transformer-12 CBSE
Transformer is essentially an ac device that transforms the electric energy from low voltage at high current to high voltage at low current and vice-versa.
Symbolic Representation of Transformer-12 CBSE
Principle of Transformer-12 CBSE
The transformer works on the principle of Mutual Induction which states that when the magnetic flux changes in one of the two inductively coupled coils due to the changing current in it, then the e.m.f. is induced in the other coil.
Construction of Transformer-12 CBSE
The transformer-12 CBSE consists of two coils P and S wound on a soft iron core of which one is called primary P while the other is called secondary S. The source of alternating e.m.f. connect to the primary coil P while the output is obtained across the load resistance connected to the secondary coil S.,
In order to avoid magnetic flux loss, the core of the transformer is made of soft iron as it has a higher value of magnetic permeability and the loss of electric energy during the process of its transformation from the primary coil to the secondary coil due to the eddy currents, is minimized by getting the soft iron core as laminated as shown in Fig- 1.
Types of Transformer-12 CBSE
- Step-up Transformer-12 CBSE
A Step-up Transformer-12 CBSE is one, which transforms the electric energy from the low voltage at high currents to high voltage at low currents. In this type of transformer, the number of turns in the secondary coil (NS) is more than the number of turns in the primary coil (NP) such that (NS) > (NP). The primary coil of the step-up transformer is made of thick insulated copper wire while the secondary coil is made of thin insulated copper wire.
- Step-down Transformer
A Step-down Transformer is one, which transforms the electric energy from high voltage at low currents to low voltage at high currents.
In this type of transformer, the number of turns in the secondary coil (NS) is less than the number of turns in the primary coil (NP) such that (NS) < (NP). The primary coil of the step-up transformer is made of thin insulated copper wire while the secondary coil is made of thick insulated copper wire.
- Coupling Transformer/isolator Transformer/1: 1 Transformer
In this type of transformer-12 CBSE, the number of turns in the secondary coil (NS) is equal to the number of turns in the primary coil (NP) such that (NS) = (NP). The primary coil and secondary coil, both, of this type of transformer, are made of thin insulated copper wire.
The input voltage at the primary coil remains equal to the output voltage at the secondary coil. It is used to connect the two electric units as an isolator and prevents the second stage unit from any type of electric damage on account of the electric fault in the first unit.
Working and Theory of Transformer-12 CBSE
The voltage continuously changes at the input of the transformer-12 CBSE (Primary Coil) with time when a source of an alternating e.m.f. is connected to it as a result the magnetic flux through the primary coil also changes with time.
This time-varying magnetic flux also links up the secondary coil through the laminated soft iron core of the transformer and thus, according to the laws of electromagnetic induction, the alternating emf is produced across the secondary coil. Almost, the entire magnetic flux, without any leakage, is coupled from the primary coil to the secondary coil through the soft iron core due to its higher value of magnetic permeability.
When the magnetic Lines of induction, remain confined to the soft iron core, then the entire magnetic lines of induction across the primary coil link up with each turn of the secondary coil. Therefore, the magnetic flux linked with the primary coil itself and the secondary coil is proportional to their number of turns. Thus,
From equation 05, it is clear that in a step-up transfer (ES /EP) > 1 ⇒ ES > EP ⇒ IP > IS . Thus, a step-up transformer increases the voltage with a proportional decrease in the current keeping energy constant and conserved. Similar is the case in step-down transformer. Therefore, the working of a transformer, is strictly in accordance with conservation law of energy and it merely transforms the voltages and currents keeping electric energy conserved.
Why does A Transformer-12 CBSE Needs For Laminated Core ?
When an alternating emf as input is applied across the primary coil of the transformer, the induced EMF is produced in the secondary coil due to a changing Magnetic flux linking it. In fact, magnetic flux changes through the soft iron core also and it produces induced emf in the soft iron core.
The induced emf developed in the soft iron core produces current in itself in the form of closed loops called eddy currents. Since the resistance of the soft iron core is quite small, the magnitude of the eddy currents is quite large. As a result, a large amount of heat is produced, and it may damage the insulation of the copper windings.
In order to annul the eddy currents so produced in the core of the transformer, and to minimize the energy loss, a laminated iron code is used in the transformer. It is prepared by joining similar iron strips together after coating them with varnish. As such, the induced e.m.f. produced in the core will cause eddy currents in each iron strip separately. Since an iron strip is quite thin and possesses very large resistance, the magnitude of eddy currents produced is quite small, and hence only a small amount of heat is produced
Energy Losses in A Transformer-12 CBSE
An ideal transformer is one which has efficiency 1 or (100 % efficiency). In an ideal transformer, the entire energy available at primary coil is transferred to the secondary coil without any loss. But in actual and practical transformers, some energy loss is accompanied during the process of transformation of electric energy from input to output of the transformer. The followings are the losses of energy in the transformers
- Magnetic Losses
- The magnetic coupling between the primary coil and secondary coil of a transformer is not perfect due to one reason or the other and so the entire magnetic flux produced in the primary coil never links up with the secondary coil.
- Hysteresis Loss
- When the transformer works, its soft iron core undergoes magnetization and demagnetization over and again due to the alternating current that flows through both of the coils. This causes some energy loss due to hysteresis during each cycle of alternating current, which, in magnitude is equal to the area of the hysteresis loop. This loss of energy due to hysteresis, is minimized by selecting the material of the core which have narrow hysteresis loop as smaller the area of hysteresis loop smaller will be the energy loss and vice-versa.
- Copper Loss
- The primary and the secondary coils of the transformer are made of copper wire, having resistivity 1.7 x 10 -8 ohm-meter at 0 degree centigrade. Thus, due to some resistance of the resistance of the windings of both the coils of the transformer causes energy loss in the form of heat which is inevitable.
- Iron Loss
- During the working of the transformer, the time varying magnetic flux from the primary coil links up with the secondary coil through the soft iron core, causing an eddy to set up within the core. This leads to the wastage of energy in the form of heat called iron loss. This loss is minimized by using the soft iron core as laminated.
- Humming Losses
- During the working of the transformer, the humming sound is produced due to the vibrations of core, a result of the alternating current flowing through the coils. Therefore, some electric energy goes waste, may be small
Efficiency of transformer-12 CBSE
The efficiency of a transformer means how much portion of the energy available at its input (primary coil) is transformed at the output (secondary coil). It is defined as the ratio of the power output to the power input, thus,
Efficiency = Output Power/Input Power
Applications of transformer-12 CBSE
- A step-down transformer is successfully used to produce large currents for welding purposes in industrial sector.
- In industrial sector, a step-down transformer is successfully used in induction furnace for melting the metals.
- The use of the transformers in voltage regulators and stabilized power supplies is now s days is very significant.
- The step-up transformers are widely used now a days to produce X-rays.
- The transformers of different types have important roles in electronics and electricity, like in radios, televisions, telephones, loud speakers and other devices.
- Use of transformer for long distance Transmission of Electric Energy
- During the transmission of electric energy over a long distant place, a considerable amount of it (I 2 R) is dissipated as heat due to the resistance R and I is the current passing through the line wire. In addition, a sufficient fall of potential IR occurs along the line wires. Hence, the effective voltage at a distant place will be much smaller than the actual value of the voltage supplied by the transmitting station.
- In addition to it, a few more difficulties are encountered, if the transmission of electric energy is done at the low voltage, 220 volts. However, by the transmission of electric energy at high voltage say (Say, 22,000 Volt.), the difficulties encountered in the power transmission can be minimized. In order to understand the role of the two factors which are important in power transmission. Consider that 1 1000 Watt of electric power is transmitted. first, at 220V and then at 22,000 volts.
- Loss of Electric Energy when transmitted at 200 V
- In this case, an electric current of I =50A (I =V/A = 11000 watt/220 V = 50A) passes through the line wires of resistance R, then the electric energy dissipated per second in the line wires will be (I 2 R) = (50) 2 R =2500 R joules/second.
- On the other hand, an electric current of 0.5 A passes through the line wires when transmitted at 22000 V (11000/22000= 0.5) amounting to the rate of dissipation of energy equal to 0.25 J/sec which is very -very small as compared to the case when transmitted at low voltages. Therefore, it is concluded that the dissipation of energy in long distance transmission can be minimized if it is done at higher voltages.
Try your knowledge [quiz master] for transformer-12 CBSE
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transformer-12 CBSE-frequently asked numerical problems
- An AC voltage of 400 V is applied to the primary of a transformer and a voltage of 2400 V is obtained from the secondary coil. Calculate the ratio of the currents through the primary and secondary coils.
- In an ideal transformer, the number of turns in primary and secondary coils are 2000, and 200 respectively. If the maximum voltage in the primary is 120 volts, what is the maximum voltage in the secondary?
- The output voltage of an ideal transformer, connected to a 240. V ac means is 24 V. When this transformer-12 CBSE is used to light a bulb with a rating of 24 V – 24 watts, calculate the current in the primary coil of the circuit.
- A step-up transformer is used on a 240V line to provide a potential difference of 2400 volts at 2 A current. If primary coil has 1000 turns, find the number of turns in the secondary and current in the primary coil.
- How much current is drawn by the primary coil of a transformer, which steps down 220 Volts to 44 volts to operate a device with an impedance of 220 ohms
transformer-12 CBSE-Solutions to frequently asked numerical problems
summary and key points of transformer-12 CBSE
- A transformer-12 CBSE is essentially an ac device and cannot work on dc direct current) supply.
- In a step-up transformer, the increase in voltage is on the cost of the current which decreases with increase in voltage.
- The transformation ratio for a step-up transformer is greater than one (k > 1).
- The transformation ratio for a step-down transformer-12 CBSE is less than one (k < 1).
- The transformation ratio for a coupling transformer is greater equal to one (k = 1).
- The core of the transformer is made of soft iron core because its magnetic permeability is quite large and area of the hysteresis curve is smaller causing a very small amount of energy dissipation.
- The transmission of electric energy (A.C) over a long distance is done at higher voltages in order to reduce the line losses in the form of heat energy.