What are the Applications of Induction Motors?

Applications of Induction Motors:

The squirrel cage induction motors with single or double pole changing windings are available as follows:

CLASS	APPLICATIONS
(1)  Variable torque, power output α N2	Fans, centrifugal pumps.
(2) Constant –torque power output α N.	Conveyors, stokers, reciprocating, Compressors, printing presses.
(3) Inverse torque power output rating constant.	Machine Tools, lathes, boring mills, drill, planers.

The Multi-speed motors are of slip ring type used for hoist, conveyor and elevator.

Read More

The three phase system has only two types of connections viz. star connection and delta connection. Why?

In the three phase system, the three phases should be so connected that we get a system that has equal line voltages displaced 120 degrees electrical from one another and acting simultaneously in the circuit. Only star and delta connections can satisfy these conditions. Any attempt made to connect the three phase in a manner other than these two schemes will result in a system of line voltages which are neither equal nor 120 degree displaced. Such a system will not serve the function as if three phase circuits being connected.
-V. K. Mehta

Read More

What are the criteria for the classification of transmission lines as short, medium and long lines?

Classification of transmission lines (Power):

The network of transmission lines is formed by three phase AC system. This is required for Bulk power transfer from large group of generating stations to main transmission network.

Short power transmission line: 

Short distance power transmission lines has voltage ≤  11000 volts. These lines are required to carry power from main sub-station to local distribution area. Further power supply is distributed through pole mounted sub- station or plinth mounted sub-station.

Medium power transmission line: 

Medium distance power transmission line has voltage range 33-132 kV. For the economic voltages for medium lines an approximate rule is 1 kV/mile or 0.6 kV/km. kV= 5.5 √km x 0.6 + kW/100. These lines supply power directly to big organization or industry, which establishes own sub-station. 

Long power transmission line:

A long distance power transmission line has voltage range 220 kV to 750 kV. These lines are used for transfer of power from sending end to receiving end or for system interconnection for exchange of power between independently controlled networks. For longer transmission lines, higher power transmission voltages are necessary (p α v^2). Higher voltage gives lesser current, lesser I^2R losses, higher power transferability.

Read More

Give a list of the factors involved for selecting a factory drive.

Factors involved in selection of factory drives: 
  - Supply system      :  DC or AC
  - Rating                :  kW, MW
  - Drive                 :  constant speed, Variable speed
  - Special Condition  :  High starting torque, Hazardous location, Traction duty etc.
  - User’s requirement : Duty cycle, noise level, load characteristics etc
off load, load condition      
  -  Enclosures & cooling requirement.
  - Environment condition

  -  Applicable standards

  -  Cost considerations 

Read More

What are the essential differences between H.V. and L.V. switchgears?

H.V. switch gears: 

Circuit breaker: Switching during normal and  abnormal conditions, interrupt the fault currents. 

Isolators: It is disconnecting switch to disconnect the system from line parts under no load condition. 

Earth switch: This is used to discharge the voltage on the lines to earth after disconnecting them. 

Surge arrester: This is used to divert the high voltage surge to earth and maintaining continuity during normal voltage. 

Current Transformer: To step down the current for measurement, protection and control purposes. 

Potential Transformer: To step down the voltage for the purpose of protection, measurement and control. 

L.V. Switchgears: 

MCBs (Miniature Circuit Breakers): Switching OFF during abnormal conditions to interrupt the fault current. 

Fuses: A short length wire having low melting point, connected in series with circuit. In the event of fault, the circuit current rises abruptly and fuse wire melts to interrupt the circuit. 

Switches: these are used to ON /OFF  the power of  a circuit. These are used in power/ control circuits.  The switches are specified as per voltage rating, current rating, number of poles, duty cycle and fault interruption capacity. 

Read More