Electrical Energy & Transformers

• Electrical energy is the most common form of energy used in homes for lighting, heating, and operating electrical appliances, hospitals, and factories.

Induced Current

• Induced current in a conductor arises from changing magnetic field lines across the conductor per unit time, or from relative motion between the conductor and the magnetic field, accompanied by a change in the intersecting magnetic flux.

Electrical Transformer

• Electrical transformers can either increase or decrease alternating voltage to achieve desired electrical output.
• Voltage can be raised as in a TV or decreased as in radios and recorders with electrical transformers
• Electrical transformers are used to change the output voltage from an alternating source.

Induction Activity

• An induction activity involves a hollow cylindrical coil (insulated wire with multiple turns), a ring-shaped coil, suitable voltage light bulb, alternating voltage source, switch, and a long soft iron rod.
• Inserting a long, soft iron rod into a cylindrical coil, connecting an alternating voltage source and switch to the cylindrical coil (primary circuit), and connecting a light bulb to the ring-shaped coil (secondary coil) enables induction, producing light in the lamp connected to the secondary coil.
• An induced current is generated in the secondary coil due to changing magnetic field lines per unit time in the primary coil, caused by alternating current flow.

Electrical Transformer Components

• Operates by either raising or lowering the alternating voltage, changing the magnitude of the alternating voltage, and either decreasing or increasing the current.
• Electrical transformers consist of two insulated copper wire coils wound around a closed soft iron core.
• When alternating current flows in the primary coil, it generates a varying magnetic field within the iron core, which in turn affects the secondary coil.
• Electrical transformers only work with alternating current because the magnetic field within the iron core needs to change to induce current in the secondary coil.

Transformer Primary and Secondary Coils

• The primary coil is connected to the alternating voltage source. The number of turns in this coil is denoted as N1
• The secondary coil is connected to the load. The number of turns in this coil is denoted as N2.
• Electric power (P) equals voltage (V) times current (I). It is measured in watts (W).

Electrical Power Formula

• Input power to the primary coil (P1) equals the primary coil current (I1) times the primary coil voltage (V1).
• Output power from the secondary coil (P2) equals the secondary coil current (I2) times the secondary coil voltage (V2).
• The input power to the primary coil equals the output power from the secondary coil, assuming a lossless (ideal) transformer.
• This means the loss of energy in the wires of the two coils and inside the iron core of the transformer is ignored
• Input power to primary coil = output power from secondary coil

Ideal Transformer Formula

• P1 = P2
• I1 x V1 = I2 x V2

Real Transformers

• Real transformers experience some power loss during operation, leading to output power being less than input power.
• Transformer efficiency (η) is calculated as the ratio of output power from the secondary coil (P2) to input power to the primary coil (P1), multiplied by 100%.
• Efficiency equation: efficiency equals the power output from its secondary coil over the input power into the primary coil, times 100%
• Voltage ratio : (Secondary voltage/ Primary voltage) = (Number of turns in secondary /Number of turns in primary)
• N2/ N1 is the "transformation ratio" or turns ratio in the transformer.

Power Transmission

• High voltage and low current is used to transmit electrical energy over long distances to reduce losses caused by the high resistance of conducting wires.
• Transformers consists of Step-up and Step-down transformers

Step-Down Transformer

• Step-down transformers have fewer turns in the secondary coil (N2) than in the primary coil (N1).
• See figure 4, the output voltage from the secondary coil (V2) is lower than the input voltage in its primary coil (V1).
• Most household electrical transformers are step-down transformers, as are those used in power distribution to cities, electric welding equipment, and mobile phone chargers.

Step-Up Transformer

• Step-up transformers have more turns in the secondary winding (N2) than in the primary winding (N1).
• See figure 6, the output voltage from the secondary coil (V2) is greater than the input voltage in its primary coil (V1).
• Step-up transformers are used in devices to prepare high voltage current for electronic purposes and in power generation plants to send electricity to cities.
• The link between voltage and turn ratio involves secondary voltage over primary voltage equaling the number of turns, secondary coil over primary coil
• (V2/V1) = (N2/N1).

Electrical Losses

• Assuming no power loss in the electrical transformer, it is ideal and therefore the output power equals the input power , P2 = P1
• I2V2 = I1V1, V2/V1 = I1/I2.
• The ratio of secondary turns to primary turns, if greater than one, indicates a step-up transformer and a lowering of amps to result in volts being larger than volts
• The ratio of secondary turns to primary, when less than one, indicates a step-down transformer.
• Step up transformers lowers current, while step down transformers raises current

Power Loss

• Power loss in electrical transformers includes losses in the coil wires, which appear as thermal energy in the primary and secondary wires caused by the ohmic resistance of the wire; to reduce this, use wires made of materials with small resistance such as copper
• Also, eddy current losses occur in the iron of the transformer, appearing as thermal energy in the core due to changing magnetic field lines that induce currents, which is reduced by making cores out of thin sheets of laminated iron.