Lincoln Electric V250-S Precharge and Protection, Figure E.2 Protection and PRE-CHARGE Circuits

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E-3E-3

THEORY OF OPERATION

FIGURE E.2 PROTECTION AND PRE-CHARGE CIRCUITS

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INPUT

INPUTRECTIFIER LINE

SWITCH

"A"

L

E

A

D

FAN

MOTORS

R

E

C

O

N

N

E

C

T

S

W

I

T

C

H

18VAC

POWER BOARD		MAIN
		TRANSFORMER
CR1
RELAY
IGBT
			POSITIVE
CAPACITOR			OUTPUT
			TERMINAL
IGBT
IGBT		SHUNT
	CURRENT
	TRANSFORMER		NEGATIVE
CAPACITOR		F	OUTPUT
			TERMINAL
		E	F
IGBT		E	E
		D	E
		B	D
		A	B
		C	A
O		K	C
V
E		THERMOSTATS	K
R
V
O
L
T	IGBT GATE SIGNALS		THERMAL
A
G
E	PROTECTION SIGNAL	CONTROL BOARD	LIGHT
CR1 RELAY DRIVE SIGNAL

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AUXILIARY

TRANSFORMER

REMOTE

RECEPTACLE

OUTPUT STRIKE ARC			LOCAL/
		MODE
			REMOTE
CONTROL CONTROL FORCE	SWITCH
CONTROL			SWITCH

PRECHARGE AND PROTECTION

The input voltage is rectified and the DC voltage is applied, through the reconnect switch, to the power board. The power board contains precharging circuit- ry for the safe charging of the input filter capacitors. Once the capacitors are precharged and balanced the control board activates the CR1 input relay which con- nects full input power to the filter capacitors. When the filter capacitors are fully charged they act as power supplies for the IGBT switching circuit. The Insulated Gate Bipolar Transistors supply the main transformer primary windings with DC current flow. See IGBT Operation Discussion and diagrams in this section.

The power board also monitors the filter capacitors for voltage balance and/or overvoltage and, if either should occur, sends the appropriate signal to the con- trol board to deactivate the CR1 input relay. The machine output will also be disabled.

NOTE: Unshaded areas of block logic diagrams are the subject of discussion.

INVERTEC V250-S