid to close a
pair of heavy contacts, thus relaying the large electric current to the starter motor.

Starter solenoids can also be built into the starter itself, often visible on the outside of the
starter. If a starter solenoid receives insufficient power from the battery, it will fail to start
the motor, and may produce a rapid 'clicking' or 'clacking' sound. This can be caused by
a low or dead battery, by corroded or loose connections in the cable, or by a broken or
damaged positive (red) cable from the battery. Any of these will result in some power to
the solenoid, but not enough to hold the heavy contacts closed, so the starter motor itself
never spins, and the engine does not start.

Gear box
Used gear box

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Transmission (mechanics)
A Transmission or gearbox provides speed and torque conversions from a rotating power
source to another device using gear ratios. In British English the term transmission refers
to the whole drive train, including gearbox, clutch, prop shaft (for rear-wheel drive),
differential and final drive shafts. The most common use is in motor vehicles, where the
transmission adapts the output of the internal combustion engine to the drive wheels.
Such engines need to operate at a relatively high rotational speed, which is inappropriate
for starting, stopping, and slower travel. The transmission reduces the higher engine
speed to the slower wheel speed, increasing torque in the process. Transmissions are also
used on pedal bicycles, fixed machines, and anywhere else rotational speed and torque
needs to be adapted.

Often, a transmission will have multiple gear ratios (or simply "gears"), with the ability to
switch between them as speed varies. This switching may be done manually (by the
operator), or automatically. Directional (forward and reverse) control may also be
provided. Single-ratio transmissions also exist, which simply change the speed and torque
(and sometimes direction) of motor output.

In motor vehicle applications, the transmission will generally be connected to the
crankshaft of the engine. The output of the transmission is transmitted via driveshaft to
one or more differentials, which in turn drive the wheels. While a differential may also
provide gear reduction, its primary purpose is to change the direction of rotation.

Conventional gear/belt transmissions are not the only mechanism for speed/torque
adaptation. Alternative mechanisms include torque converters and power transformation.

Uses
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Gearboxes have found use in a wide variety of different—often stationary—applications,
such as wind turbines.

Transmissions are also used in agricultural, industrial, construction, mining and
automotive equipment. In addition to ordinary transmission equipped with gears, such
equipment makes extensive use of the hydrostatic drive and electrical adjustable-speed
drives.

BEARINGS
Have you ever wondered how things like inline skate wheels and electric motors spin so
smoothly and quietly? The answer can be found in a neat little machine called a bearing.

A tapered roller bearing from a manual transmission
The bearing makes many of the machines we use every day possible. Without bearings,
we would be constantly replacing parts that wore out from friction. In this article, we'll
learn how bearings work, look at some different kinds of bearings and explain their
common uses, and explore some other interesting uses of bearings.

THE BASICS
The concept behind a bearing is very simple: Things roll better than they slide. The
wheels on your car are like big bearings. If you had something like skis instead of wheels,
your car would be a lot more difficult to push down the road.

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That is because when things slide, the friction between them causes a force that tends to
slow them down. But if the two surfaces can roll over each other, the friction is greatly
reduced.

Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner
and outer metal surface for the balls to roll against. These balls or rollers "bear" the load,
allowing the device to spin smoothly.

Bearing Loads
Bearings typically have to deal with two kinds of loading, radial and thrust. Depending
on where the bearing is being used, it may see all radial loading, all thrust loading or a
combination of both.

The bearings that support the shafts of motors and pulleys are subject to a radial load.
The bearings in the electric motor and the pulley pictured above face only a radial load.
In this case, most of the load comes from the tension in the belt connecting the two
pulleys.

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The bearings in this stool are subject to a thrust load.
The bearing above is like the one in a barstool. It is loaded purely in thrust, and the entire
load comes from the weight of the person sitting on the stool.

The bearings in a car wheel are subject to both thrust and
radial loads.
The bearing above is like the one in the hub of your car wheel. This bearing has to
support both a radial load and a thrust load. The radial load comes from the weight of the
car, the thrust load comes from the cornering forces when you go around a turn.
Types of Bearings
There are many types of bearings, each used for different purposes. These include ball
bearings, roller bearings, ball thrust bearings, roller thrust bearings and tapered roller
thrust bearings.

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Ball Bearings
Ball bearings, as shown below, are probably the most common type of bearing. They are
found in everything from inline skates to hard drives. These bearings can handle both
radial and thrust loads, and is usually found in applications where the load is relatively
small.

Cutaway view of a ball bearing
In a ball bearing, the load is transmitted from the outer race to the ball and from the ball
to the inner race. Since the ball is a sphere, it only contacts the inner and outer race at a
very small point, which helps it spin very smoothly. But it also means that there is not
very much contact area holding that load, so if the bearing is overloaded, the balls can
deform or squish, ruining the bearing.

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DC MOTORS

DC GEAR MOTOR
Brand HOSIDEN motors (Japan)
R.P.M: 75-100
VOLT: 12-18V. DC

One of the first electromagnetic rotary motors was invented by Michael Faraday in 1821
and consisted of a free-hanging wire dipping into a pool of mercury. A permanent magnet
was placed in the middle of the pool of mercury. When a current was passed through the
wire, the wire rotated around the magnet, showing that the current gave rise to a circular
magnetic field around the wire. This motor is often demonstrated in school physics
classes, but brine (salt water) is sometimes used in place of the toxic mercury. This is the
simplest form of a class of electric motors called homopolar motors. A later refinement is
the Barlow's Wheel.

Another early electric motor design used a reciprocating plunger inside a switched
solenoid; conceptually it could be viewed as an electromagnetic version of a two stroke
internal combustion engine.

The modern DC motor was invented by accident in 1873, when Zénobe Gramme
connected a spinning dynamo to a second similar unit, driving it as a motor.

The classic DC motor has a rotating armature in the form of an electromagnet. A rotary
switch called a commutator reverses the direction of the electric current twice every
cycle, to flow through the armature so that the poles of the electromagnet push and pull
against the permanent magnets on the outside of the motor. As the poles of the armature
electromagnet pass the poles of the permanent magnets, the commutator reverses the

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polarity of the armature electromagnet. During that instant of switching polarity, inertia
keeps the classical motor going in the proper direction. (See the diagrams below.)

A simple DC electric motor. When the coil is powered, a magnetic field is generated
around the armature. The left side of the armature is pushed away from the left magnet
and drawn toward the right, causing rotation.

The armature continues to rotate.

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When the armature becomes horizontally aligned, the commutator reverses the direction
of current through the coil, reversing the magnetic field. The process then repeats.

Fan Regulator
Description .
This is the circuit diagram of the simplest lamp dimmer or fan regulator. The circuit is
based on the principle of power control using a Triac. The circuit works by varying the
firing angle of the Triac . Resistors R1, R2 and capacitor C2 are associated with this. The
firing angle can be varied by varying the value of any of these components. Here R1 is
selected as the variable element .By varying the value of R1 the firing angle of Triac
changes (in simple words, how much time should Triac conduct) changes. This directly
varies the load power, since load is driven by Triac. The firing pulses are given to the
gate of Triac T1 using Diac D1.

Notes
Assemble the circuit on a good quality PCB or common board. The load whether lamp
,fan or any thing ,should be less than 200 Watts. To connect higher loads replace the
Triac BT 136 with a higher Watt capacity Triac. All parts of the circuit are active with
potential shock hazard. So be careful.

I advice to test the circuit with a low voltage supply (say 12V or 24V AC) and a
small load (a same volt bulb) ,before connecting the circuit to mains.

Parts List

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R1 1o K 1 Watt Resistor

R2 1o0 K Potentiometer (Variable Resistance)

C1 0.1 uF (500V or above) Polyester Capacitor

T1 BT 136 Triac

D1 DB2 Diac

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POWER SUPPLY

In alternating current the electron flow is alternate, i.e. the electron flow increases
to maximum in one direction, decreases back to zero. It then increases in the other
direction and then decreases to zero again. Direct current flows in one direction only.
Rectifier converts alternating current to flow in one direction only. When the anode of the
diode is positive with respect to its cathode, it is forward biased, allowing current to flow.
But when its anode is negative with respect to the cathode, it is reverse biased and does
not allow current to flow. This unidirectional property of the diode is useful for
rectification. A single diode arranged back-to-back might allow the electrons to flow
during positive half cycles only and suppress the negative half cycles. Double diodes
arranged back-to-back might act as full wave rectifiers as they may allow the electron
flow during both positive and negative half cycles. Four diodes can be arranged to make a
full wave bridge rectifier. Different types of filter circuits are used to smooth out the
pulsations in amplitude of the output voltage from a rectifier. The property of capacitor to
oppose any change in the voltage applied across them by storing energy in the electric
field of the capacitor and of inductors to oppose any change in the current flowing

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through them by storing energy in the magnetic field of coil may be utilized. To remove
pulsation of the direct current obtained from the rectifier, different types of combination
of capacitor, inductors and resistors may be also be used to increase to action of filtering.
NEED OF POWER SUPPLY
Perhaps all of you are aware that a ‘power supply’ is a primary requirement for
the ‘Test Bench’ of a home experimenter’s mini lab. A battery eliminator can eliminate
or replace the batteries of solid-state electronic equipment and the equipment thus can be
operated by 230v A.C. mains instead of the batteries or dry cells. Nowadays, the use of
commercial battery eliminator or power supply unit has become increasingly popular as
power source for household appliances like transreceivers, record player, cassette players,
digital clock etc.

THEORY

USE OF DIODES IN RECTIFIERS:

Electric energy is available in homes and industries in India, in the form of
alternating voltage. The supply has a voltage of 220V (rms) at a frequency of 50 Hz. In
the USA, it is 110V at 60 Hz. For the operation of most of the devices in electronic
equipment, a dc voltage is needed. For instance, a transistor radio requires a dc supply for
its operation. Usually, this supply is provided by dry cells. But sometime we use a battery
eliminator in place of dry cells. The battery eliminator converts the ac voltage into dc
voltage and thus eliminates the need for dry cells. Nowadays, almost all-electronic
equipment includes a circuit that converts ac voltage of mains supply into dc voltage.
This part of the equipment is called Power Supply. In general, at the input of the power
supply, there is a power transformer. It is followed by a diode circuit called Rectifier. The
output of the rectifier goes to a smoothing filter, and then to a voltage regulator circuit.
The rectifier circuit is the heart of a power supply.

Rectification
Rectification is a process of rendering an alternating current or voltage into a
unidirectional one. The component used for rectification is called ‘Rectifier’. A rectifier
permits current to flow only during the positive half cycles of the applied AC voltage by
eliminating the negative half cycles or alternations of the applied AC voltage. Thus

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pulsating DC is obtained. To obtain smooth DC power, additional filter circuits are
required.

A diode can be used as rectifier. There are various types of diodes. But,
semiconductor diodes are very popularly used as rectifiers. A semiconductor diode is a
solid-state device consisting of two elements is being an electron emitter or cathode, the
other an electron collector or anode. Since electrons in a semiconductor diode can flow in
one direction only-from emitter to collector- the diode provides the unilateral conduction
necessary for rectification. Out of the semiconductor diodes, copper oxide and selenium
rectifier are also commonly used.

FULL WAVE RECTIFIER
It is possible to rectify both alternations of the input voltage by using two diodes
in the circuit arrangement. Assume 6.3 V rms (18 V p-p) is applied to the circuit. Assume
further that two equal-valued series-connected resistors R are placed in parallel with the
ac source. The 18 V p-p appears across the two resistors connected between points AC
and CB, and point C is the electrical midpoint between A and B. Hence 9 V p-p appears
across each resistor. At any moment during a cycle of v in, if point A is positive relative
to C, point B is negative relative to C. When A is negative to C, point B is positive
relative to C. The effective voltage in proper time phase which each diode "sees" is in
Fig. The voltage applied to the anode of each diode is equal but opposite in polarity at
any given instant.

When A is positive relative to C, the anode of D 1 is positive with respect to its
cathode. Hence D1 will conduct but D2 will not. During the second alternation, B is
positive relative to C. The anode of D2 is therefore positive with respect to its cathode,
and D2 conducts while D1 is cut off.

There is conduction then by either D1 or D2 during the entire input-voltage cycle.

Since the two diodes have a common-cathode load resistor R L, the output voltage
across RL will result from the alternate conduction of D1 and D2. The output waveform
vout across RL, therefore has no gaps as in the case of the half-wave rectifier.

The output of a full-wave rectifier is also pulsating direct current. In the diagram,
the two equal resistors R across the input voltage are necessary to provide a voltage
midpoint C for circuit connection and zero reference. Note that the load resistor R L is
connected from the cathodes to this center reference point C.

An interesting fact about the output waveform vout is that its peak amplitude is
not 9 V as in the case of the half-wave rectifier using the same power source, but is less

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than 4½ V. The reason, of course, is that the peak positive voltage of A relative to C is
4½ V, not 9 V, and part of the 4½ V is lost across R.

Though the full wave rectifier fills in the conduction gaps, it delivers less than
half the peak output voltage that results from half-wave rectification.

BRIDGE RECTIFIER
A more widely used full-wave rectifier circuit is the bridge rectifier. It requires
four diodes instead of two, but avoids the need for a centre-tapped transformer. During
the positive half-cycle of the secondary voltage, diodes D2 and D4 are conducting and
diodes D1 and D3 are non-conducting. Therefore, current flows through the secondary
winding, diode D2, load resistor RL and diode D4. During negative half-cycles of the
secondary voltage, diodes D1 and D3 conduct, and the diodes D2 and D4 do not conduct.
The current therefore flows through the secondary winding, diode D1, load resistor RL
and diode D3. In both cases, the current passes through the load resistor in the same
direction. Therefore, a fluctuating, unidirectional voltage is developed across the load.

FILTRATION
The rectifier circuits we have discussed above deliver an output voltage that
always has the same polarity: but however, this output is not suitable as DC power supply
for solid-state circuits. This is due to the pulsation or ripples of the output voltage. This
should be removed out before the output voltage can be supplied to any circuit. This
smoothing is done by incorporating filter networks. The filter network consists of
inductors and capacitors. The inductors or choke coils are generally connected in series
with the rectifier output and the load. The inductors oppose any change in the magnitude
of a current flowing through them by storing up energy in a magnetic field. An inductor
offers very low resistance for DC whereas; it offers very high resistance to AC. Thus, a
series connected choke coil in a rectifier circuit helps to reduce the pulsations or ripples
to a great extent in the output voltage. The fitter capacitors are usually connected in
parallel with the rectifier output and the load. As AC can pass through a capacitor but DC
cannot, the ripples are thus limited and the output becomes smoothed. When the voltage
across its plates tends to rise, it stores up energy back into voltage and current. Thus, the
fluctuations in the output voltage are reduced considerable. Filter network circuits may be
of two types in general:

CHOKE INPUT FILTER
If a choke coil or an inductor is used as the ‘first- components’ in the filter
network, the filter is called ‘choke input filter’. The D.C. along with AC pulsation from
the rectifier circuit at first passes through the choke (L). It opposes the AC pulsations but
allows the DC to pass through it freely. Thus AC pulsations are largely reduced. The
further ripples are by passed through the parallel capacitor C. But, however, a little nipple

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remains unaffected, which are considered negligible. This little ripple may be reduced by
incorporating a series a choke input filters.

CAPACITOR INPUT FILTER
If a capacitor is placed before the inductors of a choke-input filter network, the
filter is called capacitor input filter. The D.C. along with AC ripples from the rectifier
circuit starts charging the capacitor C. to about peak value. The AC ripples are then
diminished slightly. Now the capacitor C, discharges through the inductor or choke coil,
which opposes the AC ripples, except the DC. The second capacitor C by passes the
further AC ripples. A small ripple is still present in the output of DC, which may be
reduced by adding additional filter network in series.

CIRCUIT DIAGRAM

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Transformer
A transformer is an electrical device that transfers energy from one circuit to another by
magnetic coupling with no moving parts. A transformer comprises two or more coupled
windings, or a single tapped winding and, in most cases, a magnetic core to concentrate
magnetic flux. A changing current in one winding creates a time-varying magnetic flux in
the core, which induces a voltage in the other windings. Michael Faraday built the first
transformer, although he used it only to demonstrate the principle of electromagnetic
induction and did not foresee the use to which it would eventually be put.

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Three-phase pole-mounted step-down transformer.

A historical Stanley transformer.

• Lucien Gaulard and John Dixon Gibbs, who first exhibited a device called a
'secondary generator' in London in 1881 and then sold the idea to American
company Westinghouse. This may have been the first practical power
transformer. They also exhibited the invention in Turin in 1884, where it was
adopted for an electric lighting system. Their early devices used an open iron
core, which was soon abandoned in favour of a more efficient circular core with a
closed magnetic path.

• William Stanley, an engineer for Westinghouse, who built the first practical
device in 1885 after George Westinghouse bought Gaulard and Gibbs' patents.

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The core was made from interlocking E-shaped iron plates. This design was first
used commercially in 1886.
• Hungarian engineers Károly Zipernowsky, Ottó Bláthy and Miksa Déri at the
Ganz company in Budapest in 1885, who created the efficient "ZBD" model
based on the design by Gaulard and Gibbs.
• Nikola Tesla in 1891 invented the Tesla coil, which is a high-voltage, air-core,
dual-tuned resonant transformer for generating very high voltages at high
frequency.

OVERVIEW

The transformer is one of the simplest of electrical devices, yet transformer designs and
materials continue to be improved. Transformers are essential for high voltage power
transmission, which makes long distance transmission economically practical. This
advantage was the principal factor in the selection of alternating current power
transmission in the "War of Currents" in the late 1880s.

Audio frequency transformers (at the time called repeating coils) were used by the
earliest experimenters in the development of the telephone. While some electronics
applications of the transformer have been made obsolete by new technologies,
transformers are still found in many electronic devices.

Transformers come in a range of sizes from a thumbnail-sized coupling transformer
hidden inside a stage microphone to huge giga watt units used to interconnect large
portions of national power grids. All operate with the same basic principles and with
many similarities in their parts.

Single phase pole-mounted step-down transformer

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Transformers alone cannot do the following:

• Convert DC to AC or vice versa
• Change the voltage or current of DC
• Change the AC supply frequency.

However, transformers are components of the systems that perform all these functions.

AN ANALOGY
The transformer may be considered as a simple two-wheel 'gearbox' for electrical voltage
and current. The primary winding is analogous to the input shaft and the secondary
winding to the output shaft. In this analogy, current is equivalent to shaft speed, voltage
to shaft torque. In a gearbox, mechanical power (torque multiplied by speed) is constant
(neglecting losses) and is equivalent to electrical power (voltage multiplied by current)
which is also constant.

The gear ratio is equivalent to the transformer step-up or step-down ratio. A step-up
transformer acts analogously to a reduction gear (in which mechanical power is
transferred from a small, rapidly rotating gear to a large, slowly rotating gear): it trades
current (speed) for voltage (torque), by transferring power from a primary coil to a
secondary coil having more turns. A step-down transformer acts analogously to a
multiplier gear (in which mechanical power is transferred from a large gear to a small
gear): it trades voltage (torque) for current (speed), by transferring power from a primary
coil to a secondary coil having fewer turns.

COUPLING BY MUTUAL INDUCTION
A simple transformer consists of two electrical conductors called the primary winding
and the secondary winding. Energy is coupled between the windings by the time-varying
magnetic flux that passes through (links) both primary and secondary windings. When
the current in a coil is switched on or off or changed, a voltage is induced in a
neighboring coil. The effect, called mutual inductance, is an example of electromagnetic
induction.

33

SIMPLIFIED ANALYSIS

A practical step-down transformer showing magnetising flux in the core

If a time-varying voltage is applied to the primary winding of turns, a current will
flow in it producing a magnetomotive force (MMF). Just as an electromotive force
(EMF) drives current around an electric circuit, so MMF tries to drive magnetic flux
through a magnetic circuit. The primary MMF produces a varying magnetic flux in
the core, and, with an open circuit secondary winding, induces a back electromotive
force (EMF) in opposition to . In accordance with Faraday's law of induction, the
voltage induced across the primary winding is proportional to the rate of change of flux:

and

where

• vP and vS are the voltages across the primary winding and secondary winding,
• NP and NS are the numbers of turns in the primary winding and secondary
winding,
• dΦP / dt and dΦS / dt are the derivatives of the flux with respect to time of the
primary and secondary windings.

Saying that the primary and secondary windings are perfectly coupled is equivalent to
saying that . Substituting and solving for the voltages shows that:

where

34

• vp and vs are voltages across primary and secondary,
• Np and Ns are the numbers of turns in the primary and secondary, respectively.

Hence in an ideal transformer, the ratio of the primary and secondary voltages is equal to
the ratio of the number of turns in their windings, or alternatively, the voltage per turn is
the same for both windings. The ratio of the currents in the primary and secondary
circuits is inversely proportional to the turns ratio. This leads to the most common use of
the transformer: to convert electrical energy at one voltage to energy at a different voltage
by means of windings with different numbers of turns. In a practical transformer, the
higher-voltage winding will have more turns, of smaller conductor cross-section, than the
lower-voltage windings.

The EMF in the secondary winding, if connected to an electrical circuit, will cause
current to flow in the secondary circuit. The MMF produced by current in the secondary
opposes the MMF of the primary and so tends to cancel the flux in the core. Since the
reduced flux reduces the EMF induced in the primary winding, increased current flows in
the primary circuit. The resulting increase in MMF due to the primary current offsets the
effect of the opposing secondary MMF. In this way, the electrical energy fed into the
primary winding is delivered to the secondary winding. Also because of this, the flux
density will always stay the same as long as the primary voltage is steady.

For example, suppose a power of 50 watts is supplied to a resistive load from a
transformer with a turns ratio of 25:2.

• P = EI (power = electromotive force × current)

50 W = 2 V × 25 A in the primary circuit if the load is a resistive load. (See note
1)
• Now with transformer change:

50 W = 25 V × 2 A in the secondary circuit.

ANALYSIS OF THE IDEAL TRANSFORMER
This treats the windings as a pair of mutually coupled coils with both primary and
secondary windings passing currents and with each coil linked with the same magnetic
flux. In an ideal transformer the core requires no MMF. The primary and secondary
MMFs, acting in opposite directions, are exactly balancing each other and hence, there is
no overall resultant MMF acting on the core. There is, however, no need for any MMF
acting on the core of an ideal transformer to create a magnetic flux. The flux in the core is
unambiguously determined by the applied primary voltage in accordance with Faraday's
law of induction, or rather by an integration of the aforesaid law.

In the ideal transformer at no load, i.e. with the secondary load removed, the voltage
applied to the primary winding is opposed by an induced EMF in the winding equal to the
applied voltage in accordance with Faraday's law of induction. No current will flow in

35

the winding since no MMF is required by the core. One might also say that the
inductance of the primary winding at no load is infinitely large.

Further on, the balance of the primary and secondary MMFs i.e. NPiP = NSiS , gives the
ratio of the secondary and primary currents as:

That is, the ratio between the primary and secondary currents is the inverse of the ratio
between the corresponding voltages.

DC VOLTAGES AND CURRENTS
A DC voltage applied to a winding of an ideal transformer will cause a DC voltage to be
induced in the other winding. This is because any voltage applied will create a changing
flux. However, using a transformer with DC voltages would require the magnetic flux in
the core (and current supplied by the DC voltage source) to increase without bound. If
there is resistance in the winding, the final current and final flux will be limited by that.
Once the flux stops changing, no voltage is induced in the other winding. If the core is
made of anything other than air (e.g. iron) it will also saturate. Saturation will drastically
reduce the amount of power that can be transferred, as well as causing the current to rise
even more steeply. For these reasons it is very important to avoid having any DC
component in the voltages being applied to a transformer. The amount of power being
dissipated in the winding will be limited solely by the winding resistance.

It is possible to draw DC current from a transformer, as a DC current merely represents a
constant offset to the flux in the core. DC currents are caused by some non-linear loads
(e.g. a half-wave rectifier). Most transformers are designed to be driven to near
saturation without any DC current components, so having a DC current will make the
transformer saturate more easily. Full-wave rectifiers do not have this issue, since the
current they draw has no DC component.

THE UNIVERSAL EMF EQUATION
If the flux in the core is sinusoidal, the relationship for either winding between its
number of turns, voltage, magnetic flux density and core cross-sectional area is given by
the universal emf equation (from Faraday's law):

36

where

• E is the sinusoidal rms or root mean square voltage of the winding,
• f is the frequency in hertz,
• N is the number of turns of wire on the winding,
• a is the cross-sectional area of the core in square metres
• B is the peak magnetic flux density in teslas,

Other consistent systems of units can be used with the appropriate conversions in the
equation.

Practical considerations

CLASSIFICATIONS
Transformers are adapted to numerous engineering applications and may be classified in
many ways:

• By power level (from fraction of a volt-ampere(VA) to over a thousand MVA),
• By application (power supply, impedance matching, circuit isolation),
• By frequency range (power, audio, radio frequency(RF))
• By voltage class (a few volts to about 750 kilovolts)
• By cooling type (air cooled, oil filled, fan cooled, water cooled, etc.)
• By purpose (distribution, rectifier, arc furnace, amplifier output, etc.).
• By ratio of the number of turns in the coils

• Step-up

The secondary has more turns than the primary.
• Step-down

The secondary has fewer turns than the primary.
• Isolating

Intended to transform from one voltage to the same voltage. The two coils have
approximately equal numbers of turns, although often there is a slight difference
in the number of turns, in order to compensate for losses (otherwise the output
voltage would be a little less than, rather than the same as, the input voltage).

• Variable

The primary and secondary have an adjustable number of turns which can be
selected without reconnecting the transformer.

37

CIRCUIT SYMBOLS
Standard symbols

Transformer with two windings and iron core.

Transformer with three windings.
The dots show the relative winding configuration of the windings.

Step-down or step-up transformer.

The symbol shows which winding has more turns,

but does not usually show the exact ratio.

Transformer with electrostatic screen,
which prevents capacitive coupling between the windings.

BIKE TIMING CHAIN

38

DIAMENSION:
LENTH: 560MM
GROOVE: 84

BIKE TIMING GEAR

DIAMENSION:
TEETH: 28
LENTH: 60MM

Two of the three books mentioned in the lead-up to this page, "Model Making for Young
Physicists" by A.D.Bulman and "The Boy Electrician" by Alfred P. Morgan, each
presented a model which could be described as a "Solenoid Engine". The most obvious
difference between them is that one of them (Bulman's) had only one solenoid, while
Morgan's had two. The most obvious thing that they had in common is that they both
relied on moving contacts.

39

Having built my two-pole electric motor, and thus knowing the hassles moving contacts
can cause, I decided in 2010 to build a solenoid engine built on very different principles.

The fact is, my …. and I did build a four-solenoid engine in the late 1960's, based
somewhat along the lines of Bulman's model, using an old solenoid my ………… had
lying around (goodness only knows where he got it from, or what its original function
was!). The model did work, although not very well; eventually it was dismantled, and
some of the parts found other uses. As you've probably guessed, the moving contacts
were the main cause of its ultimate demise.

Reduced to its bare essentials, a solenoid engine of the moving-contact type can be
represented as in the following diagram:

At the right is the solenoid - a coil of wire wound on a tube of suitable non-ferrous
material with a movable soft-iron core. This is attached to a crankshaft (at left) which
bears a slip-ring and a cam, both made from some suitable metal (eg. brass) and
electrically connected together.

40

Summer Training Report on Maintenance of the Electric Loco's

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