(a)  Draw the diagram of a device which is used to decrease high ac voltage into a low ac voltage and state its working principle. Write four sources of energy loss in this device.

(b)  A small town with a demand of  1200\; kW of electric power at  220\; V is situated 20\; km away from an electric plant generating power at 440\; V. The resistance of the two wire line carrying power is 0.5\; \Omega\; per\; km. The town gets the power from the line through a 4000-220\; V.  step- down transformer at a sub-station in the town. Estimate the line power loss in the form of heat.

 
 
 
 
 

Answers (1)

(a)    A device which is used to decrease high ac voltage is known as a step- down transformer,

It works on the principle of mutual induction, It states that, if the current is changing through the primary coil, then there is a change in magnetic flux in the secondary coil. This change in flux induces an emf in the secondary coil.

   

The four sources of energy loss in the device are : 

Flux leakage, eddy currents, Resistance of the windings and the hysteresis loss.

(b) Given,

       The  town has a power demand of 12000\; kw at 220 \; V 

        Resistance per unit length =0.5\; \Omega /km

        Length of each wire =20 \; km

        Total resistance, r=2\times 0.5\times 20\; \Omega =20\; \Omega

The transformers step down from 4000 V (V_1)  to  220\; V(V_{2}) .

If there is no power loss in the transformers, then we can calculate the RMS current in the lines by :

I=\frac{P}{V_{1}}=\frac{1200\times 10^{3}w}{4000v}=300A

The power loss in the lines is 

    P_{loss}=I^{2}r

              =(300\; A)^{2}\times 20\; \Omega

              =1800000\; w

                =1800\; kw

Most Viewed Questions

Preparation Products

Knockout NEET May 2023 (Easy Installments)

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Mentorship from our Experts, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 5499/-
Buy Now
Knockout JEE Main April 2021 (One Month)

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Mentorship from our Experts, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 14000/- ₹ 4999/-
Buy Now
Knockout NEET Aug 2021 (One Month)

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Mentorship from our Experts, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 14000/- ₹ 4999/-
Buy Now
Knockout JEE Main May 2021

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Mentorship from our Experts, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 22999/- ₹ 9999/-
Buy Now
Knockout NEET Aug 2021

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Mentorship from our Experts, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 22999/- ₹ 9999/-
Buy Now
Boost your Preparation for JEE Main with our Foundation Course
 
Exams
Articles
Questions