Tuesday, January 17, 2012

Balanced Three phase AC circuit Delta connected

A balanced three phase AC circuit systems is energized by three equal alternating emf's of the same frequency but 120 degree apart. The phase impedance are equal. Also the currents are equal and 120 degree apart.
Three AC emf's differing in time phase by 120 degree
Three AC emf's differing in time phase by 120 degree
This type of connection is reffered to as 3 phase, 3 wire system. In this connection , the dissimilar ends of the 3 phase windings of a 3 phase ac generator are joined together,  for example the starting ends of one phase is joined to finishing end of the other phase so on. In other words the three winding's are joined in series to form a closed mesh. three leads are taken out from the juntions to serve as the generator terminals.
Delta mesh connected system
Delta connected System
Relationships: VØ = VL       :  IØ = IL/(3)   
        VØ  - phase voltage
        IØ  - phase current
       VL -  line voltage
       IL -  line voltage

The three phase voltages of this circuit always sum to zero  Va + Vb + Vc =0

As seen from the diaram, there is only one phase winding completely included between any pair of terminals. Hence, in delta connection, the voltage between any pair of lines is equal of the phase voltage of the phase winding connected between the two lines considered.

Monday, January 16, 2012

Electronics :Traffic light Circuit

This is a two way continuous traffic light circuit which uses  LED, diodes and IC's . 
Usually most traffic light in the world is PLC controlled but this circuit is  simple  and easy to build . 

 In the image below is the schematic diagram of the project . I used Yenka Free Software to simulate and see if its properly working . You can download it free on Yenka website.

two way 555 traffic light circuit

The  clock pulses from the 555 astable circuit is sent into the 4017 decade counter . Each output becomes high in turn as the clock pulses are received. Appropriate outputs are combined with diodes to supply the amber and green LEDs. 
simple 2-waytraffic light circuit
components :
  • resistors: ,50k ohm, 10k ohm, two-100k ohm
  • capacitors: 10µF 16V radial
  • diodes:  16 pieces of 1N4148 
  • LEDs: 2 sets of ( red, amber or yellow, green)
  • IC:555 timer ,  4017 counter
  •  on/off switch
You can adjust the timing of light-shifting by adjusting the  value of the resistor in the astable circuit .