28 July 2017

Three Phase Welding

  • The main disadvantage of single phase welding system is that it will draw high current in small duration of time. 
  • This will result in large voltage drop and it affects supply system of all the other electrical equipments which are connected through it. 
  • The single phase welding system is used whose metal conductivity is higher and lower resistivity. 
  • The three phase welding system is explained below. 
  • The three phase welding system consists of transformer which has one primary winding and three secondary winding. 
  • When the load current passes through secondary winding, the balance current flows through primary winding. 
  • The SCR 1 – SCR 2 – SCR 3 – SCR 4 – SCR 5 – SCR 6 are sequentially on during welding process. The conduction period of each SCR is 120o
  • When SCR 1 is turned on, the phase current flows through path phase R to phase Y. 
  • Similarly the phase current flows though path from phase Y to phase B and phase B to phase R when SCR 2 and SCR 3 are sequentially turned on. 
  • It should be noted that the core magnetize only in one direction. When the SCR 4, SCR 5 and SCR 6 are sequentially turns on, the phase current flows through path phase Y to phase R, phase B to phase Y and phase R to phase B. 
  • The core magnetize in the reverse direction due to reverse direction of current. 
  • As there are two cycles in the primary winding, only one cycle in the secondary winding which results in output frequency is 25 Hz.

three phase welding system

  • If SCR is tuned on in sequence of 1 – 2 – 3 – 1 – 2 – 3 – 4 – 5 – 6 – 4 – 5 – 6, the secondary frequency becomes 25 Hz. 
  • The frequency of secondary current depends upon secondary winding reactance and iron loss
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