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†
All marks shown within this document are properties o
f
their respective owners.
www
.
u
smotors.
com
v
T
hermal Overloads and Sin
g
le Phase Motors
M
otors with thermal overloads installed ma
y
not operate properl
y
on a
VFD. The current carr
y
in
g
thermal overload is desi
g
ned
f
or sine wave
p
ower.
O
peration on a VFD ma
y
cause nuisance trippin
g
or potentiall
y
n
ot protect the motor as would be expected on line power. Thermo-stats
or thermistors installed in the motor and connected properl
y
to the VFD
ma
y
provide suitable thermal overload protection when operatin
g
on a
VFD.
(C
onsult
C
odes
)
S
in
g
le phase motors and other
f
ractional horsepower ratin
g
s are not
desi
g
ned to be operated on a VFD. Within Nidec Motor Corporation
standard products, all motors NEMA
®†
A
A
48 frame
(
5.5” diameter
)
and
s
maller are not suitable
f
or VFD applications. Three phase 56 and
143
/
145
f
rame applications should be noted on the catalo
g
price pa
g
e;
or i
f
in doubt ask an Nidec Motor
C
orporation technical representative
f
or
r
ecommendations on compatibilit
y
with a VFD.
Slow S
p
eed Motors
M
otors with a base desi
g
n o
f
slower than six poles require special
c
onsideration re
g
ardin
g
VFD sizin
g
and minimizin
g
harmonic distortion
c
r
ea
t
ed
a
t th
e
m
o
t
o
r t
e
rmin
a
l
s
due
t
o
cab
l
e
in
s
t
a
ll
a
ti
o
n
c
h
a
r
ac
t
e
ri
s
ti
cs
.
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HV
desi
g
ned
f
or PWM power ma
y
be required to provide acceptable motor
l
i
f
e. Harmonic distortion on the output wave
f
orm should be kept to a
minimum level
(
less than 10%
)
.
690V A
pp
lications
M
otors that will be applied to 690VAC PWM VFDs require the use of an
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rade to a 2300V insulation s
y
stem.
L
ow Volta
g
e TITA
N
®
Motors
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When usin
g
449
f
rame and lar
g
er motors on PWM t
y
pe VFDs consider
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p
ower to minimize harmonic distortion and peak volta
g
es at the motor
terminals. Harmonic distortion on the output wave
f
orm should be kept to
a minimum level
(
less than 10
%)
.
Bearin
g
Currents related to PWM wavefor
m
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the motor bearin
g
s
f
rom sha
f
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common mode
volta
g
es is not a standard feature on sine wave or Inverter Dut
y
motor
p
roducts, unless explicitl
y
noted. Some installations ma
y
be prone to a
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Flutin
g
dama
g
e is related to characteristics o
f
the PWM wave
f
orm, VFD
p
ro
g
rammin
g
and characteristics and installation.
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p
revented b
y
the installation o
f
a sha
f
t
g
roundin
g
device such as a
brush or rin
g
and
/
or correction o
f
the installation characteristics causin
g
the sha
f
t volta
g
e condition. Insulated bearin
g(
s
)
ma
y
be required. VFD
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M
ultiple Motors on a Sin
g
le VFD
S
pecial considerations are required when multiple motors are powered
f
rom a sin
g
le VFD unit. Most VFD manu
f
acturers can provide
g
uidelines
f
or proper motor thermal considerations and startin
g/
stoppin
g
o
f
motors. T
y
picall
y
, motors with automatic thermal protection are not
recommended.
C
able runs from the VFD and each motor can create
c
onditions that will cause extra stress on the motor windin
g
. Filters ma
y
be required at the motor to provide maximum motor li
f
e.
G
roundin
g
and Cable Installation Guidelines
Proper output windin
g
and
g
roundin
g
practices can be instrumental
in minimizin
g
motor related
f
ailures caused b
y
PWM wave
f
orm
c
haracteristics and installation
f
actors. VFD manu
f
acturers t
y
picall
y
provide detailed
g
uidelines on the proper
g
roundin
g
of the motor to
the VFD and output cable routin
g
.
C
ablin
g
manu
f
acturers provide
recommended cable t
y
pes
f
or PWM installations and critical in
f
ormation
c
oncernin
g
output wirin
g
impedance and capacitance to
g
round.
V
ertical Motors on VFDs
Vertical motors operated on VFD power present unique conditions that
ma
y
require consideration b
y
the user or installation en
g
ineer:
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causin
g
locked rotor and drive trippin
g
.
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aused b
y
the torque pulsation characteristics of the PWM waveform,
a s
y
stem critical frequenc
y
fallin
g
inside the variable speed ran
g
e o
f
the process or the added harmonic content o
f
the PWM wave
f
orm
e
xcitin
g
a s
y
stem componen
t
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deceleration and torque o
f
the motor on VFD power and the buildin
g
of s
y
stem pressure/ load.
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the motor bearin
g
s
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Humidit
y
and Non-operational Conditions
The possible build-up o
f
condensation inside the motor due to stora
g
e in
an uncontrolled environment or non-operational periods in an installation,
c
an lead to an increased rate o
f
premature windin
g
or bearin
g
f
ailures
wh
e
n
co
m
b
in
ed
with th
e
s
tr
esses
assoc
i
a
t
ed
with PWM w
a
v
efo
rm
c
haracteristics. Moisture and condensation in and on the motor windin
g
over time can provide trackin
g
paths to
g
round, lower the Me
g
ohm
resistance o
f
the motor windin
g
to
g
round, and lower the
C
orona
Inception Volta
g
e level o
f
the windin
g
.
Proper stora
g
e and maintenance
g
uidelines are important to minimize the
potential of premature failures. Space heaters or trickle volta
g
e heatin
g
methods are the preferred methods for dr
y
in
g
out a windin
g
that has low
me
g
aohm readin
g
s. Dama
g
e caused b
y
these
f
actors are not covered
b
y
the limited warrant
y
provided unless appropriate heatin
g
methods
are properl
y
utilized durin
g
non-operational periods and prior to motor
s
tart-up
.
NEMA
®
†
A
A
Application Guide for AC Ad
j
ustable Speed Drive
S
y
stems: http://www.nema.or
g
/stds/acad
j
ustable.cfm#download
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®
†
& CSA
®†
A
A
listin
g
s where indicated.
M
otor
/
Inverter
Compatibilit
y