Question

A power transmission line feeds input power at 2400 V to a step-down transformer with its primary winding having 4000 turns. What should be the number of turns in the secondary winding in order to get output power at 240 V?
(A) 400
(B) 420
(C) 424
(D) 436

Answer 1

Hint: We know that a transformer is defined as a passive electrical device that transfers electrical energy from one circuit to another through the process of electromagnetic induction. It is most commonly used to increase ('step up') or decrease ('step down') voltage levels between circuits. In all types of transformer construction, the central iron core is constructed from a highly permeable material made from thin silicon steel laminations. These thin laminations are assembled together to provide the required magnetic path with the minimum of magnetic losses. There are three primary types of voltage transformers (VT): electromagnetic, capacitor, and optical. The electromagnetic voltage transformer is a wire-wound transformer. The capacitor voltage transformer uses a capacitance potential divider and is used at higher voltages due to a lower cost than an electromagnetic VT.

Complete step by step answer
We know that the transformation ratio is defined as the ratio of the secondary voltage to the primary voltage. It is denoted by K. The transformation ratio is defined as the ratio of the secondary voltage to primary voltage. And Turns Ratio would be the number turns of the primary winding to the secondary winding. Some transformers have multiple secondary windings as well to create multiple outputs.
As the transformer is basically a linear device, a ratio now exists between the number of turns of the primary coil divided by the number of turns of the secondary coil. This ratio, called the ratio of transformation, more commonly known as a transformer turns ratio. The different types of transformer are Step up and Step-down Transformer, Power Transformer, Distribution Transformer, Instrument transformer comprising current and Potential Transformer, Single phase and Three phase transformer, Auto transformer, etc. A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation is performed by the inverter. The process is known as rectification, since it "straightens" the direction of current.
$\dfrac{\mathrm{E}_{\mathrm{s}}}{\mathrm{E}_{\mathrm{p}}}=\dfrac{\mathrm{N}_{\mathrm{s}}}{\mathrm{N}_{\mathrm{p}}}$
$\mathrm{E}_{\mathrm{p}}=2400$
$\mathrm{N}_{\mathrm{p}}=4000$
$\mathrm{E}_{\mathrm{s}}=240$
$\mathrm{N}_{\mathrm{s}}=?$
After we put the values, we get that:
$\dfrac{240}{2400}=\dfrac{\mathrm{N}_{\mathrm{s}}}{4000}$
$\mathrm{N}_{\mathrm{s}}=400$

So, the correct answer is option A.

Note: It can be said that a transformer that increases the voltage from primary to secondary (more secondary winding turns than primary winding turns) is called a step-up transformer. Conversely, a transformer designed to do just the opposite is called a step-down transformer. If the primary voltage is higher than the secondary, then the transformer is acting as a step-down transformer; if the secondary voltage is higher than the primary, then the transformer is acting as a step-up transformer. A transformer converts alternating current (AC) from one voltage to another voltage. It has no moving parts and works on a magnetic induction principle; it can be designed to "step-up" or "step-down" voltage. So, a step-up transformer increases the voltage and a step-down transformer decreases the voltage.