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SECTION
8-
PLASMA ARC CUTTING
(PAC)
INSTALLATION
GUIDELINES
8-1.
GENERAL
The
following
information is necessary
to
make
a
proper
installation
of the
high-frequency plasma
arc
cutting
(PAC) equipment
described in this instruction manual.
The
importance
of
a
correct installation cannot be
over
emphasized
since
case
histories of interference due
to
high-frequency plasma
arc
cutting (PAC) equipment
have shown
that,
in most
cases,
an
inadequate
installa
tion
was
at fault. In the event that
interference with
authorized FCC services
occurs, the
user
is
required
to
take suitable
steps
to
clear the situation.
In
such
cases,
these instructions could
serve as a
guide
in
minimizing
interference that
might
be caused
by
the
high-frequency
plasma
arc
cutting (PAC) equipment.
The
Factory
Serv
ice
Department personnel
will assist the
user
by supply
ing
technical information.
Many
processes and
applications
of processes
require
open-circuit voltages
sufficient
to
jump
from the elec
trode
to
the work without
making
direct
contact.
The
maximum
open-circuit
voltage
(OCV)
of
a
plasma
arc
cutting (FAG)
power
source
is
not
sufficient for this.
It
takes several thousand volts
to
cause
an
electrical
spark
to
jump
the
gap between the torch electrode and
the
pilot, creating
an
initial
path
of
ionization,
that the
arc
current
can
follow without the hazards that would be pre
sent at low
power
frequencies.
In order to
provide
these
higher voltages,
it is
common
practice
to
superimpose
a
high open-circuit voltage
on
the
output
of
a
plasma
arc
cutting (PAC)
power
source
by using high-frequency techniques.
The
resulting high-
frequency voltage
can
be
a source
of
interference
and
will be discussed in this section.
8-2.
DEFINITIONS
A.
High-Frequency
AssIsted Plasma Arc
Cutting
(PAC)
Power Sources
In the
plasma
arc
cutting
(PAC)
process,
high frequency
may
be used for
initiating
the
cutting
arc
and,
in the
case
of
an arc
outage,
reinitiating
the
cutting
arc.
The
energyfromthe high-frequency
source
mustflowto
the torch electrode via
a
good quality,
low
impedance,
and well insulated
connecting
cable.
B.
Cutting
CIrcuIt
The circuit consists of all attachments connected
to the
electrode,
pilot
arc,
and work terminals.
C.
Output
Terminals
Output
terminals
are
the terminals which
provide
the
cutting
current
and
pilot
arc.
D.
Electrode Terminal
The electrode terminal is the terminal
to
which the elec
trode lead
or
cutting
torch is connected.
E.
Pilot Arc Terminal
The
pilot
arc
terminal is
the terminal
to
which the
pilot
lead is connected.
F.
Work Terminal
The work terminal is the terminal
to which the
cutting
workpiece
is connected.
G.
Cutting
Torch
A
device used
in the
plasma
arc
cutting (PAC)
process
to control the
position
of
the
electrode,
to
transfer
cur
rent to
the
arc,
and
to
direct
the flow of
plasma
gas.
H.
Cutting
Zone
The
cutting
zone
is the space within 50 ft.
(15 m)
in all
directions
from the
midpoint
between the
power
source
and the
cutting
arc
(see
Figure
8-6).
I.
Bonding
Bonding
refers
to
connecting
metallic
objects together
to
cause
the
objects
to
be
at
the
same
potential regard
less of any
current
flow between them
(see
Figure
8-3
and
Figure 8-4).
J.
Grounding (Earthing)
Depending
on
the
practices
within
jurisdictions,
one
of
these terms is
commonly
used
to
indicate the
connec
tion,
or
bonding,
of
parts
of the
apparatus
to
the
earth .The
terms
may be used
interchangeabiy.
K.
Receiver
A receiver is
any
device
normally
used for
receiving
electromagnetic
energy
and
converting
it
to
useful
com
munications purposes.
L.
Conduction
Conduction
is the transmission of
high-frequency
en
ergy
via
an
electrical conductor
or
conducting
medium.
M.
HIgh Frequency
High frequency
is radio
frequency
energy, either
con
tinuous
or
pulsed,
used
to start
a
plasma
arc.
N.
High-Frequency
Assisted Plasma Arc
Cutting
(PAC)
High-frequency
assisted
plasma
arc
culling (PAC)
re
fers
to
any of the
plasma
arc
cutting (PAC)
processes
requiring high frequency.
0.
Interference
Interference is the
unwanted and
problematic reception
of
high-frequency
energy.
P.
Radiation
Radiation is the transmission of
high-frequency
energy
through
space.
OM-296
Page
20
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