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Q.

Indian Railways have started running trains on AC current. But why it was chosen to run them on DC current earlier ?

Tags: indian railways, ac, railways
Asked by Manoj, 16 Dec '09 03:37 pm
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Answers (5)

1.

The AC (alternating current) Drive, also known as Variable Frequency Drive, has been the standard in industry for many years. While it has been used in locomotives for over two decades (especially in Europe), it has only been recently that the price of the drives has allowed them to be used in most of the new diesel-electric locomotives in the United States.

AC traction for locomotives is a major improvement over the old DC systems. The primary advantages of AC traction are adhesion levels up to 100% greater than DC and much higher reliability and reduced maintenance requirements of AC traction motors.

The tractive effort of a locomotive (whether AC or DC) is defined by the equations:

Tractive effort = Weight on drivers x Adhesion
Adhesion = Coefficient of friction x Locomotive adhesion variable

The friction coefficient between wheel and rail is usually in the range of .40 to .45 for relatively clean, dry rail in reasonable condition and is essentially the same for a ...more
Answered by Jack Johnson, 16 Dec '09 04:39 pm

 
  
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2.

DC Motors were invented earlier. However with AC drive you virtually have contact less drive motors which are maintenance free and ensures longer life and reliability. Secondly, AC power source is easily available.
Answered by Lucky, 16 Dec '09 03:51 pm

 
  
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3.

Technology upgradation and economic criteria
Answered by saranathan Narasimhan, 16 Dec '09 03:39 pm

 
  
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4.

The railways need motors where speeds can be varied "stepless-ly". This was possible only in DC motors upto 2 decades ago. Therefore DC systems were common in railways.
With technological advancement AC Varaiable Speed drives became available - but for the railways a decision on that was a major once as costs would run into hundreds of crores.
But Indian Railways should definitely change over to AC systems at the earliest !!
Answered by Sunil Dodeja, 01 Mar '12 06:55 pm

 
  
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5.

For longer life and easy supply.
Answered by ashis, 16 Dec '09 04:03 pm

 
  
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