SCR COMMUTATION PART 1
Download as PPTX, PDF2 likes1,780 views
This document discusses commutation of SCRs (silicon controlled rectifiers). Commutation is the process of turning off an SCR. There are natural and forced commutation methods. Natural commutation occurs automatically in AC when the load current drops below the holding current or the SCR becomes reverse biased. Forced commutation is required in DC applications using an extra circuit to forcefully turn off the SCR. Commutation can occur through reducing the current below the holding current level or applying a reverse voltage. There are different classes of commutation depending on the method used.
1 of 12
Download to read offline
SCR COMMUTATION PART 1
- 3. COMMUTATION means what? •It is a process to TURN OFF SCR •No more current should pass through it •It should act as an OPEN switch
- 4. • Forward Voltage Triggering • Gate Triggering • dv/dt Triggering • Temperature or Thermal Triggering • Light Triggering Methods to TURN ON an SCR
- 5. Conditions to keep SCR in ON position •Anode to cathode current should remain more than Holding current •SCR must remain in FOREWARD bias means Va>Vk
- 6. Conditions to turn Off SCR •If foreward Current becomes less than Holding current, means : IAK < I H •Sufficient reverse voltage must be applied across the SCR for sufficient time as to regain its forward blocking state
- 8. Natural Commutation • Its NOT possible in DC,Occurs naturally in AC • It turns OFF automatically • Either load current becomes lesser than holding current value • or SCR reverse biases
- 9. FORCED COMMUTATION • In DC, SCR do NOT turn OFF naturally • So extra circuit is required to forcefully turn OFF it • Hence, it is called Forced Commutation • Most widely used in all applications
- 10. Commutation may also be classifies as Voltage Commutation If Reverse voltage is applied across SCR Current Commutation If thyristor current is forced to reduce below holding current
- 11. Types of Commutation •Class A •Class B •Class C •Class D •Class E •Class F
- 12. Remember To turn Thyristor OFF: Either thyristor current should be reduced to lesser than holding current OR Voltage across it must be reversed