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Transformer is an electrical device which transfers
electrical power from one coil (primary) to another (secondary) by the
principle of mutual induction. The input is given through the primary and the
output is tapped from the secondary.
If the secondary coil has more number of turns than that of the primary it is called "STEP UP" transformer. Because , the secondary voltage will be more than that of the primary voltage. If it is the other way it is called "STEP DOWN" transformer. Here the secondary voltage will be less than that of the primary.
In an ideal transformer, the power input will be equal to the power output. But practically it is impossible due to certain transformer losses.
Actually the transformer increases or decreases the voltage. So the current will be inversely proportional. ie. if the voltage is increased current will be decreased. and vice versa.
If the secondary coil has more number of turns than that of the primary it is called "STEP UP" transformer. Because , the secondary voltage will be more than that of the primary voltage. If it is the other way it is called "STEP DOWN" transformer. Here the secondary voltage will be less than that of the primary.
In an ideal transformer, the power input will be equal to the power output. But practically it is impossible due to certain transformer losses.
Actually the transformer increases or decreases the voltage. So the current will be inversely proportional. ie. if the voltage is increased current will be decreased. and vice versa.
Difference between step-up
transformer and voltage amplifier
Than a very strange but thinkable question comes what is the difference between the two and can we use a small step up transformer in place of voltage amplifier and vice-versa?
Differences
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Transformer
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Amplifier
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Transformers are unable to amplify (step up) an ac input
Voltage without reducing (stepping down) it`s current capability.
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Amplifier can amplify both current and Voltage at the same
time. We can have 1V at 1uA to drive the input but might also get many volts
at many Amps at the output.
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Transformer`s coil windings never requires a dc Voltage to
operate. Sometimes a dc Voltage might be present in a transformer winding for
auxiliaries but the dc is not required for the operation of the transformer.
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Amplifier almost always requires a dc working supply
Voltage to operate.
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Transformer has more winding added to its secondary
winding to obtain Voltage amplification.
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An Amplifier actually modulates a fixed dc source Voltage
in response to an ac input Voltage to obtain output Voltage amplification.
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A transformer`s input current is proportional to its load
current.
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Amplifier’s input current is normally almost independent
of its load current.
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A transformer is like a gearbox, whereas an amplifier is
like an engine. The gearbox converts energy like a transformer.
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Amplifier is like an engine, which consumes fuel to give
output. Similarly amplifier consumed DC supply to give output.
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A step up transformer can amplify a specified type of
input which is the sinusoidal input or time varying input and add to that the
range of input the transformer is very flexible in range.
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Amplifier can amplify any signal and while the amplifier
would have a limited range then in the saturation state.
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In an ideal transformer output impedance is equal to the
source impedance times the square of the turns ratio.
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An amplifier can have output impedance that is independent
of the source impedance.
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Rule for a Step-Up Transformer
Electrical Codes
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Under the National Electrical Code, a step-up
transformer must have certain current carrying protections in place. There must
be a main circuit breaker installed in a load center served by the transformer,
and the main breaker can be no larger than 70 percent of the maximum current
capacity of the transformer.
KVA Rating
·
All transformers have a KVA rating. This rating
represents the transformer's maximum capacity in kilowatts (thousands of
watts). In calculating what KVA means in practical terms, Watt's Law is
applied. In Watt's Law, power (P) equals the output voltage (E) times the
ampere capacity (I). Using this formula, P = E x I, and its direct derivatives,
I = P / E and E = P / I, all transformer attributes can be calculated. For
example, if the transformer's rating is 10 KVA and has a 240-volt output, it
has a current capacity of 41.67 amperes (10,000 watts / 240 volts = 41.67
amps).
Application
·
Watt's Law also applies when choosing a step-up
transformer for an application. If a transformer needs to step-up 240 volts to
480 volts, and you need a maximum current capacity of 40 amps, you must first
calculate the number of amps needed to comply with electrical codes. If the
codes require a maximum usage of 70 percent of the transformer's capacity,
multiply 40 times 1.43. The product will be 57.2 amps, 70 percent of which is
40.0 amps. Knowing you need 57.2 amps (I) and the output of 480 volts (E)
Watt's law can be applied as P = I x E. Therefore, 57.2 x 480 = 27,456 watts,
or 27.456 KVA. This would be the minimum size transformer required for this
application
How Calculate turn ratio on step up transformers?
For example: if the primery winding on the transformer were 250 turns and the 1250 turns on the secondary, what is the turn ratio? Well what you do is you take 1250 divide that by 250 will give you 5. So the answer would be 1:5 since 1 will be on the top of the 250 and the 5 would be on the top of the 1250. IN ALL STEP UP TRANSFORMERS HAVING A TURNS RATIO MORE THAN ONE...BECAUSE IT STEPS UP VOLTAGE.
Step up Transfromer Calculation
Step down transformer: is one whose secondary voltage is less than its primary voltage. It is designed to reduce the voltage from the primary winding to the secondary winding. This kind of transformer “steps down” the voltage applied to it.
As a step-down unit, the transformer converts high-voltage, low-current power into low-voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary due to the increase in current. The primary winding, which doesn’t have to conduct as much current, may be made of smaller-gauge wire.
Step-down transformers are
commonly used to convert the 220 volt electricity found in most parts of the
world to the 110 volts required by North American equipment.
How
to Wire a Step Down Transformer
- Observe and identify the schematic and rating of the step down transformer to be installed. Remove the terminal connection box cover placed at the lower side of the transformer. Only the high amperage types will have this enclosure, while lower powered transformers will have an exposed screw terminal.
- Know termination identification follows for all step down transformers: H1, H2, H3 and H4 signify the high voltage side or power feed end of the transformer. This holds true regardless of the size of the transformer. Interconnection of the transformer will vary depending on the manufacturer and voltage used for feeding the transformer.
- Terminate the feed power wires first by cutting the wires to length. If you are using large wire lugs be sure to take into consideration the length of the lug and the amount of wire that can be inserted into the female crimp area.
- Strip back the outer insulating of the wires with the pocketknife or wire strippers. Insert the eye ring or wire lug over the bare copper wire and crimp the connection device, using the appropriate-size crimper, permanently to the wire.
- Terminate the high side, high voltage of the step down transformer. If the high side terminals are bolts, be sure to follow any torque requirements that are listed by the manufacturer.
- Terminate the low side, low voltage of the transformer. Note these terminals will be identified by X1, X2, X3 and X4. Again follow the manufacturer’s individual schematics for that particular type of transformer. Note that on small control transformers there will only be an X1 and X2. X1 is the power or “hot” side and X2 is generally the grounding and neutral portion of the low voltage.
- Terminate the small control transformer for X1 and X2. X1 will go directly to the control circuit after passing through a small fuse that is rated for the circuit. X2 will be terminated not only to the neutral side of the control circuit, but the grounding safety as well. In other words, the X2 side of the small control transformer must be tied to the grounding system of the electrical circuit.
- Replace all covers on the transformer and any enclosures that protect you from electricity. Apply the high voltage to the transformer by switching on the feeder power circuit. Turn on the low side safety circuit control.
- Use a volt meter to test for proper voltage on the step down side of the transformer. It should be the same that is listed on the specs tag provided by the manufacturer.
- Remove all wires from the transformer terminals using the screwdriver. Identify the wires if they are not already identified. Use a clear tape and pen. Write the terminal that the wires are attached to and place the identified tape on the wire’s end.
- Turn the volt ohmmeter to the “Ohms” position and place the red lead into the connector identified as “Ohms.” Touch the black lead to the metal frame of the transformer.
- Touch the red lead to the transformer’s terminals in the following order: H1, H2, X1 and then X2. The meter should read infinite ohms or wide open. Infinite ohms on a digital meter will be identified as a blank screen or a wide open will have the word “Open” displayed. If the meter registers any form of resistance, there is an internal problem with the windings. The copper coils may be shorted to the metal frame of the transformer. The transformer will have to be replaced.
- Check the continuity of each separate coil using the ohmmeter. Touch the black lead to H1 and the red lead to H2. The meter should give a resistance reading. Generally, it should read in the range of 3 to 100 ohms, depending on the style and type of transformer. Perform the same test to the X1 and X2 terminals. You should receive the same results. If the meter reads infinite ohms or a wide open when checking between the terminals of the same coil, the wires are broken. Replace the transformer.
- Use the ohmmeter to conduct the transformers isolation circuit. Touch the red lead to H1 and the black lead to X1. The meter should read infinite ohms or a wide-open circuit. Perform the same test, but to H2 and X2 respectively. If any resistance at all is read on the meter other than a wide-open circuit, the isolation of the transformer has been compromised and must be replaced.
The problem with surge protectors
Usually, having 220 volts between neutral and ground in an appliance designed for 110 volts is not a problem the insulation has a large safety margin. However, if you connect a surge protector (or a piece of equipment with built-in surge protection) on the 110 volt side, bad things can happen.Surge protectors contain varistors components which protect against surges by effectively shorting out any excess voltage. Some surge protectors contain only a single varistor connected between hot and neutral; those will work fine with a step-down transformer. However, many surge protectors have additional varistors connected between hot and ground and between neutral and ground. When a surge protector of this kind is used with a step-down tranformer, one of these varistors can be subjected to the full 220 volts. This is enough to trigger the varistor into its conducting mode, effectively treating the 220 volts as a surge.
Varistors are designed to absorbed short-lived surges, but they can't handle a persistent overvoltage. A varistor subjected to twice its rated voltage will quickly be destroyed, usually causing a short circuit and a blown fuse.
step down transformer
working
The function of any transformer is to change one AC voltage
value to another AC voltage value. A step down transformer will transform a
higher AC voltage to a lower AC voltage. A step up transformer will transform a
lower AC voltage to a higher AC voltage. The transmission of electrical power
uses both of these types of transformers. From the generation station the
voltage is stepped up to a very high transmission voltage and at the end of the
transmission line it is stepped down to a voltage that consumers can utilize.
step down transformer
calculation
EMF Equation of transformer
can be established in a very easy way. Actually in electrical power transformer
one alternating electrical source is applied to the primary winding and due to
this, magnetizing current flowing through the primary winding which produces
alternating flux in the core of transformer. This flux links with both primary
and secondary windings. As this flux is alternating in nature, there must be a
rate of change of flux. According to Faraday’s law of electromagnetic induction
if any coil or conductor links with any changing flux, there must be an induced
emf in it. As the current source to
primary is sinusoidal, the flux induced by it will be also sinusoidal. Hence,
the function of flux may be considered as a sine function. Mathematically,
derivative of that function will give a function for rate of change of flux
linkage with respect to time. This later function will be a cosine function
since d(sinθ)/dt = cosθ. So, if we derive the expression for rms value of this
cosine wave and multiply it with number of turns of the winding, we will easily
get the expression for rms value of induced emf of that winding. In this way,
we can easily derive the emf equation of transformer
Instructions
1.Obtain
the windings ratio of the transformer. This number is often printed on the
transformer case, and will take the form of "primary:secondary." For
example, a "2:1" transformer will have twice as many windings in the
primary as it has in the secondary.
2.Divide
the secondary number by the primary number. For a 2:1 transformer, this number
is 1/2, or 0.5.
3.Multiply
the input voltage you intend to apply to the transformer by the number you
calculated in the previous step. For example, if you apply 12 volts to a 2:1
transformer's primary, you will obtain 6 volts across the transformer's
secondary.
Define Kirchhoff's circuit laws:
Kirchhoff's circuit laws are two equalities that deal with the current and potential difference (commonly known as voltage) in the lumped element model of electrical circuits. They were first described in 1845 by German physicist Gustav Kirchhoff. This generalized the work of Georg Ohm and preceded the work of Maxwell. Widely used in electrical engineering, they are also called Kirchhoff's rules.
Kirchhoff's current law (KCL):
or equivalently
- The algebraic sum of currents in a network of conductors meeting at a point is zero.
Kirchhoff's voltage law (KVL)
- The directed sum of the electrical potential differences (voltage) around any closed network is zero, or:
- More simply, the sum of the emfs in any closed loop is equivalent to the sum of the potential drops in that loop, or:
- The algebraic sum of the products of the resistances of the conductors and the currents in them in a closed loop is equal to the total emf available in that loop.
- More simply, the sum of the emfs in any closed loop is equivalent to the sum of the potential drops in that loop, or:
