Page 188 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

AC DC
It is generated in the ranges of 6,600 V, 11000 V It is generated up to 6,600 V only
and 33,000 V.
Voltage can be stepped up or stepped down by using It is not possible
transformer
Transmission cost is less Cost High
Less maintenance High maintenance
Power up to 5,00,000 kw can be generated in a single Power up to 10,000 kw can be generated in a
alternator. single generator
AC generator can run at high speeds. So, speed control It can’t run at high speeds. Speed control is
is not easy. easy.
Slip rings and brushes are used to collect the current. Commutator and brushes are used to collect the
current

Advantages of A.C
i In transmission there is saving in copper wire.
ii Since there is no spark in A.C. machine there is no interference in Radio sound.
iii This can be produced to maximum voltage i.e. 33000 volts.
iv Voltage can be dropped or raised with the help of transformers.

v Its mechanism is simple and cheap.
vi Output is more due to availability of more than one phase.
Disadvantages of A.C
i A single phase motor is not self-starter.

ii Due to thin wire in A.C., the voltage drop is more.
iii It cannot be used for electroplating and in charging secondary cells.
iv The speed of motors run by it is difficult to change.
v There is danger to security due to high voltage.
Electrical terms and units
Quantity of electricity

The strength of the current in any conductor is equal to the quantity of electrical charge that flows across any
section of it in one second. If ‘Q’ is the charge and ‘t’ is the time taken

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CITS : WCS - Electrical - Exercise 18