WTC MedWeld 3005, Operator'S Manual

Page: 32 / 206

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(indicating Weld Mode is selected and the control stop is not
selected) before the weld processor will pull in the isolation
contactor to provide weld current.
When the isolation contactor is closed, 480/600 VAC is supplied
to the SCR through 2L1. The 2L2 connector from the isolation
contactor provides the interface with the weld transformer.
In a three-phase configuration, power is applied to the SCRs
through 2L1, 2L2 and 2L3. These connections also provide the
interface with a distribution block at the bottom of the enclosure
for the weld transformer.
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Refer to the drawing packet provided with your control for more
information.
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Supply voltage (380, 480 or 600 VAC) from the circuit breaker
goes to the control transformer. It reduces the supply voltage to
the 120 VAC required by the internally-powered safety I/O,
including the isolation contactor. (Refer to the drawing package
provided with your weld control for more information.)
When the control is internally powered, the control transformer
powers the isolation contactor coil, any AC I/O, the circuit
breaker shunt trip and the programmable controller.
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The current coil is the doughnut-shaped device located near the
SCR contactors in the control enclosure. The control uses this
device to measure the welder’s primary current.
Welding current flows through the center of the coil, inducing a
current in the secondary of the coil at the ratio of 200:1. (I.e., for
every 1,000 A. of primary current, 5 A. flows in the secondary.)
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The firing card performs the following tasks:
• Provides sense signals to the processor to provide voltage,
current and power factor reading, as well as properly
regulating the SCRs
• Provides gate signals to turn on the SCRs
• Inputs and outputs all of the control’s current monitoring
and
• Performs high-voltage sensing.