Lincoln Electric IM10063 TCV400 - Manual (Page 18)

B-7 OPERATION B-7
TCV400
MACHINE AND CIRCUIT PROTECTION
(THERMAL PROTECTION LIGHT)
The power source is thermostatically protected with
proximity thermostats against overload or insufficient
cooling. One thermostat is located on the nose of the
center bottom primary coil and a second thermostat is
attached to the lead connecting the secondaries.
Both thermostats are connected in series with the trig-
ger circuit. If the machine is overloaded, the primary
thermostat will open, the output will be zero, and the
thermal protection light will be on; the fan will continue
to run. The secondary thermostat will open either with
an excessive overload or insufficient cooling. The out-
put will be zero and the protection light will be on; the
fan will continue to run. When the thermostats reset
the protection light will be off.
The power source is also protected against overloads
on the SCR bridge assembly through an electronic
protection circuit. This circuit senses an overload on
the power source and limits the output to 550 amps by
phasing back the SCRʼs.
Protection is provided to protect the circuitry from
accidental grounds. If the customer accidentally
“grounds” 75, 76, or 77 to the positive output lead, the
output will be reduced to a low value, thus preventing
any damage to the machine. If the ground occurs
between 75, 76, 77 and the negative output lead, one
of the PC board “self-restoring” fuses will trip, prevent-
ing any machine damage. After the ground is cleared,
the fuses automatically reset within a few seconds.
STARTING THE MACHINE
The POWER toggle switch at the extreme right side of
the control panel in the “ I “ position energizes and
closes the three phase input contactor from a 115 volt
auxiliary transformer. This in turn energizes the main
power transformer.
The machine is de-energized when the POWER
switch is in the “0” position.
The white light next to the POWER switch indicates
when the input contactor is energized.