The large-scale transmission and distribution of electrical energy over long distances is done with the use of transformers. The voltage output of the generator is stepped-up. It is then transmitted over long distances to an area sub-station near the consumers. There the voltage is stepped down. It is further stepped down at distributing sub-stations and utility poles before a power supply of 240 V reaches our homes.

(a) Which of the following statement is true?

(i) Energy is created when a transformer steps up the voltage

(ii) A transformer is designed to convert an AC voltage to DC voltage

(iii) Step–up transformer increases the power for transmission

(iv) Step–down transformer decreases the AC voltage

(b) If the secondary coil has a greater number of turns than the primary,

(i) the voltage is stepped-up (Vs >Vp ) and arrangement is called a step-up transformer

(ii) the voltage is stepped-down (Vs

(iii) the current is stepped-up (Is >Ip ) and arrangement is called a step-up transformer

(iv) the current is stepped-down (Is

(c) We need to step-up the voltage for power transmission, so that

(i) the current is reduced and consequently, the I2R loss is cut down

(ii) the voltage is increased , the power losses are also increased

(iii) the power is increased before transmission is done

(iv) the voltage is decreased so V2/R losses are reduced

(d) A power transmission line feeds input power at 2300 V to a step down transformer with its primary windings having 4000 turns. The number of turns in the secondary in order to get output power at 230 V are

(i) 4

(ii) 40

(iii) 400

(iv) 4000

Asked by Pragya Singh | 1 year ago |  455

##### Solution :-

(a) Right answer is (iv) Step–down transformer decreases the AC voltage

(b) Right answer is (i) the voltage is stepped-up (Vs >Vp ) and arrangement is called a step-up transformer

Explanation:-

$$\dfrac{N_s}{N_p}=\dfrac{E_s}{E_p}$$

if no. of turns in secondary coil are more than no. of turns in primary, then voltage is increased or stepped up in secondary, so called step up transformer.

(c) Right answer is (i) the current is reduced and consequently, the I2R loss is cut down

Explanation:-

current is reduced if voltage is stepped – up so corresponding I2R losses are cut down.

(d) Right answer is (iii) 400

Explanation:-

Ei = 2300V

E= 230V

Np = 4000

Ns = ?

$$\dfrac{E_i}{E_o}=\dfrac{N_p}{N_s}$$

$$\dfrac{2300}{230}=\dfrac{4000}{x}$$

x = 400

N= No of turns in secondary coil

Answered by Pragya Singh | 1 year ago

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