LMV
Series
Technical
Instructions
Document
No.
LV5
‐
1000
SCC
Inc.
Page
5
Section
5
NOTE:
The
DC
bus
runs
at
voltages
substantially
higher
than
the
incoming
voltage
to
the
drive
(about
35%
higher)
and
typically
employs
large
capacitors.
These
capacitors
remain
charged
for
a
period
of
time
after
the
incoming
power
to
the
drive
is
de
‐
energized,
and
are
a
shock
hazard
until
they
discharge.
See
the
VFD
manufacturer's
recommendations
for
minimum
waiting
time
to
work
on
the
drive
after
the
drive
is
de
‐
energized.
If
wire
length
cannot
be
kept
to
less
than
150
feet
on
the
drive
output,
correction
options
are
available.
These
are
listed
in
Figure
5
‐
2:
Wire
Length
‐
up
to
(ft)
Correction
Option
150
None
Required
300
Load
Reactor
at
VFD
Output
650
Load
Reactor
at
Motor
Input
2000
dV/dT
Filter
on
VFD
Output
Consult
Motor
OEM
Inverter
Duty
Motor
Figure
5
‐
2:
Correction
Options
for
Long
Wire
Length
between
VFD
and
Motor
Shaft
Current
As
was
mentioned
earlier,
the
fast
switching
or
"firing"
of
the
IGBTs
enable
the
VFD
to
produce
modified
sine
waves
of
different
frequencies
and
different
voltages
in
order
to
speed
up
or
slow
down
a
motor.
The
fast
switching
of
the
IGBTs
does
have
electrical
side
effects,
some
of
which
are
detailed
on
the
previous
pages.
This
fast
switching
of
the
IGBTs
can
also
cause
"shaft
current"
on
the
motor.
When
this
happens,
a
voltage
charge
builds
up
on
the
motor's
shaft.
When
this
voltage
gets
high
enough,
it
will
arc
to
ground
through
the
path
of
least
resistance.
The
path
of
least
resistance
is
typically
the
ball
bearings
that
support
the
rotor
of
the
motor.
When
this
arcing
occurs
in
the
bearings,
damage
occurs
to
the
bearings.
Over
time,
the
bearings
will
be
destroyed,
and
the
motor
will
fail.
Shaft
current
can
be
mitigated
by
using
a
grounding
ring,
which
is
typically
bolted
to
the
motor
housing
and
has
some
type
of
conductive
filament
that
contacts
the
shaft,
thus
grounding
the
shaft.
Some
motor
OEMs
have
grounding
rings
built
into
the
motor,
so
an
external
ring
is
not
necessary.
Braking
Resistors
Three
‐
phase
AC
induction
motors
can
also
function
as
three
‐
phase
AC
generators
if
they
become
driven
by
what
they
typically
drive.
In
the
case
of
a
blower,
the
motor
drives
the
blower
wheel
when
the
speed
of
the
wheel
is
increased
(accelerated).
Conversely,
the
blower
wheel
can
drive
the
motor
when
the
speed
of
the
blower
wheel
is
decreased
(decelerated)
with
a
closed
air
damper.
When
the
motor
is
driven
by
the
blower
wheel,
it
will
act
as
a
generator
and
"push"
electrical
energy
back
to
the
VFD.
This
energy
will
be
seen
as
a
voltage
increase
on
the
VFD’s
DC
bus.
HOME
Summary of Contents for LMV 5 Series
Page 2: ...Intentionally Left Blank ...
Page 41: ...LMV Series Technical Instructions Document No LV5 1000 SCC Inc Page 7 Section 2 HOME ...
Page 42: ...Technical Instructions LMV Series Document No LV5 1000 Section 2 Page 8 SCC Inc HOME ...
Page 43: ...LMV Series Technical Instructions Document No LV5 1000 SCC Inc Page 9 Section 2 HOME ...
Page 44: ...Technical Instructions LMV Series Document No LV5 1000 Section 2 Page 10 SCC Inc HOME ...
Page 45: ...LMV Series Technical Instructions Document No LV5 1000 SCC Inc Page 11 Section 2 HOME ...
Page 46: ...Technical Instructions LMV Series Document No LV5 1000 Section 2 Page 12 SCC Inc HOME ...
Page 47: ...LMV Series Technical Instructions Document No LV5 1000 SCC Inc Page 13 Section 2 HOME ...
Page 48: ...Technical Instructions LMV Series Document No LV5 1000 Section 2 Page 14 SCC Inc HOME ...
Page 49: ...LMV Series Technical Instructions Document No LV5 1000 SCC Inc Page 15 Section 2 HOME ...
Page 50: ...Technical Instructions LMV Series Document No LV5 1000 Section 2 Page 16 SCC Inc HOME ...
Page 51: ...LMV Series Technical Instructions Document No LV5 1000 SCC Inc Page 17 Section 2 HOME ...
Page 52: ...Technical Instructions LMV Series Document No LV5 1000 Section 2 Page 18 SCC Inc HOME ...
Page 53: ...LMV Series Technical Instructions Document No LV5 1000 SCC Inc Page 19 Section 2 HOME ...
Page 54: ...Technical Instructions LMV Series Document No LV5 1000 Section 2 Page 20 SCC Inc HOME ...
Page 55: ...LMV Series Technical Instructions Document No LV5 1000 SCC Inc Page 21 Section 2 HOME ...
Page 373: ...Intentionally Left Blank ...
