Lincoln Electric IDEALARC DC-1500 Service Manual page 29

TABLE OF CONTENTS-THEORY OF OPERATION SECTION
E-1
Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-1
General Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-2
Output Rectification, Control & Feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-3
Protection Devices & Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-4
SCR Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-5
T R A N S F O R M E R T E R M I N A L S
3 S C R B R I D G E P A I R S R E L A Y P I L O T R E S I S T O R 6 C R I N T E R - P H A S E M A I N C I R C U I T S T S C R G A T E S F A U L T P R O T E C T I O N 5 C R 2 C R H O L D - I N C O N T A C T O R C F I R I N G B O A R D T I M I N G C O N T A C T O R T R A N S F O R M E R S ( 3 e a ) R E A C T O R R L A T C H I N G E D 1 C P I L O T O 6 C R 1 1 5 V A C R E L A Y T R A N S F O R M E R C O N T R O L B O A R D T R A N S F O R M E R N E N F I R I N G B O A R D C O N T R O L B S W I T C H E F E T E R M I N A L S S H U N T P O S I T I V E N E G A T I V E B O A R D D A K K M O D E A C D B E E F C
C O N T R O L T E R M I N A L S T R I P L O W E R D E V I C E S & 2 / 4 P R O T E C T I O N R E M O T E C O N T R O L U P P E R F A N S C O N T R O L O U T P U T
UPPER
FANS
LOWER
PROTECTION
DEVICES &
CONTROL
CIRCUITS
TRANSFORMER
CONTACTOR
HOLD-IN
2CR
R
E
C
O
N
N
E
C
T
CONTACTOR
FIGURE E.1 BLOCK LOGIC DIAGRAM
TERMINAL STRIP
CONTROL BOARD
115 VAC
FAULT PROTECTION
5CR
FIRING BOARD TIMING
TRANSFORMERS (3 ea)
3 SCR BRIDGE PAIRS
MAIN
TRANSFORMER
IDEALARC® DC-1500
2 / 4
REMOTE CONTROL
TRANSFORMER
FIRING BOARD
SCR
GATES
6CR
PILOT
RELAY
6CR
PILOT
RELAY
D1
LATCHING
RESISTOR
INTER-PHASE
REACTOR
OUTPUT
CONTROL
MODE
CONTROL
SWITCH
BOARD
F
E
E
D
B
A
POSITIVE
C
K TERMINALS
SHUNT
F
E
E
D
B
A
C
K
NEGATIVE
TERMINALS
E-1