Lincoln Electric SVM146-A service manual Figure E.4 Main Transformer

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E-4 E-4

THEORY OF OPERATION

FIGURE E.4 – MAIN TRANSFORMER

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INPUT
LINE	INPUT
SWITCH	RECTIFIER
	AIR
	PRESSURE
	SWITCH
	"A"

POWER BOARD

	CR 1&2
	RELAY
				IGBT
		CAPACITOR
R
E				IGBT
C
O
N
N
E
C				IGBT
T							CURRENT
S							TRANSFORMER
W
I		CAPACITOR
T
C
H
				IGBT
P
R
O
T	CR 1		& 2			IGBT
E	RELAY
C					GATE
	DRIVE
T					SIGNALS

MAIN

TRANSFORMER

TRIGGER & SAFETY

		WORK
		NOZZLE
	ELECTRODE
		TORCH
OUTPUT	BOARD	CONNECTOR
		E
		L
		E
		C
		T
		R
		O
		D
		E
	CHOKE	S
	PILOT	O
		L
TRANSISTOR		E
		N
		O
		I
		D
	TRIGGER & SAFETY
		AIR
		SOLENOID
		REMOTE
		INTERFACE
		RECEPTACLE

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L

E

A

D

I			SIGNAL
O
N	SIGNAL
				CONTROL BOARD
	18/36VAC
				R	A	T	S
				E	I	H	A
		THERMOSTATS		A	R	E	F
					L	R	E
				D		M	T
				Y	O	A	Y
					W	L

OUTPUT CONTROL

DISPLAY BOARD

ELECTRODE & TRANSFER

CURRENT FEEDBACK

PILOT ENABLE

ELECTRODE SOLENOID ENABLE

AIR SOLENOID ENABLE

12VAC

24VAC

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115VAC

AUXILIARY

TRANSFORMER FAN MOTOR

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MAIN TRANSFORMER

Each IGBT pair acts as a switch assembly. Each assembly feeds a separate, oppositely wound primary winding of the main transformer. The reverse direction of current flow through the main transformer primaries and the offset timing of the IGBT pairs induce an AC square wave output signal at the secondary of the main transformer.

The DC current flow through each primary winding is redirected or "clamped" back to each respective filter capacitor when the IGBTs are turned off. This is need- ed due to the inductance of the transformer primary winding.

The primary currents also pass through the current transformer, which sends a signal to the control board. If the primary currents are not equal, the control board compensates by adjusting the IGBT gate signals.

The firing of both IGBT pairs occurs during halves of the 50 microsecond intervals, creating a constant 20KHZ output.

The secondary portion of the main transformer is made up of two separate windings. One secondary winding supplies the electrode-to-work voltage. This is the high current winding, which is capable of supplying maximum output current during the cutting process.

The other secondary winding supplies the electrode- to-nozzle voltage for the pilot arc current. The con- ductor in this winding is smaller since the pilot current is considerably less than the cutting current. While one winding is conducting the other winding is at a lim- ited voltage and aids in the arc transfer to and from the workpiece.

PRO-CUT 80